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The role of brain dopamine systems in anticipatory and consummatory aspects of sexual behavior in the… Pfaus, James George 1990

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THE ROLE OF BRAIN DOPAMINE SYSTEMS IN ANTICIPATORY AND CONSUMMATORY ASPECTS OF SEXUAL BEHAVIOR IN THE MALE RAT by JAMES GEORGE PFAUS B.A., The American University, 1983 M.A., Uni v e r s i t y of B r i t i s h Columbia, 1986 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES Department of Psychology We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA A p r i l 1990 © James George Pfaus, 1990 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of The University of British Columbia Vancouver, Canada Date DE-6 (2/88) Abstract The r o l e of brain dopamine (DA) systems i n the control of an t i c i p a t o r y and consummatory aspects of the sexual behavior of male rats was examined i n the present experiments. Experiment I explored the s t a t i s t i c a l r e l a t i o n s h i p among a n t i c i p a t o r y and consummatory measures of male sexual behavior using multiple c o r r e l a t i o n s and factor a n a l y s i s . Level changing, a measure of an t i c i p a t o r y behavioral excitement, was not rel a t e d s t a t i s t i c a l l y to any of the consummatory measures of copulation, whereas several consummatory measures were co r r e l a t e d . The factor analysis revealed the existence of f i v e f a c t o r s : copulatory rate, i n i t i a t i o n , h i t rate, mount count, and a n t i c i p a t i o n ; given tentative names.based on the measures that loaded most heavily onto each f a c t o r . These r e s u l t s established that a n t i c i p a t o r y and consummatory measures of* male sexual behavior are unrelated s t a t i s t i c a l l y . Experiment II examined the dose-response e f f e c t s of several DA receptor antagonists on a n t i c i p a t o r y and consummatory measures of male sexual behavior. Systemic administration of the t y p i c a l neuroleptics haloperidol and pimozide, and the D l - s e l e c t i v e antagonist SCH 23390, s i g n i f i c a n t l y reduced the number of l e v e l changes, increased the intromission l a t e n c i e s , and decreased the number of intromissions and the t o t a l number of ejaculations. The a t y p i c a l neuroleptic clozapine and the D2-selective antagonist s u l p i r i d e reduced the number of l e v e l changes and s i g n i f i c a n t l y increased the intromission l a t e n c i e s , but did not a f f e c t the number of intromissions or ejaculations. In almost every case, the doses required to reduce l e v e l changing were lower than those required to increase the intromission l a t e n c i e s , i n d i c a t i n g that the measure of a n t i c i p a t o r y sexual behavior was more s e n s i t i v e to d i s r u p t i o n by DA antagonists than were consummatory measures of sexual behavior. The antiemetic agent metoclopramide decreased the number of intromissions but did not a f f e c t other a n t i c i p a t o r y or consummatory measures of sexual behavior s i g n i f i c a n t l y . High doses of haloperidol, pimozide, or clozapine delayed or abolished l e v e l changing and the i n i t i a t i o n of copulation. These r e s u l t s indicated that a n t i c i p a t o r y and consummatory measures of male sexual behavior are affected d i f f e r e n t i a l l y by DA antagonists. Experiment III provided the f i r s t evidence that haloperidol a f f e c t s a n t i c i p a t o r y and consummatory measures of male sexual behavior s e l e c t i v e l y i n d i f f e r e n t brain DA terminals. B i l a t e r a l infusions of haloperidol to the nucleus accumbens reduced l e v e l changing without a f f e c t i n g the i n i t i a t i o n of copulation or other consummatory measures. B i l a t e r a l infusions of haloperidol to the striatum increased the t o t a l number of ejaculations but d i d not a f f e c t other consummatory or a n t i c i p a t o r y measures. U n i l a t e r a l infusions of haloperidol to the medial preoptic area (MPOA) produced nearly a l l of the e f f e c t s of systemic administration, including reduced number of l e v e l changes, increased intromission l a t e n c i e s , and decreased number of intromissions and ejacula t i o n s . These r e s u l t s indicated that DA i n the nucleus accumbens and striatum are involved in the di s p l a y of ant i c i p a t o r y sexual behavior and copulatory rate, r e s p e c t i v e l y , whereas DA in the MPOA i s involved in a n t i c i p a t o r y sexual behavior, the i n i t i a t i o n of copulation, and copulatory rate. In Experiment IV, in vivo voltammetry revealed a d i f f e r e n t i a l pattern of DA e f f l u x in the nucleus accumbens and striatum, and catecholamine e f f l u x i n the MPOA, during a n t i c i p a t o r y and consummatory phases of sexual behavior in male r a t s . Increased DA e f f l u x i n the nucleus accumbens and increased catecholamine e f f l u x in the MPOA were associated with the presentation of a receptive female behind a screen and with the i n i t i a t i o n of copulation. E f f l u x in both regions decreased following e j a c u l a t i o n but increased p r i o r to each r e i n i t i a t i o n of copulation. DA e f f l u x in the striatum increased n o n s p e c i f i c a l l y during copulation. Use of in vivo m i c r o d i a l y s i s confirmed the general pattern of DA e f f l u x in the nucleus accumbens and striatum observed with voltammetry. These r e s u l t s were interpreted as supporting a r o l e of DA terminals in the nucleus accumbens and MPOA, but not the striatum, in the di s p l a y of a n t i c i p a t o r y sexual behavior and in the i n i t i a t i o n of copulation. In p a r t i c u l a r , the increased release of DA i n the MPOA was viewed as s e n s i t i z i n g hypothalamic mechanisms involved in the control of penile erection whereas the increased release of DA in the nucleus accumbens was viewed as s e n s i t i z i n g motor programs necessary for the execution of ant i c i p a t o r y sexual responses and the i n i t i a t i o n of mounting. V Table of Contents Abstract ... . i i L i s t of Tables v i i i L i s t of Figures ix Acknowledgements x i INTRODUCTION 1 The neurobiology of dopamine 1 Dopamine and incentive motivation ............. — . . . 6 Relevance of dopamine to sexual behavior 9 Description of the sexual behavior of male rats 13 Role of dopamine in the sexual behavior of male r a t s : A review . . 22 Level changing: A new measure of a n t i c i p a t o r y sexual behavior 45 Overview of the present experiments 48 EXPERIMENT I: STATISTICAL ANALYSIS OF MALE SEXUAL BEHAVIOR IN THE BI LEVEL CHAMBER 51 Method . 57 Results and Discussion 60 EXPERIMENT I I : EFFECTS OF SYSTEMIC ADMINISTRATION OF DOPAMINE ANTAGONISTS ON ANTICIPATORY AND CONSUMMATORY ASPECTS OF SEXUAL BEHAVIOR IN THE MALE RAT. 76 Method 78 v i R e s u l t s 81 D i s c u s s i o n . . . . 106 EXPERIMENT I I I : EFFECTS OF CENTRAL ADMINISTRATION OF HALOPERIDOL ON ANTICIPATORY AND CONSUMMATORY ASPECTS OF SEXUAL BEHAVIOR IN THE MALE RAT 114 Method 117 R e s u l t s 124 D i s c u s s i o n 133 EXPERIMENT I V : ELECTROCHEMICAL DETECTION OF CENTRAL DOPAMINE EFFLUX DURING ANTICIPATORY AND CONSUMMATORY PHASES OF SEXUAL BEHAVIOR IN THE MALE RAT . . 140 E x p e r i m e n t I V a : 14 6 Method 146 R e s u l t s 153 D i s c u s s i o n 162 E x p e r i m e n t I V b : 165 Method 166 R e s u l t s 168 D i s c u s s i o n 172 E x p e r i m e n t I V c : 175 Method 177 R e s u l t s . 183 D i s c u s s i o n 192 v i i GENERAL DISCUSSION 198 The r o l e o f b r a i n dopamine sys tems i n male s e x u a l b e h a v i o r 205 C l i n i c a l i m p l i c a t i o n s 219 Male s e x u a l b e h a v i o r as a f o r m o f m o t i v a t e d b e h a v i o r . . 223 Summary and c o n c l u s i o n s 226 REFERENCES 228 v i i i L i s t o f T a b l e s T a b l e I . Means, s t a n d a r d e r r o r s , and i n t e r c o r r e l a t i o n s among t h e 11 measures o f s e x u a l b e h a v i o r d i s p l a y e d by male r a t s i n t h e b i l e v e l chambers 61 T a b l e I I . C o r r e l a t i o n c o e f f i c i e n t s w i t h s t a t i s t i c a l s i g n i f i c a n c e o f p_<.05 62 T a b l e I I I . E s t i m a t e s o f c o m m u n a l i t y f o r each measure o f s e x u a l b e h a v i o r 66 T a b l e I V . F a c t o r s and t h e i r v a r i a b l e l o a d i n g s 67 i x L i s t o f F i g u r e s F i g u r e 1 . Schemat i c r e p r e s e n t a t i o n o f t h e ma jo r DA c e l l g r o u p s and t h e i r e f f e r e n t * p r o j e c t i o n s i n t h e r a t b r a i n 4 F i g u r e 2 . L e v e l changes d i s p l a y e d by s e x u a l l y a c t i v e males i n t h e b i l e v e l chambers 47 F i g u r e 3. P e r c e n t a g e o f r a t s d i s p l a y i n g l e v e l c h a n g e s , m o u n t s , i n t r o m i s s i o n s , and e j a c u l a t i o n s f o l l o w i n g t r e a t m e n t w i t h h a l o p e r i d o l i n E x p e r i m e n t I I 83 F i g u r e 4 . E f f e c t o f h a l o p e r i d o l on t h e 9 p r i m a r y measures o f male s e x u a l b e h a v i o r i n E x p e r i m e n t I I 85 F i g u r e 5. P e r c e n t a g e o f r a t s d i s p l a y i n g l e v e l c h a n g e s , m o u n t s , i n t r o m i s s i o n s , and e j a c u l a t i o n s f o l l o w i n g t r e a t m e n t w i t h p i m o z i d e in E x p e r i m e n t I I 88 F i g u r e 6. E f f e c t o f p i m o z i d e on t h e 9 p r i m a r y measures o f male s e x u a l b e h a v i o r i n E x p e r i m e n t I I 90 F i g u r e 7. P e r c e n t a g e o f r a t s d i s p l a y i n g l e v e l c h a n g e s , m o u n t s , i n t r o m i s s i o n s , and e j a c u l a t i o n s f o l l o w i n g t r e a t m e n t w i t h c l o z a p i n e i n E x p e r i m e n t I I . . 93 F i g u r e 8. E f f e c t o f c l o z a p i n e on t h e 9 p r i m a r y measures o f male s e x u a l b e h a v i o r i n E x p e r i m e n t I I 95 F i g u r e 9 . E f f e c t o f m e t o c l o p r a m i d e on t h e 9 p r i m a r y measures o f male s e x u a l b e h a v i o r i n E x p e r i m e n t I I 98 F i g u r e 10 . P e r c e n t a g e o f r a t s d i s p l a y i n g l e v e l c h a n g e s , m o u n t s , i n t r o m i s s i o n s , and e j a c u l a t i o n s f o l l o w i n g t r e a t m e n t w i t h SCH 23390 i n E x p e r i m e n t I I 101 F i g u r e 1 1 . E f f e c t o f SCH 23390 on t h e 9 p r i m a r y measures o f male s e x u a l b e h a v i o r i n E x p e r i m e n t I I 103 F i g u r e 1 2 . E f f e c t o f s u l p i r i d e on t h e 9 p r i m a r y measures o f male s e x u a l b e h a v i o r i n E x p e r i m e n t I I 105 F i g u r e 13 . B i l a t e r a l c a n n u l a p l a c e m e n t s d i r e c t e d a t t h e n u c l e u s accumbens i n E x p e r i m e n t I I I 121 F i g u r e 14 . B i l a t e r a l c a n n u l a p l a c e m e n t s d i r e c t e d a t t h e s t r i a t u m i n E x p e r i m e n t I I I 122 F i g u r e 15 . U n i l a t e r a l c a n n u l a p l a c e m e n t s d i r e c t e d a t t h e m e d i a l p r e o p t i c a r e a i n E x p e r i m e n t i l l 123 X F i g u r e 16 . E f f e c t o f b i l a t e r a l i n f u s i o n s o f h a l o p e r i d o l t o t h e n u c l e u s accumbens on measures o f male s e x u a l b e h a v i o r i n E x p e r i m e n t I I I 126 F i g u r e 1 7 . E f f e c t o f b i l a t e r a l i n f u s i o n s o f h a l o p e r i d o l t o t h e s t r i a t u m on measures o f male s e x u a l b e h a v i o r i n E x p e r i m e n t I I I 129 F i g u r e 18 . E f f e c t o f u n i l a t e r a l i n f u s i o n s o f h a l o p e r i d o l t o t h e m e d i a l p r e o p t i c a r e a on measures o f male s e x u a l b e h a v i o r i n E x p e r i m e n t I I I 131 F i g u r e 19 . E l e c t r o d e p l a c e m e n t s d i r e c t e d a t t h e n u c l e u s accumbens i n E x p e r i m e n t IVa 149 F i g u r e 20 . E l e c t r o d e p l a c e m e n t s d i r e c t e d a t t h e s t r i a t u m i n E x p e r i m e n t IVa 150 F i g u r e 2 1 . E l e c t r o d e p l a c e m e n t s d i r e c t e d a t t h e m e d i a l p r e o p t i c a r e a i n E x p e r i m e n t IVa 151 F i g u r e 2 2 . Changes i n DA o x i d a t i o n c u r r e n t i n t h e n u c l e u s accumbens d u r i n g phases o f male s e x u a l b e h a v i o r i n E x p e r i m e n t I V a 155 F i g u r e 23 . Changes i n DA o x i d a t i o n c u r r e n t i n t h e s t r i a t u m d u r i n g phases o f male s e x u a l b e h a v i o r i n E x p e r i m e n t IVa 158 F i g u r e 24 . Changes i n c a t e c h o l a m i n e o x i d a t i o n c u r r e n t i n t h e m e d i a l p r e o p t i c a r e a d u r i n g phases o f male s e x u a l b e h a v i o r i n E x p e r i m e n t IVa 161 F i g u r e 25 . Changes i n DA o x i d a t i o n c u r r e n t i n t h e n u c l e u s accumbens and s t r i a t u m , and changes i n c a t e c h o l a m i n e o x i d a t i o n c u r r e n t i n t h e m e d i a l p r e o p t i c a r e a , d u r i n g t h e p r e s e n t a t i o n o f v a r i o u s s t i m u l i b e h i n d t h e s c r e e n , i n E x p e r i m e n t IVb 171 F i g u r e 26 . M i c r o d i a l y s i s p r o b e p l a c e m e n t s d i r e c t e d a t t h e n u c l e u s accumbens i n E x p e r i m e n t IVc 181 F i g u r e 27 . M i c r o d i a l y s i s p r o b e p l a c e m e n t s d i r e c t e d a t t h e s t r i a t u m i n E x p e r i m e n t IVc 182 F i g u r e 28 . L e v e l s o f DA and i t s m e t a b o l i t e s i n d i a l y s a t e s f r o m t h e n u c l e u s accumbens d u r i n g phases o f male s e x u a l b e h a v i o r i n E x p e r i m e n t IVc 187 F i g u r e 29 . L e v e l s o f DA and i t s m e t a b o l i t e s i n d i a l y s a t e s f r o m t h e s t r i a t u m d u r i n g phases o f male s e x u a l b e h a v i o r i n E x p e r i m e n t IVc 191 Acknowledgements I am indebted to my advisor, Tony P h i l l i p s , for his encouragement, patience, and support throughout the course of my research in his laboratory and during the preparation of t h i s t h e s i s . Our many discussions about the role of dopamine in motivated behavior kept me on track and helped frame the ideas put forward here. I am also indebted to John Pi n e l for being a fri e n d and teacher, and for providing me with laboratory space for several of the experiments reported in t h i s t h e s i s . The confidence that both Tony and John showed in my a b i l i t i e s kept me in graduate school at a time when my own confidence was waning. I would l i k e to thank the other member of my thesis committee, Di m i t r i Papageorgis, for helping to make t h i s whole endeavor i n t e r e s t i n g and relevant. I would also l i k e to thank Scott Mendelson, Jim Blackburn, Mike Mana, Jon Druhan, Joe Klancnik, Tim Harpur, Chuck Blaha, Cathy Rankin, Dave Mumby, Emma Wood, Lorinda Holmes, and Barry E v e r i t t for many hours of discussion and d i g r e s s i o n . The t e c h n i c a l assistance of Chuck Blaha, Mike Jung, Shayne Kardel, and Fred LePiane i s appreciated. I am also g r a t e f u l to Geert Damsma, George Nomikos, Danielle Wenkstern, and Chris Fibiger at the D i v i s i o n of Neurological Sciences, Department of Psychiatry, for allowing me to use t h e i r f a c i l i t i e s and expertise to perform the m i c r o d i a l y s i s experiments. What began there as just another question resulted in a highly successful and creative c o l l a b o r a t i o n . F i n a l l y , I would l i k e to thank K r i s t i n Buhrmann. She knows why. This thesis is dedicated to the late Frank Ambrose Beach (1911-1988), whose pioneering e f f o r t s and penetrating insights into the neurobiology of mammalian sexual behavior remain a source of great i n s p i r a t i o n . 1 THE ROLE OF BRAIN DOPAMINE SYSTEMS IN ANTICIPATORY AND CONSUMMATORY ASPECTS OF SEXUAL BEHAVIOR IN THE MALE RAT This thesis has two objectives. The f i r s t i s to describe the r o l e of brain dopamine (DA) systems in various aspects of the sexual motivation and copulatory behavior of male r a t s . The second i s to re l a t e the rol e of DA in male sexual behavior to the more general role that DA plays in the regulation of incentive motivation. Although these two li n e s of research have advanced independently, t h e i r convergence is long overdue. Accordingly, the introduction of t h i s thesis f i r s t outlines the neurobiology of DA and i t s proposed role in incentive motivation before reviewing the human and animal l i t e r a t u r e on the rol e of DA in male sexual behavior. This review of the l i t e r a t u r e leads to several methodological and t h e o r e t i c a l c r i t i c i s m s , most notably, that knowledge of the role of DA in the sexual behavior of male rats has not kept pace with more general theories about the role of DA in motivated behaviors. A new method of assessing sexual motivation in male rats i s presented as part of an integrated approach to the study of DA in male sexual behavior that combines behavioral, pharmacological, and electrochemical techniques. The Neurobiology of Dopamine Dopamine was o r i g i n a l l y proposed as a neurotransmitter in the late 1950s (Bertler & Rosengren, 1959; Carlsson, 1959; Carlsson, Lindqvist, Magnusson, & Waldeck, 1958; Montague, 1957). 2 Subsequent histofluorescence techniques revealed i n t r a c e l l u l a r concentrations of DA in s p e c i f i c brain areas (Carlsson, 1963), thus s a t i s f y i n g an important c r i t e r i o n of neurotransmitter c l a s s i f i c a t i o n . Further evidence of a neurotransmitter r o l e for DA was provided by Hokfelt (1968) who demonstrated with electron microscopy that DA was contained in dense core v e s i c l e s within synaptic terminals. Using these techniques, the neuroanatomic l o c a l i z a t i o n of major DA-containing c e l l bodies, projection " f i b r e s , and terminal regions was described in d e t a i l (Dahlstrom & Fuxe, 1964; Hokfelt, Johannson, Fuxe, Goldstein, & Park, 1977; Jacobowitz & Palkovits, 1972) and i s shown in Figure 1. The i d e n t i f i c a t i o n of DA as a major synaptic transmitter was complemented by demonstrations that both the DA precursor 1-DOPA and several DA agonists (e.g., apomorphine', p i r i b i d e l , and bromocriptine) could attenuate the symptoms of Parkinson's disease. Likewise, four classes of putative DA antagonists, the phenothiazines (e.g., chlorpromazine), thioxanthenes (e.g., c i s -f l u p e n t h i x o l ) , butyrophenones (e.g., haloperidol), and the substituted benzamides (e.g., s u l p i r i d e ) , had emerged with successful therapeutic value in the treatment of various psychoses (Wyatt, 1976). In addition, antipsychotic or neuroleptic drugs were subsequently shown to antagonize the behavioral e f f e c t s ' o f DA agonists and precursors, to antagonize the s i n g l e - u n i t e f f e c t s of iontophoretically-applied DA, to block DA-stimulated adenylate cyclase, and to increase the f i r i n g rate of DA neurons by compensatory transneuronal feedback. 3 F i g u r e 1 . Schemat i c r e p r e s e n t a t i o n o f t h e m a j o r DA c e l l g r o u p s and t h e i r e f f e r e n t p r o j e c t i o n s i n t h e r a t b r a i n . A: M e s o t e l e n c e p h a l i c and r e t i n a l DA sys tems (A8 , A9, A10, A16, and A 1 7 ) ; B: D i e n c e p h a l i c DA sys tems ( A l l , A12, A13, A14, and A 1 5 ) ; a f t e r Moore ( 1 9 8 7 ) ; R o t h , W u l f , and Deu tsch ( 1 9 8 7 ) . 4 cord 5 Autoradiographic studies revealed the existence of binding s i t e s for a v a r i e t y of DA agonists and antagonists within brain areas innervated by DA terminals, such as the o l f a c t o r y bulbs, f r o n t a l cortex, caudate-putamen, globus p a l l i d u s , nucleus accumbens, bed nucleus of the s t r i a t e r m inalis, medial nucleus of the septum, basolateral nuclei of the amygdala, and mediobasal hypothalamus (Creese, Burt, & Snyder, 1976; Kebabian, Petzold, & Greengard, 1972; Seeman, Chau-Wong, Tedesco, & Wong, 1975). I n i t i a l l y , these binding s i t e s were thought to represent a s i n g l e , complex receptor protein. Subsequent analyses, however, demonstrated at least two pharmacologically d i s t i n c t receptors, one linked to the stimulation of adenylate cyclase (DI), and the other either not linked or i n h i b i t o r y to cAMP formation (D2) (Creese, 1983; Kebabian & Calne, 1979). Although further studies suggested the existence of four d i s t i n c t receptor subtypes (e.g., Seeman, 1980), a more recent review of t h i s l i t e r a t u r e proposed that DI and D2 receptors exist in both a high- and l o w - a f f i n i t y state (Creese, 1985). In general, DA acts as an agonist in micromolar quantities at DI receptors but in nanomolar quantities at D2 receptors (Kebabian, Beaulieu, & Itoh, 1984). A l l classes of DA antagonist bind to both types of receptor but with somewhat d i f f e r e n t a f f i n i t i e s (Tamminga & Gerlach, 1987). Both DI and D2 receptors can be located pre- and postsynaptically in major DA terminal regions (Creese, 1985), although p r e f e r e n t i a l s i t e s for t h e i r high- and l o w - a f f i n i t y subtypes i s s t i l l a matter of debate. 6 S e v e r a l DA p a t h w a y s , most n o t a b l y t h e m e s o s t r i a t a l ( A 9 ) , m e s o l i m b i c / m e s o c o r t i c a l ( A 1 0 ) , t u b e r o i n f u n d i b u l a r ( A 1 2 ) , and i n c e r t o h y p o t h a l a m i c (A13 , A 1 4 ) , have been i m p l i c a t e d i n a v a r i e t y o f p h y s i o l o g i c a l and b e h a v i o r a l f u n c t i o n s , i n c l u d i n g motor c o o r d i n a t i o n (F reed & Zee, 1 9 8 2 ) , r e s p o n s e i n i t i a t i o n ( F i b i g e r , Z i s , & P h i l l i p s , 1 9 7 5 ) , s e n s o r i m o t o r r e s p o n s i v e n e s s ( W h i t e , 1986) , p r e p a r a t o r y b e h a v i o r s ( B l a c k b u r n , P h i l l i p s , & F i b i g e r , 1987) , g e n e r a l m o t i v a t i o n a l a c t i v a t i o n ( C a r l i , Evenden , & R o b b i n s , 1985; Salamone, 1 9 8 8 ) , i n c e n t i v e m o t i v a t i o n (Crow, 1973; F i b i g e r & P h i l l i p s , 1986 ; Mogenson & P h i l l i p s , 1 9 7 6 ) , r e w a r d ( W i s e , 1 9 8 2 ) , a t t e n t i o n (Solomon e t a l . , 1 9 8 1 ; Weiner & F e l d o n , 1988) , l e a r n i n g ( B e n i n g e r , 1 9 8 8 ) , and n e u r o e n d o c r i n e r e g u l a t i o n (Moore , 1 9 8 7 ) . T h i s v a r i e t y o f p r o c e s s e s has a l s o g e n e r a t e d a s u b s t a n t i a l amount o f c o n t r o v e r s y . L i t t l e agreement e x i s t s c o n c e r n i n g t h e p r e c i s e r o l e t h a t DA p l a y s i n b e h a v i o r . However, g i v e n t h e l a r g e number o f b e h a v i o r a l p r o c e s s e s a f f e c t e d by t r e a t m e n t s t h a t d i s r u p t DA a c t i v i t y , i t i s d i f f i c u l t t o i m a g i n e t h a t b r a i n DA sys tems p l a y a s i n g l e r o l e i n t h e i n t e g r a t i o n or c o o r d i n a t i o n o f b e h a v i o r , a l t h o u g h i t has been d e m o n s t r a t e d t h a t c e r t a i n a s p e c t s o f b e h a v i o r a r e more s e n s i t i v e t o DA d i s r u p t i o n t h a n o t h e r s . Dopamine and I n c e n t i v e M o t i v a t i o n An i m p o r t a n t example o f d i f f e r e n t i a l b e h a v i o r a l s e n s i t i v i t y t o t h e d i s r u p t i o n o f DA sys tems comes f r o m t h e a n a l y s i s o f i n c e n t i v e m o t i v a t i o n , i n w h i c h e n v i r o n m e n t a l s t i m u l i t h a t have 7 been a s s o c i a t e d w i t h b i o l o g i c a l l y i m p o r t a n t e v e n t s come t o i n i t i a t e and m a i n t a i n b e h a v i o r ( B i n d r a , 1968; B o l l e s , 1972; T o a t e s , 1 9 8 1 ; W e i n g a r t e n , 1 9 8 5 ) . A c o m p l e m e n t a r y a n a l y s i s o f i n c e n t i v e m o t i v a t i o n r e c o g n i z e s t h e d i s t i n c t i o n made e a r l i e r t h i s c e n t u r y between p r e p a r a t o r y and consummatory a s p e c t s o f b e h a v i o r ( C r a i g , 1918; K o n o r s k i , 1967 ; Woodwor th , 1 9 1 8 ) . P r e p a r a t o r y b e h a v i o r s , such as h o a r d i n g and f o r a g i n g , a r e v a r i a b l e a c t i o n p a t t e r n s made i n r e s p o n s e t o i n c e n t i v e s t i m u l i t h a t l e a d t o a p a r t i c u l a r f o r m o f consummatory r e s p o n d i n g , such as f e e d i n g , f i g h t i n g , f l e e i n g , or m a t i n g . T h e o r e t i c a l l y , p r e p a r a t o r y b e h a v i o r s may be c o n t a i n e d w i t h i n t h e more g e n e r a l c l a s s e s o f a p p e t i t i v e or a n t i c i p a t o r y b e h a v i o r s ( M a c p h a i l , 1 9 8 2 ) . T h i s taxonomy assumes t h a t s e c o n d a r y cues a s s o c i a t e d w i t h p r i m a r y i n c e n t i v e s can come t o e l i c i t p r e p a r a t o r y or o t h e r a n t i c i p a t o r y r e s p o n s e s because a n i m a l s a n t i c i p a t e t h e p r e s e n t a t i o n o f t h e p r i m a r y i n c e n t i v e based on i n f o r m a t i o n p r o v i d e d by t h e s e c o n d a r y c u e s . A l t h o u g h t h e d i v i s i o n between a n t i c i p a t o r y / p r e p a r a t o r y and consummatory b e h a v i o r s i s o f t e n open t o d e b a t e , a number o f s t u d i e s have shown t h a t t h e two can be d i s s o c i a t e d w i t h t h e a p p r o p r i a t e e x p e r i m e n t a l m a n i p u l a t i o n s , e s p e c i a l l y t h o s e t h a t u t i l i z e DA a n t a g o n i s t s or l e s i o n s o f DA neurons t o d i s r u p t DA t r a n s m i s s i o n . For examp le , h o a r d i n g b e h a v i o r i n r a t s can be d i s r u p t e d by l ow doses o f t h e DA r e c e p t o r a n t a g o n i s t p i m o z i d e ( B l u n d e l l , S t r u p p , & L a t h a m , 1977) w i t h o u t a f f e c t i n g t h e a b i l i t y o f t h o s e r a t s t o i n g e s t f o o d . L e s i o n s o f m e s o l i m b i c DA neurons 8 w i t h 6 - h y d r o x y d o p a m i n e d i s r u p t or e l i m i n a t e h o a r d i n g b e h a v i o r i n r a t s b u t do n o t a l t e r f o o d or w a t e r i n t a k e s i g n i f i c a n t l y ( K e l l e y & S t i n u s , 1985; Koob, R i l e y , S m i t h , & R o b b i n s , 1 9 7 8 ) . S i m i l a r l y , l o w t o modera te doses o f DA a n t a g o n i s t s or l e s i o n s o f m e s o l i m b i c DA neurons d i s r u p t or e l i m i n a t e i n s t r u m e n t a l r e s p o n d i n g f o r f o o d i n r a t s ( F i b i g e r , P h i l l i p s , & Z i s , 1974 ; Wise & S c h w a r t z , 1 9 8 1 ) , and i n c r e a s e t h e l a t e n c y t o i n i t i a t e a f e e d i n g bou t (Tombaugh, Tombaugh, & An isman , 1 9 7 9 ) , b u t do n o t a f f e c t t h e r a t s ' a b i l i t y t o e a t once f e e d i n g has begun . I n t h o s e s t u d i e s , however , t h e r e s p o n s e s made t o w a r d s e c o n d a r y r e i n f o r c e r s were c o n f o u n d e d by t h e p r e s e n c e o f f o o d . T y p i c a l l y , t h e r a t s made r e p e a t e d c o n t a c t w i t h t h e f o o d between b o u t s o f o p e r a n t r e s p o n d i n g . T h i s c o n f o u n d l e d t o s u g g e s t i o n s t h a t DA a n t a g o n i s t s d i d n o t n e c e s s a r i l y r e d u c e p r e p a r a t o r y b e h a v i o r by d i s r u p t i n g t h e a b i l i t y o f a n i m a l s t o p r o c e s s r e s p o n s e - e l i c i t i n g c u e s , b u t r a t h e r t h e y i n d u c e d a s t a t e o f " a n h e d o n i a " i n w h i c h t h e f o o d i t s e l f was p e r c e i v e d as l e s s r e w a r d i n g ( W i s e , 1982, 1 9 8 5 ) . To c o n t r o l f o r t h e p r e s e n c e o f f o o d , B l a c k b u r n e t a l . (1987) examined t h e e f f e c t o f t h e DA r e c e p t o r a n t a g o n i s t p i m o z i d e on c o n d i t i o n e d p r e p a r a t o r y r e s p o n s e s made by r a t s t o a p o s i t i v e c o n d i t i o n e d s t i m u l u s (CS+) t h a t s i g n a l l e d t h e d e l i v e r y o f a m e a l . Low doses o f p i m o z i d e a t t e n u a t e d t h e c o n d i t i o n e d p r e p a r a t o r y r e s p o n s e s b u t d i d n o t a f f e c t t h e a b i l i t y o f r a t s t o consume t h e meal f o l l o w i n g i t s d e l i v e r y . Thus , i n c o n t r a s t t o W i s e ' s a n h e d o n i a h y p o t h e s i s , t h e s e r e s u l t s i n d i c a t e d t h a t p i m o z i d e a f f e c t e d t h e p r e p a r a t o r y 9 responding to the external CS+ d i r e c t l y , without a f f e c t i n g the reward value of the food. Although the feeding l i t e r a t u r e contains perhaps the best examples of the s e n s i t i v i t y of preparatory responding to disruptions of forebrain DA systems, t h i s s e n s i t i v i t y i s not limited to feeding. Preparatory aspects of one-way avoidance behavior in rats are attenuated by doses of DA antagonists that do not a f f e c t subsequent escape responses (Blackburn, 1989). In summary, i t would appear that DA plays an equally important r o l e in both feeding and avoiding: that of preparing an animal to act based on d i s t a l cues in the environment. Although animals are capable of learning associations following the administration of DA antagonists (Beninger, 1983), they are unable to i n i t i a t e responses on the basis of these associations. In contrast, when DA systems are stimulated by DA agonists, animals become more responsive to relevant cues in the environment (Beninger, Hanson, & P h i l l i p s , 1981; H i l l , 1970; Robbins, 1978). This l i t e r a t u r e does not support the idea that DA plays an important r o l e in consummatory responses directed at l o c a l or in t e r n a l cues. Unfortunately, our knowledge of the ro l e played by DA in other motivated behaviors, and in p a r t i c u l a r , sexual behavior, has not A kept pace with either the t h e o r e t i c a l or empirical developments in the feeding and avoidance l i t e r a t u r e . Relevance of Dopamine to Sexual Behavior The impetus to study the involvement of central DA systems 10 in mammalian sexual behavior comes from a v a r i e t y of anecdotal and experimental sources. Stimulation of sexual arousal and performance has been reported by r e c r e a t i o n a l users of drugs that stimulate DA pathways or receptors, such as d-amphetamine, cocaine, and apomorphine (Carter & Davis, 1976; H o l l i s t e r , 1975; Schneiden & Rees, 1985; Waud, 1933). Apomorphine has also proven useful in the treatment of e r e c t i l e dysfunction (Lai et a l . , 1987). In contrast, drugs that i n h i b i t DA transmission, such as the major t r a n q u i l i z e r s and antipsychotic agents, either delay orgasm or i n h i b i t aspects of sexual arousal (Kotin, Wilbert, Verberg, & Soldinger, 1977; P e t r i e , 1985). Consistent with these reports, the loss of sexual desire or arousal associated with c e r t a i n medical conditions, such as Parkinson's disease, diabetes, renal f a i l u r e , and hyperprolactinemia, has been counteracted with the DA precursor 1-DOPA or the DA receptor agonists l i s u r i d e , bromocriptine, and apomorphine (Bartke, Svare, Doherty, Smith, & Klemcke, 1983; Barwin, 1985; Bowers & Van Woert, 1972; P i e r i n i & Nusimovich, 1981; Ruilope et a l . , 1985). However, the human l i t e r a t u r e is fraught with inconsistencies. It i s not known exactly what aspects of sexual arousal or performance are f a c i l i t a t e d by DA agonists or disrupted by DA antagonists. Part of the problem stems from the lack of well-c o n t r o l l e d experiments that u t i l i z e double-blind drug administration procedures or that contrast drug e f f e c t s with baseline assessments of sexual function. These procedures are necessary to control for both placebo e f f e c t s and any preexisting 11 sexual dysfunction. In addition, assessments of sexual function are made almost e n t i r e l y on the basis of patient s e l f - r e p o r t ; few studies have examined p h y s i o l o g i c a l measures of sexual arousal following the administration of DA agonists or antagonists and none have attempted to measure sexual behavior d i r e c t l y . A second problem in the human l i t e r a t u r e involves the conceptual r e l a t i o n s h i p of d i f f e r e n t aspects of human sexual behavior and the terminology used to describe them. Ear l y theories of human sexual behavior emphasized the role of two conceptually separate, but p h y s i o l o g i c a l l y integrated, substrates of sexual arousal and performance (e.g., Moll, 1897; K r a f f t -Ebing, 1929; E l l i s , 1938); however, each used d i f f e r e n t terms and operational d e f i n i t i o n s . Unfortunately, t h i s problem continues to plague the human l i t e r a t u r e . Although attempts have been made empi r i c a l l y to specify conceptually d i s t i n c t aspects of the human sexual response cycle (e.g., Kaplan, 1974; Masters & Johnson, 1966), and to define sexual disorders and dysfunctions within an empirically-derived framework (e.g., DSM-IIIR, American P s y c h i a t r i c Association, 1987), a majority of published case h i s t o r i e s use i l l - d e f i n e d and outdated terminology to describe human sexual behavior. For example, the DSM-IIIR divides the human sexual response cycle into four phases: the appetitive phase (consisting of fantasies about, and a desire to engage i n , sexual a c t i v i t y ) , the excitement phase (consisting of the subjective and ph y s i o l o g i c a l changes that accompany sexual excitement and pleasure), the orgasm phase (consisting of the subjective and ph y s i o l o g i c a l changes that accompany the peaking of sexual pleasure), and the resolution phase (consisting of the subjective and p h y s i o l o g i c a l changes following orgasm). Consistent with these phases, the DSM-IIIR distinguishes among sexual desire disorders (in which ind i v i d u a l s experience either a persistent and recurring absence of sexual fantasies and desire for sexual a c t i v i t y or an extreme aversion to, or avoidance of, g e n i t a l sexual a c t i v i t y ) , sexual arousal disorders (in which in d i v i d u a l s experience either an i n a b i l i t y to a t t a i n or maintain p h y s i o l o g i c a l aspects of sexual excitement, or a lack of subjective excitement or pleasure during sexual a c t i v i t y ) , orgasm disorders (in which i n d i v i d u a l s experience either a delay i n , or the absence of, orgasm following normal sexual excitement, or premature ejaculation derived from minimal sexual stimulation), and sexual pain disorders (in which ind i v i d u a l s experience either recurrent or persistent g e n i t a l pain before, during, or after sexual intercourse, or vaginismus, an involuntary spasm of the outer t h i r d of the vagina that i n t e r f e r e s with sexual a c t i v i t y ) . Despite the wealth of information that could be derived from the a p p l i c a t i o n of t h i s taxonomy, many c l i n i c i a n s continue to use terms l i k e " l i b i d o " and "potency" to describe various processes of sexual desire, arousal, and capacity for orgasm. As a r e s u l t , i t is d i f f i c u l t to know exactly what aspects of human sexual behavior are affected by drugs, in p a r t i c u l a r , DA agonists and antagonists. In recent years, i n t e r e s t has grown in the use of animal models to study drug e f f e c t s on sexual behavior. The experimental control offered by an animal model circumvents many of the problems inherent in the use of human subjects. An equally important advantage i s that a large l i t e r a t u r e e xists on the biochemical, pharmacological, and behavioral properties of drugs in laboratory animals. This l i t e r a t u r e can be used to compare the e f f e c t s of drugs on sexual behavior with t h e i r e f f e c t s in other behavioral paradigms, and can help determine mechanisms of action. The e f f e c t s of DA agonists and antagonists on animal sexual behavior have been studied most extensively in male r a t s . Before reviewing these data, several important methodological and th e o r e t i c a l issues about sexual motivation must be considered. Description of the Sexual Behavior of Male Rats Analysis of Copulatory Behavior The sexual behavior of male rats depends upon the integrated a c t i v i t y of a v a r i e t y of central and peripheral neural systems. The basic components of the copulatory pattern, including orie n t a t i o n toward a receptive female, precopulatory approach and inve s t i g a t i o n of the female, penile erection, mounting, p e l v i c thrusting, vaginal intromission, seminal emission into the urethra, e j a c u l a t i o n , and a postejaculatory i n t e r v a l or re f r a c t o r y phase, are cont r o l l e d by neural centers in the spinal cord and brain, each of which interact continuously during copulation. This pattern of copulation, from pursuit and i n s p e c t i o n o f t h e f e m a l e , t o t h e i n i t i a t i o n o f m o u n t s , i n t r o m i s s i o n s , and f i n a l l y e j a c u l a t i o n , i s r e f e r r e d t o as an e j a c u l a t o r y s e r i e s . F o l l o w i n g t h e i n i t i a l p o s t e j a c u l a t o r y i n t e r v a l , t h e male t y p i c a l l y resumes c o p u l a t i o n f o r a n o t h e r f i v e t o seven e j a c u l a t o r y s e r i e s b e f o r e becoming s e x u a l l y e x h a u s t e d (Beach & J o r d a n , 1956 ; L a r s s o n , 1956; Sachs & B a r f i e l d , 1976 ; Sachs & M e i s e l , 1 9 8 8 ) . S t u d i e s o f t h e s e x u a l b e h a v i o r o f male r a t s g e n e r a l l y r e p o r t t h e p e r c e n t a g e o f r a t s t h a t d i s p l a y m o u n t s , i n t r o m i s s i o n s , and e j a c u l a t i o n s , t h e number o f mounts and i n t r o m i s s i o n s t h a t p r e c e d e e j a c u l a t i o n , t h e number o f e j a c u l a t i o n s d i s p l a y e d d u r i n g a f i n i t e t e s t i n g p e r i o d , t h e l a t e n c i e s t o f i r s t mount , f i r s t i n t r o m i s s i o n , e j a c u l a t i o n , and t h e l a t e n c y t o r e i n i t i a t e e i t h e r mounts or i n t r o m i s s i o n s f o l l o w i n g e j a c u l a t i o n ( t h e p o s t e j a c u l a t o r y i n t e r v a l , or P E I ) . Secondary measu res , such as t h e i n t e r -i n t r o m i s s i o n i n t e r v a l ( I I I , c a l c u l a t e d as t h e e j a c u l a t i o n l a t e n c y / n u m b e r o f i n t r o m i s s i o n s ) and t h e i n t r o m i s s i o n r a t i o ( I R , c a l c u l a t e d as t h e number o f i n t r o m i s s i o n s / n u m b e r o f mounts w i t h and w i t h o u t i n t r o m i s s i o n ) a r e a l s o r e p o r t e d . Some s t u d i e s use u l t r a s o n i c r e c o r d i n g t e c h n i q u e s t o d i v i d e t h e PEI i n t o i t s a b s o l u t e and r e l a t i v e p h a s e s . S h o r t l y a f t e r e j a c u l a t i o n , male r a t s e m i t a 22 kHz v o c a l i z a t i o n t h a t c o n t i n u e s f o r a p p r o x i m a t e l y 50% t o 75% o f t h e PEI ( B a r f i e l d & Geye r , 1975; Sachs & B a r f i e l d , 1 9 7 6 ) . T h i s p e r i o d i s c o n s i d e r e d t h e a b s o l u t e r e f r a c t o r y phase because d u r i n g i t males a r e t y p i c a l l y i n a c t i v e , and a r e d r a m a t i c a l l y h y p o s e n s i t i v e t o a v a r i e t y o f e x t e r n a l s t i m u l i , i n c l u d i n g shock ( P o l l a k & Sachs , 1 9 7 5 ) . Once t h e 22 kHz v o c a l i z a t i o n s c e a s e , males become more a c t i v e b e h a v i o r a l l y and can be i n d u c e d t o c o p u l a t e w i t h shock or t a i l p i n c h (Sachs & M e i s e l , 1 9 8 8 ) . D u r i n g t h i s r e l a t i v e r e f r a c t o r y p h a s e , males d i s p l a y more i n t e r e s t i n t h e fema le and b e g i n a p a t t e r n o f a n o g e n i t a l i n v e s t i g a t i o n and p u r s u i t t h a t f i n a l l y l e a d s t o t h e r e i n i t i a t i o n o f c o p u l a t i o n . A l t h o u g h most s t u d i e s t h a t examine d r u g e f f e c t s on t h e s e x u a l b e h a v i o r o f male r a t s assess s e v e r a l o f t h e s e measures t h r o u g h t h e f i r s t e j a c u l a t o r y s e r i e s and p o s t e j a c u l a t o r y i n t e r v a l , o t h e r s have examined d r u g e f f e c t s t h r o u g h s e v e r a l e j a c u l a t o r y s e r i e s or t o s e x u a l e x h a u s t i o n ( e . g . G r a y , D a v i s , & Dewsbury , 1974 ; H u l l , B i t r a n , Pehek, Warner , Band & Holmes, 1986; Hyyppa, L e h t i n e n , & R i n n e , 1 9 7 1 ; M i l l e r & Baum, 1987 ; P faus & G o r z a l k a , 1 9 8 7 ) . A n a l y s i s o f Sexua l M o t i v a t i o n T r a d i t i o n a l l y , t h e e v a l u a t i o n o f s e x u a l m o t i v a t i o n i n t h e male r a t has been approached i n two f u n d a m e n t a l l y d i f f e r e n t ways The f i r s t a p p r o a c h has been t o a n a l y z e measures o f b e h a v i o r p e r f o r m e d by t h e male i n i n t e r a c t i o n w i t h t h e f e m a l e r a t . These measures have g e n e r a l l y i n c l u d e d a l l o f t h e c o p u l a t o r y b e h a v i o r s l i s t e d a b o v e , w i t h s p e c i a l s t a t u s b e i n g g i v e n t o mount and i n t r o m i s s i o n l a t e n c i e s because t h e y r e f l e c t t h e f i r s t c o p u l a t o r y c o n t a c t made by t h e m a l e , a l t h o u g h b o t h may c o n s i s t o f m o t i v a t i o n a l and p e r f o r m a n c e components (Cherney & Berman t , 1970 Sachs & B a r f i e l d , 1 9 7 6 ) . The number o f i n t r o m i s s i o n s p r e c e d i n g e j a c u l a t i o n , t h e I I I , and t h e e j a c u l a t i o n l a t e n c y have a l s o been viewed as measures of sexual motivation that r e f l e c t either the rate of copulation or the amount of g e n i t a l stimulation required for e j a c u l a t i o n . For example, Larsson (1956) described the "enforced i n t e r v a l e f f e c t " , in which an experimenter-imposed lengthening of the III (achieved by presenting a sexually receptive female to a male at i n t e r v a l s longer than the male's normal III) reduced the number of intromissions required for e j a c u l a t i o n . Larsson noted that the interruption in copulation made the males appear " r e s t l e s s and apparently excited" (p. 121). In addition, copulation would resume immediately upon replacement of the female. These observations suggest that the i n t e r r u p t i o n of copulation increases sexual arousal and reduces the amount of penile stimulation required for e j a c u l a t i o n . Likewise, the III i t s e l f appears to be related inversely to a r o u s a b i l i t y . Karen and B a r f i e l d (1975) demonstrated that males with short I l l s (and thus a faster copulatory rate) achieved more ejaculations p r i o r to sexual exhaustion than males with long I l l s . F i n a l l y , some studies have used the persistence of mounting behavior following penile anesthesia or c a s t r a t i o n as a measure of sexual motivation (e.g., Malmnas, 1973; Dorsa & Smith, 1980). There are several problems in the i n t e r p r e t a t i o n of data derived from t h i s f i r s t approach. Behaviors performed by the male in i n t e r a c t i o n with the female can be confounded by her l e v e l of sexual r e c e p t i v i t y . The use of penile anesthesia or c a s t r a t i o n generally precludes the f u l l expression of copulatory behavior. Although each measure of copulatory behavior may be 17 s e x u a l l y m o t i v a t e d by d e f i n i t i o n , t h e use o f some or a l l o f t h e s e measures t o i n f e r s e x u a l m o t i v a t i o n r e s u l t s i n a f a i l u r e t o s p e c i f y t h e r e l a t i v e c o n t r i b u t i o n o f e a c h . I n d e e d , d i s t i n c t components o f s e x u a l m o t i v a t i o n may e x i s t t h a t p r i m e d i f f e r e n t a s p e c t s o f c o p u l a t o r y b e h a v i o r (Sachs & B a r f i e l d , 1 9 7 6 ) . The second a p p r o a c h has been t o a n a l y z e b e h a v i o r s p e r f o r m e d by t h e male e i t h e r t o g a i n access t o , or i n a n t i c i p a t i o n o f , a s e x u a l l y r e c e p t i v e f e m a l e r a t . Such b e h a v i o r s have i n c l u d e d p e r f o r m a n c e i n o b s t r u c t i o n boxes (Warner , 1 9 2 7 ) , s t r a i g h t a l l e y r u n n i n g ( S h e f f i e l d , W u l f f , & B a c k e r , 1 9 5 1 ) , maze l e a r n i n g (Wha len , 1 9 6 1 ) , c r o s s i n g o f e l e c t r i f i e d g r i d s (Moss, 1 9 2 4 ) , and b a r - p r e s s i n g b e h a v i o r ( E v e r i t t , F r a y , K o s t a r c z y k , T a y l o r , & S t a c e y , 1987; J o w a i s a s , T a y l o r , Dewsbury , & M a l a g o d i , 1 9 7 1 ; Sachs , M a c a i o n e , & F a g y , 1974 ; S c h w a r t z , 1 9 5 6 ) . A l t h o u g h t h e i n t e r p r e t a t i o n o f d a t a d e r i v e d f r o m t h i s second a p p r o a c h i s s t r a i g h t f o r w a r d and t h e o r e t i c a l l y e l e g a n t , some o f t h e s i t u a t i o n s a r e r e l a t i v e l y a r t i f i c i a l and t h e e s t a b l i s h m e n t o f b a s e l i n e r a t e s o f p e r f o r m a n c e i s o f t e n e x t r e m e l y t i m e - c o n s u m i n g . Perhaps because o f h i s t o r i c a l p r e c e d e n t , or t h e t i m e - c o n s u m i n g n a t u r e o f t e a c h i n g a n i m a l s i n s t r u m e n t a l r e s p o n s e s t h a t have no n a t u r a l p l a c e i n t h e e x p r e s s i o n o f s e x u a l b e h a v i o r , many i n v e s t i g a t o r s use measures o f c o p u l a t o r y b e h a v i o r , i n p a r t i c u l a r t h e mount and i n t r o m i s s i o n l a t e n c i e s , t o make g e n e r a l i n f e r e n c e s a b o u t s e x u a l m o t i v a t i o n . Based on t h e f i r s t a p p r o a c h , Beach (1956) p r o p o s e d a t w o -f a c t o r t h e o r y o f s e x u a l m o t i v a t i o n t h a t e s s e n t i a l l y r e s t a t e d t h e 18 d i s t i n c t i o n noted above between a n t i c i p a t o r y and consummatory aspects of behavior. He suggested that the i n i t i a t i o n and consummation of copulatory behavior were under the control of two independent motivational processes. The f i r s t process, c a l l e d the "sexual arousal mechanism" was thought to orient the male toward the female and i n i t i a t e mounts. The second process, c a l l e d the "intromission and ejaculation mechanism" was thought to drive the stereotyped pattern of penile intromissions that culminates in e j a c u l a t i o n . More recently, Sachs (1978) published the r e s u l t s of a factor analysis of ten measures of sexual behavior performed by the male in i n t e r a c t i o n with the female. From the r e s u l t s of t h i s analysis, Sachs proposed the existence of at least four independent processes underlying the performance of sexual behavior by the male r a t . These processes were characterized by factors c a l l e d the i n i t i a t i o n factor, the copulatory rate factor, the h i t rate (the percentage of mounts r e s u l t i n g in intromission), and the intromission count. Although Sachs' approach retained a d i s t i n c t i o n between preparatory and consummatory aspects of copulatory behavior, i t separated the consummatory aspect into three independent, but obviously i n t e r a c t i v e , processes (copulatory rate factor, h i t rate, and intromission count). One of the most complex models of sexual motivation comes from the work of Toates (Toates, 1986; Toates & O'Rourke, 1978). This model assumes that sexual motivation or arousal depends upon both the magnitudes of the external incentive and the inte r n a l state of sexual a r o u s a b i l i t y . Although i n d i v i d u a l measures of copulatory behavior are viewed as forming part of an i n t r i c a t e cascade, from the f i r s t mount to ej a c u l a t i o n , with each behavior a f f e c t i n g the l i k e l i h o o d of subsequent events, p o t e n t i a l motivational factors are nested within c e r t a i n measures. For example, blood hormone l e v e l s contribute to sexual a r o u s a b i l i t y by a l t e r i n g the e x c i t a b i l i t y of c e r t a i n neurons. This a l t e r s the response that male rats make towards a sexually-arousing incentive and controls the threshold of arousal that must be reached before mounts and intromissions are i n i t i a t e d . Once copulation has been i n i t i a t e d , however, blood hormone le v e l s do not appear to play a decisive r o l e . Other i n t e r n a l events, such as the g e n i t a l stimulation derived from each intromission and the active pursuit of the female, appear to s e n s i t i z e an ejaculation mechanism. Ej a c u l a t i o n , in turn, desensitizes the pathways involved in sexual arousal or a r o u s a b i l i t y . Although Toates discusses the importance of using instrumental behavior or pursuit of the female as indices of motivation, he notes that the rate at which male rats w i l l bar press for a primary sexual incentive (e.g., a receptive female) i s low r e l a t i v e to rats reinforced with food (instrumental behavior i s dependent upon both the nature of the task and the s i z e of the d i s c r e t e units that constitute the goal). Toates, however, makes no attempt to place instrumental responding for a sexual reward within the framework of the model system he proposes for sexual motivation. It i s not clear in Toates' model what aspects of sexual 20 motivation might be inferred from instrumental responding, nor what a f f e c t such responding might have on the subsequent expression of copulation. In summary, elements of the second approach described above have not been integrated within major t h e o r e t i c a l models of sexual motivation or behavior. This makes i t d i f f i c u l t to es t a b l i s h a clear d i s t i n c t i o n between a n t i c i p a t o r y or preparatory sexual behaviors and consummatory sexual behaviors based on empirical evidence. As noted previously, both mount and intromission latencies and the PEI (measures that constitute Beach's sexual arousal mechanism and Sachs' i n i t i a t i o n factor) can be confounded by the degree of sexual r e c e p t i v i t y of the female. It i s incorrect to use mount or intromission latencies to i n f e r a n t i c i p a t o r y or preparatory sexual motivation because both can be considered consummatory acts. Unfortunately, other behaviors that males may engage in p r i o r to mounting the female (e.g., grooming, searching, and pursuit) are r a r e l y reported in assessments of sexual behavior although they may constitute important sexually motivated preparatory or a n t i c i p a t o r y behaviors. Separating sexual behavior into anticipatory/preparatory and consummatory components may be a valuable h e u r i s t i c for i d e n t i f y i n g the neural mechanisms that control p a r t i c u l a r aspects of sexual behavior. Several studies have noted that the active pursuit of a sexually receptive female does not nece s s a r i l y r e s u l t in copulation. For example, castrated male rats w i l l m a i n t a i n a h i g h r a t e o f p r e c o p u l a t o r y i n v e s t i g a t i o n o f a r e c e p t i v e f e m a l e ' s a n o g e n i t a l a r e a l o n g a f t e r t h e y have ceased t o d i s p l a y c o p u l a t o r y b e h a v i o r ( M a d l a f o u s e k , H l i n a k , & B e r a n , 1 9 7 6 ) . T r e a t m e n t w i t h o p i o i d d r u g s ( M e y e r s o n , 1981) o r l e s i o n s o f t h e m e d i a l p r e o p t i c a r e a (Heimer & L a r s s o n , 1966) e l i m i n a t e male c o p u l a t o r y b e h a v i o r b u t l e a v e p r e c o p u l a t o r y i n v e s t i g a t i o n and p u r s u i t o f t h e f e m a l e i n t a c t . Perhaps t h e most c o n v i n c i n g d e m o n s t r a t i o n o f a p r e p a r a t o r y and consummatory d i s t i n c t i o n i n t h e s e x u a l b e h a v i o r o f male r a t s was made by E v e r i t t and S t a c y ( 1 9 8 7 ) , i n w h i c h c e r t a i n l e s i o n s o f t h e m e d i a l p r e o p t i c a r e a e l i m i n a t e d c o p u l a t o r y b e h a v i o r i n t h o s e males b u t had no e f f e c t on r a t e s o f b a r - p r e s s i n g t o g a i n access t o a s e x u a l l y r e c e p t i v e f e m a l e . Had mount o r i n t r o m i s s i o n l a t e n c i e s been t h e o n l y measures o f " p r e p a r a t o r y " s e x u a l b e h a v i o r i n t h o s e s t u d i e s , t h e r e wou ld have been r e a s o n t o s u g g e s t t h a t t h e t r e a t m e n t s e l i m i n a t e d c o p u l a t o r y b e h a v i o r by d i s r u p t i n g a s e x u a l a r o u s a l mechanism or an i n i t i a t i o n f a c t o r . A l t h o u g h i t i s p o s s i b l e t h a t p r e c o p u l a t o r y b e h a v i o r s a r e d r i v e n by t h e same mechanism t h a t i n i t i a t e s m o u n t i n g , b u t a r e s i m p l y l e s s s e n s i t i v e t o t h e p a r t i c u l a r s u r g i c a l or c h e m i c a l t r e a t m e n t s d e s c r i b e d a b o v e , i t i s a l s o p o s s i b l e t h a t b e h a v i o r s p e r f o r m e d by t h e male t o g a i n access t o a s e x u a l l y r e c e p t i v e f e m a l e , or o t h e r w i s e i n a n t i c i p a t i o n o f he r p r e s e n c e , may be d i s s o c i a t e d f r o m t h e i n i t i a t i o n o f c o p u l a t o r y b e h a v i o r much l i k e f o r a g i n g can be d i s s o c i a t e d f r o m f e e d i n g . Thus s e v e r a l m o t i v a t i o n a l components may c o n v e r g e t o i n d u c e consummatory s e x u a l b e h a v i o r s . This section has outlined some of the t h e o r e t i c a l issues that must be considered when making inferences about the sexual motivation of male r a t s . Although the l i t e r a t u r e on the role of DA in feeding and avoidance behavior makes r e l a t i v e l y clear d i s t i n c t i o n s between anticipatory/preparatory behaviors and consummatory behaviors, the l i t e r a t u r e on DA and sexual behavior does not. This makes i t d i f f i c u l t to place the e f f e c t s of treatments that either enhance or disrupt DA transmission within a more general t h e o r e t i c a l framework. Role of DA in the Sexual Behavior of Male Rats: A Review Numerous reviews of the neuropharmacology of DA in the sexual behavior of male rats conclude that elevated DA a c t i v i t y serves to increase sexual arousal in the presence of appropriate incentive s t i m u l i (see e.g., Bitran & H u l l , 1987; Crowley & Zemlan, 1981; Sachs & Meisel, 1988). This evidence i s generally taken from studies using both systemic and c e n t r a l administration of DA agonists or antagonists, in addition to lesions of major DA f i b e r s or terminals. However, a c a r e f u l reading of t h i s l i t e r a t u r e reveals a complex and often c o n t r o v e r s i a l role of DA in both motivational and performance aspects of sexual behavior. This section reviews the e f f e c t s of pharmacological treatment with DA agonists or antagonists on male sexual behavior, e l e c t r o l y t i c and neurochemical lesions of DA pathways and terminal regions on male sexual behavior, and ex vivo analyses of DA and i t s metabolites following periods of copulation. 23 E f f e c t o f DA a g o n i s t s S y s t e m i c a d m i n i s t r a t i o n o f a v a r i e t y o f DA a g o n i s t s , such as a p o m o r p h i n e , N - n - p r o p y l - n o r a p o m o r p h i n e , t h e e r g o t d e r i v a t i v e s l i s u r i d e and p e r g o l i d e , t h e D I s e l e c t i v e b e n z a z e p i n e d e r i v a t i v e SKF 38393; t h e D 2 - s e l e c t i v e p a r t i a l e r g o l i n e s q u i n p i r o l e and LY 163502, t h e a m i n o i n d a n e RDS-127, t h e (+ ) i somer o f t h e p h e n y l p i p e r i d i n e 3-PPP, t h e a z e p i n e d e r i v a t i v e B-HT 9 2 0 , t h e DA r e l e a s e p r o m o t e r d - a m p h e t a m i n e , and t h e DA p r e c u r s o r 1-DOPA ( i n c o m b i n a t i o n w i t h a p e r i p h e r a l d e c a r b o x y l a s e i n h i b i t o r ) , g e n e r a l l y f a c i l i t a t e s s e x u a l a r o u s a l and b e h a v i o r i n i n t a c t , s e x u a l l y a c t i v e male r a t s e i t h e r by d e c r e a s i n g t h e number o f i n t r o m i s s i o n s r e q u i r e d f o r e j a c u l a t i o n , by d e c r e a s i n g t h e e j a c u l a t i o n l a t e n c y , o r , i n some c a s e s , by d e c r e a s i n g t h e PEI ( A h l e n i u s & L a r s s o n , 1 9 8 4 a , b ; A h l e n i u s , E n g e l , L a r s s o n , & Svensson , 1982 ; B e n a s s i -B e n e l l i & F e r r a r i , 1979; B i g n a m i , 1966; C a g i a n o , B a r f i e l d , W h i t e , P l e i m , & Cuomo, 1987; C l a r k , S t a f a n i c k , S m i t h , & D a v i d s o n , 1983; F a l a s c h i e t a l . , 1 9 8 1 ; F e r r a r i , B a g g i o , & M a n g i a f i c o , 1985; Foreman & H a l l , 1987; Gessa & T a g l i a m o n t e , 1975; N a p o l i - F a r r i s , F r a t t a , & Gessa, 1984; P a g l i e t t i , P e l l e g r i n i - Q u a r a n t o t t i , Mereu , & Gessa, 1978; P faus & P h i l l i p s , 1987 ; S o u l a i r a c & S o u l a i r a c , 1 9 7 5 ) . S i m i l a r l y , 1-DOPA, a p o m o r p h i n e , d - a m p h e t a m i n e , and t h e e r g o t s b r o m o c r i p t i n e and l i s u r i d e , have been r e p o r t e d t o s t i m u l a t e c o p u l a t o r y b e h a v i o r i n e i t h e r i n t a c t , s e x u a l l y i n a c t i v e males ( D a l l o , L e k k a , & K n o l l , 1986; T a g l i a m o n t e , F r a t t a , De l F i a c c o , & Gessa, 1 9 7 4 ) , i n t a c t , s e x u a l l y i n a c t i v e h y p e r p r o l a c t i n e m i c males ( B a r t k e e t a l . , 1 9 8 3 ) , i n t a c t , s e x u a l l y i n a c t i v e males w i t h l e s i o n s o f t h e m e d i a l p r e o p t i c a r e a (Hansen, K o h l e r , & Ross , 1 9 8 2 ) , and s e x u a l l y i n a c t i v e c a s t r a t e d males w i t h or w i t h o u t s u b t h r e s h o l d t e s t o s t e r o n e r e p l a c e m e n t (Agmo & F e r n a n d e z , 1989 ; Malmnas, 1973, 1976, 1 9 7 7 ) . The D2 s e l e c t i v e a g o n i s t q u i n p i r o l e has a l s o been r e p o r t e d t o a b o l i s h t h e p o s t e j a c u l a t o r y 22 kHz v o c a l i z a t i o n (Cag iano e t a l . , 1 9 8 7 ) . Some o f t h e s e d r u g s , e . g . , apomorph ine and 1-DOPA, a r e assumed t o e x e r t t h e i r e f f e c t s on male c o p u l a t o r y b e h a v i o r c e n t r a l l y , because t h e c e n t r a l l y - a c t i n g DA r e c e p t o r a n t a g o n i s t s p i m o z i d e , s u l p i r i d e , m e t o c l o p r a m i d e , and h a l o p e r i d o l , b u t n o t t h e p e r i p h e r a l l y - a c t i n g DA r e c e p t o r a n t a g o n i s t d o m p e r i d o n e , r e v e r s e t h e s e e f f e c t s ( F a l a s c h i e t a l . , 1 9 8 1 ; Malmnas, 1976 ; T a g l i a m o n t e e t a l . , 1 9 7 4 ) . Low doses o f apomorph ine or RDS-127 a l s o f a c i l i t a t e t h e d i s p l a y o f p e n i l e r e f l e x e s such as e r e c t i o n and s e m i n a l e m i s s i o n i n i n t a c t , s e x u a l l y a c t i v e males ( C l a r k e t a l . , 1983 ; Pehek, Thompson, E a t o n , B a z z e t , & H u l l , 1 9 8 8 a ) , e f f e c t s t h a t a r e s e l e c t i v e l y r e v e r s e d w i t h c e n t r a l l y - a c t i n g DA a n t a g o n i s t s . F i n a l l y , h i g h doses o f DA a g o n i s t s d i s r u p t c o p u l a t i o n e i t h e r by d e l a y i n g e j a c u l a t i o n or by d e c r e a s i n g t h e p r o p o r t i o n o f r a t s t h a t i n i t i a t e c o p u l a t o r y b e h a v i o r . T h i s d i s r u p t i o n may o c c u r because h i g h doses o f DA a g o n i s t s i n d u c e c o m p e t i n g s t e r e o t y p y r e s p o n s e s . A l t h o u g h t h e s e d a t a s u g g e s t t h a t modera te i n c r e a s e s i n DA a c t i v i t y f a c i l i t a t e p e n i l e r e f l e x e s and e j a c u l a t i o n i n s e x u a l l y a c t i v e r a t s , and s t i m u l a t e c o p u l a t o r y a c t i v i t y i n s e x u a l l y i n a c t i v e r a t s , some o f t h e e f f e c t s a r e c o n t r o v e r s i a l . For 25 e x a m p l e , some s t u d i e s r e p o r t no e f f e c t o f b r o m o c r i p t i n e or 1-DOPA on t h e c o p u l a t o r y b e h a v i o r o f i n t a c t , s e x u a l l y a c t i v e males ( A h l e n i u s , E n g e l , L a r s s o n , & Svensson , 1982; Hyyppa e t a l . , 1 9 7 1 ; P faus & P h i l l i p s , u n p u b l i s h e d o b s e r v a t i o n s ) , o r c a s t r a t e d males w i t h t e s t o s t e r o n e r e p l a c e m e n t (Agmo & F e r n a n d e z , 1 9 8 9 ) , whereas o t h e r s r e p o r t t h a t r e l a t i v e l y l ow doses o f 1-DOPA i n c r e a s e , r a t h e r t h a n d e c r e a s e , t h e e j a c u l a t i o n l a t e n c y ( e . g . , Gray e t a l . , 1 9 7 4 ) . I n a d d i t i o n , t h e f a c i l i t a t i o n o f e j a c u l a t i o n i n d u c e d by some DA r e c e p t o r a g o n i s t s ( e . g . , l i s u r i d e , L Y - 1 4 1 8 6 5 , and RDS-127) i s n o t r e v e r s e d by p r e t r e a t m e n t w i t h DA a n t a g o n i s t s ( A h l e n i u s & L a r s s o n , 1984b; C l a r k & S m i t h , 1 9 8 6 ) . However , t h e f a c i l i t a t i o n o f m o u n t i n g b e h a v i o r by l i s u r i d e i n s e x u a l l y i n a c t i v e r a t s can be r e v e r s e d by a h i g h dose o f h a l o p e r i d o l ( B a g g i o & F e r r a r i , 1 9 8 3 ) . U n f o r t u n a t e l y , some o f t h e DA a g o n i s t s t e s t e d ( e . g . , t h e e r g o t s ) b i n d t o a v a r i e t y o f r e c e p t o r s o t h e r t h a n t h e DA s u b t y p e s . T h i s makes assessments o f r e c e p t o r s e l e c t i v i t y q u e s t i o n a b l e . A n o t h e r ma jo r p r o b l e m w i t h t h e s y s t e m i c a d m i n i s t r a t i o n o f DA a g o n i s t s i s t h a t t h e y may b i n d t o DA r e c e p t o r s i n s e v e r a l DA t e r m i n a l r e g i o n s s i m u l t a n e o u s l y . Thus i t i s i m p o s s i b l e f r o m t h o s e s t u d i e s t o d e t e r m i n e whe the r p a r t i c u l a r DA t e r m i n a l r e g i o n s m e d i a t e t h e e f f e c t s o f t h o s e d r u g s . To d a t e , two g r o u p s have examined t h e e f f e c t s o f c e n t r a l a d m i n i s t r a t i o n o f DA a g o n i s t s . Svenssen and Hansen (1984)- f o u n d no s i g n i f i c a n t e f f e c t o f i n t r a t h e c a l a d m i n i s t r a t i o n o f a range o f doses o f DA (up t o 400 ug) t o t h e s u b a r a c h n o i d space on t h e c o p u l a t o r y b e h a v i o r o f 26 i n t a c t , sexually active r a t s , i n d i c a t i n g that s p i n a l DA terminals were not important for the regulation of copulatory behavior by DA. However, in that study a 400 ug dose of DA infused into the l a t e r a l v e n t r i c l e s s i g n i f i c a n t l y decreased the number of intromissions/min, an e f f e c t consistent with the decreased number of intromissions t y p i c a l l y observed with systemic administration of DA agonists. This suggested that supraspinal s i t e s alone were responsible for the modulation of copulatory behavior by DA agonists. A comprehensive seri e s of experiments was conducted by Hull et a l . (1986) in which apomorphine was infused u n i l a t e r a l l y into either the medial preoptic area (MPOA), caudate-putamen, nucleus accumbens, l a t e r a l septum, or l a t e r a l v e n t r i c l e of i n t a c t , sexually active r a t s . Infusion of the lowest dose into the v e n t r i c l e decreased the t o t a l number of ejaculations, increased the III (meaning that i t slowed the rate of copulation), and decreased the number of intromissions. Two higher doses (0.5 and 2.0 ug) infused into ^either the v e n t r i c l e or the MPOA increased the t o t a l number of ejaculations, increased the intromission ratio,, and decreased the I I I , the ejaculation latency, and the PEI. Although the highest dose infused into the nucleus accumbens decreased the intromission latency, t h i s e f f e c t was of borderline s t a t i s t i c a l s i g n i f i c a n c e . F i n a l l y , apomorphine had no ef f e c t on copulatory behavior following infusions into either the caudate-putamen or l a t e r a l septum. These r e s u l t s implicated the MPOA as an important s i t e in the regulation of male sexual 27 behavior by DA agonists. Subsequent studies by Hull's group have shown that the ef f e c t of apomorphine infusions into the MPOA on male copulatory behavior can be reversed with the DA antagonist c i s - f l u p e n t h i x o l (Pehek et a l . , 1988c), and that apomorphine increases penile reflexes when infused into either the MPOA or paraventricular nucleus (Pehek, Thompson, & Hu l l , 1988b). Apomorphine infusions into the paraventricular nucleus also increased the number of seminal emissions in that study, an e f f e c t not observed following infusion of apomorphine into the MPOA. These data suggest that the populations of DA receptors that regulate penile reflexes and seminal emission may have separate anatomical l o c a l i z a t i o n s . In contrast to the r e s u l t s of Svenssen and Hansen (1984), Pehek et a l . (1988b) also reported that i n t r a t h e c a l administration of apomorphine (50 ug) to the lumbosacral but not midthoracic sections of the sp i n a l cord decreased the number of intromissions and increased the III in in t a c t , sexually active r a t s . This dose of apomorphine also decreased the percentage of rats d i s p l a y i n g penile r e f l e x e s , suggesting that DA receptors in both the MPOA and lumbosacral section of the spina l cord may integrate penile reflexes and motor aspects of copulation. F i n a l l y , Hull et a l . (1990) reported that infusion of the D2-selective agonist LY 163502 (10 ug) to the MPOA increased mount and intromission latencies and decreased the number of intromissions in in t a c t , sexually active r a t s . The D l - s e l e c t i v e agonist SKF-82526 had no ef f e c t alone or together with LY 163502 on any aspect of 28 c o p u l a t o r y b e h a v i o r . I n c o n t r a s t t o t h e r e s u l t s o f H u l l e t a l . ( 1 9 8 6 ) , E v e r i t t , Cador , and Robb ins (1989) d e m o n s t r a t e d t h a t b i l a t e r a l i n f u s i o n o f d -amphetamine t o t h e n u c l e u s accumbens a f f e c t e d s e v e r a l measures o f c o p u l a t o r y b e h a v i o r . Bo th mount and i n t r o m i s s i o n l a t e n c i e s were r e d u c e d f o l l o w i n g i n f u s i o n o f 1 u g , b u t n o t f o l l o w i n g 3 or 10 u g . However, a l l doses i n c r e a s e d t h e PEI and t h e 3 ug dose r e d u c e d t h e p r o p o r t i o n o f r a t s t h a t e j a c u l a t e d . E v e r i t t e t a l . a l s o examined t h e e f f e c t o f i n t r a a c c u m b e n s a d m i n i s t r a t i o n o f d -amphetamine f o l l o w i n g e x c i t o t o x i c l e s i o n s o f c e l l b o d i e s i n t h e b a s o l a t e r a l amygdala ( w h i c h send p r o j e c t i o n s t o t h e accumbens ) . A l t h o u g h l e s i o n s o f t h e b a s o l a t e r a l amygdala had no s i g n i f i c a n t e f f e c t on c o p u l a t o r y b e h a v i o r , t h e y s i g n i f i c a n t l y r e d u c e d t h e r a t e o f i n s t r u m e n t a l r e s p o n d i n g f o r a c o n d i t i o n e d s t i m u l u s t h a t s i g n a l l e d t h e p r e s e n t a t i o n o f a s e x u a l l y r e c e p t i v e f e m a l e . None o f t h e doses o f d -amphetamine a f f e c t e d t h e c o p u l a t o r y b e h a v i o r o f r a t s w i t h a m y g d a l o i d l e s i o n s ; however , a l l doses i n c r e a s e d t h e r a t e o f i n s t r u m e n t a l r e s p o n d i n g f o r t h e c o n d i t i o n e d s t i m u l u s . I n a d d i t i o n , b i l a t e r a l i n f u s i o n o f 1 ug t o t h e accumbens i n c r e a s e d r a t e s o f i n s t r u m e n t a l r e s p o n d i n g i n b o t h l e s i o n e d and sham-c o n t r o l r a t s d u r i n g s e s s i o n s i n w h i c h t h e c o n d i t i o n e d s t i m u l u s was o m i t t e d . These d a t a i n d i c a t e t h a t b o t h t h e b a s o l a t e r a l amygda la and n u c l e u s accumbens p l a y an i m p o r t a n t r o l e i n t h e c o n t r o l o f c o n d i t i o n e d r e s p o n d i n g f o r a s e x u a l r e w a r d . Taken t o g e t h e r , t h e r e s u l t s o f s t u d i e s e x a m i n i n g t h e c e n t r a l a d m i n i s t r a t i o n o f DA a g o n i s t s s u g g e s t t h a t b o t h s p i n a l and hypothalamic DA terminals play an important role in the f a c i l i t a t i o n of copulatory rate, e j a c u l a t i o n , and penile reflexes by DA agonists. Although the administration of apomorphine to mesolimbic and mesostriatal DA terminals did not a l t e r copulatory behavior s i g n i f i c a n t l y , the administration of d-amphetamine to the nucleus accumbens decreased both mount and intromission latencies and restored the a b i l i t y of rats with amygdaloid lesions to perform instrumental responses for a secondary sexual reward. These data suggest that DA transmission in d i f f e r e n t brain areas may be important for d i f f e r e n t aspects of copulatory behavior. E f f e c t of DA antagonists Inferences about the normal r o l e of DA in sexual behavior can be made by assessing the e f f e c t s of DA antagonists. The f i r s t report of an e f f e c t of a DA antagonist on sexual behavior was made by Zimbardo and Barry (1958), who observed that chlorpromazine (1 mg/kg, IP) increased mount and intromission l a t e n c i e s , decreased the ejaculation latency, and decreased the number of intromissions required for ejaculation in i n t a c t , sexually active r a t s . Subsequent studies have reported s i m i l a r e f f e c t s with a v a r i e t y of DA antagonists. the systemic administration of low-to-moderate doses of c e n t r a l l y - a c t i n g DA antagonists, such as the t y p i c a l neuroleptic drugs haloperidol and pimozide, increases mount and intromission l a t e n c i e s , decreases the number of intromissions required for ejacu l a t i o n , and, in some cases, decreases the ejaculation latency and increases the PEI in in t a c t , sexually active rats (Agmo& Fernandez, 1989; Ahlenius & Larsson, 1984a; Mcintosh & B a r f i e l d , 1984; Pfaus & P h i l l i p s , 1989). Higher doses of these drugs t y p i c a l l y abolish copulatory behavior. Some a t y p i c a l neuroleptics, such as clozapine and s u l p i r i d e , increase intromission latencies but have no e f f e c t on the number of intromissions once copulatory behavior has been i n i t i a t e d (Pfaus & P h i l l i p s , 1989), whereas others, such as t h i o r i d a z i n e , also increase the eja c u l a t i o n latency (Ahlenius, Heimann, & Larsson, 1979). Other c e n t r a l l y - a c t i n g DA antagonists, such as the antiemetic drug metoclopramide, decrease the number of intromissions but have no e f f e c t on the intromission latency (Pfaus & P h i l l i p s , 1989). Pimozide blocks the stimulation of copulatory behavior induced by e l e c t r i c footshock in i n t a c t , sexually inactive rats (Antelman, Herndon, Caggiula, & Shaw, 1975). A dose of the D2 s e l e c t i v e antagonist raclopride (0.5 mg/kg, SC) that blocked the supression of the 22 kHz v o c a l i z a t i o n induced by the D2 s e l e c t i v e agonist quinpirole, i t s e l f abolished copulatory behavior in i n t a c t , sexually active rats (Cagiano et a l . , 1987). A low dose of the DI s e l e c t i v e antagonist SCH 23390 (0.01 mg/kg, SC) had no e f f e c t on any measure of copulatory behavior in that study. The pe r i p h e r a l l y - a c t i n g DA antagonist domperidone does not a f f e c t the copulatory behavior or penile reflexes of i n t a c t , sexually active rats (Falaschi et a l . , 1981; Pehek et a l . , 1988); however, i t elevates serum p r o l a c t i n l e v e l s and produces a s l i g h t increase in the mount and intromission 31 latencies of castrated, testosterone-treated male rats after a s i n g l e administration (Bailey & Herbert, 1982). F i n a l l y , both spiperone and clozapine decrease the number of mounts and intromissions/min in castrated rats given s t e r o i d replacement with dihydrotestosterone or e s t r a d i o l (Baum & Starr, 1980). Unfortunately, there are numerous inconsistencies in t h i s l i t e r a t u r e . For example, low doses of haloperidol have been reported both to decrease (Ahlenius & Larsson, 1984a) and increase (Ahlenius & Larsson, 1984b) the number of intromissions. Some investigators report substantial increases in the PEI following the administration of t y p i c a l neuroleptics (Ahlenius & Larsson, 1984a,b; Mcintosh & B a r f i e l d , 1984), whereas others find no e f f e c t on t h i s measure at comparable doses of these drugs (Napoli-Farris et a l . , 1984; P a g l i e t t i et a l . , 1978; Pfaus & P h i l l i p s , 1989). A low dose of pimozide was reported to increase ejaculation latencies in one study ( P a g l i e t t i et a l . , 1978) whereas other studies reported either no e f f e c t of comparably low doses (e.g., 0.1 or 0.25 mg/kg; Agmo & Fernandez, 1989; Clark & Smith, 1986; Malmnas, 1973; Pfaus & P h i l l i p s , 1989), decreased ejaculation latencies with moderate doses (e.g., 1.0 mg/kg; Mcintosh & B a r f i e l d , 1984), or the elimination of ejaculation with higher doses (e.g., 5.0 mg/kg; Pfaus & P h i l l i p s , 1989). The a t y p i c a l neuroleptic clozapine does not a f f e c t the number of intromissions in i n t a c t , sexually active rats (Pfaus & P h i l l i p s , 1989) but decreases the mounting rate in castrated rats maintained on either dihydrotestosterone or e s t r a d i o l (Baum & 32 S t a r r , 1 9 8 0 ) . As w i t h many DA a g o n i s t s , many DA a n t a g o n i s t s b i n d t o r e c e p t o r s o t h e r t h a n t h e DA s u b t y p e s (Tamminga & G e r l a c h , 1 9 8 7 ) . M o r e o v e r , s u b s t a n t i a l d i f f e r e n c e s i n e x p e r i m e n t a l m e t h o d o l o g y may c o n t r i b u t e t o t h e s e i n c o n s i s t e n t f i n d i n g s . A l t h o u g h s y s t e m i c a d m i n i s t r a t i o n o f DA a n t a g o n i s t s a r e b e l i e v e d t o e x e r t t h e i r e f f e c t s on male s e x u a l b e h a v i o r c e n t r a l l y , few s t u d i e s have examined t h e e f f e c t s o f c e n t r a l l y -a d m i n i s t e r e d DA a n t a g o n i s t s . H u l l ' s g r o u p r e p o r t e d t h e r e s u l t s o f two s t u d i e s i n w h i c h DA a n t a g o n i s t s were a d m i n i s t e r e d t o t h e MPOA o f i n t a c t , s e x u a l l y a c t i v e r a t s . Pehek e t a l . (1988c) o b s e r v e d t h a t i n f u s i o n s o f c i s - f l u p e n t h i x o l (20 and 40 ug) t o t h e MPOA d r a m a t i c a l l y r e d u c e d t h e p r o p o r t i o n o f r a t s t h a t i n i t i a t e d c o p u l a t i o n . I n t h o s e t h a t d i d , c i s - f l u p e n t h i x o l r e d u c e d t h e t o t a l number o f e j a c u l a t i o n s and i n c r e a s e d b o t h t h e I I I and t h e l a t e n c y t o f i r s t e j a c u l a t i o n , measures t h a t f o r m p a r t o f Sachs ' c o p u l a t o r y r a t e f a c t o r . These doses had l i t t l e e f f e c t on o t h e r a s p e c t s o f c o p u l a t o r y b e h a v i o r or g e n e r a l motor a c t i v i t y . S u b s e q u e n t l y , H u l l e t a l . (1990) r e p o r t e d t h a t t h e D l - s e l e c t i v e a n t a g o n i s t SCH 23390 (10 ug) i n c r e a s e d t h e mount and i n t r o m i s s i o n l a t e n c i e s and d e c r e a s e d t h e number o f i n t r o m i s s i o n s f o l l o w i n g i n f u s i o n i n t o t h e MPOA. These e f f e c t s were i d e n t i c a l t o t h o s e f o u n d a f t e r i n f u s i o n o f t h e D 2 - s e l e c t i v e a g o n i s t LY 163502. M o r e o v e r , a b e h a v i o r a l l y - i n a c t i v e dose o f SCH 23390 (3 ug) p o t e n t i a t e d t h e e f f e c t s o f LY 163502. I t - is d i f f i c u l t t o e x p l a i n why SCH 23390 i n c r e a s e d mount and i n t r o m i s s i o n l a t e n c i e s and r e d u c e d t h e number o f i n t r o m i s s i o n s f o l l o w i n g i n f u s i o n t o t h e MPOA but c i s - f l u p e n t h i x o l (which binds to both DI and D2 receptors) did not. At f i r s t glance, i t would seem that blockade of DI receptors in the MPOA i s responsible for the major e f f e c t s of systemically administered DA antagonists. However, these data suggest that the D2/D1 r a t i o in the MPOA i s an important factor in the regulation of male sexual behavior because the s e l e c t i v e stimulation of D2 receptors or the s e l e c t i v e blockade of DI receptors in that area produces i d e n t i c a l e f f e c t s : a delay in the i n i t i a t i o n of copulation and a reduction in the ejaculatory threshold. Although DA receptors in the MPOA obviously play an important r o l e in the i n i t i a t i o n and rate of male copulatory behavior, a ro l e of DA receptors i n other brain areas cannot be ruled out. No studies have yet been published that have examined the e f f e c t of DA antagonists in other brain regions or in the spinal cord. In summary, the re s u l t s of studies using DA antagonists indicate that decreases in central DA a c t i v i t y delay or abolish the i n i t i a t i o n of copulation in sexually active male r a t s . In rats that i n i t i a t e copulation, these drugs disrupt measures of copulatory rate and h i t rate by decreasing both the number of intromissions before ejaculation and the t o t a l number of ejaculations. DA receptors in the MPOA may play an important role in the disrupt i o n of male sexual behavior induced by these drugs. Lesions of DA pathways Another way to in f e r the normal functioning of brain DA 34 systems in male sexual behavior i s to destroy DA c e l l bodies, projection f i b e r s , or terminal regions. This can be accomplished either e l e c t r o l y t i c a l l y , by passing s u f f i c i e n t current through an electrode to destroy surrounding t i s s u e , or neurochemically, by infusing a neurotoxin such as 6-hydroxydopamine (6-OHDA) which s e l e c t i v e l y destroys catecholamine neurons in the brain. Some studies also examine the a b i l i t y of DA agonists or antagonists to af f e c t male sexual behavior following lesions of DA c e l l bodies or terminals. Although copulatory behavior has been assessed in male rats following lesions of several brain areas that contain DA receptors or f i b e r s , only three systems have been studied in some d e t a i l : the incertohypothalamic (with DA terminals in the MPOA), the mesostriatal (with DA terminals in the dorsal striatum), and the mesolimbic/mesocortical (with DA terminals of inte r e s t in the nucleus accumbens, amygdala, and o l f a c t o r y t u b e r c l e ) . The e f f e c t of a general depletion of brain catecholamines on the copulatory behavior of in t a c t , sexually active male rats was investigated by Caggiula, Shaw, Antelman, and Edwards (1976). In that study, 6-OHDA was infused into the l a t e r a l v e n t r i c l e s following peripheral i n j e c t i o n of the monoamine oxidase i n h i b i t o r pargyline (to increase the amount of catecholamine depletion). Despite the fact that the combination of 6-OHDA and pargyline produced a 74% depletion of caudate DA, and 81% and 54% depletions of c o r t i c a l and hypothalamic norepinephrine, t h i s treatment produced only a transient reduction in the t o t a l number of e j aculations, in contrast to rats treated with either pargyline alone or the v e h i c l e . This e f f e c t was observed one week after treatment but had disappeared by the second week. However, subsequent administration of the tyrosine hydroxylase i n h i b i t o r alpha-methyl-p_-tyrosine (AMPT), at a dose that did not a f f e c t the copulatory behavior of nonlesioned r a t s , increased the intromission l a t e n c i e s , I l l s , and PEIs, reduced the number of intromissions, and dramatically reduced the percentage of rats that achieved an e j a c u l a t i o n . I n t e r e s t i n g l y , some of these rats did not i n i t i a t e copulatory behavior unless t h e i r t a i l s were pinched, a procedure that t y p i c a l l y stimulates copulation in sexually inactive r a t s . Furthermore, only half of the rats given 6-OHDA and pargyline copulated with females treated with haloperidol (which blocks proceptive behavior but leaves l o r d o s i s i n t a c t ) . Lesioned rats that did i n i t i a t e copulation with the "haloperidolized" females displayed increased mount and intromission l a t e n c i e s , increased PEIs and I l l s , and a reduced number of ejaculations. Some nonlesioned rats also displayed increased mount and intromission latencies with the "haloperidolized" females, but almost a l l i n i t i a t e d copulatory behavior with them. Thus, large catecholamine depletions have l i t t l e e f f e c t on the copulatory behavior of male rats under r e l a t i v e l y normal conditions, but they render those males hypersensitive to treatments that decrease catecholamine synthesis and they reduce the males* behavioral responsiveness to some external sexual cues. E l e c t r o l y t i c l e s i o n s o f t h e c a u d a l p a r t o f t h e MPOA s e v e r e l y d i s r u p t or a b o l i s h t h e c o p u l a t o r y b e h a v i o r o f male r a t s (Heimer & L a r s s o n , 1 9 6 6 / 6 7 ; Van de P o l l & van D i s , 1 9 7 9 ) . T h i s e f f e c t can a l s o be p r o d u c e d f o l l o w i n g t h e i n f u s i o n o f i b o t e n i c a c i d , a n e u r o t o x i n t h a t s e l e c t i v e l y d e s t r o y s c e l l b o d i e s (Hansen e t a l . , 1982) . These r e s u l t s a r e e s p e c i a l l y i m p o r t a n t because t h e MPOA i s a ma jo r s i t e o f s t e r o i d - c o n c e n t r a t i n g neurons i n t h e b r a i n ( P f a f f , 1968 ; Sar & S t u m p f , 1973) and i m p l a n t a t i o n o f t e s t o s t e r o n e d i r e c t l y i n t o t h e MPOA f a c i l i t a t e s c o p u l a t i o n i n c a s t r a t e d r a t s ( D a v i d s o n , 1966 ; L i s k , 1 9 6 7 ) . Rats w i t h MPOA l e s i o n s a r e i n s e n s i t i v e t o many p r o c e d u r e s t h a t can s t i m u l a t e c o p u l a t i o n i n i n t a c t , s e x u a l l y e x h a u s t e d or i n a c t i v e r a t s ( e . g . , h a n d l i n g , p r e s e n t a t i o n o f a n o v e l f e m a l e , t a i l p i n c h , or f l a n k s h o c k ; B a r f i e l d & Sachs , 1968; Heimer & L a r s s o n , 1 9 6 6 / 6 7 ; M e i s e l , 1983) . However, as n o t e d p r e v i o u s l y , t r e a t i n g MPOA- les ioned r a t s w i t h t h e n o n s e l e c t i v e D2-S1 r e c e p t o r a g o n i s t l i s u r i d e a c t i v a t e s p a r t i a l or f u l l p a t t e r n s o f c o p u l a t o r y b e h a v i o r (Hansen e t a l . , 1 9 8 2 ) . T h i s s u g g e s t s t h a t d e c r e a s e d monoamine rg i c t o n e i n t h e MPOA c o n t r i b u t e s t o t h e d i s r u p t i o n i n c o p u l a t o r y b e h a v i o r o b s e r v e d a f t e r MPOA l e s i o n s . I n c o n t r a s t t o t h e a b i l i t y o f e l e c t r o l y t i c or i b o t e n i c a c i d l e s i o n s o f t h e MPOA t o d i s r u p t or a b o l i s h male c o p u l a t o r y b e h a v i o r , u n i l a t e r a l i n f u s i o n s o f 6-OHDA i n t o t h e MPOA were r e p o r t e d n o t t o a f f e c t t h e c o p u l a t o r y b e h a v i o r o f i n t a c t , s e x u a l l y a c t i v e r a t s ( B i t r a n , H u l l , Ho lmes, & L o o k i n g l a n d , 1 9 8 8 ) . A l t h o u g h t h e 6-OHDA r e g i m e n used i n t h a t s t u d y r e s u l t e d i n a 37 small but s i g n i f i c a n t decrease in DA concentration (23%), lev e l s of the DA metabolite dihydroxyphenylacetic acid (DOPAC) did not d i f f e r s i g n i f i c a n t l y among 6-OHDA-treated rats and controls, suggesting that impulse flow had not changed in the 6-OHDA-treated r a t s . However, a dose of AMPT that did not a f f e c t the copulatory behavior of nonlesioned r a t s , decreased the t o t a l number of ejaculations and increased both the eja c u l a t i o n latencies and PEIs of 6-OHDA-treated rats af t e r infusion into the MPOA, suggesting that these rats were more s e n s i t i v e to the disrupti o n produced by AMPT. S i m i l a r l y , a dose of apomorphine infused into the MPOA that had no e f f e c t on the t o t a l number of ejaculations in nonlesioned rats (0.2 ug) increased t h i s number in 6-OHDA-treated r a t s . F i n a l l y , the di s r u p t i v e e f f e c t s of a low dose of apomorphine infused into the MPOA of nonlesioned rats (e.g., increased e j a c u l a t i o n latency, PEI, I I I , and decreased number of ejaculations) were abolished following 6-OHDA treatment, suggesting that these e f f e c t s were due in nonlesioned rats to the stimulation of presynaptic DA autoreceptors. Together, these r e s u l t s suggest that rats with 6-OHDA lesions of the MPOA are hypersensitive both to treatments that decrease catecholamine synthesis and to agonist a c t i v a t i o n of postsynaptic DA receptors. E l e c t r o l y t i c lesions of the A9 c e l l bodies in the substantia nigra pars compacta (which project DA f i b e r s mainly to the dorsal striatum) disrupt several measures of male copulatory behavior. B i l a t e r a l lesions have been reported to increase mount la t e n c i e s , 38 decrease the number of mounts/min, and decrease the number of ejaculations in i n t a c t , sexually active rats (Brackett, Iuvone, & Edwards, 1986), but not to a f f e c t other measures of copulatory behavior. These lesions depleted DA l e v e l s in the caudate by an average of 56%. In contrast, u n i l a t e r a l lesions of the compacta have been reported to increase mount and intromission l a t e n c i e s , decrease the number of intromissions, and increase both the postejaculatory v o c a l i z a t i o n duration and the PEI in i n t a c t , sexually active rats (Mcintosh & B a r f i e l d , 1984). Although these e f f e c t s were i d e n t i c a l to those produced by pimozide in that study, u n i l a t e r a l infusions of 6-OHDA produced a only a small, but s i g n i f i c a n t , increase in the PEI. B i l a t e r a l 6-OHDA lesions of the dorsal striatum also increased mount latencies (Robbins, Cador, Taylor & E v e r i t t , 1989), but only i f the males were given access to receptive females that displayed proceptive behavior. Mount latencies were not elevated s i g n i f i c a n t l y i f the males in that study were given access to receptive females treated with the DA antagonist - f l u p e n t h i x o l , a treatment that eliminates proceptive behaviors. The r e s u l t s of these studies suggest that mesostriatal DA systems are involved in both arousal and performance aspects of male copulatory behavior. B i l a t e r a l e l e c t r o l y t i c lesions of the A10 c e l l bodies in the ventral tegmental area (VTA) increased mount latencies and PEIs in i n t a c t , sexually active rats (Brackett et a l . , 1986), but did not a f f e c t other measures of copulatory behavior. Those lesions produced an average 77% depletion of DA in the nucleus accumbens. 39 S i m i l a r l y , b i l a t e r a l 6-OHDA lesions of the nucleus accumbens, an important terminal region of the A10 DA projections, also increased mount latencies (Robbins et a l . , 1989). Lesions of the corticomedial amygdala, another terminal region of the A10 DA projections, increased the number of intromissions, the I I I , and the e j a c u l a t i o n latency, and decreased the number of ejaculations to sexual exhaustion in i n t a c t , sexually active rats (Giantonio, Lund, & G e r a l l , 1970; Harris & Sachs, 1975). However, some of these e f f e c t s were reproducible only i f the stimulus females were primed with estrogen alone, a treatment that reduces the incidence of proceptive behaviors (Perkins, Perkins, & H i t t , 1980). Rats with corticomedial amygdala lesions displayed apparently normal copulatory behavior in that study with females primed with estrogen and progesterone. As noted above, E v e r i t t et a l . (1989) demonstrated that b i l a t e r a l e x c i t o t o x i c lesions of the basolateral amygdala had no e f f e c t on the copulatory behavior of i n t a c t , sexually active r a t s ; however, these lesions reduced the rate of operant responding for a secondary sexual reward. F i n a l l y , lesions of the o l f a c t o r y tubercle, another terminal region of the A10 DA projections, had no e f f e c t on the copulatory behavior of male rats (Perkins et a l , 1980). Taken together, these r e s u l t s suggest that the mesolimbic, mesocortical, n i g r o s t r i a t a l , and diencephalic DA systems play a complicated r o l e in the control of both arousal and performance aspects of male copulatory behavior. It i s i n t e r e s t i n g to note that lesions of the d o r s o l a t e r a l tegmentum abolish copulatory b e h a v i o r i n a manner s i m i l a r t o l e s i o n s o f t h e MPOA ( B r a c k e t t e t a l . , 1 9 8 6 ) . The MPOA p r o j e c t s e f f e r e n t f i b e r s t h r o u g h t h e m e d i a l f o r e b r a i n b u n d l e t o t h e d o r s o l a t e r a l tegmentum, i n a d d i t i o n t o b o t h t h e A9 and A10 c e l l g r o u p s . M o r e o v e r , t h e c o r t i c o m e d i a l amygda la p r o j e c t s e f f e r e n t f i b e r s t o t h e MPOA. I t i s d i f f i c u l t t o d i s e n t a n g l e t h e r e s u l t s o f l e s i o n s t u d i e s i n l i g h t o f t h e i n t e r c o n n e c t i o n o f t h e s e s y s t e m s . F u r t h e r m o r e , t h e g e n e r a l l a c k o f e f f e c t o f 6-OHDA i s p u z z l i n g g i v e n b o t h t h e l a r g e e f f e c t s o f e l e c t r o l y t i c l e s i o n s and t h e e f f e c t s p r o d u c e d by s y s t e m i c or c e n t r a l a d m i n i s t r a t i o n o f DA a n t a g o n i s t s . Ex v i v o a n a l y s e s o f DA and m e t a b o l i t e s Recent advances i n t h e e l e c t r o c h e m i c a l d e t e c t i o n o f t r a n s m i t t e r s u b s t a n c e s and t h e i r m e t a b o l i t e s w i t h h i g h p r e s s u r e l i q u i d c h r o m a t o g r a p h y (HPLC) have g i v e n i n v e s t i g a t o r s a new t o o l f o r a s s e s s i n g t r a n s m i t t e r a c t i v i t y i n v a r i o u s b r a i n r e g i o n s f o l l o w i n g c o n t r o l l e d p e r i o d s o f b e h a v i o r . To d a t e , t h r e e s t u d i e s have been p u b l i s h e d t h a t have examined r e g i o n a l DA a c t i v i t y f o l l o w i n g p e r i o d s o f c o p u l a t o r y b e h a v i o r i n i n t a c t , s e x u a l l y a c t i v e r a t s . A h l e n i u s , C a r l s s o n , H i l l e g a a r t , H j o r t h , and L a r s s o n (1987) examined t h e a c c u m u l a t i o n o f DOPA i n t h e n e o s t r i a t u m , s e p t u m , n u c l e u s accumbens, and a n t e r i o r h y p o t h a l a m u s f o l l o w i n g e i t h e r 10 min o f r e l a t i v e l y u n s p e c i f i e d s e x u a l a c t i v i t y ( a t l e a s t one e j a c u l a t i o n ) w i t h a r e c e p t i v e f e m a l e , 25 min o f t r e a d m i l l l o c o m o t i o n , or 10 min i n t h e home c a g e . Sexua l a c t i v i t y i n c r e a s e d DOPA a c c u m u l a t i o n i n t h e n e o s t r i a t u m and n u c l e u s accumbens, b u t n o t i n t h e sep tum or a n t e r i o r h y p o t h a l a m u s , i n comparison with control rats l e f t in the home cage. Treadmill locomotion increased DOPA accumulation in the neostriatum, but not in the other three regions. These r e s u l t s suggest that catecholamine synthesis (as determined by DOPA accumulation) increases in the nucleus accumbens as a s p e c i f i c function of sexual a c t i v i t y and i n the neostriatum as a nonspecific function of either sexual a c t i v i t y or treadmill locomotion. Although suggestive, these r e s u l t s do not sp e c i f y exactly what aspects of copulatory a c t i v i t y contributed to the increased DOPA accumulation in either the nucleus accumbens or neostriatum. Moreover, these r e s u l t s do not indicate whether the increased DOPA accumulation leads to increased DA release or u t i l i z a t i o n , because l e v e l s of DA or i t s metabolite dihydroxyphenylacetic acid (DOPAC) le v e l s were not evaluated. Levels of DA and DOPAC in the p a r i e t a l cortex, preoptic region, mediobasal hypothalamus, and lumbosacral spi n a l cord have been examined in rats that achieved either one ejaculation or intromissions but no eja c u l a t i o n , compared to sexually i n a c t i v e rats that did not i n i t i a t e copulatory behavior with receptive females (Mas, del C a s t i l l o , Guerra, Davidson, & Battaner, 1987). In that study, both DA and DOPAC le v e l s were s i g n i f i c a n t l y elevated in the preoptic region a f t e r e j a c u l a t i o n . Although both DA and DOPAC le v e l s were elevated in the preoptic region after intromission alone, only the DOPAC elevation reached s t a t i s t i c a l s i g n i f i c a n c e . DA l e v e l s in the lumbosacral cord were also elevated s i g n i f i c a n t l y after intromission alone, but not after 42 e j a c u l a t i o n , suggesting that DA mechanisms in th i s region of the cord may contribute to the descending i n h i b i t i o n of ejaculatory reflexes during intromission. Unfortunately, DOPAC l e v e l s in the cord were undetectable, thus DA u t i l i z a t i o n could not be evaluated. Changes in DA or DOPAC level s did not occur in either the p a r i e t a l cortex or mediobasal hypothalamus. These r e s u l t s suggest that DA release and u t i l i z a t i o n in the preoptic region i s increased following an ej a c u l a t i o n . Intromission alone increases DA u t i l i z a t i o n but not necessarily DA release in the preoptic region. F i n a l l y , a study by Hoffman, G e r a l l , and Kalivas (1987) examined DA and DOPAC le v e l s in the MPOA, arcuate nucleus/median eminence, or medial forebrain bundle of in t a c t , sexually active rats that had either copulated to sexual exhaustion or were run in a motor-driven wheel, compared to in t a c t , sexually inactive control r a t s . Each rat in the wheel-running condition was yoked to a rat in the sexual exhaustion condition such that the wheel started r o t a t i n g when mounts were i n i t i a t e d and stopped ro t a t i n g aft e r e j a c u l a t i o n . DA le v e l s in the MPOA, but not in the arcuate nucleus or medial forebrain bundle, were elevated s i g n i f i c a n t l y in both sexually exhausted and active r a t s . Although no differences in DOPAC concentration were detected among groups in the three brain regions, there was a s i g n i f i c a n t negative c o r r e l a t i o n between the number of ejaculations and DOPAC concentration in the medial forebrain bundle. This suggests that DA u t i l i z a t i o n in t h i s region was inversely related to the number of ejaculations. The increased DA concentration in the MPOA, together with the lack of change in DOPAC concentration, suggests that DA u t i l i z a t i o n and/or release was attenuated in the MPOA following lengthly bouts of locomotor a c t i v i t y , the manipulation common to both the sexual exhaustion and forced a c t i v i t y groups. Taken together, these r e s u l t s indicate that DA synthesis, release, and/or u t i l i z a t i o n may increase during copulation in several DA terminal regions, notably the nucleus accumbens, neostriatum, and MPOA. However, in the two studies that c o n t r o l l e d for locomotor a c t i v i t y , the ef f e c t s observed in the neostriatum and MPOA were not s p e c i f i c to copulatory behavior. An analysis of DA release with f i n e r temporal r e s o l u t i o n would help resolve the question of behavioral s p e c i f i c i t y . Problems of in t e r p r e t a t i o n This review of the l i t e r a t u r e does not lend i t s e l f to a simple explanation of the role of DA in male sexual behavior. In ce r t a i n cases, DA agonists f a c i l i t a t e e j a culation or increase the rate of copulation in sexually active rats and f a c i l i t a t e the i n i t i a t i o n of copulation in sexually inactive r a t s . Although DA antagonists can disrupt the i n i t i a t i o n of copulation in sexually active r a t s , they also f a c i l i t a t e e j a culation in those rats once copulation has been i n i t i a t e d . Under c e r t a i n circumstances, lesions of DA terminals produce e f f e c t s s i m i l a r to the administration of DA antagonists. In general agreement with these findings, ex vivo analyses of DA synthesis, release, and u t i l i z a t i o n reveal that DA a c t i v i t y i s increased in mesolimbic, n i g r o s t r i a t a l , and diencephalic DA terminal regions following d i f f e r e n t kinds of copulatory experience. Although inferences can be made about the ro l e of DA in male sexual behavior based on these approaches, none provides an adequate account of what DA systems do during male sexual behavior. Moreover, there are numerous inconsistencies that are d i f f i c u l t to resolve. These inconsistencies may r e s u l t from a combination of d i f f e r e n t methodological procedures, including the use of animals with d i f f e r e n t baselines of sexual behavior, d i f f e r e n t routes of drug administration, d i f f e r e n t time courses, d i f f e r e n t methods of te s t i n g sexual behavior, d i f f e r e n t types of te s t i n g chambers, and the use of s t a t i s t i c a l procedures that vary in power. R e l a t i v e l y l i t t l e attempt has been made to c r i t i c a l l y evaluate the ro l e of DA in sexual motivation. It cannot be assumed, for example, that DA agonists stimulate copulation in sexually inactive rats and f a c i l i t a t e e jaculation in sexually active rats by a common mechanism. It is also d i f f i c u l t to ascribe a simple incentive r o l e to DA systems in the sexual behavior of male r a t s . These systems appear to regulate many aspects of sexual behavior, including penile r e f l e x e s . Unlike the feeding or avoidance l i t e r a t u r e s , there i s no reason to suspect that the i n i t i a t i o n of copulation i s any more s e n s i t i v e to the disruption of DA systems than other aspects of copulation. Without a clear d i s t i n c t i o n between a n t i c i p a t o r y and consummatory aspects of copulatory behavior, i t i s impossible to determine from the present l i t e r a t u r e what r o l e DA plays in incentive 45 sexual motivation. Level Changing: A New Measure of Anticipatory Sexual Behavior Recently, a new form of sexually motivated a n t i c i p a t o r y behavior was characterized for male rats in the b i l e v e l chambers designed by Mendelson and Gorzalka (1987). This behavior, which i s depicted in Figure 2 (Panel A, f i l l e d c i r c l e s , squares, and t r i a n g l e s ) , appeared as high rates of l e v e l changing during the 5-min adaptation periods p r i o r to the introduction of a sexually receptive female rat for a test of copulation (Mendelson & Pfaus, 1989; Pfaus, Mendelson, & P h i l l i p s , 1988). This increased l e v e l changing did not develop in sexually active males given access to either sexually nonreceptive females or other males following the 5-min adaptation periods (Panel A, open squares and t r i a n g l e s ) . This behavior was attenuated when the presentation of a female was discontinued (Panel B, closed c i r c l e s ) or following c a s t r a t i o n (Panel C). This indicates that the a c q u i s i t i o n of increased rates of l e v e l changing requires the presentation of a sexually receptive female; however, once stable rates of l e v e l changing are acquired, they can be maintained by the presentation of either a sexually receptive or nonreceptive female. The analysis of l e v e l changing has several advantages over previous methods used to assess a n t i c i p a t o r y sexual motivation. For example, in contrast to analyses of running speed in s t r a i g h t a l l e y s or T-mazes, the evaluation of l e v e l changing i s u n l i k e l y to be hindered by c e i l i n g e f f e c t s . Baseline rates of l e v e l 4 6 Figure 2. Level changes displayed by sexually active males in the b i l e v e l chambers designed by Mendelson and Gorzalka (1987). A: A c q u i s i t i o n ; Group R was given access to sexually receptive females on each t e s t ; Group N was given access to sexually nonreceptive females on tests 1 through 8, afte r which they were given access to sexually receptive females; and Group M was given access to other males on tests 1 through 8, after which they were given access to sexually receptive females. B: E x t i n c t i o n ; Group N was given access to sexually nonreceptive females on each t e s t ; and Group 0 did not receive access to any con s p e c i f i c following the 5-min habituation periods. C: E f f e c t of c a s t r a t i o n . Values are means + SE. From Pfaus, Mendelson, and P h i l l i p s (1988). O 09 MEAN NUMBER OF LEVEL CHANGES MEAN NUMBER OF LEVEL CHANGES o ••» * • a 8 o M »• • » S I i 1 i L j i i 1 1 1 I MEAN NUMBER OF LEVEL CHANGES o M *. o> « 5 I 1 I 1 1 1 > • • • • r-1 1 1 * * 3 48 c h a n g i n g a r e a c q u i r e d r a p i d l y a n d a l a r g e n u m b e r o f r a t s c a n b e o b s e r v e d a t o n e t i m e . T h i s m a k e s t h e a n a l y s i s o f l e v e l c h a n g i n g l e s s t i m e c o n s u m i n g t h a n t r a i n i n g r a t s t o r u n m a z e s o r b a r p r e s s f o r a c c e s s t o s e x u a l l y r e c e p t i v e f e m a l e s . I n c o m p a r i s o n w i t h b a r p r e s s i n g b e h a v i o r o r t h e c r o s s i n g o f e l e c t r i f i e d g r i d s t o r e a c h f e m a l e r a t s , l e v e l c h a n g i n g a p p e a r s m o r e n a t u r a l : t h e l e v e l - t o -l e v e l m o v e m e n t s b y t h e m a l e a r e r e m i n i s c e n t o f t h e d e s c r i p t i o n b y C a l h o u n ( 1 9 6 2 ) o f t h e s e a r c h f o r e s t r o u s f e m a l e s b y m a l e r a t s i n b u r r o w s i n t h e w i l d . A l t h o u g h p r e l i m i n a r y e x p e r i m e n t s d e m o n s t r a t e d t h a t l e v e l c h a n g i n g w a s l e s s s e n s i t i v e t h a n m o u n t o r i n t r o m i s s i o n l a t e n c i e s t o t h e d i s r u p t i v e e f f e c t s o f c a s t r a t i o n , i t w a s m o r e s e n s i t i v e t h a n t h o s e m e a s u r e s t o d i s r u p t i o n b y l o w d o s e s o f t h e DA r e c e p t o r a n t a g o n i s t h a l o p e r i d o l . T h u s l e v e l c h a n g i n g m a y r e p r e s e n t a s i m p l e , s e n s i t i v e , a n d o b j e c t i v e m e a s u r e o f a n t i c i p a t o r y s e x u a l m o t i v a t i o n t h a t c a n b e u s e d i n c o n j u n c t i o n w i t h t r a d i t i o n a l m e a s u r e s o f c o n s u m m a t o r y s e x u a l b e h a v i o r t o e v a l u a t e t h e e f f e c t s o f DA a n t a g o n i s t s . O v e r v i e w o f t h e P r e s e n t E x p e r i m e n t s T h e e x p e r i m e n t s r e p o r t e d i n t h i s t h e s i s r e p r e s e n t a n i n t e g r a t e d a p p r o a c h t o t h e s t u d y o f DA i n m a l e s e x u a l b e h a v i o r t h a t i n c o r p o r a t e s b o t h p h a r m a c o l o g i c a l a n d e l e c t r o c h e m i c a l a n a l y s e s o f DA f u n c t i o n d u r i n g b o t h a n t i c i p a t o r y a n d c o n s u m m a t o r y a s p e c t s o f s e x u a l b e h a v i o r . T h e u s e o f r a t s w i t h r e l a t i v e l y s t a b l e b a s e l i n e s o f l e v e l c h a n g i n g a n d c o p u l a t o r y b e h a v i o r i n t h e 49 present experiments also allows more meaningful comparisons of drug e f f e c t s and electrochemical p r o f i l e s . Experiment I investigated the s t a t i s t i c a l r e l a t i o n among the measures of a n t i c i p a t o r y and consummatory sexual behavior displayed by male rats in the b i l e v e l chamber. Accordingly, multiple c o r r e l a t i o n s among these measures were calculated and subjected to factor analysis using orthogonal r o t a t i o n s . This approach generated the minimum number of factors necessary to account for the variance among the measures, and thus provided a t h e o r e t i c a l basis for understanding the' deep structure of male sexual behavior in the b i l e v e l chambers. The r e s u l t s of t h i s analysis were compared to the r e s u l t s of a previous factor analysis study conducted by Sachs (1978). Experiment II examined the dose-response e f f e c t s of systemic administration of DA antagonists on a n t i c i p a t o r y and consummatory aspects of male sexual behavior. This study extended previous findings that t y p i c a l and a t y p i c a l neuroleptics a f f e c t the sexual behavior of male rats d i f f e r e n t l y (Pfaus & P h i l l i p s , 1989), and provided a preliminary assessment of the roles of DI and D2 receptors in male sexual behavior. In Experiment I I I , the dose-response e f f e c t s of ce n t r a l administration of the DA receptor antagonist haloperidol into the nucleus accumbens, neostriatum, and MPOA were examined during a n t i c i p a t o r y and consummatory aspects of male sexual behavior. The r e s u l t s of t h i s study indicate that mesolimbic, mesostriatal, and incertohypothalamic DA systems control d i f f e r e n t aspects of 50 sexual behavior in the male r a t . F i n a l l y , in Experiment IV, in vivo voltammetry was used to examine DA e f f l u x in the nucleus accumbens and striatum, and catecholamine e f f l u x in the MPOA, of in t a c t , sexually active rats during a n t i c i p a t o r y and consummatory aspects of sexual behavior. Direct comparisons of the sexual behavior and voltammetric record of each rat allows a finely-grained temporal analysis of DA or catecholamine e f f l u x in these regions during sexual behavior. In  vivo microdialysis i s used subsequently to confirm the voltammetric r e s u l t s i n the nucleus accumbens and striatum. Several hypotheses about DA function in male sexual behavior were presented in the general discussion to account for the re s u l t s of the present experiments. A cautious attempt was made to f i t these r e s u l t s into the general t h e o r e t i c a l framework postulated for mesotelencephalic DA systems in the control of incentive motivation and goal-directed behavior, and for diencephalic DA systems in the neuroendocrine regulation of penile r e f l e x e s . The c l i n i c a l relevance of these r e s u l t s to the control of sexual desire, arousal, and dysfunction in human males was also considered. 51 EXPERIMENT I: STATISTICAL ANALYSIS OF MALE SEXUAL BEHAVIOR IN THE BILEVEL CHAMBER An important goal of research on the sexual behavior of male rats i s to understand the mechanisms that control various aspects of male copulation. This goal can be approached in d i f f e r e n t ways at many level s of analysis, but a l l require a formal taxonomy that distinguishes various measures of sexual behavior. The development of such a taxonomy depends upon the analysis of normative data which allows "baseline" rates of copulatory behavior to be defined formally and o b j e c t i v e l y . Conceptual mechanisms that r e f l e c t the deep structure of male copulatory behavior can be generated from the analysis of normative data. These conceptual mechanisms can be assembled into hypothetical models of sexual behavior, many of which are useful h e u r i s t i c a l l y for i d e n t i f y i n g p o t e n t i a l neural mechanisms. There are two types of hypothetical models of male sexual behavior. The f i r s t type, exemplified by the model proposed by Toates (1986), t r i e s to account for a l l possible facets of sexual behavior. T y p i c a l l y , t h i s approach generates a large number of conceptually d i s t i n c t mechanisms that are based, in large part, on the inspired i n t u i t i o n of the observer. For example, in Toates' model, ejaculation depends upon several mechanisms that process the incentive q u a l i t i e s of the female, the i n t e r n a l state of sexual arousal, and the s e n s i t i v i t y to g e n i t a l stimulation. 52 Each of these mechanisms, in turn, can be acted upon by i n h i b i t o r y mechanisms that d i s s i p a t e sexual arousal, desensitize the g e n i t a l s , and decrease the incentive value of the female (e.g., aft e r e j a c u l a t i o n ) . Although models such as t h i s generate testable hypotheses, they often do not sp e c i f y how i n d i v i d u a l measures of sexual behavior are related to the conceptual mechanisms. For example, a decrease in the number of intromissions before ejaculation may be viewed either as an increase in sexual arousal, an increase in s e n s i t i v i t y to g e n i t a l stimulation, s e n s i t i z a t i o n of a system that f a c i l i t a t e s seminal emission, a decrease in e r e c t i l e c a p a b i l i t y , or any combination of these. The second type of model, exemplified by the analyses of Beach (1956) and Sachs (1978), t r i e s to reduce male sexual behavior to a minimum number of conceptually independent mechanisms. This approach can be aided by c e r t a i n s t a t i s t i c a l procedures. For example, Beach used multiple c o r r e l a t i o n s among normative measures of male sexual behavior to determine both the s t a b i l i t y and r e l a t i o n s h i p of those measures. This analysis helped him infer that a minimum of two mechanisms co n t r o l l e d the sexual behavior of male r a t s : a sexual arousal mechanism that c o n t r o l l e d both precopulatory i n v e s t i g a t i o n of the female and the i n i t i a t i o n of mounts, and an intromission and ejaculation mechanism that focused the male's sexual responses almost e n t i r e l y on g e n i t a l stimulation through vaginal intromission u n t i l e j a culation occurred. However, Beach presented very few of 53 the i n t e r c o r r e l a t i o n s in that paper, and thus i t is not clear whether multiple c o r r e l a t i o n s were calculated for a l l measures of copulatory behavior. Sachs (1978) provided an i n t e r e s t i n g s o l u t i o n to the question of the minimum number of mechanisms involved in the sexual behavior of male rats by subjecting the multiple c o r r e l a t i o n s among normative measures of male sexual behavior to factor a n a l y s i s . Ten measures of copulatory behavior were analyzed in Long-Evans rats through the f i r s t ejaculatory s e r i e s : the mount and intromission l a t e n c i e s , the e j a c u l a t i o n latency measured from the f i r s t intromission, the number of mounts and intromissions preceding e j a c u l a t i o n , the " h i t rate" (intromission r a t i o ) , the I I I , and both the absolute and r e l a t i v e r e f r a c t o r y periods (measured as the time from ej a c u l a t i o n to the termination of 22 kHz v o c a l i z a t i o n , and the time from v o c a l i z a t i o n termination to the f i r s t intromission after e j a c u l a t i o n , r e s p e c t i v e l y ) . The i n t e r c o r r e l a t i o n s among those measures were examined separately in three data sets from the laboratories of three investigators, Sachs (n = 18), B a r f i e l d (n = 23), and Bermant (n = 74). Unfortunately, l i t t l e information about the subjects was presented, except that most of the data were taken from the r a t s ' second test with receptive females. Although no information about the t e s t i n g conditions was given, i t may be assumed that the rats were tested in small square or c i r c u l a r u n i l e v e l chambers under r e l a t i v e l y optimal conditions (e.g., during the dark phase of the c i r c a d i a n light/dark c y c l e ) . 54 Several c o r r e l a t i o n s among the measures of copulatory behavior were found to be s t a t i s t i c a l l y s i g n i f i c a n t in at least two of the three data sets. Mount and intromission latencies were correlated, as were the number of mounts and the intromission r a t i o . The III was correlated with the e j a c u l a t i o n latency, the absolute r e f r a c t o r y phase, and the t o t a l PEI. Likewise, the ejaculation latency was correlated with the absolute r e f r a c t o r y phase and the t o t a l PEI. F i n a l l y , the t o t a l PEI was correlated with both the absolute and r e l a t i v e r e f r a c t o r y phases. Subsequent factor analysis of the s i g n i f i c a n t c o r r e l a t i o n s using orthogonal (varimax) rotations revealed four factors that accounted for over 90% of the variance. These factors were given tentative names based on the measures that loaded most heavily on ( i . e . , whose variance was accounted for by) each f a c t o r . The factor that accounted for the largest proportion of the variance was termed the copulatory rate f a c t o r . This factor was loaded by the I I I , the e j a c u l a t i o n latency, the absolute r e f r a c t o r y period, and the t o t a l PEI. The factor that accounted for the second largest proportion of the variance was c a l l e d the i n i t i a t i o n  f a ctor . This factor, reminiscent of Beach's sexual arousal mechanism, was loaded heavily by mount and intromission l a t e n c i e s , and moderately by the r e l a t i v e r e f r a c t o r y period. The t h i r d largest proportion of the variance was accounted for by the h i t rate f a c t o r . This factor was loaded heavily by the number of mounts and the intromission r a t i o . The fourth largest proportion 55 of the variance was accounted for by an intromission count  factor. This factor, reminiscent of Beach's intromission and ejaculation mechanism, was loaded by the number of intromissions and the r e l a t i v e r e f r a c t o r y period. At f i r s t glance, i t would seem that the measures contained within each factor share common c o n t r o l l i n g mechanisms. However, as Sachs pointed out, t h i s does not mean that the mechanisms are i n d i v i s i b l e or the measures redundant. In f a c t , c e r t a i n measures that f a l l within a s i n g l e factor can be dissociated with the appropriate pharmacological or neurosurgical treatments (e.g., the PEI and the ejaculation latency; B a r f i e l d , Wilson, & McDonald, 1975; Clark, Caggiula, McConnell, & Antelman, 1975; Pfaus & P h i l l i p s , 1987). The fact that c e r t a i n measures of copulatory behavior can be dissociated does not render the factors i n v a l i d . Simply, the r e s u l t s of Sachs' analysis suggest that a minimum of four general conceptual mechanisms ( r e f l e c t i n g the rate of copulation, the i n i t i a t i o n of copulation, the r a t i o of mounts with and without intromission, and the number of intromissions before ejaculation) must be considered in any model of the sexual behavior of male r a t s . Although t h i s study i s laudable for being the f i r s t to use factor analysis to derive conceptual mechanisms of male sexual behavior, there are several methodological questions that need to be addressed before the r e s u l t s can be generalized. As mentioned above, no information was provided about the conditions under which sexual behavior was tested. Estimates of communality were 56 made for Sachs' and B a r f i e l d * s samples, but not for Bermant's sample. This was an unfortunate omission because Sachs 1 and B a r f i e l d ' s samples were r e l a t i v e l y small (ns = 18 and 23, respectively) whereas Bermant's sample was much larger (n = 74). There were also several inconsistencies regarding the loading of c e r t a i n measures of copulatory behavior on the four f a c t o r s . For example, in Bermant's sample, the number of mounts, the I I I , and the e j a c u l a t i o n latency loaded onto the i n i t i a t i o n factor whereas in Sach's and B a r f i e l d ' s samples they did not. It i s impossible to determine whether the d i f f e r e n t number of subjects or any possible differences in t e s t i n g procedure contributed to the inconsistent loadings. F i n a l l y , Sachs noted that none of the analyses took the contribution of the female's behavior into consideration. Given evidence that the s o l i c i t a t i o n and pacing behavior of the female can a l t e r the copulatory behavior of the male (Madlafousek & Hlinak, 1978; McClintock, 1984), i t i s important to contrast measures of male copulatory behavior in conditions in which the females can control the sexual i n t e r a c t i o n s . The b i l e v e l chambers designed by Mendelson and Gorzalka (1987) provide an opportunity to assess the copulatory behavior of male rats in a s i t u a t i o n where the female can pace the copulatory contact. T y p i c a l l y , a female rat runs from l e v e l to l e v e l several times in these chambers following each intromission by the male. This behavior forces the male to chase her and i s reminiscent of the chasing behavior observed in male rats given access to receptive females in a large open f i e l d (McClintock, 1984). Preliminary evidence suggests that c e r t a i n measures of male copulatory behavior are altered in the b i l e v e l chambers. For example, the number of mounts and intromissions that precede eja c u l a t i o n appears to be lower in the b i l e v e l chambers than in the t r a d i t i o n a l u n i l e v e l chambers (in which females do not d i s p l a y complex patterns of pacing behavior). Likewise, both the ej a c u l a t i o n latency and PEI appear shorter in the b i l e v e l chambers than in the t r a d i t i o n a l u n i l e v e l chambers. Because i t i s desirable in the present thesis to analyze l e v e l changing as a measure of a n t i c i p a t o r y sexual motivation, i t was necessary to examine the sexual behavior of male rats in the b i l e v e l chambers in more d e t a i l . Therefore, in the f i r s t experiment of t h i s t h e s i s , i n t e r c o r r e l a t i o n s among 11 measures of sexual behavior derived from 80 male rats that had reached i n d i v i d u a l asymptotes of sexual performance were subjected to factor a n a l y s i s . Method Subjects and Surgery Female and male Long-Evans rats were obtained from Charles River Canada, Inc., St. Constant, Quebec. They were housed by sex in groups of s i x in 18x25x65 cm wire mesh cages in a colony room maintained on a reversed 12 h light/12 h dark cycle at approximately 21°C. Food and water were continuously a v a i l a b l e in the home cages. The females were b i l a t e r a l l y ovariectomized v i a lumbar i n c i s i o n s under sodium pentobarbital anesthesia 58 (Somnital, 40 mg/kg) and allowed at least one week of recovery before t e s t i n g . Sexual r e c e p t i v i t y was induced in the females by subcutaneous (SC) inj e c t i o n s of e s t r a d i o l benzoate (10 ug) and progesterone (500 ug) 48 h and 4 h, res p e c t i v e l y , before each test in which they p a r t i c i p a t e d as stimulus females. The housing conditions for a l l r a t s , and the surgery and steroid-priming regimen for the stimulus females, were used throughout the experiments reported in t h i s t h e s i s . Apparatus The t e s t i n g chambers used in t h i s study were s i m i l a r to those described by Mendelson and Gorzalka (1987). Each chamber was constructed of Pl e x i g l a s with outside dimensions of 51x70x15 cm. The narrowness of the chambers forced animals to mate with t h e i r flanks to the observer, the optimal o r i e n t a t i o n for evaluating the sexual behavior of r a t s . However, the chambers were not so narrow as to prevent animals from turning about f r e e l y inside. A platform 40 cm in length, centered, and set 28 cm above the f l o o r , divided each chamber into two l e v e l s . A set . of ramps and narrow landings at each end of each the chamber allowed animals to move f r e e l y from one l e v e l to another. Behavioral Testing Procedures Eighty males (450 to 700 g) were given 10 screening tests for masculine copulatory behavior. Screening tests were 25 min in duration and were conducted one every 4 days during the middle t h i r d of the dark cy c l e . During these screening t e s t s , each male was placed into one of the b i l e v e l chambers for a 5-min test of 59 l e v e l c h a n g i n g a f t e r w h i c h a s e x u a l l y r e c e p t i v e f e m a l e was p l a c e d i n t o t h e chamber f o r 20 m i n . The o c c u r r e n c e o f each l e v e l c h a n g e , moun t , i n t r o m i s s i o n , and e j a c u l a t i o n was r e c o r d e d on a c o m p u t e r i z e d e v e n t r e c o r d e r w h i c h d e r i v e d t h e f o l l o w i n g measu res : (1 ) t h e number o f l e v e l changes (LC) i n t h e 5 -m in p e r i o d ; (2 ) l a t e n c y i n seconds t o i n i t i a t e l e v e l changes ( L C D ; ( 3 ) mount and (4 ) i n t r o m i s s i o n l a t e n c i e s (ML and I L ; t i m e f r o m t h e i n t r o d u c t i o n o f t h e f e m a l e t o t h e f i r s t mount or i n t r o m i s s i o n i n s e c o n d s ) ; (5 ) t h e e j a c u l a t i o n l a t e n c y (EL ; t i m e f r o m t h e f i r s t i n t r o m i s s i o n t o e j a c u l a t i o n i n seconds . ) ; (6 ) t h e PEI ( t i m e f r o m e j a c u l a t i o n t o t h e n e x t i n t r o m i s s i o n i n s e c o n d s ) ; (7 ) t h e number o f mounts (NM) and (8 ) t h e number o f i n t r o m i s s i o n s ( N I ) p r i o r t o each e j a c u l a t i o n ; (9 ) t h e I I I ( t h e e j a c u l a t i o n l a t e n c y / t h e number o f i n t r o m i s s i o n s ) ; (10 ) t h e i n t r o m i s s i o n r a t i o ( I R ) ; t h e number o f mounts w i t h i n t r o m i s s i o n / t h e t o t a l number o f mounts w i t h and w i t h o u t i n t r o m i s s i o n ) ; and (11 ) t h e t o t a l number o f e j a c u l a t i o n s a c h i e v e d i n t h e 2 0 - m i n t e s t ( N E ) . By t h e t e n t h b a s e l i n e t e s t , a l l 80 males had r e a c h e d t h e c r i t e r i a f o r i n c l u s i o n : s t a b l e r a t e s o f l e v e l c h a n g i n g d u r i n g t h e 5 -m in a d a p t a t i o n p e r i o d ; i n t r o m i s s i o n w i t h i n 5 min o f t h e p r e s e n t a t i o n o f t h e f e m a l e ; e j a c u l a t i o n w i t h i n 15 min o f t h e f i r s t i n t r o m i s s i o n ; and t h e r e i n i t i a t i o n o f i n t r o m i s s i o n w i t h i n 10 min o f e j a c u l a t i o n , on each o f t h e l a s t t h r e e s c r e e n i n g t e s t s . A f i n a l t e s t o f m a s c u l i n e c o p u l a t o r y b e h a v i o r was c o n d u c t e d 4 days a f t e r t h e l a s t s c r e e n i n g t e s t . The d a t a f r o m t h i s t e s t were s u b j e c t e d t o s t a t i s t i c a l a n a l y s i s . 60 S t a t i s t i c a l Analysis Means, standard errors, and i n t e r c o r r e l a t i o n s among the 11 measures of sexual behavior were calculated using a comercially a v a i l a b l e s t a t i s t i c a l package (Complete S t a t i s t i c a l System, StatSoft, Tulsa, OK). Factor analysis was conducted with the same s t a t i s t i c a l package using orthogonal (varimax) rotations of the matrices of c o r r e l a t i o n c o e f f i c i e n t s . This reproduced the method used by Sachs (1978). Results and Discussion Correlations The means, standard errors, and i n t e r c o r r e l a t i o n s among the 11 measures of sexual behavior described on Page 59 are shown in Table I. Correlation c o e f f i c i e n t s that had a s t a t i s t i c a l s i g n i f i c a n c e of p_<.05 are shown in Table I I . The most in t e r e s t i n g finding in t h i s analysis was that LC did not c o r r e l a t e s i g n i f i c a n t l y with any of the other measures of sexual behavior. This distinguishes LC from measures that are t y p i c a l l y used to infer sexual motivation, e.g., the ML or IL. The LCL however, was correlated p o s i t i v e l y and s i g n i f i c a n t l y with the ML, NM, and NI, although the c o r r e l a t i o n c o e f f i c i e n t s were small (<.26). This indicates that the i n i t i a t i o n of l e v e l changing and mounting may not be independent processes. Consistent with Sachs' analysis, the ML and IL were highly p o s i t i v e l y correlated. This was expected because highly trained rats usually gain vaginal intromission during t h e i r f i r s t or second mount. 61 Table I Means, standard e r r o r s , and i n t e r c o r r e l a t i o n s among the 11 measures of sexual behavior d i s p l a y e d by male r a t s l n the b i l e v e l chambers. LC LCL ML IL EL PEI NM NI NE IR III Mean 11.21 18.00 13.80 17.31 286. 66 270.04 4.22 10.75 2.47 .74 26. 99 SEM .35 1.46 1.64 1.96 14. 09 5.87 .32 .37 .07 .01 1. 17 C o r r e l a t i o n s LC LCL -.18 ML -.04 + .25 IL -.01 + .17 + .87 EL -.06 + .11 -.05 -.07 PEI + .12 -.06 + .05 + .01 + .43 NM -.10 + .22 + .01 + .04 + .42 + .27 -NI -.03 + .25 -.13 -.12 + .54 + .11 + .46 NE -.10 -.02 -.15 - -.16 -.50 -.28 - .24 -.35 IR + .15 -.19 -.15 -.20 -.26 -.26 - .84 -.06 + .12 II I -.08 -.01 + .10 + .07 + .76 + .44 + .23 -.09 -.29 -.32 -Table I I C o r r e l a t i o n c o e f f i c i e n t s w i t h s t a t i s t i c a l s i g n i f i c a n c e of p_<.05. C o r r e l a t e d measures R(X,Y) P. LCL x ML + .254 .022 LCL x NM + .223 .044 LCL x NI + .249 .025 ML x I L + .875 .000 EL x PEI + .432 .000 EL X NM + .416 .000 EL x NI + .541 .000 EL x NE - . 5 0 3 .000 EL x IR - . 2 5 7 .020 EL X I I I + .758 .000 PEI x NM + .268 .015 PEI X NE - . 2 7 7 .013 PEI x IR - . 2 6 4 .017 PEI x I I I + .436 .000 NM x NI + .465 .000 NM x NE - . 2 3 9 .031 NM x IR - . 8 4 3 .000 NM x I I I + .226 . 041 NI X NE - . 3 4 5 .001 IR X I I I - . 3 1 7 .004 6 3 Sachs reported that the EL was p o s i t i v e l y correlated with the III and the PEI in his and B a r f i e l d ' s data, and with the NM in Bermant's data. Those three c o r r e l a t i o n s were r e p l i c a t e d , although the c o e f f i c i e n t s were generally smaller in the present study (as they were in Bermant's sample). However, three other measures were correlated with the EL in the present study that were either not evaluated or did not reach s i g n i f i c a n c e in Sachs' anal y s i s . The EL was negatively correlated with the NE and the IR. The f i r s t of these was expected because the number of ejaculations possible in a 20-min te s t decreases as the latency to each ejaculation increases. However, the negative c o r r e l a t i o n between the EL and the IR requires amore extensive explanation. At f i r s t glance, t h i s c o r r e l a t i o n would seem to indicate that the r e l a t i v e number of intromissions predicts the latency to ejaculate. However, the EL was also p o s i t i v e l y correlated with the NI in the present study. This c o r r e l a t i o n , together with the po s i t i v e c o r r e l a t i o n between the EL and the NM, suggests that a r e l a t i v e l y larger increase in mounts over intromissions causes the decrease in the IR. Thus longer ELs in these rats may be accompanied by an increase in the proportion of mounts without intromission, a s i t u a t i o n that could indicate either a r e l a t i v e f a i l u r e to gain erection, penile d e s e n s i t i z a t i o n , or fatigue. The PEI was p o s i t i v e l y correlated with the I I I , as i t was in Sachs' ana l y s i s . However, in the present study, the PEI was also p o s i t i v e l y correlated with the NM, i n d i c a t i n g that animals displaying more mounts without intromission also have longer 64 l a t e n c i e s t o r e i n i t i a t e i n t r o m i s s i o n a f t e r e j a c u l a t i o n . The PEI was n e g a t i v e l y c o r r e l a t e d w i t h b o t h t h e NE and t h e IR i n t h e p r e s e n t s t u d y . The f i r s t n e g a t i v e c o r r e l a t i o n i s s i m i l a r t o t h a t d e s c r i b e d f o r t h e EL and NE, i n t h a t l o n g e r PEIs would l i k e l y dec rease t h e number o f e j a c u l a t i o n s a c h i e v e d i n a 20 -min t e s t . The second n e g a t i v e c o r r e l a t i o n between t h e PEI and IR s u g g e s t s t h a t a n i m a l s w i t h l ower IRs ( p r e s u m a b l y a f u n c t i o n o f a r e l a t i v e i n c r e a s e i n t h e number o f mounts w i t h o u t i n t r o m i s s i o n ) may t a k e l o n g e r t o e j a c u l a t e and r e i n i t i a t e i n t r o m i s s i o n f o l l o w i n g e j a c u l a t i o n . A g a i n , t h i s p a t t e r n c o u l d occur i n a n i m a l s t h a t e x p e r i e n c e e i t h e r e r e c t i l e d y s f u n c t i o n , p e n i l e d e s e n s i t i z a t i o n , or f a t i g u e . S e v e r a l o t h e r c o r r e l a t i o n s found by Sachs were r e p l i c a t e d i n t h e p r e s e n t s t u d y . The NM was h i g h l y n e g a t i v e l y c o r r e l a t e d w i t h t h e I R , i n agreement w i t h t h e a n a l y s i s p r e s e n t e d above . A l t h o u g h t h e p o s i t i v e c o r r e l a t i o n between t h e NM and t h e I I I i n t h e p r e s e n t s t u d y r e p l i c a t e d t h a t found i n B e r m a n t ' s d a t a samp le , t h i s c o r r e l a t i o n was n o t e v i d e n t i n e i t h e r Sachs ' or B a r f i e l d ' s s a m p l e s . Two c o r r e l a t i o n s between t h e NM and o t h e r measures i n t h e p r e s e n t s t u d y were n o t found i n Sachs ' a n a l y s i s . The NM was p o s i t i v e l y c o r r e l a t e d w i t h t h e NI and n e g a t i v e l y c o r r e l a t e d w i t h t h e NE, a g a i n i n agreement w i t h t h e a n a l y s i s p r e s e n t e d above . Two o t h e r c o r r e l a t i o n s were found i n t h e p r e s e n t s t u d y . The NI was n e g a t i v e l y c o r r e l a t e d w i t h t h e NE and t h e IR was n e g a t i v e l y c o r r e l a t e d w i t h t h e I I I . Bo th o f t h e s e c o r r e l a t i o n s a r e c o n s i s t e n t w i t h t h e a n a l y s i s p r e s e n t e d above. 65 The p i c t u r e t h a t emerges f r o m t h e i n t e r c o r r e l a t i o n s s u p p o r t s t h e i d e a t h a t a n i m a l s t h a t d i s p l a y a l a r g e number o f mounts and i n t r o m i s s i o n s i n t h e b i l e v e l chambers a r e l i k e l y a l s o t o d i s p l a y low I R s , l o n g I l l s , ELs , and P E I s , and few e j a c u l a t i o n s . I t may t h u s be i n f e r r e d t h a t a n i m a l s t h a t d i s p l a y a r e l a t i v e l y s m a l l e r number o f mounts and i n t r o m i s s i o n s i n t h e s e chambers d i s p l a y h i g h I R s , s h o r t I l l s , ELs, and P E I s , and many e j a c u l a t i o n s . F a c t o r A n a l y s i s The c o r r e l a t i o n m a t r i x was s u b j e c t e d t o f a c t o r a n a l y s i s u s i n g n o r m a l i z e d v a r i m a x r o t a t i o n s t o a l l o w d i r e c t c o m p a r i s o n w i t h t h e f a c t o r s p r e s e n t e d by Sachs. E s t i m a t e s o f . c o m m u n a l i t y f o r each measure a r e shown i n Tab le I I I . A t o t a l o f e i g h t f a c t o r s were e x t r a c t e d , f i v e o f w h i c h accoun ted f o r 95% o f t h e t o t a l i n t e r s u b j e c t v a r i a n c e f o r a l l measures . A c c o r d i n g t o common p r a c t i c e , t h e r e m a i n i n g t h r e e f a c t o r s were i g n o r e d ( e . g . , H a k s t i a n & M u l l e r , 1 9 7 3 ) . Measures w i t h f a c t o r l o a d i n g s o f l e s s t h a n .30 ( i . e . , t h a t a c c o u n t e d f o r l e s s t h a n 9% o f t h a t measu re ' s v a r i a n c e ) were a l s o i g n o r e d . The f i v e f a c t o r s t h a t emerged were r e m a r k a b l y c o n s i s t e n t w i t h t h o s e d e s c r i b e d by Sachs and were g i v e n t e n t a t i v e names based on t h e measures t h a t l oaded most h e a v i l y o n t o e a c h . These f a c t o r s and t h e i r ma jo r v a r i a b l e l o a d i n g s a r e shown i n T a b l e I V . The s t r o n g e s t f a c t o r i n t h i s a n a l y s i s was l oaded by f o u r measures : t h e I I I , EL, P E I , and NE. T h i s f a c t o r , s i m i l a r t o Sachs 1 c o p u l a t o r y r a t e f a c t o r , accoun ted f o r more t h a n 26% o f t h e Table I I I E s t i m a t e s of communa l i t y f o r each measure of sexua l behav io r Measure Communal i ty LC .141 LCL .253 ML .791 I L .789 EL .963 PEI .284 NM .908 NI .935 NE .372 IR .887 I I I .946 67 T a b l e IV F a c t o r s and t h e i r v a r i a b l e l o a d i n g s F a c t o r Measure V a r i a b l e Load ing 1 . C o p u l a t o r y Rate I I I +.948 EL +.853 PEI +.461 NE - . 3 9 0 % v a r i a n c e 26 2. I n i t i a t i o n ML +.909 I L +.907 % v a r i a n c e 22 3. H i t Rate IR +.905 NM - . 8 7 6 % v a r i a n c e 21 4. Mount Count NI +.945 EL +.464 NE - . 3 9 1 NM +.331 % v a r i a n c e 18 5. A n t i c i p a t i o n LCL +.462 LC - . 4 5 6 % v a r i a n c e 8 r 68 i n t e r s u b j e c t v a r i a n c e f o r a l l measu res . Sachs ' c o p u l a t o r y r a t e f a c t o r was l o a d e d by t h e I I I , EL, a b s o l u t e P E I , and t o t a l P E I . The a d d i t i o n o f t h e NE t o t h i s f a c t o r i n t h e p r e s e n t a n a l y s i s i n d i c a t e s t h a t t h e NE may a l s o be used as a measure o f c o p u l a t o r y r a t e . The r e l a t i o n o f t h e f a c t o r l o a d i n g s f o r t h e I I I , EL, and PEI was i d e n t i c a l t o t h a t r e p o r t e d by Sachs , a l t h o u g h t h e f a c t o r l o a d i n g f o r t h e PEI was c o n s i d e r a b l y l e s s i n t h e p r e s e n t a n a l y s i s ( + . 4 6 v e r s u s + . 7 5 ) . I n a d d i t i o n , Sachs ' c o p u l a t o r y r a t e f a c t o r a c c o u n t e d f o r a l a r g e r p r o p o r t i o n o f t h e t o t a l v a r i a n c e (be tween 37% and 43% i n t h e t h r e e d a t a s a m p l e s ) . N e v e r t h e l e s s , t h e p r e s e n t r e s u l t s s u g g e s t t h a t t h e c o p u l a t o r y r a t e o f male r a t s i n t h e b i l e v e l chambers i s n o t q u a l i t a t i v e l y d i f f e r e n t f r o m t h e c o p u l a t o r y r a t e o f r a t s i n t r a d i t i o n a l u n i l e v e l chambers . As n o t e d a b o v e , s e v e r a l o f t h e measures t h a t c o n t r i b u t e t o t h e c o p u l a t o r y r a t e f a c t o r can be d i s s o c i a t e d w i t h t h e a p p r o p r i a t e e x p e r i m e n t a l m a n i p u l a t i o n s . I t i s t h e r e f o r e i m p o r t a n t t o r e i t e r a t e Sachs ' s u g g e s t i o n t h a t t h e c o p u l a t o r y r a t e o f male r a t s may c o n s i s t o f s u b p r o c e s s e s t h a t a r e n o r m a l l y c o o r d i n a t e d d u r i n g c o p u l a t i o n . An i n i t i a t i o n f a c t o r was a l s o f o u n d i n t h e p r e s e n t a n a l y s i s . T h i s f a c t o r was l o a d e d h e a v i l y by t h e ML and I L and a c c o u n t e d f o r 22% o f t h e i n t e r s u b j e c t v a r i a n c e f o r a l l measures . U n l i k e Sachs ' and B a r f i e l d ' s d a t a s a m p l e s , however , t h e PEI d i d n o t l o a d o n t o t h i s f a c t o r , s u g g e s t i n g t h a t t h e p r o c e s s t h a t i n i t i a t e s t h e f i r s t b o u t o f c o p u l a t i o n may i ndeed be d i s t i n c t f r o m t h e p r o c e s s t h a t r e i n i t i a t e s c o p u l a t i o n a f t e r each e j a c u l a t i o n , an i d e a f i r s t 69 p r e s e n t e d f o r m a l l y by M c G i l l ( 1 9 6 5 ) . The t h i r d l a r g e s t f a c t o r was l o a d e d by t h e NM and I R . T h i s f a c t o r , a l m o s t i d e n t i c a l t o Sachs ' h i t r a t e f a c t o r , a c c o u n t e d f o r 21% o f t h e t o t a l i n t e r s u b j e c t v a r i a n c e f o r a l l measu res . The PEI l o a d e d o n t o Sachs ' h i t r a t e f a c t o r , b u t n o t r e l i a b l y a c r o s s h i s d a t a s a m p l e s . I n t h e p r e s e n t s a m p l e , t h e PEI d i d n o t l o a d o n t o t h e h i t r a t e f a c t o r . As i n Sachs ' a n a l y s i s , however , t h e NM and IR were n e g a t i v e l y r e l a t e d t o one a n o t h e r and were e s s e n t i a l l y r e d u n d a n t measu res . The f o u r t h l a r g e s t f a c t o r was l o a d e d by t h e N I , EL, NE, and NM. T h i s f a c t o r , t e rmed t h e mount c o u n t f a c t o r , a c c o u n t e d f o r 18% o f t h e t o t a l i n t e r s u b j e c t v a r i a n c e f o r a l l m e a s u r e s . I t can be d i s t i n g u i s h e d f r o m Sachs ' i n t r o m i s s i o n c o u n t f a c t o r by t h e a d d i t i o n o f t h e EL, NE, and NM, and t h e e x c l u s i o n o f t h e P E I . T h i s s u g g e s t s t h a t m o u n t i n g and i n t r o m i t t i n g o c c u r d i f f e r e n t l y i n t h e b i l e v e l chambers, t h a n i n t r a d i t i o n a l u n i l e v e l chambers , and may be a c c o u n t e d f o r by t h e f a c t t h a t f e m a l e r a t s can pace t h e c o p u l a t o r y c o n t a c t more e f f i c i e n t l y i n t h e b i l e v e l chambers . A l t h o u g h t h e EL and NE a l s o l o a d e d o n t o t h e c o p u l a t o r y r a t e f a c t o r , t h e i r r e l a t i o n s h i p t o t h e NI and NM makes t h e mount c o u n t f a c t o r c o n c e p t u a l l y d i f f e r e n t . I t i s p o s s i b l e t h a t m o u n t i n g and i n t r o m i t t i n g per se a r e d r i v e n by mechanisms t h a t a r e d i s t i n c t f r o m t h o s e t h a t u n d e r l i e t h e t o t a l r a t e o f c o p u l a t i o n . T h i s e x p l a n a t i o n wou ld be c o n s i s t e n t w i t h t h e s u g g e s t i o n n o t e d above by Sachs c o n c e r n i n g s u b p r o c e s s e s w i t h i n t h e c o p u l a t o r y r a t e f a c t o r . 70 The f i f t h factor was loaded by LC and the LCL. This factor, termed the a n t i c i p a t i o n factor, accounted for s l i g h t l y more than 8% of the t o t a l intersubject variance for a l l measures. The extraction of t h i s factor complements the finding that LC does not c o r r e l a t e s i g n i f i c a n t l y with other measures of copulatory behavior and supports the conclusion that t h i s measure i s both conceptually and s t a t i s t i c a l l y d i s t i n c t from those that measure the i n i t i a t i o n of copulation, e.g., the ML or IL. There are several important implications of the present r e s u l t s . F i r s t , the extraction of f i v e factors suggests that a minimum of f i v e conceptual mechanisms are necessary for an adequate explanation of male copulatory behavior in the b i l e v e l chambers: a n t i c i p a t i o n , i n i t i a t i o n , copulatory rate, h i t rate and mount count. The fact that three of these factors (copulatory rate, i n i t i a t i o n , and h i t rate) aire v i r t u a l l y i d e n t i c a l to those found by Sachs (1978) suggests that measures of copulatory behavior are r e l a t i v e l y stable in well-trained r a t s , regardless of the type of t e s t i n g chamber used. However, the mount count factor was conceptually and s t a t i s t i c a l l y d i f f e r e n t from Sachs 1 intromission count f a c t o r . This indicates that the d i s p l a y of mounts and intromissions in the b i l e v e l chambers i s d i f f e r e n t from the d i s p l a y of those behaviors i n the t r a d i t i o n a l u n i l e v e l chambers. As noted above, t h i s difference may be due to the fact that female rats can pace the copulatory contact more e f f i c i e n t l y in the b i l e v e l chambers. The pattern of mounts and intromissions by the male i s probably very s e n s i t i v e to the pacing behavior of the female. This hypothesis could be examined d i r e c t l y in the b i l e v e l chambers by giving males access to sexually receptive females treated with the DA antagonist haloperidol (to eliminate proceptive s o l i c i t a t i o n and pacing behavior). It would also be important to examine whether other p o t e n t i a l a n t i c i p a t o r y measures (e.g., rates of bar pressing for secondary r e i n f o r c e r s associated with the presentation of a receptive female; E v e r i t t et a l . , 1987) co r r e l a t e with LC and load onto a common an t i c i p a t i o n factor. The i n t e r c o r r e l a t i o n s among a l l the measures of sexual behavior except LC indicate that some of these measures are not independent s t a t i s t i c a l l y , although they may indeed be independent conceptually or neu r o b i o l o g i c a l l y . This raises a very important issue. Experiment-wise or Type 1 error i s elevated beyond the .05 c r i t e r i o n when related measures are analyzed as though they are independent (as i s the case in most s t a t i s t i c a l analyses of male copulatory behavior). The existence of i n t e r c o r r e l a t i o n s among the measures of male copulatory behavior requires that steps be taken to reduce the elevated error. The so l u t i o n to t h i s problem l i e s in the type of question being asked. Multiple univariate or nonparametric s t a t i s t i c s are t y p i c a l l y used in experiments to analyze treatment e f f e c t s on ind i v i d u a l measures of sexual behavior. This is j u s t i f i e d in si t u a t i o n s where the outcome variables are "conceptually independent"; where the research being conducted is exploratory in nature ( i . e . , when new treatment or outcome variables are 72 being assessed); where some or a l l of the outcome variables have been studied previously in univariate contexts; or where i t i s of i n t e r e s t to show that two or more treatment conditions are equivalent with respect to a number of outcome variables (Huberty & Morris, 1989). However, because many of the measures of male sexual behavior are correlated, experiment-wise error w i l l be elevated i f separate univariate analyses are conducted for each measure. In these cases, f u l l or p a r t i a l Bonferroni corrections should be applied to the multiple univariate or nonparametric 0 tests to reduce experiment-wise error by elevating the l e v e l of s i g n i f i c a n c e required for each test (e.g., Pfaus & P h i l l i p s , 1989). The second s o l u t i o n to the problem of elevated experiment-wise error i s to use multivariate s t a t i s t i c s . The questions addressed by t h i s s t a t i s t i c a l technique, however, are d i f f e r e n t from those addressed in multiple univariate or nonparametric analyses. M u l t i v a r i a t e s t a t i s t i c s are generally concerned with o v e r a l l treatment e f f e c t s and are used either to determine subgroups of outcome variables that account for the s i g n i f i c a n c e of treatment conditions or to determine the r e l a t i v e contribution of d i f f e r e n t outcome variables in each subgroup, both of which require analysis of the i n t e r c o r r e l a t i o n s among the outcome variables (Huberty & Morris, 1989). Like factor anlaysis, multivariate procedures can be used to i d e n t i f y underlying constructs associated with the obtained multivariate r e s u l t s and thus provide a t h e o r e t i c a l framework for i n t e r p r e t a t i o n . The experiment-wise error is held at .05 for the entire multivariate matrix; therefore a s i g n i f i c a n t o v e r a l l multivariate F indicates that the subsequent analysis of s i g n i f i c a n t simple or i n t e r a c t i o n e f f e c t s within the multivariate framework does not elevate experiment-wise error. For t h i s reason, i t is somewhat common in the psychological l i t e r a t u r e to see a s i g n i f i c a n t multivariate test followed by multiple univariate analyses instead of l i n e a r composites of the outcome variables (e.g., canonical variates or l i n e a r discriminant functions). Such a strategy is used to "protect" the univariate analyses from elevated experiment-wise error, even though the tests themselves address very d i f f e r e n t questions. However, finding a s i g n i f i c a n t o v e r a l l multivariate e f f e c t does not guarantee Type 1 error protection within a matrix of multiple univariate tests (Huberty & Morris, 1989; Share, 1984). Bonferroni corrections are s t i l l necessary in those cases. It seems reasonable to base the choice of a s t a t i s t i c a l procedure on the questions to be answered. If i t is of i n t e r e s t to s e l e c t or order a set of outcome var i a b l e s , or to i d e n t i f y underlying variable constructs, then multivariate analyses should be done. If i t i s of i n t e r e s t to analyze treatment e f f e c t s on each measure separately, either because the measures are conceptually independent or the research i s of an exploratory nature, then multiple univariate or nonparametric analyses should be done, provided they are corrected for elevated experiment-wise error. The a p p l i c a t i o n of either one of these techniques wou ld b e n e f i t t h e s t u d y o f male s e x u a l b e h a v i o r c o n s i d e r a b l y by r e d u c i n g Type 1 e r r o r . I n summary, t h e p r e s e n t s t u d y has v a l i d a t e d measures o f male s e x u a l b e h a v i o r i n t h e b i l e v e l chambers . A l t h o u g h i t was n o t t h e p u r p o s e o f t h i s s t u d y t o p r e s e n t a model o f t h e s e x u a l b e h a v i o r o f male r a t s , t h e r e s u l t s p r o v i d e a p r e l i m i n a r y t h e o r e t i c a l f ramework f o r i n t e r p r e t a t i o n o f t h e m e a s u r e s . To t h e e x t e n t t h a t t h e f a c t o r s d e r i v e d i n t h i s a n a l y s i s can be v iewed as c o n c e p t u a l mechan isms, t h e f ramework p r e s e n t e d h e r e c o r r e s p o n d s r e m a r k a b l y w e l l w i t h t h e one p r e s e n t e d by Sachs ( 1 9 7 8 ) . An i m p o r t a n t d i f f e r e n c e was t h e e x t r a c t i o n o f a mount c o u n t f a c t o r i n t h e p r e s e n t a n a l y s i s i n s t e a d o f t h e i n t r o m i s s i o n c o u n t f a c t o r f o u n d by Sachs . The f a c t t h a t f e m a l e r a t s can pace t h e c o p u l a t o r y c o n t a c t e a s i l y i n t h e b i l e v e l chambers ( i n c o n t r a s t t o s m a l l u n i l e v e l chambers i n w h i c h t h e f e m a l e s c a n n o t escape f r o m t h e ma le) s u g g e s t s t h a t t h e t e m p o r a l p a t t e r n o f mounts and i n t r o m i s s i o n s i s s e n s i t i v e t o t h e p a c i n g b e h a v i o r o f t h e f e m a l e . A second i m p o r t a n t d i f f e r e n c e i n t h e p r e s e n t s t u d y was t h e i n c l u s i o n o f measures o f a n t i c i p a t o r y s e x u a l m o t i v a t i o n (LC and t h e L C L ) . The e x t r a c t i o n o f s e p a r a t e a n t i c i p a t i o n and i n i t i a t i o n f a c t o r s s t r o n g l y s u g g e s t s t h a t t h e s e f a c e t s o f c o p u l a t o r y b e h a v i o r a r e d i s t i n c t . T h i s h y p o t h e s i s i s c o n s i s t e n t w i t h e a r l i e r s u g g e s t i o n s t h a t t h e p r e c o p u l a t o r y s e a r c h , i n v e s t i g a t i o n , and p u r s u i t o f t h e f e m a l e summates ( B e a c h , 1956) or i s " g a t e d " (Sachs & B a r f i e l d , 1976) i n t o t h e i n i t i a t i o n o f mounts and i n t r o m i s s i o n s by t h e m a l e . The s e p a r a t i o n o f t h e s e a s p e c t s o f sexual behavior is also reminiscent of the d i s t i n c t i o n in the human c l i n i c a l l i t e r a t u r e between sexual desire and arousal (e.g., DSM-IIIR; APA, 1987). Thus, the use of b i l e v e l chambers may allow both e t h o l o g i c a l l y and c l i n i c a l l y relevant assessments of the sexual behavior of male r a t s . EXPERIMENT I I : EFFECTS OF SYSTEMIC ADMINISTRATION OF DOPAMINE ANTAGONISTS ON ANTICIPATORY AND CONSUMMATORY ASPECTS OF SEXUAL BEHAVIOR IN THE MALE RAT I t i s w i d e l y b e l i e v e d t h a t c e n t r a l DA sys tems f a c i l i t a t e male s e x u a l m o t i v a t i o n and b e h a v i o r ( B i t r a n & H u l l , 1987 ; C r o w l e y & Zemlan , 1 9 8 1 ; Sachs & M e i s e l , 1 9 8 8 ) . As o u t l i n e d i n t h e I n t r o d u c t i o n , DA a g o n i s t s such as 1-DOPA, d - a m p h e t a m i n e , and apomorph ine can s t i m u l a t e s e x u a l d e s i r e and a r o u s a l i n human males and can f a c i l i t a t e i n t r o m i s s i o n and e j a c u l a t i o n i n male r a t s . C o n v e r s e l y , DA a n t a g o n i s t s such as h a l o p e r i d o l and p i m o z i d e d i s r u p t s e x u a l d e s i r e and a r o u s a l i n human m a l e s . I n male r a t s , t h e s e d r u g s d e l a y or a b o l i s h t h e i n i t i a t i o n o f c o p u l a t i o n and d i s r u p t a s p e c t s o f c o p u l a t o r y r a t e and h i t r a t e i n males t h a t d i s p l a y c o p u l a t i o n . The e f f e c t s o f DA a n t a g o n i s t s a r e b e l i e v e d t o r e f l e c t t h e b l o c k a d e o f c e n t r a l DA r e c e p t o r s because d o m p e r i d o n e , a DA a n t a g o n i s t t h a t does n o t r e a d i l y c r o s s t h e b l o o d - b r a i n b a r r i e r , does n o t a f f e c t t h e c o p u l a t o r y b e h a v i o r o f i n t a c t , s e x u a l l y a c t i v e male r a t s ( F a l a s c h i e t a l . , 1 9 8 1 ) . A l t h o u g h i n f e r e n c e s a b o u t t h e n o r m a l r o l e o f DA i n t h e s e x u a l m o t i v a t i o n and c o p u l a t o r y b e h a v i o r o f male r a t s can be made by a s s e s s i n g t h e e f f e c t s o f DA a n t a g o n i s t s , some o f t h e s e e f f e c t s a r e p a r a d o x i c a l . For e x a m p l e , w i t h r e s p e c t t o s e x u a l m o t i v a t i o n , t h e i n c r e a s e d mount and i n t r o m i s s i o n l a t e n c i e s t y p i c a l l y o b s e r v e d f o l l o w i n g t h e a d m i n i s t r a t i o n o f DA a n t a g o n i s t s can be interpreted as a disruption whereas the decreased number of intromissions before ejaculation can be interpreted as a f a c i l i t a t i o n (e.g., Sachs & B a r f i e l d , 1976). However, there i s evidence that haloperidol decreases the number of penile erections displayed by intact male rats (Pehek et a l . , 1988), an e f f e c t that could explain both the increased intromission latency and decreased number of intromissions before e j a c u l a t i o n . Although mount latencies may be a more appropriate measure of the motivation to i n i t i a t e copulatory a c t i v i t y , they can be confounded by the female's l e v e l of sexual r e c e p t i v i t y . Thus, i t may be misleading to s p e c i f y a role of c e n t r a l DA systems in male sexual behavior based on the e f f e c t s of DA antagonsits on consummatory measures of copulation. A more informative way to assess the r o l e of DA in the sexual motivation of male rats i s to evaluate the e f f e c t s of DA receptor antagonists on both a n t i c i p a t o r y and consummatory measures of male sexual behavior. Thus, in the second experiment of t h i s t h e s i s , the dose-response e f f e c t s of c e n t r a l l y - a c t i v e DA receptor antagonists were examined on l e v e l changing and copulatory behavior in sexually active male r a t s . These antagonists comprised several classes, including the t y p i c a l neuroleptics haloperidol and pimozide, the a t y p i c a l neuroleptic clozapine, the antiemetic agent metoclopramide, the D l - s e l e c t i v e antagonist SCH 23390, and the D2-selective a t y p i c a l neuroleptic s u l p i r i d e . 7 8 Method Subjects and Surgery The male Long-Evans rats used in Experiment II were purchased from Charles River Canada and housed as in Experiment I. The stimulus females used in Experiment I were used in Experiment I I . Sexual r e c e p t i v i t y was induced in the females as in Experiment I. Drugs Haloperidol (McNeil) was dissolved in d i s t i l l e d water with a few drops of d i l u t e g l a c i a l a c e t i c acid to obtain concentrations of 0, 0.05, 0.1, 0.2, and 0.5 mg/ml. A l l doses of haloperidol were injected SC 1 hr before t e s t i n g . Pimozide (McNeil) was dissolved in d i s t i l l e d water containing 0.1 N HC1 and brought to pH 6 with 0.01 N NaOH to obtain concentrations of 0, 0.1, 0.5, 1, and 5 mg/ml. A l l doses of pimozide were injected SC 4 hr before t e s t i n g . Clozapine (Sandoz) was dissolved in d i s t i l l e d water containing 0.1 N HC1 and brought to pH 6 with 0.01 N NaOH to obtain concentrations of 0, 0.1, 0.5, 1, and 5 mg/ml. A l l doses of clozapine were injected SC 1 hr before t e s t i n g . Metoclopramide hydrochloride (Sigma) was dissolved in d i s t i l l e d water with a few drops of g l a c i a l a c e t i c acid to obtain concentrations of 0, 0.1, 0.5, 1, and 5 mg/ml. A l l doses of metoclopramide were injected SC 1 hr before t e s t i n g . The s e l e c t i v e DI receptor antagonist SCH 23390 hydrochloride (Schering Co) was dissolved in d i s t i l l e d water to obtain concentrations of 0, 0.01, 0.05, 0.1, and 0.5 mg/ml. A l l doses of SCH 23390 were injected SC 1 hr before 79 t e s t i n g . The s e l e c t i v e D2 r e c e p t o r a n t a g o n i s t s u l p i r i d e (Sigma) was d i s s o l v e d i n d i s t i l l e d w a t e r c o n t a i n i n g 0 . 1 N HC1 and b r o u g h t t o pH 6 w i t h 0 . 0 1 N NaOH t o o b t a i n c o n c e n t r a t i o n s o f 0 , 0 . 5 , 1 , 5, and 10 m g / m l . A l l doses o f s u l p i r i d e were i n j e c t e d SC 1 h r b e f o r e t e s t i n g . A l l d r u g s were i n j e c t e d i n a c o n s t a n t vo lume o f 1 m l / k g body w e i g h t . The v e h i c l e s o l u t i o n s e r v e d as t h e c o n t r o l i n each d r u g c o n d i t i o n . A p p a r a t u s The b i l e v e l t e s t i n g chambers used i n E x p e r i m e n t I were used i n E x p e r i m e n t I I . B e h a v i o r a l T e s t i n g P r o c e d u r e s A t o t a l o f 300 male r a t s (450 t o 700 g) were g i v e n a t l e a s t 10 t e s t s o f m a s c u l i n e c o p u l a t o r y b e h a v i o r p r i o r t o E x p e r i m e n t I I . These t e s t s were 25 min i n d u r a t i o n and were c o n d u c t e d one e v e r y 4 days d u r i n g t h e m i d d l e t h i r d o f t h e d a r k c y c l e . D u r i n g t h e s e t e s t s , each male was p l a c e d i n t o one o f t h e b i l e v e l chambers f o r a 5 -m in t e s t o f l e v e l c h a n g i n g a f t e r w h i c h a s e x u a l l y r e c e p t i v e f e m a l e was p l a c e d i n t o t h e chamber f o r 20 m i n . The o c c u r r e n c e o f each mount , i n t r o m i s s i o n , and e j a c u l a t i o n was r e c o r d e d on a c o m p u t e r i z e d e v e n t r e c o r d e r w h i c h d e r i v e d t h e same 11 measures a n a l y z e d i n E x p e r i m e n t I (Page 5 9 ) . I n a d d i t i o n , t h e p e r c e n t a g e o f males t h a t d i s p l a y e d l e v e l c h a n g e s , m o u n t s , i n t r o m i s s i o n s , and e j a c u l a t i o n s was r e c o r d e d . A l l males a c h i e v e d t h e c r i t e r i a f o r i n c l u s i o n s p e c i f i e d i n E x p e r i m e n t I . E x p e r i m e n t a l P r o c e d u r e s F o l l o w i n g t h e l a s t b a s e l i n e s c r e e n i n g t e s t , e x p e r i m e n t a l 80 rats were assigned randomly to one of s i x drug groups (n = 50/ group). Within each group, 10 rats were assigned randomly to one of the f i v e doses of the drug and received the dose or the control s o l u t i o n i n a randomized order at 4-day i n t e r v a l s . Experimental tests began 4 days afte r the l a s t screening test and were conducted i d e n t i c a l l y to i t . S t a t i s t i c a l Analyses The e f f e c t s of d i f f e r e n t doses of each drug on the 11 measures of sexual behavior were compared s t a t i s t i c a l l y using the data of those rats in each group that displayed the sexual behavior under analysis; no a r b i t r a r y scores were assigned. Where appropriate, the s i g n i f i c a n c e of the differences in the proportion of rats in each drug dose condition that displayed mounts, intromissions, or ejaculations was assessed using c h i -square t e s t s , p_<.05, two-tailed. The 11 measures of sexual behavior within each drug group were subjected to multiple one-way analyses of covariance (ANCOVA) across d i f f e r e n t doses, with the control measures serving as the covariates for the respective drug dose measures. This procedure allowed animals to be used as t h e i r own controls and provided a true index of change for the e f f e c t s of each drug dose on each measure of sexual behavior. Because a l l of the measures of sexual behavior except l e v e l changing were found to be related s t a t i s t i c a l l y in Experiment I, the ANCOVAs run on these measures in the present analysis were corrected for elevated experiment-wise error using the Bonferroni method (Overall & Rhodes, 1987). The adjusted Bonferroni alpha 81 for each ANCOVA was .005. For each s i g n i f i c a n t ANCOVA, post-hoc comparisons of the e f f e c t s of each dose were made using the Tukey method. Results Haloper i d o l The highest dose of haloperidol (0.5 mg/kg) s i g n i f i c a n t l y decreased the proportion of rats that displayed l e v e l changes, X 1 (1, N=20) = 5.95, p_<.025; mounts, X l ( l , N=20) = 7.91, p_<.005; intromissions, X L(1, N=20) = 7.91, p_<.005; and ejaculations, X*" (1, N=20) = 10.21, p_<.005 (Figure 3). These rats appeared sedated and did not disp l a y much i n t e r e s t in the receptive females. Because haloperidol has sedative e f f e c t s at high doses, data from the rats in t h i s group were not subjected further to s t a t i s t i c a l a n a l y s i s . None of the other doses of haloperidol s i g n i f i c a n t l y decreased the proportion of rats that displayed l e v e l changes, mounts, intromissions, or ejaculations. Consistent with e a r l i e r data, the ANCOVA detected s i g n i f i c a n t e f f e c t s of haloperidol on the LC, F(3,35)=29.91, p_<. 00001; the IL, F( 3, 35 ) =21. 05, p_<.0001; the NI, F( 3, 35 ) =8 . 26, p_<.0004; and the NE, F ( 3, 35) =8. 89, p_<.0003 (Figure 4). The ANCOVA also detected an e f f e c t of haloperidol on the ML, F(3,35)=3.99, p_<.01; the PEI, F( 3,34) =2 .93, p_<.04; the I I I , F(3,34)=3.51, p_<.03; and the IR, F( 3, 35) =3. 72, p_<.02; however, these e f f e c t s did not reach the l e v e l of s i g n i f i c a n c e required by the Bonferroni c o r r e c t i o n . Haloperidol had no s i g n i f i c a n t 82 F i g u r e 3. P e r c e n t a g e o f r a t s d i s p l a y i n g l e v e l c h a n g e s , m o u n t s , i n t r o m i s s i o n s , and e j a c u l a t i o n s f o l l o w i n g t r e a t m e n t w i t h d i f f e r e n t doses o f h a l o p e r i d o l i n E x p e r i m e n t I I . * * p_<.05, * p_<.01, f r o m c o n t r o l v a l u e s . DOSE OF HALOPERIDOL ( m g / k g ) 84 F i g u r e 4 . E f f e c t o f d i f f e r e n t doses o f h a l o p e r i d o l on t h e 9 p r i m a r y measures o f male s e x u a l b e h a v i o r o b s e r v e d i n E x p e r i m e n t I I . V a l u e s a r e means a d j u s t e d f o r t h e c o v a r i a t e + SE. * * p < . 0 5 , * p_<.01 / f r o m c o n t r o l v a l u e s . MEAN NUMBER i i i i i i i — i ' • • ' < • i i MEAN NUMBER MEAN LATENCY (sec) • K t s s s i i s i • • ' • • ' • • » • • • • • • • • • MEAN LATENCY (sec) 8 B 8 fi MEAN NUMBER o MEAN LATENCY (eec) • ttsssiitss _ i • » • * • i > MEAN LATENCY (sec) 0 8 6 8 8 8 8 8 8 8 86 o v e r a l l e f f e c t on o t h e r measures o f s e x u a l b e h a v i o r . P o s t - h o c c o m p a r i s o n s o f t h e e f f e c t o f each dose r e v e a l e d t h a t t h e two h i g h e r d o s e s , 0 . 1 and 0 .2 m g / k g , s i g n i f i c a n t l y r e d u c e d LC compared t o t h e e f f e c t s o f t h e c o n t r o l s o l u t i o n and t h e l o w e r d o s e . The e f f e c t o f t h e 0 . 2 - m g / k g dose on LC was a l s o s i g n i f i c a n t l y l o w e r t h a n t h e e f f e c t o f t h e 0 . 1 - m g / k g d o s e . I n c o n t r a s t , o n l y t h e 0 . 2 - m g / k g dose s i g n i f i c a n t l y i n c r e a s e d t h e I L and r e d u c e d t h e NI and NE compared t o t h e e f f e c t s o f t h e c o n t r o l s o l u t i o n and t h e l o w e r d o s e s . P i m o z i d e The e f f e c t s o f p i m o z i d e were s t r i k i n g l y s i m i l a r t o t h o s e o f h a l o p e r i d o l . The h i g h e s t d o s e , 5 .0 m g / k g , s i g n i f i c a n t l y d e c r e a s e d t h e p r o p o r t i o n o f r a t s t h a t d i s p l a y e d l e v e l c h a n g e s , X z ( 1 , N=20)=4 .27, p_<.05; m o u n t s , X X ( 1 , N = 2 0 ) = 7 . 9 1 , p_<.005; i n t r o m i s s i o n s , X * ( l , N = 2 0 ) = 1 0 . 2 1 , p_<.005; and e j a c u l a t i o n s , X l ( l ; N = 2 0 ) = 1 6 . 2 0 , p_<.005 ( F i g u r e 5 ) . As w i t h h a l o p e r i d o l , t h e r a t s t h a t r e c e i v e d t h i s dose appeared s e d a t e d and d i d n o t d i s p l a y much i n t e r e s t i n t h e r e c e p t i v e f e m a l e s . Da ta f r o m t h e r a t s i n t h i s dose g r o u p t h a t engaged i n s e x u a l b e h a v i o r were n o t s u b j e c t e d f u r t h e r t o s t a t i s t i c a l a n a l y s i s . A l t h o u g h t h e 1 . 0 - m g / k g dose o f p i m o z i d e a l s o d e c r e a s e d t h e p r o p o r t i o n o f r a t s t h a t e j a c u l a t e d , t h i s e f f e c t d i d n o t r e a c h s t a t i s t i c a l s i g n i f i c a n c e . The p r o p o r t i o n o f r a t s t h a t d i s p l a t e d l e v e l c h a n g e s , m o u n t s , and i n t r o m i s s i o n s was n o t a f f e c t e d by t h e l ower doses o f p i m o z i d e . The ANCOVA d e t e c t e d s i g n i f i c a n t o v e r a l l e f f e c t s o f p i m o z i d e on LC, F ( 3 , 3 5 ) = 1 5 . 1 2 , p_< . 00002 ; t h e I L , F ( 3, 35) =6 . 79 , p_<.001; t h e 87 Figure 5. Percentage of rats displaying l e v e l changes, mounts, intromissions, and ejaculations following treatment with d i f f e r e n t doses of pimozide in Experiment II. * * p_<.05, * p_<.01, from control values. DOSE OF PIMOZIDE ( m g / k g ) 89 Figure 6. E f f e c t of d i f f e r e n t doses of pimozide on the 9 primary measures of male sexual behavior observed in Experiment I I . Values are means adjusted for the covariate + SE. * * p_<.05, * p_<.01, from control values. MEAN NUMBER O M « « » S S S » 1 I I I I I I I I I MEAN NUMBER • • • • • • MEAN NUMBER — i — i 1 1 • • • • MEAN LATENCY (soc) 0 8 ft 8 8 8 8 1 • i i i i — i — i i i • • • ** MEAN LATENCY (sec) 8 B B § J i i i i i » » • MEAN LATENCY (ssc) i I fi I MEAN NUMBER O M » * » S S « 5 * 8 I i • i i » • i i i i i i • I I MEAN LATENCY (ssc) 8 8 8 8 8 8 4 I I I I I 1 1 • • • • MEAN LATENCY (ssc) 8 8 8 8 8 8 91 P E I , F ( 3 , 3 0 ) = 5 . 8 8 , p_<.003; t h e N I , F ( 3 , 35) =7 . 6 9 , p_<.0007; t h e NE, F ( 3 , 3 5 ) = 7 . 7 8 , p_<.0006; and t h e I I I , F ( 3 , 3 0 ) = 5 . 7 7 , p_<.004 ( F i g u r e 6 ) . The ANCOVA a l s o d e t e c t e d an e f f e c t o f p i m o z i d e on t h e EL, F ( 3 , 3 0 ) = 4 . 8 9 , p_<.007, b u t t h i s e f f e c t d i d n o t r e a c h t h e l e v e l o f s i g n i f i c a n c e r e q u i r e d by t h e B o n f e r r o n i c o r r e c t i o n . P i m o z i d e had no e f f e c t on o t h e r measures o f s e x u a l b e h a v i o r . P o s t - h o c c o m p a r i s o n s o f t h e e f f e c t o f each dose r e v e a l e d t h a t t h e 0 .5 and 1 . 0 - m g / k g doses s i g n i f i c a n t l y r e d u c e d LC f r o m t h e c o n t r o l v a l u e . A l l doses o f p i m o z i d e s i g n i f i c a n t l y r e d u c e d t h e NE f r o m t h e c o n t r o l v a l u e whereas o n l y t h e 1.0 mg/kg dose s i g n i f i c a n t l y i n c r e a s e d t h e I L , P E I , and I I I , and d e c r e a s e d t h e NI f r o m c o n t r o l v a l u e s . C l o z a p i n e None o f t h e r a t s t r e a t e d w i t h t h e 5 . 0 - m g / k g dose o f c l o z a p i n e i n i t i a t e d c o p u l a t o r y b e h a v i o r , whereas 9 o f t h e 10 r a t s d i s p l a y e d r e d u c e d r a t e s o f l e v e l c h a n g i n g ( F i g u r e 7 ) . The 1 . 0 -mg/kg dose a l s o s i g n i f i c a n t l y d e c r e a s e d t h e p r o p o r t i o n o f r a t s t h a t d i s p l a y e d m o u n t s , X z ( 1 , N = 2 0 ) = 7 . 9 1 , p_< . 005 ; i n t r o m i s s i o n s , X z ( 1 , N = 2 0 ) = 7 . 9 1 , p_<.005; and e j a c u l a t i o n s , X 2 - (1 ,N=20 ) = 10 . 2 1 , p_<.005, whereas a l l o f t h e s e r a t s d i s p l a y e d r e d u c e d r a t e s o f l e v e l c h a n g i n g . The r a t s t r e a t e d w i t h t h e two h i g h e s t doses o f c l o z a p i n e appeared l e s s s e d a t e d t h a n t h e r a t s t r e a t e d w i t h t h e h i g h e s t doses o f h a l o p e r i d o l o r p i m o z i d e . Most o f t h e s e r a t s moved f r e e l y a b o u t t h e chambers and a l l d i s p l a y e d p e r i o d s o f a n o g e n i t a l i n v e s t i g a t i o n o f t h e r e c e p t i v e f e m a l e s . Because t h e p e r c e n t a g e o f r a t s t h a t engaged i n c o p u l a t o r y b e h a v i o r was 92 Figure 7. Percentage of rats displaying l e v e l changes, mounts, intromissions, and ejaculations following treatment with d i f f e r e n t doses of clozapine in Experiment II. * * p_<.05, * p_<.01, from control values. DOSE OF CLOZAPINE ( m g / k g ) 94 F i g u r e 8. E f f e c t o f d i f f e r e n t doses o f c l o z a p i n e on t h e 9 p r i m a r y measures o f male s e x u a l b e h a v i o r o b s e r v e d i n E x p e r i m e n t I I . V a l u e s a r e means a d j u s t e d f o r t h e c o v a r i a t e + SE. * p_<.05, * p_<.01, f r o m c o n t r o l v a l u e s . MEAN NUMBER MEAN LATENCY (sac) MEAN NUMBER _i i i • • • i i i i i i i • • • z O o CO m o ~n o r~ O NI > 2 m uQ MEAN NUMBER MEAN NUMBER 7T 2 m MEAN LATENCY (sac) 8 1 8 8 MEAN LATENCY (sec) 1 8 8 8 o MEAN LATENCY (sec) 8 8 8 8 8 8 o MEAN LATENCY (sec) 8 ft 8 8 8 8 96 s i g n i f i c a n t l y l o w e r i n t h e s e two dose g r o u p s , t h e measures o f c o p u l a t o r y b e h a v i o r f r o m t h e s e r a t s were n o t s u b j e c t e d f u r t h e r t o s t a t i s t i c a l a n a l y s i s . However, because t h e p r o p o r t i o n o f r a t s t h a t d i s p l a y e d l e v e l c h a n g i n g was n o t s i g n i f i c a n t l y d i f f e r e n t i n t h e s e g r o u p s , l e v e l c h a n g i n g d a t a f r o m a l l g r o u p s were s u b j e c t e d t o a n a l y s i s o f c o v a r i a n c e . I n r a t s t h a t d i s p l a y e d measures o f s e x u a l b e h a v i o r , t h e ANCOVA d e t e c t e d a s i g n i f i c a n t o v e r a l l e f f e c t o f c l o z a p i n e on LC, F ( 4 , 4 4 ) = 2 2 . 0 4 , p_<. 00001 ( F i g u r e 8 ) . The ANCOVA a l s o d e t e c t e d an e f f e c t o f c l o z a p i n e on t h e ML, F( 2 , 2 6 ) = 3 . 9 8 , p_<.03; t h e I L , F ( 2 , 2 6 ) = 3 . 8 7 , p_<.03; and t h e NE, F( 2 , 25) =5 . 0 0 , p_<.01, a l t h o u g h t h e s e e f f e c t s d i d n o t r e a c h t h e l e v e l o f s i g n i f i c a n c e r e q u i r e d by t h e B o n f e r r o n i c o r r e c t i o n . C l o z a p i n e had no e f f e c t on o t h e r measures o f s e x u a l b e h a v i o r . P o s t - h o c c o m p a r i s o n s o f t h e e f f e c t o f each dose r e v e a l e d t h a t r a t e s o f LC were s i g n i f i c a n t l y r e d u c e d f r o m t h e c o n t r o l v a l u e by t h e 0 . 5 , 1 . 0 , and 5 . 0 - m g / k g d o s e s . T r e a t m e n t w i t h t h e 5 . 0 - m g / k g dose r e d u c e d r a t e s o f LC s i g n i f i c a n t l y f r o m t h o s e o f t h e o t h e r d o s e s . M e t o c l o p r a m i d e None o f t h e doses o f m e t o c l o p r a m i d e d e c r e a s e d t h e p r o p o r t i o n o f r a t s t h a t d i s p l a y e d l e v e l c h a n g i n g , m o u n t s , i n t r o m i s s i o n s , or e j a c u l a t i o n s . The ANCOVA d e t e c t e d an e f f e c t o f m e t o c l o p r a m i d e on t h e N I , F ( 4 , 4 4 ) = 3 . 2 2 , p_<.02; and t h e I I I , F( 4 , 44 ) =3 . 2 3 , p_<.02 ( F i g u r e 9 ) ; however , n e i t h e r o f t h e s e e f f e c t s r e a c h e d t h e l e v e l o f s i g n i f i c a n c e r e q u i r e d by t h e B o n f e r r o n i c o r r e c t i o n . No o t h e r measures o f s e x u a l b e h a v i o r were a f f e c t e d s i g n i f i c a n t l y . 97 Figure 9. E f f e c t of d i f f e r e n t doses of metoclopramide on the 9 primary measures of male sexual behavior observed in Experiment I I . Values are means adjusted for the covariate + SE. * * p_<.05, * p_<.01, from control values. MEAN NUMBER MEAN LATENCY (sec)_ MEAN NUMBER MEAN NUMBER MEAN LATENCY (sec) MEAN LATENCY (sec) o i B B 8 o 8 * 8 8 8 i • • • I I I . , • 1 • • 1 1 1 1 • • • i — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 99 SCH 23390 A l t h o u g h SCH 23390 d e c r e a s e d t h e p r o p o r t i o n o f r a t s t h a t d i s p l a y e d l e v e l c h a n g e s , m o u n t s , i n t r o m i s s i o n s , and e j a c u l a t i o n s , t h e s e e f f e c t s d i d n o t r e a c h s t a t i s t i c a l s i g n i f i c a n c e ( F i g u r e 1 0 ) . The ANCOVA d e t e c t e d s i g n i f i c a n t o v e r a l l e f f e c t s o f SCH 23390 on LC, F ( 4 , 4 4 ) = 5 5 . 0 1 , p_< . 0 0 0 0 1 ; t h e ML, F ( 4 , 41) =12 . 6 2 , p_<.0001; t h e I L , F ( 4 , 4 1 ) = 1 3 . 5 1 , p_<.0001; and t h e P E I , F ( 4 , 39 ) =6 . 4 3 , p_<.0007 ( F i g u r e 1 1 ) . The ANCOVA a l s o d e t e c t e d an o v e r a l l e f f e c t o f SCH 23390 on t h e N I , F( 4 , 41) =3 . 2 7 , p_<.02; t h e NE, F( 4 , 39 ) =2 . 9 5 , p_<.03; and t h e I I I , F( 4 , 39 ) =2 . 9 2 , p_<.03; however , t h e s e e f f e c t s d i d n o t r e a c h t h e l e v e l of s i g n i f i c a n c e r e q u i r e d by t h e B o n f e r r o i n i c o r r e c t i o n . D e s p i t e t h e f a c t t h a t SCH 23390 i n c r e a s e d t h e LCL and p r o d u c e d a l a r g e d e g r e e o f v a r i a t i o n i n t h e EL , t h e ANCOVA d i d n o t d e t e c t o v e r a l l s i g n i f i c a n t e f f e c t s f o r t h e s e or o t h e r measures o f s e x u a l b e h a v i o r . P o s t - h o c c o m p a r i s o n s o f t h e e f f e c t o f each dose r e v e a l e d t h a t a l l doses o f SCH 23390 s i g n i f i c a n t l y reduced LC compared t o t h e e f f e c t o f t h e c o n t r o l s o l u t i o n . The e f f e c t o f a l l doses o f SCH 23390 on LC were a l s o s i g n i f i c a n t l y d i f f e r e n t f r o m one a n o t h e r . I n c o n t r a s t , o n l y t h e h i g h e s t d o s e , 0 .5 m g / k g , s i g n i f i c a n t l y i n c r e a s e d t h e ML, I L , and PEI compared t o t h e e f f e c t s o f t h e c o n t r o l s o l u t i o n and t h e lower d o s e s . S u l p i r i d e None o f t h e doses o f s u l p i r i d e d e c r e a s e d t h e p r o p o r t i o n o f r a t s t h a t d i s p l a y e d l e v e l c h a n g e s , m o u n t s , i n t r o m i s s i o n s , or e j a c u l a t i o n s . The ANCOVA d e t e c t e d a s i g n i f i c a n t o v e r a l l e f f e c t 100 F i g u r e 10 . P e r c e n t a g e o f r a t s d i s p l a y i n g l e v e l c h a n g e s , m o u n t s , i n t r o m i s s i o n s , and e j a c u l a t i o n s f o l l o w i n g t r e a t m e n t w i t h d i f f e r e n t doses o f SCH 23390 i n E x p e r i m e n t I I . * * p_<.05, * p_<.01, f r o m c o n t r o l v a l u e s . LEVEL CHANGES MOUNTS DOSE OF SCH 23390 ( m g / k g ) 102 F i g u r e 1 1 . E f f e c t o f d i f f e r e n t doses o f SCH 23390 on t h e 9 p r i m a r y measures o f male s e x u a l b e h a v i o r o b s e r v e d i n E x p e r i m e n t I I . V a l u e s a r e means a d j u s t e d f o r t h e c o v a r i a t e + SE. * * p_<.05 / * p_<.01, f r o m c o n t r o l v a l u e s . MEAN NUMBER i i i i i i i i—i—i—i i • • • • MEAN NUMBER j i i i i i i i—i i i i i i i i z MEAN NUMBER - M M * •* 1 1 1 1 1 L J MEAN LATENCY (sec^ MEAN NUMBER i i i • • • • • • i i i i i i i i i i i i i 104 Figure 12. E f f e c t of d i f f e r e n t doses of s u l p i r i d e on the 9 primary measures of male sexual behavior observed in Experiment I I . Values are means adjusted for the covariate + SE. * * p_<.05, * p_<.01/ from control values. r / MEAN NUMBER MEAN LATENCY (sec) MEAN NUMBER . . s s : s 0 8 6 8 8 8 8 6 8 8 o - * . - s s : s 5 8 MEAN NUMBER MEAN LATENCY (sac) MEAN LATENCY (sec) : , • 7 ^ 7 . ? 0 8 S B I . 8 6 8 8 8 8 6 8 8 ' 1 1 ' 1 1 1 1 1 1 1 1 1 1 • • 1 1—1—1—J—1 1 1 1 1 1 1 1 • 1 • 1 • 1 1 106 o f s u l p i r i d e on LC, F( 4 , 44 ) =6 . 56 , p_<.0005. A l t h o u g h t h e ANCOVA d e t e c t e d an o v e r a l l e f f e c t o f s u l p i r i d e on t h e I L , F ( 4 , 4 4 ) = 2 . 9 2 , p_<.03, t h i s e f f e c t d i d n o t r e a c h t h e l e v e l o f s i g n i f i c a n c e r e q u i r e d by t h e B o n f e r r o n i c o r r e c t i o n . None o f t h e o t h e r measures o f s e x u a l b e h a v i o r were a f f e c t e d s i g n i f i c a n t l y by s u l p i r i d e ( F i g u r e 1 2 ) . P o s t - h o c c o m p a r i s o n s o f t h e e f f e c t o f each dose r e v e a l e d t h a t t h e 10 -mg /kg dose s i g n i f i c a n t l y r e d u c e d LC compared t o t h e e f f e c t s o f t h e c o n t r o l s o l u t i o n and t h e l o w e r d o s e s . D i s c u s s i o n E x p e r i m e n t I I c o n f i r m e d t h e p r e v i o u s f i n d i n g t h a t DA a n t a g o n i s t s d i f f e r e n t i a l l y a f f e c t t h e c o p u l a t o r y b e h a v i o r o f i n t a c t , s e x u a l l y a c t i v e male r a t s ( P f a u s & P h i l l i p s , 1 9 8 9 ) , and i t e x t e n d s t h e s e f i n d i n g s t o l e v e l c h a n g i n g , a f o r m o f a n t i c i p a t o r y s e x u a l b e h a v i o r o b s e r v e d i n b i l e v e l chambers . The t y p i c a l n e u r o l e p t i c s h a l o p e r i d o l and p i m o z i d e d e c r e a s e d t h e number o f l e v e l changes i n t h e 5 -min p e r i o d t h a t p r e c e d e d t h e i n t r o d u c t i o n o f a s e x u a l l y r e c e p t i v e f e m a l e , i n c r e a s e d t h e i n t r o m i s s i o n l a t e n c i e s , and d e c r e a s e d t h e p r o p o r t i o n o f mounts w i t h i n t r o m i s s i o n . H i g h doses o f t h e s e d r u g s a b o l i s h e d c o p u l a t o r y b e h a v i o r . S i m i l a r l y , t h e a t y p i c a l n e u r o l e p t i c c l o z a p i n e and t h e D 2 - s e l e c t i v e a t y p i c a l n e u r o l e p t i c s u l p i r i d e b o t h d e c r e a s e d t h e number o f l e v e l changes and i n c r e a s e d t h e i n t r o m i s s i o n l a t e n c i e s , a l t h o u g h t h e e f f e c t o f s u l p i r i d e on i n t r o m i s s i o n l a t e n c i e s was o f m a r g i n a l s i g n i f i c a n c e . However, 107 n e i t h e r d r u g a f f e c t e d t h e p r o p o r t i o n o f mounts w i t h i n t r o m i s s i o n . H i g h doses o f c l o z a p i n e a l s o a b o l i s h e d c o p u l a t o r y b e h a v i o r . The D l - s e l e c t i v e a n t a g o n i s t SCH 23390 d e c r e a s e d t h e number o f l e v e l c h a n g e s , i n c r e a s e d b o t h t h e mount and i n t r o m i s s i o n l a t e n c i e s , and d e c r e a s e d t h e p r o p o r t i o n o f mounts w i t h i n t r o m i s s i o n . F i n a l l y , t h e a n t i e m e t i c a g e n t m e t o c l o p r a m i d e d e c r e a s e d t h e p r o p o r t i o n o f mounts w i t h i n t r o m i s s i o n b u t d i d n o t a f f e c t t h e number o f l e v e l changes or t h e l a t e n c y t o i n i t i a t e mounts and i n t r o m i s s i o n s . These r e s u l t s c o n f i r m p r e v i o u s r e p o r t s t h a t t y p i c a l and a t y p i c a l n e u r o l e p t i c d r u g s d e l a y o r a b o l i s h t h e I n i t i a t i o n o f c o p u l a t i o n ( M c i n t o s h & B a r f i e l d , 1984; N a p o l i - F a r r i s e t a l . , 1984 ; P faus & P h i l l i p s , 1989) and t h a t t h e s e two c l a s s e s o f DA a n t a g o n i s t d i f f e r e n t i a l l y r e d u c e t h e number o f mounts w i t h i n t r o m i s s i o n ( A h l e n i u s & L a r s s o n , 1984a ; M c i n t o s h & B a r f i e l d , 1984 ; P f a u s & P h i l l i p s , 1 9 8 9 ) . D e s p i t e t h e c o n s i s t e n c y o f t h e s e f i n d i n g s , s e v e r a l r e s u l t s i n E x p e r i m e n t I I were i n c o n s i s t e n t w i t h p r e v i o u s r e p o r t s . F i r s t , s u b s t a n t i a l i n c r e a s e s i n t h e p o s t e j a c u l a t o r y i n t e r v a l have been r e p o r t e d f o l l o w i n g t r e a t m e n t w i t h modera te doses o f h a l o p e r i d o l or p i m o z i d e ( A h l e n i u s & L a r s s o n , 1 9 8 4 a , b ; M c i n t o s h & B a r f i e l d , 1 9 8 4 ) . A l t h o u g h modera te doses o f h a l o p e r i d o l and p i m o z i d e i n c r e a s e d t h e p o s t e j a c u l a t o r y i n t e r v a l i n t h e p r e s e n t e x p e r i m e n t s , o n l y t h e e f f e c t o f p i m o z i d e reached t h e l e v e l o f s t a t i s t i c a l s i g n i f i c a n c e r e q u i r e d by t h e B o n f e r r o n i c o r r e c t i o n . However , i n our p r e v i o u s s t u d y , t h e e f f e c t o f p i m o z i d e on t h e p o s t e j a c u l a t o r y i n t e r v a l was o f m a r g i n a l s i g n i f i c a n c e ( P f a u s & 108 P h i l l i p s , 1 9 8 9 ) . S i m i l a r l y , p i m o z i d e has been r e p o r t e d t o d e c r e a s e t h e e j a c u l a t i o n l a t e n c y ( M c i n t o s h & B a r f i e l d , 1 9 8 4 ) . A l t h o u g h t h e d e c r e a s e i n t h e e j a c u l a t i o n l a t e n c y p r o d u c e d by p i m o z i d e i n t h e p r e s e n t s t u d y was m a r g i n a l l y s i g n i f i c a n t , our p r e v i o u s s t u d y f a i l e d t o f i n d any e f f e c t o f p i m o z i d e on t h i s measure ( P f a u s & P h i l l i p s , 1 9 8 9 ) . I n our p r e v i o u s s t u d y , s u l p i r i d e s i g n i f i c a n t l y i n c r e a s e d t h e i n t r o m i s s i o n l a t e n c y ; however , i n t h e p r e s e n t s t u d y t h i s e f f e c t was o f m a r g i n a l s i g n i f i c a n c e . These i n c o n s i s t e n c i e s may have r e s u l t e d f r o m a c o m b i n a t i o n o f d i f f e r e n t m e t h o d o l o g i c a l p r o c e d u r e s , i n c l u d i n g t h e use o f d i f f e r e n t t e s t i n g chambers , a n i m a l s w i t h d i f f e r e n t b a s e l i n e s o f s e x u a l b e h a v i o r , and t h e use i n t h e p r e s e n t e x p e r i m e n t s o f a c o n s e r v a t i v e s t a t i s t i c a l p r o c e d u r e ( t h e B o n f e r r o n i method) t o c o r r e c t f o r t h e e l e v a t e d e x p e r i m e n t - w i s e e r r o r t h a t o c c u r s when t h e s t a t i s t i c a l s i g n i f i c a n c e o f r e l a t e d measures i s assessed i n d e p e n d e n t l y . I t i s i n t e r e s t i n g t o n o t e t h a t h a l o p e r i d o l , p i m o z i d e , c l o z a p i n e , s u l p i r i d e , and SCH 23390 d e c r e a s e d t h e number o f l e v e l changes a t doses t h a t d i d n o t i n c r e a s e t h e l a t e n c y t o i n i t i a t e l e v e l changes and t h a t , w i t h few e x c e p t i o n s , d i d n o t a f f e c t measures o f c o p u l a t o r y b e h a v i o r . T h i s i n d i c a t e s t h a t l e v e l c h a n g i n g , as a measure o f a n t i c i p a t o r y s e x u a l m o t i v a t i o n , i s more s e n s i t i v e t o t h e d i s r u p t i v e e f f e c t o f DA a n t a g o n i s t s t h a n t r a d i t i o n a l , c o p u l a t o r y - b a s e d measures o f s e x u a l m o t i v a t i o n ( e . g . , mount and i n t r o m i s s i o n l a t e n c i e s or t h e p r o p o r t i o n o f mounts w i t h i n t r o m i s s i o n ) . T h i s i s c o n s i s t e n t w i t h d a t a f r o m t h e 109 f e e d i n g and a v o i d a n c e l i t e r a t u r e s s u g g e s t i n g t h a t a n t i c i p a t o r y or p r e p a r a t o r y b e h a v i o r s , such as i n s t r u m e n t a l r e s p o n d i n g , a r e more s e n s i t i v e t h a n consummatory b e h a v i o r s , such as f e e d i n g or a v o i d i n g , t o t h e d i s r u p t i v e e f f e c t s o f DA a n t a g o n i s t s ( B l a c k b u r n , 1989; B l a c k b u r n e t a l . , 1987; F i b i g e r e t a l . , 1974; Tombaugh e t a l . , 1 9 7 9 ) . The f a c t t h a t a measure o f a n t i c i p a t o r y s e x u a l m o t i v a t i o n can be d i s s o c i a t e d w i t h l o w doses o f DA a n t a g o n i s t s f r o m t h e i n i t i a t i o n o f c o p u l a t i o n a l s o adds s u p p o r t t o t h e f i n d i n g i n E x p e r i m e n t 1 t h a t t h e s e measures a r e i n d e p e n d e n t . However , t h e p r e s e n t r e s u l t s do n o t s u p p o r t a s s e r t i o n s made i n t h e f e e d i n g and a v o i d a n c e l i t e r a t u r e s t h a t DA a n t a g o n i s t s do n o t g e n e r a l l y i n f l u e n c e consummatory r e s p o n d i n g e x c e p t a t doses t h a t p r o d u c e r e l a t i v e a t a x i a . C l e a r l y , a s p e c t s o f c o p u l a t o r y r a t e ( e . g . , t h e number o f e j a c u l a t i o n s ) , i n i t i a t i o n ( e . g . , t h e i n t r o m i s s i o n l a t e n c i e s ) , and mount c o u n t ( e . g . , t h e number o f mounts w i t h i n t r o m i s s i o n ) were a f f e c t e d by doses o f DA a n t a g o n i s t s t h a t d i d n o t d i s r u p t o t h e r a s p e c t s o f c o p u l a t o r y b e h a v i o r or e l i m i n a t e i t a l t o g e t h e r . I t wou ld appear t h a t c e n t r a l DA sys tems a r e i n v o l v e d i n b o t h a n t i c i p a t o r y / p r e p a r a t o r y and consummatory a s p e c t s o f m a s c u l i n e s e x u a l b e h a v i o r i n t h e r a t , a l t h o u g h t h e a n t i c i p a t o r y / p r e p a r a t o r y a s p e c t s a r e more s e n s i t i v e t o d i s r u p t i o n by DA a n t a g o n i s t s . P r e v i o u s s t u d i e s have s u g g e s t e d a d i f f e r e n t i a l r o l e o f m e s o l i m b i c and m e s o s t r i a t a l DA t e r m i n a l s i n t h e a n t i p s y c h o t i c and e x t r a p y r a m i d a l e f f e c t s o f DA a n t a g o n i s t s (Ch iodo & Bunney, 1984; Lane & B l a h a , 1986; W h i t e & Wang, 1 9 8 3 ) . The s y s t e m i c 110 a d m i n i s t r a t i o n o f h a l o p e r i d o l and p i m o z i d e a f f e c t s DA r e l e a s e n o n s e l e c t i v e l y i n m e s o l i m b i c and m e s o s t r i a t a l t e r m i n a l s (Lane & B l a h a , 1 9 8 6 ) . I n c o n t r a s t , t h e s y s t e m i c a d m i n i s t r a t i o n o f b o t h c l o z a p i n e and s u l p i r i d e a f f e c t s DA r e l e a s e s e l e c t i v e l y i n m e s o l i m b i c t e r m i n a l s , whereas t h e a d m i n i s t r a t i o n o f m e t o c l o p r a m i d e a f f e c t s DA r e l e a s e s e l e c t i v e l y i n m e s o s t r i a t a l t e r m i n a l s (Lane & B l a h a , 1 9 8 6 ) . I n E x p e r i m e n t I I , h a l o p e r i d o l , p i m o z i d e , c l o z a p i n e , and s u l p i r i d e d e c r e a s e d t h e number o f l e v e l changes and i n c r e a s e d t h e i n t r o m i s s i o n l a t e n c i e s , whereas m e t o c l o p r a m i d e had no e f f e c t on t h e s e measu res . A l t h o u g h i t was n o t t h e pu rpose o f t h e p r e s e n t e x p e r i m e n t t o d e t e r m i n e t h e DA t e r m i n a l r e g i o n s i n v o l v e d i n t h e e f f e c t s o f s y s t e m i c a l l y a d m i n i s t e r e d DA a n t a g o n i s t s , t h e s e r e s u l t s s u g g e s t t h a t m e s o l i m b i c , r a t h e r t h a n m e s o s t r i a t a l , DA t e r m i n a l s may be i n v o l v e d i n t h e d i s p l a y o f a n t i c i p a t o r y s e x u a l m o t i v a t i o n and t h e i n i t i a t i o n o f c o p u l a t i o n i n male r a t s . The r e s u l t s o f E x p e r i m e n t I I a l s o i n d i c a t e t h a t t h e r e l a t i v e l y s e l e c t i v e a n t a g o n i s m o f DI and D2 r e c e p t o r s has s i m i l a r e f f e c t s on t h e a n t i c i p a t i o n and i n i t i a t i o n o f male c o p u l a t o r y b e h a v i o r . B o t h t h e D l - s e l e c t i v e a n t a g o n i s t SCH 23390 and t h e D 2 - s e l e c t i v e a n t a g o n i s t s u l p i r i d e d e c r e a s e d t h e number o f l e v e l changes and i n c r e a s e d t h e i n t r o m i s s i o n l a t e n c i e s , a l t h o u g h SCH 23390 a l s o d e c r e a s e d t h e number o f mounts w i t h i n t r o m i s s i o n . H a l o p e r i d o l and p i m o z i d e , b o t h o f w h i c h possess a g r e a t e r a f f i n i t y f o r D2 t h a n DI r e c e p t o r s (Tamminga & G e r l a c h , 1 9 8 7 ) , had e f f e c t s t h a t were v i r t u a l l y i d e n t i c a l t o SCH 23390. These I l l e f f e c t s a r e c o n s i s t e n t w i t h r e p o r t s o f s y n e r g i s t i c a c t i o n s o f D l -and D 2 - s e l e c t i v e compounds. For e x a m p l e , D 2 - s e l e c t i v e a g o n i s t s i n h i b i t neu rons i n t h e n u c l e u s accumbens, g l o b u s p a l l i d u s , and s u b s t a n t i a n i g r a p a r s r e t i c u l a t a , and such i n h i b i t i o n i s enhanced by t h e c o a d m i n i s t r a t i o n o f D l - s e l e c t i v e a g o n i s t s ( C a r l s o n , B e r g s t r o m , Demo, & W a l t e r s , 1988 ; W a l t e r s , B e r g s t r o m , C a r l s o n , Chase, & B r a u n , 1987; Weick & W a l t e r s , 1987; W h i t e & Wang, 1 9 8 6 ) . I n a d d i t i o n , D I and D2 r e c e p t o r s have been r e p o r t e d t o a c t s y n e r g i s t i c a l l y i n t h e d i s p l a y o f s t e r e o t y p i e s ( A r n t , H y t t e l , & P e r r e g a a r d , 1987 ; Mashurano & W a d d i n g t o n , 1 9 8 6 ) , b e h a v i o r a l a c t i v a t i o n ( J a c k s o n & Hash izume, 1 9 8 6 ) , t u r n i n g b e h a v i o r f o l l o w i n g u n i l a t e r a l m e s o s t r i a t a l t r a c t l e s i o n s ( R o b e r t s o n & R o b e r t s o n , 1 9 8 6 ) , and t h e y a w n i n g and p e n i l e e r e c t i o n syndrome ( M e l i s , A r g i o l a s , & Gessa, 1 9 8 7 ) . However , t h e r e a r e a l s o r e p o r t s o f o p p o s i t e a c t i o n s o f DI and D2 r e c e p t o r s , i n c l u d i n g o p p o s i t e e f f e c t s o f s e l e c t i v e DA r e c e p t o r a g o n i s t s on GABA and ACh r e l e a s e i n t h e s t r i a t u m (Fage & S c a t t o n , 1986 ; G i r a u l t , S p a m p i n a t o , G l o w i n s k i , & Besson , 1 9 8 4 ) , on t h e a b i l i t y o f DA t o i n d u c e h y p e r p o l a r i z a t i o n s or d e p o l a r i z a t i o n s o f n u c l e u s accumbens neu rons ( U c h i m u r a , H i g a s h i , & N i s h i , 1 9 8 6 ) , and on t h e d i s p l a y o f o r a l s t e r e o t y p i e s ( J o h a n s e n , L e v i n , Gunne, & E l l i s o n ) and c o n t r a l a t e r a l r o t a t i o n i n r a t s f o l l o w i n g i n t r a n i g r a l i n f u s i o n s ( A s i n & Mon tana , 1 9 8 8 ) . The d i s r u p t i v e e f f e c t s o f t h e D l - s e l e c t i v e a n t a g o n i s t SCH 23390 and t h e D 2 - s e l e c t i v e a n t a g o n i s t s u l p i r i d e on l e v e l c h a n g i n g and t h e . i n t r o m i s s i o n l a t e n c i e s a r e a l s o i n c o n s i s t e n t w i t h a 112 r e c e n t r e p o r t by H u l l e t a l . (1990) i n w h i c h b o t h SCH 23390 and t h e D 2 - s e l e c t i v e a g o n i s t LY 163502 i n c r e a s e d mount and i n t r o m i s s i o n l a t e n c i e s and d e c r e a s e d t h e p r o p o r t i o n o f mounts w i t h i n t r o m i s s i o n i n r a t s f o l l o w i n g i n f u s i o n i n t o t h e MPOA. The c o a d m i n i s t r a t i o n o f t h o s e d r u g s i n t h a t s t u d y was more e f f e c t i v e t h a n e i t h e r d r u g a l o n e . A l t h o u g h a r e l a t i v e l y s e l e c t i v e D2 r e c e p t o r a n t a g o n i s t was n o t assessed i n t h a t s t u d y , t h e r e s u l t s c l e a r l y i n d i c a t e t h a t t h e s t i m u l a t i o n o f DI and D2 r e c e p t o r s i n t h e MPOA has o p p o s i t e a c t i o n s on t h e d i s p l a y o f mounts and i n t r o m i s s i o n s i n t h e male r a t . A l t h o u g h t h o s e r e s u l t s s u g g e s t t h a t t h e r a t i o o f D2 t o DI r e c e p t o r s t i m u l a t i o n i n t h e MPOA i s an i m p o r t a n t f a c t o r i n t h e r e g u l a t i o n o f c e r t a i n a s p e c t s o f m a s c u l i n e s e x u a l b e h a v i o r i n t h e r a t , i t i s n o t c l e a r w h e t h e r a s i m i l a r r e l a t i o n among t h e s e r e c e p t o r t y p e s e x i s t s i n o t h e r DA t e r m i n a l r e g i o n s . The r e s u l t s o f E x p e r i m e n t I I s u g g e s t i t may n o t . However , t h e e f f e c t s o f s u l p i r i d e i n t h i s e x p e r i m e n t s h o u l d be i n t e r p r e t e d c a u t i o u s l y , as t h e doses used were v e r y l o w . The e f f e c t s o f o t h e r D 2 - s e l e c t i v e a n t a g o n i s t s , e . g . , r a c l o p r i d e , need t o be examined b e f o r e a g e n e r a l r o l e o f D2 r e c e p t o r s i n male s e x u a l b e h a v i o r can be h y p o t h e s i z e d . F i n a l l y , i t s h o u l d be n o t e d t h a t many t y p i c a l and a t y p i c a l n e u r o l e p t i c s b i n d t o 5-HT2, c < l , and HI r e c e p t o r s (Tamminga & G e r l a c h , 1 9 8 7 ) , and some a t y p i c a l n e u r o l e p t i c s a l s o possess a n t i c h o l i n e r g i c a c t i v i t y (Snyder e t a l . , 1 9 7 4 ) . I t i s t h u s c o n c e i v a b l e t h a t n e u r o l e p t i c d r u g s c o u l d a c t a t n o n d o p a m i n e r g i c s i t e s t o a f f e c t c e r t a i n a s p e c t s o f m a s c u l i n e s e x u a l b e h a v i o r . 113 T h i s t e n t a t i v e h y p o t h e s i s i s s u p p o r t e d by e v i d e n c e t h a t t h e r e l a t i v e l y s e l e c t i v e oil a n t a g o n i s t p r a z o s i n or t h e r e l a t i v e l y s e l e c t i v e 5-HT2 a n t a g o n i s t p l r e n p e r o n e b o t h i n c r e a s e mount and i n t r o m i s s i o n l a t e n c i e s ( C l a r k , S m i t h , & D a v i d s o n , 1985 ; Mende lson & G o r z a l k a , 1 9 8 5 ) . I n a d d i t i o n , p i r e n p e r o n e , l i k e h a l o p e r i d o l , p i m o z i d e , SCH 23390, and m e t o c l o p r a m i d e , a l s o d e c r e a s e s t h e number o f mounts w i t h i n t r o m i s s i o n (Mende lson & G o r z a l k a , 1 9 8 5 ) . However , t h e f a c t t h a t t h e s e d r u g s e x e r t a s i m i l a r i n f l u e n c e on m a s c u l i n e c o p u l a t o r y b e h a v i o r does n o t n e c e s s a r i l y mean t h a t t h e y work by a s i n g l e t r a n s m i t t e r mechanism. I t i s p o s s i b l e t h a t c o n s i d e r a b l e o v e r l a p e x i s t s i n t h e c o n t r o l o f m a s c u l i n e s e x u a l b e h a v i o r by monoamines o r t h e i r r e c e p t o r s u b t y p e s . T h i s i d e a c o u l d be t e s t e d by e x a m i n i n g w h e t h e r s p e c i f i c monoamine r e c e p t o r a g o n i s t s can s e l e c t i v e l y a t t e n u a t e t h e e f f e c t s o f DA a n t a g o n i s t s . 114 EXPERIMENT I I I : EFFECTS OF CENTRAL ADMINISTRATION OF HALOPERIDOL ON ANTICIPATORY AND CONSUMMATORY ASPECTS OF SEXUAL BEHAVIOR IN THE MALE RAT The systemic administration of t y p i c a l and a t y p i c a l DA receptor antagonists disrupted both a n t i c i p a t o r y and consummatory aspects of male sexual behavior in Experiment I I . The t y p i c a l neuroleptics haloperidol and pimozide, and the DI s e l e c t i v e antagonist SCH 23390, dose-dependently decreased the number of l e v e l changes, increased the intromission l a t e n c i e s , and decreased the number of mounts with intromission and the t o t a l number of ejacula t i o n s . The a t y p i c a l neuroleptic clozapine and the D2-selective antagonist s u l p i r i d e reduced the number of l e v e l changes and increased the intromission l a t e n c i e s , but did not af f e c t the number of intromissions. Unlike s u l p i r i d e , clozapine also reduced the number of ejacula t i o n s . In contrast, the antiemetic agent metoclopramide reduced the number of intromissions but did not a f f e c t other measures of sexual behavior. Higher doses of haloperidol, pimozide, and clozapine delayed or abolished l e v e l changes and the i n i t i a t i o n of copulatory behavior. Currently, i t i s unclear where DA antagonists act to disrupt these aspects of sexual behavior in the male r a t . Although a peripheral e f f e c t i s un l i k e l y , given that the p e r i p h e r a l l y - a c t i v e DA antagonist domperidone has no e f f e c t on the copulatory b e h a v i o r o f i n t a c t , s e x u a l l y a c t i v e r a t s ( P a l a s c h i e t a l . , 1 9 8 1 ) , t h e c e n t r a l s i t e s f o r t h e a c t i o n s o f DA a n t a g o n i s t s on t h e s e x u a l b e h a v i o r o f male r a t s have n o t been s t u d i e d e x t e n s i v e l y . To d a t e , o n l y two s t u d i e s have examined t h e e f f e c t o f DA r e c e p t o r a n t a g o n i s t s i n t h e m e d i a l p r e o p t i c a r e a (MPOA), a t e r m i n a l r e g i o n o f t h e i n c e r t o h y p o t h a l a m i c DA s y s t e m , w h i c h i s c r i t i c a l f o r t h e d i s p l a y o f c o p u l a t o r y b e h a v i o r i n male r a t s . I n t h e f i r s t o f t h o s e two s t u d i e s , t h e e f f e c t o f u n i l a t e r a l i n f u s i o n s o f a r a n g e o f doses o f t h e mixed D1/D2 a n t a g o n i s t c i s - f l u p e n t h i x o l t o t h e MPOA was examined on t h e c o p u l a t o r y b e h a v i o r o f i n t a c t , s e x u a l l y a c t i v e males (Pehek e t a l . , 1 9 8 8 c ) . Two d o s e s , 20 and 40 u g , s i g n i f i c a n t l y r e d u c e d t h e p r o p o r t i o n o f r a t s t h a t m o u n t e d , i n t r o m i t t e d , o r e j a c u l a t e d . I n r a t s t h a t d i s p l a y e d c o p u l a t i o n , t h e s e doses o f c i s - f l u p e n t h i x o l d e c r e a s e d t h e t o t a l number o f e j a c u l a t i o n s and i n c r e a s e d t h e i n t e r i n t r o m i s s i o n i n t e r v a l s . These doses a l s o i n c r e a s e d t h e e j a c u l a t i o n l a t e n c i e s , a l t h o u g h t h i s e f f e c t r e a c h e d s t a t i s t i c a l s i g n i f i c a n c e f o l l o w i n g t r e a t m e n t w i t h 20 ug o n l y . T h u s , b l o c k a d e o f b o t h DI and D2 r e c e p t o r s i n t h e MPOA a f f e c t e d b o t h t h e i n i t i a t i o n and r a t e o f c o p u l a t i o n i n s e x u a l l y a c t i v e m a l e s . The second o f t h o s e two s t u d i e s examined t h e e f f e c t o f a range o f doses o f t h e D l - s e l e c t i v e a n a t a g o n i s t SCH 23390 on t h e c o p u l a t o r y b e h a v i o r o f i n t a c t , s e x u a l l y a c t i v e r a t s f o l l o w i n g u n i l a t e r a l i n f u s i o n s t o t h e MPOA ( H u l l e t a l . , 1 9 9 0 ) . The h i g h e s t d o s e , 10 u g , s i g n i f i c a n t l y i n c r e a s e d b o t h t h e mount and i n t r o m i s s i o n l a t e n c i e s and d e c r e a s e d t h e number o f mounts w i t h i n t r o m i s s i o n . These e f f e c t s were n e a r l y i d e n t i c a l t o t h o s e o b t a i n e d f o l l o w i n g s y s t e m i c a d m i n i s t r a t i o n o f t h i s d r u g i n E x p e r i m e n t I I . However , t h e D 2 - s e l e c t i v e a g o n i s t LY 163502 a l s o i n c r e a s e d mount and i n t r o m i s s i o n l a t e n c i e s and d e c r e a s e d t h e number o f mounts w i t h i n t r o m i s s i o n f o l l o w i n g i n f u s i o n s t o t h e MPOA, s u g g e s t i n g t h a t DI and D2 r e c e p t o r s i n t h e MPOA may have o p p o s i t e a c t i o n s on t h e i n i t i a t i o n o f c o p u l a t i o n and c o p u l a t o r y r a t e . L i t t l e i s known a b o u t t h e r o l e o f o t h e r DA t e r m i n a l s i n t h e s e x u a l b e h a v i o r o f male r a t s . A l t h o u g h t h e DA r e c e p t o r a g o n i s t apomorph ine does n o t s i g n i f i c a n t l y a f f e c t t h e c o p u l a t o r y b e h a v i o r o f s e x u a l l y a c t i v e male r a t s f o l l o w i n g u n i l a t e r a l i n f u s i o n s t o e i t h e r t h e n u c l e u s accumbens o r s t r i a t u m ( H u l l e t a l . , 1 9 8 6 ) , ex  v i v o a n a l y s e s d e m o n s t r a t e an i n c r e a s e i n DOPA c o n c e n t r a t i o n w i t h i n b o t h o f t h e s e r e g i o n s f o l l o w i n g 10 min o f c o p u l a t o r y b e h a v i o r ( A h l e n i u s e t a l . , 1 9 8 7 ) . There i s a l s o e v i d e n c e t h a t m e s o l i m b i c and m e s o s t r i a t a l DA sys tems p l a y a d i f f e r e n t i a l r o l e i n t h e a n t i p s y c h o t i c and e x t r a p y r a m i d a l e f f e c t s o f DA a n t a g o n i s t s (Ch iodo & Bunney, 1984 ; Lane & B l a h a , 1986; W h i t e & Wang, 1 9 8 3 ) . T y p i c a l n e u r o l e p t i c s such as h a l o p e r i d o l and p i m o z i d e a f f e c t DA r e l e a s e n o n s e l e c t i v e l y i n b o t h t h e n u c l e u s accumbens and s t r i a t u m (Lane & B l a h a , 1 9 8 6 ) . I n c o n t r a s t , a t y p i c a l n e u r o l e p t i c s such as c l o z a p i n e and s u l p i r i d e a f f e c t DA r e l e a s e s e l e c t i v e l y i n t h e n u c l e u s accumbens, whereas t h e a n t i e m e t i c a g e n t m e t o c l o p r a m i d e a f f e c t s DA r e l e a s e s e l e c t i v e l y i n t h e s t r i a t u m (Lane & B l a h a , 1 9 8 6 ) . I n E x p e r i m e n t I I , b o t h t y p i c a l and a t y p i c a l n e u r o l e p t i c s 117 disrupted a n t i c i p a t o r y sexual behavior and the i n i t i a t i o n of copulatory behavior, whereas t y p i c a l neuroleptics and metoclopramide reduced the number of mounts with intromission. It i s thus possible that mesolimbic DA terminals are involved in the d i s p l a y of an t i c i p a t o r y sexual behavior and the i n i t i a t i o n of copulation whereas mesostriatal DA terminals are involved in the dis p l a y of mounts with intromission. However, some of these functions may be shared with diencephalic DA systems, most notably the MPOA. To further evaluate the rol e of mesolimbic, mesostriatal, and diencephalic DA terminals in the sexual motivation and copulatory behavior of male r a t s , Experiment III examined the ef f e c t s of haloperidol following b i l a t e r a l infusions to either the nucleus accumbens or striatum, and u n i l a t e r a l infusions to the MPOA. Method Subjects and Surgery The male Long-Evans rats used i n Experiment III were purchased from Charles River Canada and housed as in Experiments I and I I . The stimulus females used in Experiment III were used in Experiments I and I I . Sexual r e c e p t i v i t y was induced in the females as in the previous experiments. T h i r t y male rats were given 10 tests of copulatory behavior in the b i l e v e l chambers pr i o r to Experiment III and a l l achieved the c r i t e r i a for sexual experience outlined in Experiment I (Page 118 5 9 ) . The 30 r a t s were i m p l a n t e d w i t h 23-gauge s t a i n l e s s s t e e l g u i d e c a n n u l a e ( P l a s t i c s One, -Roanoke, VA) a imed a t e i t h e r t h e n u c l e u s accumbens ( n = 1 0 ) , d o r s a l s t r i a t u m ( n = 1 0 ) , or MPOA ( n = 1 0 ) . A l l s u r g e r y was p e r f o r m e d under sod ium p e n t o b a r b i t a l a n e s t h e s i a ( S o m n i t o l , 60 mg/kg) u s i n g a Kopf s t e r e o t a x i c f r a m e . B r i e f l y , t h e s c a l p was c u t , r e t r a c t e d , and f o u r sc rews were i n s e r t e d i n t o t h e s k u l l . S m a l l b u r r h o l e s were d r i l l e d i n t o t h e s k u l l above t h e m e d i o l a t e r a l c o o r d i n a t e s f o r each r e g i o n , and g u i d e c a n n u l a e l o w e r e d t o t h e a p p r o p r i a t e d e p t h . The g u i d e c a n n u l a e were a n c h o r e d t o t h e s k u l l sc rews u s i n g d e n t a l cement t h a t s u r r o u n d e d b o t h t h e sc rews and t h e c a n n u l a e . Ra ts r e c e i v e d b i l a t e r a l c a n n u l a i m p l a n t s t o t h e n u c l e u s accumbens (AP: 1.7 mm, ML: 3 .0 mm, DV: - 6 . 5 mm f r o m t h e s u r f a c e o f t h e b r a i n , w i t h t h e ML c o o r d i n a t e s o f f s e t 1 4 ° l a t e r a l l y ) or s t r i a t u m (AP: 0 .7 mm, ML: 2 .6 mm, DV: - 4 . 0 mm f r o m t h e s u r f a c e o f t h e b r a i n ) a c c o r d i n g t o t h e a t l a s o f P a x i n o s and Watson ( 1 9 8 2 ) . Ra ts r e c e i v e d u n i l a t e r a l c a n n u l a i m p l a n t s t o t h e MPOA (AP: 2 .4 mm, ML: 0 .2 mm, DV: - 7 . 0 mm f r o m t h e s u r f a c e o f t h e b r a i n ) a c c o r d i n g t o t h e a t l a s o f P e l l e g r i n o , P e l l e g r i n o , and Cushman ( 1 9 7 9 ) . U n i l a t e r a l c a n n u l a i m p l a n t a t i o n i n t h e MPOA was chosen t o r e p l i c a t e t h e method and c o o r d i n a t e s r e p o r t e d i n Pehek e t a l . ( 1 9 8 8 ) . To p r o t e c t g u i d e c a n n u l a e when n o t i n u s e , 27-gauge s t a i n l e s s s t e e l o b d u r a t o r s ( P l a s t i c s One, Roanoke, V A ) , s l i g h t l y l o n g e r t h a n t h e g u i d e c a n n u l a e , were i n s e r t e d . F o l l o w i n g s u r g e r y , t h e males were housed i n d i v i d u a l l y i n 44x21x23 cm p l a s t i c h o l d i n g chambers . They were g i v e n a t l e a s t one week o f r e c o v e r y b e f o r e t e s t i n g . 119 Drug T r e a t m e n t H a l o p e r i d o l ( M c N e i l ) was d i s s o l v e d i n d i s t i l l e d w a t e r w i t h a few d r o p s o f g l a c i a l a c e t i c a c i d t o o b t a i n c o n c e n t r a t i o n s o f 0 , 1 , 5, 10 , and 20 p g / p l . Doses o f h a l o p e r i d o l were a d m i n i s t e r e d v i a 27-gauge i n j e c t i o n c a n n u l a e ( P l a s t i c s One, Roanoke, VA) i n a c o n s t a n t vo lume o f 1 j u l . A l l c e n t r a l i n j e c t i o n s were made u s i n g an e l e c t r i c a l l y d r i v e n i n f u s i o n pump (Sage I n s t r u m e n t s Model 3H1A) a t a r a t e o f 1 p l / m i n . The v e h i c l e s o l u t i o n s e r v e d as t h e c o n t r o l . A p p a r a t u s The b i l e v e l t e s t i n g chambers used i n E x p e r i m e n t s I and I I were used i n E x p e r i m e n t I I I . B e h a v i o r a l T e s t i n g P r o c e d u r e s The male r a t s were g i v e n s i x p o s t s u r g i c a l t e s t s o f s e x u a l b e h a v i o r b e g i n n i n g a t l e a s t 1 week a f t e r s u r g e r y . These t e s t s were 25 min i n d u r a t i o n and were c o n d u c t e d one e v e r y 4 days d u r i n g t h e m i d d l e t h i r d o f t h e d a r k c y c l e . D u r i n g t h e f i r s t two o f t h e s e t e s t s , t h e males r e c e i v e d m i c r o i n j e c t i o n s o f t h e v e h i c l e s o l u t i o n 5 min b e f o r e b e i n g p l a c e d i n one o f t h e b i l e v e l chambers . M i c r o i n j e c t i o n s were made by r e p l a c i n g t h e o b d u r a t o r w i t h t h e i n j e c t i o n c a n n u l a , w h i c h was l e f t i n p l a c e f o r 30 s a f t e r each i n f u s i o n t o p r e v e n t t h e d i f f u s i o n o f s o l u t i o n back up t h e g u i d e c a n n u l a . F o l l o w i n g t h e i n f u s i o n s , each male was p l a c e d i n one o f t h e b i l e v e l chambers f o r a 5 -m in t e s t o f l e v e l c h a n g i n g a f t e r w h i c h a s e x u a l l y r e c e p t i v e f e m a l e was p l a c e d i n t h e chamber f o r 20 m i n . The o c c u r r e n c e o f each mount , i n t r o m i s s i o n , and 120 e j a c u l a t i o n was r e c o r d e d on a c o m p u t e r i z e d e v e n t r e c o r d e r , w h i c h d e r i v e d t h e same measures o f s e x u a l b e h a v i o r used i n E x p e r i m e n t s I and I I (Page 5 9 ) . A l l 30 males d i s p l a y e d l e v e l c h a n g i n g and c o p u l a t o r y b e h a v i o r d u r i n g t h e f i r s t two p o s t s u r g i c a l t e s t s . Four s u b s e q u e n t e x p e r i m e n t a l t e s t s o f s e x u a l b e h a v i o r were c o n d u c t e d . D u r i n g t h e s e t e s t s , t h e males r e c e i v e d f o u r doses o f h a l o p e r i d o l , a d m i n i s t e r e d a c c o r d i n g t o a l a t i n i z e d d e s i g n , 5 min b e f o r e each t e s t . Males w i t h b i l a t e r a l c a n n u l a p l a c e m e n t s t o t h e n u c l e u s accumbens and s t r i a t u m r e c e i v e d 0, 1 , 5, and 10 u g / s i d e o f h a l o p e r i d o l . Males w i t h u n i l a t e r a l c a n n u l a p l a c e m e n t s t o t h e MPOA r e c e i v e d 0 , 2 , 10 , and 20 ug o f h a l o p e r i d o l . A l t h o u g h t h i s p r o c e d u r e d i d n o t e q u a t e t h e amount o f d r u g d e l i v e r e d per u n i t d f t i s s u e , or e q u a t e t h e deg ree o f t i s s u e damage d u r i n g c a n n u l a i m p l a n t a t i o n , i t d i d e q u a t e t h e t o t a l amount o f d r u g r e c e i v e d by each r a t . H i s t o l o g y A f t e r each e x p e r i m e n t , males were a n e s t h e t i z e d w i t h s o d i u m p e n t o b a r b i t a l (60 mg/kg) and d e c a p i t a t e d , and t h e i r b r a i n s were removed and s t o r e d i n a 40% f o r m a l i n / s u c r o s e s o l u t i o n . . The b r a i n s were s u b s e q u e n t l y f r o z e n i n a c r y o s t a t and 40-um s e c t i o n s were c u t , mounted on g l a s s s l i d e s , and examined under a m i c r o s c o p e . E x a m i n a t i o n o f t h e s l i d e s i n d i c a t e d t h a t t h e a l l o f t h e males i n each g r o u p had c a n n u l a t r a c k s e n d i n g i n t h e i r r e s p e c t i v e t a r g e t s t r u c t u r e s ! The c a n n u l a p l a c e m e n t s a r e shown i n F i g u r e s 13 t o 1 5 . 121 Figure 13. Bilateral cannula placements (n = 10) directed at the nucleus accumbens in Experiment III. +0.2 mm 122 124 S t a t i s t i c a l A n a l y s e s The e f f e c t s o f d i f f e r e n t doses o f h a l o p e r i d o l on measures o f a n t i c i p a t o r y and consummatory s e x u a l b e h a v i o r were compared s t a t i s t i c a l l y u s i n g t h e d a t a o f t h o s e r a t s i n each g r o u p t h a t d i s p l a y e d t h e s e x u a l b e h a v i o r under a n a l y s i s ; no a r b i t r a r y s c o r e s were a s s i g n e d . Where a p p r o p r i a t e , t h e s i g n i f i c a n c e o f t h e d i f f e r e n c e s i n t h e p e r c e n t a g e o f r a t s i n each dose c o n d i t i o n t h a t d i s p l a y e d l e v e l c h a n g e s , m o u n t s , i n t r o m i s s i o n s , and e j a c u l a t i o n s was assessed u s i n g c h i - s q u a r e t e s t s , p_<.05, t w o - t a i l e d . The 11 measures o f s e x u a l b e h a v i o r (see Page 59) were s u b j e c t e d t o m u l t i p l e w i t h i n - s u b j e c t s a n a l y s e s o f v a r i a n c e w i t h dose as t h e r e p e a t e d measure . Because a l l o f t h e measures o f s e x u a l b e h a v i o r e x c e p t l e v e l c h a n g i n g were f o u n d t o be r e l a t e d s t a t i s t i c a l l y i n E x p e r i m e n t I , t h e s e p a r a t e ANOVAs r u n on t h e s e measures were c o r r e c t e d f o r e l e v a t e d e x p e r i m e n t - w i s e e r r o r u s i n g t h e B o n f e r r o n i method ( O v e r a l l & Rhodes, 1 9 8 7 ) . As i n E x p e r i m e n t I I , t h e a d j u s t e d B o n f e r r o n i a l p h a f o r each ANOVA was . 0 0 5 . For each s i g n i f i c a n t ANOVA, p o s t - h o c c o m p a r i s o n s o f t h e e f f e c t s o f each dose were made u s i n g t h e Tukey m e t h o d . R e s u l t s N u c l e u s Accumbens None o f t h e doses o f h a l o p e r i d o l d e c r e a s e d t h e p e r c e n t a g e o f r a t s t h a t d i s p l a y e d l e v e l c h a n g i n g , m o u n t s , i n t r o m i s s i o n s , or e j a c u l a t i o n s . The ANOVA d e t e c t e d a s i g n i f i c a n t o v e r a l l e f f e c t o f h a l o p e r i d o l on LC, F( 3, 27 ) =10 . 09 , p_< . 00026 ( F i g u r e 1 6 ) , b u t n o t 125 Figure 16. E f f e c t of b i l a t e r a l infusions of d i f f e r e n t doses of haloperidol to the nucleus accumbens on the 9 primary measures of male sexual behavior observed in Experiment I I I . Values are means + SE. * * p_<.05, * p_<.01, from control values. MEAN NUMBER • i i i i i i i i i i i—i—i—•—i z MEAN NUMBER J— i— i— i— i— i— i— i— i i • • • i i i MEAN NUMBER » u » J 1 1 1 I I I I MEAN LATENCY (soc) 0 a » s s i i 1 • • i i i i — i — i — J — i — i i MEAN LATENCY (soc) I 3 . f i -i i i i • • i i MEAN LATENCY (soc) § 8 8 8 i i — J — i i i • i i MEAN NUMBER H . . . . s ; s s 8 • • MEAN LATENCY (soc) 8 f t 8 8 8 8 • • • i i i i i i i i i MEAN LATENCY (soc) 8 ft 8 8 8 8 J — i — i — i — i — i — i — ' • • i i 127 on any o t h e r measure o f s e x u a l b e h a v i o r . P o s t - h o c c o m p a r i s o n s r e v e a l e d t h a t t h e h i g h e s t d o s e , 10 j u g / s i d e , s i g n i f i c a n t l y r e d u c e d LC compared t o t h e e f f e c t o f t h e c o n t r o l s o l u t i o n or t h e e f f e c t o f t h e l o w e r d o s e s . S t r i a t u m None o f t h e doses o f h a l o p e r i d o l d e c r e a s e d t h e p e r c e n t a g e o f r a t s t h a t d i s p l a y e d l e v e l c h a n g i n g , m o u n t s , i n t r o m i s s i o n s , or e j a c u l a t i o n s . The ANOVA d e t e c t e d a s i g n i f i c a n t o v e r a l l e f f e c t o f h a l o p e r i d o l on t h e NE, F( 3 , 2 7 ) = 5 . 4 5 , p_<.005 ( F i g u r e 1 7 ) , b u t n o t on any o t h e r measure o f s e x u a l b e h a v i o r . P o s t - h o c c o m p a r i s o n s r e v e a l e d t h a t t h e h i g h e s t d o s e , 10 j u g / s i d e , s i g n i f i c a n t l y i n c r e a s e d t h e NE compared t o t h e e f f e c t o f t h e c o n t r o l s o l u t i o n or t h e e f f e c t o f t h e l o w e r d o s e s . M e d i a l P r e o p t i c A rea None o f t h e doses o f h a l o p e r i d o l d e c r e a s e d t h e p e r c e n t a g e o f r a t s t h a t d i s p l a y e d l e v e l c h a n g i n g , m o u n t s , o r i n t r o m i s s i o n s . O n l y one r a t t h a t r e c e i v e d t h e h i g h e s t dose (20 jug) f a i l e d t o e j a c u l a t e . The e f f e c t s o f h a l o p e r i d o l i n f u s i o n s t o t h e MPOA were v e r y s i m i l a r t o t h o s e o f s y s t e m i c a d m i n i s t r a t i o n i n E x p e r i m e n t I I ( F i g u r e 1 8 ) . The ANOVA d e t e c t e d s i g n i f i c a n t o v e r a l l e f f e c t s o f h a l o p e r i d o l on LC, F( 3 , 27 ) =53 . 53 , p_<.0001; t h e LCL, F ( 3, 27 ) =5 . 57 , p_<.005; t h e I L , F( 3 , 27 )=12 . 4 8 , p_<.0001; t h e N I , F( 3 , 27 )=7 . 8 6 , p_<.0009; t h e NE, F ( 3 , 27 ) = 5 . 6 2 , p_<.005; and t h e I R , F( 3 , 27 ) =9 . 7 5 , p_<.0003. A l t h o u g h t h e ANOVA d e t e c t e d an e f f e c t o f h a l o p e r i d o l on t h e ML, F( 3 ,27 ) = 4 . 5 9 , p_<.02, t h i s e f f e c t d i d n o t r e a c h t h e l e v e l o f s t a t i s t i c a l s i g n i f i c a n c e r e q u i r e d by t h e B o n f e r r o n i 128 F i g u r e 17 . E f f e c t o f b i l a t e r a l i n f u s i o n s o f d i f f e r e n t doses o f h a l o p e r i d o l t o t h e s t r i a t u m on t h e 9 p r i m a r y measures o f male s e x u a l b e h a v i o r o b s e r v e d i n E x p e r i m e n t I I I . V a l u e s a r e means + SE. * p_<.05, * p K . O l , f r o m c o n t r o l v a l u e s . MEAN NUMBER j i i i i i i i i — i — i 2 MEAN NUMBER MEAN LATENCY (soc) 8 6 8 8 8 8 T MEAN LATENCY (soc) i 8 8 8 m MEAN LATENCY (soc) 8 8 8 8 MEAN NUMBER • • • • ' • • ' 1 1 1 ' ' 1 ' 1 • 1 • • MEAN LATENCY (soc) 8 8 8 8 8 8 J — i i i i — i — i — i i i i i MEAN LATENCY (soc) 8 8 8 8 8 8 J — i — i — i — i — i — i — i i i i i 130 Figure 18. E f f e c t of u n i l a t e r a l infusions of d i f f e r e n t doses of haloperidol to the medial preoptic area on the 9 primary measures of male sexual behavior observed in Experiment I I I . Values are means + SE. * * p_<.05, * p_<,01, from control values. MEAN NUMBER J i i i i i—i i—i i i i i • • i z 2 MEAN NUMBER J i i i i i i i i i MEAN LATENCY (soc) 8 & 8 8 8 8 6* i • i i i i i i i i i i i—i MEAN LATENCY (soc) § 8 8 8 -i i i i — i i ' • m MEAN LATENCY (soc) § 8 8 8 j i i i i • i i MEAN NUMBER O t # « * » O M * o > £ 8 • ' • ' ' 1 1 ' 1 ' ' 1 ' ' ' • ' • * • MEAN LATENCY (soc) 8 6 8 8 8 8 J — i — i — i — i — i i • • • • • MEAN LATENCY (soc) 8 6 8 8 8 8 J — i — i — i — i — i — i i i • • • 132 c o r r e c t i o n . P o s t - h o c c o m p a r i s o n s o f t h e e f f e c t o f each dose r e v e a l e d t h a t t h e 10 and 20 jug doses s i g n i f i c a n t l y r e d u c e d LC and t h e I L compared t o t h e e f f e c t s o f t h e c o n t r o l s o l u t i o n and t h e l o w e r d o s e s , whereas o n l y t h e 20 ^pg dose s i g n i f i c a n t l y i n c r e a s e d t h e LCL and d e c r e a s e d t h e N I , NE, and IR compared t o t h e e f f e c t s o f t h e c o n t r o l s o l u t i o n and t h e l o w e r d o s e s . I n t e r e s t i n g l y , o n l y t h r e e o f t h e r a t s t h a t r e c e i v e d t h e 10 ug dose p u r s u e d t h e f e m a l e f r o m l e v e l t o l e v e l d u r i n g b o u t s o f c o p u l a t o r y a c t i v i t y whereas none o f t h e r a t s t h a t r e c e i v e d t h e 20 ug dose p u r s u e d t h e f e m a l e . These r a t s t y p i c a l l y s t a y e d on t h e b o t t o m l e v e l t h r o u g h o u t t h e 2 0 - m i n t e s t , a l t h o u g h a l l o r i e n t e d t o w a r d t h e f e m a l e as she moved f r o m t h e t o p l e v e l t o t h e b o t t o m . T h i s r e s u l t c o u l d be t a k e n as e v i d e n c e o f a g e n e r a l motor or s e n s o r y d i s r u p t i o n ; however , t h e f a c t t h a t h a l o p e r i d o l d i d n o t s i g n i f i c a n t l y i n c r e a s e t h e EL or I I I i n d i c a t e s t h a t most o f t h e s e r a t s were c a p a b l e o f c o m p l e t i n g t h e f i r s t c o p u l a t o r y s e r i e s i n a n o r m a l amount o f t i m e . Thus , h a l o p e r i d o l i n f u s i o n s t o t h e MPOA may have d i m i n i s h e d a r e l a t i v e l y u n c h a r a c t e r i z e d measure o f consummatory s e x u a l b e h a v i o r i n t h e b i l e v e l chambers : p u r s u i t o f t h e f e m a l e . D i s c u s s i o n E x p e r i m e n t I I I p r o v i d e s t h e f i r s t e v i d e n c e t h a t h a l o p e r i d o l a f f e c t s a n t i c i p a t o r y and consummatory a s p e c t s o f t h e s e x u a l b e h a v i o r o f male r a t s s e l e c t i v e l y i n d i f f e r e n t DA t e r m i n a l r e g i o n s . B i l a t e r a l i n f u s i o n s o f h a l o p e r i d o l t o t h e n u c l e u s accumbens, a major terminal of the mesolimbic A10 pathway, attenuated l e v e l changing without a f f e c t i n g other measures of sexual behavior s i g n i f i c a n t l y . B i l a t e r a l infusions of haloperidol to the striatum, a major terminal of the mesostriatal A9 pathway, increased the t o t a l number of ejaculations displayed during the 20-min t e s t . F i n a l l y , u n i l a t e r a l infusions of haloperidol to the MPOA, a major terminal of the incerto-hypothalamic A14 pathway, produced nearly a l l of the e f f e c t s of systemic administration, including a decreased number of l e v e l changes, increased intromission l a t e n c i e s , and a decreased number of intromissions and ejaculations. These r e s u l t s suggest that DA terminals in the nucleus accumbens and striatum are involved in the d i s p l a y of an t i c i p a t o r y sexual behavior and copulatory rate, r e s p e c t i v e l y , whereas DA terminals in the MPOA are involved in the d i s p l a y of an t i c i p a t o r y sexual behavior, the i n i t i a t i o n of copulation, copulatory rate, and h i t rate. The e f f e c t s of haloperidol infusions to the MPOA are consistent with previous reports that u n i l a t e r a l infusions of the mixed D1/D2 antagonist c i s - f l u p e n t h i x o l or the D l - s e l e c t i v e antagonist SCH 23390 to the MPOA disrupt the i n i t i a t i o n and rate of sexual behavior i n male rats (Hull et a l . , 1990; Pehek et a l . , 1988c). Although DA terminals in the MPOA appear to play an important multifaceted r o l e in the control of an t i c i p a t o r y and consummatory aspects of male sexual behavior, several of the eff e c t s observed following infusions of haloperidol to the MPOA may be due to a common mechanism. Pehek et a l . (1988a) have 134 shown t h a t s y s t e m i c a d m i n i s t r a t i o n s o f h a l o p e r i d o l i n c r e a s e t h e l a t e n c y t o f i r s t e r e c t i o n and d e c r e a s e t h e number o f e r e c t i o n s i n i n t a c t , s e x u a l l y a c t i v e male r a t s . Pehek e t a l . (1988b) have a l s o d e m o n s t r a t e d t h a t i n f u s i o n s o f apomorph ine t o e i t h e r t h e MPOA or p a r a v e n t r i c u l a r n u c l e u s a f f e c t t h e s y m p a t h e t i c a c t i v a t i o n o f p e n i l e r e f l e x e s . I t may t h e r e f o r e be a rgued t h a t t h e i n c r e a s e d i n t r o m i s s i o n l a t e n c y and d e c r e a s e d number o f i n t r o m i s s i o n s and e j a c u l a t i o n s f o l l o w i n g s y s t e m i c a d m i n i s t r a t i o n o f DA a n t a g o n i s t s r e f l e c t s t h e a n t a g o n i s m o f d i e n c e p h a l i c DA t e r m i n a l s , w h i c h d i s r u p t s t h e d i s p l a y o f p e n i l e r e f l e x e s . A l t h o u g h t h e d i s r u p t i o n o f c o p u l a t o r y i n i t i a t i o n , r a t e , and h i t r a t e can be a t t r i b u t e d t o such a mechan ism, t h e d e c r e a s e i n l e v e l changes c a n n o t . T h i s s u g g e s t s t h a t t h e MPOA c o n t r i b u t e s i m p o r t a n t i n f o r m a t i o n f o r t h e d i s p l a y o f a n t i c i p a t o r y s e x u a l b e h a v i o r i n male r a t s . T h i s s u g g e s t i o n i s c o n s i s t e n t w i t h e v i d e n c e t h a t l e s i o n s o f t h e MPOA d e c r e a s e t h e p r e f e r e n c e o f male r a t s f o r a s e x u a l l y r e c e p t i v e fema le (Edwards & E i n h o r n , 1 9 8 6 ) . As w i t h t h e MPOA, h a l o p e r i d o l i n f u s i o n s t o t h e n u c l e u s accumbens s i g n i f i c a n t l y d e c r e a s e d t h e number o f l e v e l c h a n g e s . However , h a l o p e r i d o l i n f u s i o n s d i d n o t s i g n i f i c a n t l y a f f e c t consummatory measures o f male s e x u a l b e h a v i o r , s u g g e s t i n g t h a t DA t e r m i n a l s i n t h e n u c l e u s accumbens p l a y a s e l e c t i v e r o l e i n t h e c o n t r o l o f a n t i c i p a t o r y s e x u a l b e h a v i o r . T h i s s u g g e s t i o n i s c o n s i s t e n t w i t h a r e c e n t r e p o r t t h a t b i l a t e r a l i n f u s i o n s o f amphetamine t o t h e n u c l e u s accumbens can r e s t o r e r a t e s o f o p e r a n t r e s p o n d i n g f o r a s e c o n d a r y s e x u a l r e i n f o r c e r f o l l o w i n g l e s i o n s o f 135 t h e b a s o l a t e r a l amygda la i n male r a t s w i t h o u t a f f e c t i n g consummatory measures o f s e x u a l b e h a v i o r ( E v e r i t t e t a l . , 1 9 8 9 ) . I t i s a l s o c o n s i s t e n t w i t h a l a r g e body o f e v i d e n c e i m p l i c a t i n g DA t e r m i n a l s i n t h e n u c l e u s accumbens i n t h e c o n t r o l o f p r e p a r a t o r y b u t n o t consummatory a s p e c t s o f f e e d i n g b e h a v i o r ( e . g . , K e l l e y & S t i n u s , 1985 ; Koob e t a l . , 1 9 7 8 ) . However , e l e c t r o l y t i c l e s i o n s o f t h e A10 c e l l b o d i e s i n t h e VTA t h a t p r o d u c e d an a v e r a g e 77% d e p l e t i o n o f DA i n t h e n u c l e u s accumbens have been r e p o r t e d t o i n c r e a s e mount l a t e n c i e s and PEIs i n i n t a c t , s e x u a l l y a c t i v e r a t s ( B r a c k e t t e t a l . , 1 9 8 6 ) . M o r e o v e r , b i l a t e r a l 6-OHDA l e s i o n s o f DA t e r m i n a l s i n t h e n u c l e u s accumbens have been r e p o r t e d t o i n c r e a s e mount l a t e n c i e s i n s e x u a l l y a c t i v e r a t s (Robb ins e t a l . , 1 9 8 9 ) . None o f t h e s e e f f e c t s were o b s e r v e d f o l l o w i n g i n f u s i o n s o f h a l o p e r i d o l t o t h e n u c l e u s accumbens. T h u s , t h e a p p a r e n t b e h a v i o r a l s e l e c t i v i t y o f h a l o p e r i d o l i n f u s i o n s t o t h e n u c l e u s accumbens i n t h i s e x p e r i m e n t s h o u l d be v i e w e d c a u t i o u s l y . The e f f e c t o f i n f u s i o n s o f h i g h e r doses o f h a l o p e r i d o l , or o f o t h e r DA a n t a g o n i s t s , t o t h e n u c l e u s accumbens needs t o be examined on a n t i c i p a t o r y o r consummatory a s p e c t s o f male s e x u a l b e h a v i o r b e f o r e t h e r e s u l t s r e p o r t e d h e r e can be g e n e r a l i z e d . I n f u s i o n o f t h e h i g h e s t dose o f h a l o p e r i d o l t o t h e s t r i a t u m i n c r e a s e d t h e t o t a l number o f e j a c u l a t i o n s d i s p l a y e d d u r i n g t h e 2 0 - m i n t e s t , s u g g e s t i n g t h a t DA t r a n s m i s s i o n i n t h e s t r i a t u m may s e r v e t o d e l a y or i n h i b i t e j a c u l a t i o n . T h i s r e s u l t was u n e x p e c t e d because t h e s y s t e m i c a d m i n i s t r a t i o n o f h a l o p e r i d o l 136 d e c r e a s e d , r a t h e r t h a n i n c r e a s e d , t h e t o t a l number o f e j a c u l a t i o n s i n E x p e r i m e n t I I . However , t h i s e f f e c t may be due t o t h e l a r g e b u t n o n s i g n i f i c a n t d e c r e a s e i n t h e e j a c u l a t i o n l a t e n c y o b s e r v e d w i t h t h e h i g h e s t d o s e . I n t e r e s t i n g l y , e l e c t r o l y t i c l e s i o n s o f t h e A9 c e l l b o d i e s i n t h e s u b s t a n t i a n i g r a p a r s compacta t h a t p r o d u c e d an a v e r a g e 56% d e p l e t i o n o f DA i n t h e s t r i a t u m have been r e p o r t e d t o i n c r e a s e mount and i n t r o m i s s i o n l a t e n c i e s , d e c r e a s e t h e number o f i n t r o m i s s i o n s , and d e c r e a s e t h e number o f e j a c u l a t i o n s i n s e x u a l l y a c t i v e r a t s ( B r a c k e t t e t a l . , 1 9 8 6 ) . B i l a t e r a l 6-OHDA l e s i o n s o f t h e d o r s a l s t r i a t u m have a l s o been r e p o r t e d t o i n c r e a s e t h e mount l a t e n c i e s o f s e x u a l l y a c t i v e r a t s (Robb ins e t a l . , 1 9 8 9 ) . None o f t h o s e e f f e c t s were o b s e r v e d f o l l o w i n g i n f u s i o n s o f h a l o p e r i d o l t o t h e s t r i a t u m . C l e a r l y , more work i s r e q u i r e d t o s p e c i f y t h e e x a c t r o l e o f m e s o s t r i a t a l DA t e r m i n a l s i n t h e s e x u a l b e h a v i o r o f male r a t s . I n p a r t i c u l a r , a r e p l i c a t i o n o f t h e i n c r e a s e d number o f e j a c u l a t i o n s f o l l o w i n g i n f u s i o n o f t h e same or h i g h e r doses o f h a l o p e r i d o l t o t h e s t r i a t u m i s r e q u i r e d b e f o r e t h e r e l i a b i l i t y o f t h i s e f f e c t can be s t a t e d w i t h c e r t a i n t y . I t i s d i f f i c u l t t o compare t h e r e s u l t s o f b i l a t e r a l and u n i l a t e r a l i n f u s i o n s because t h e amount o f d r u g i n f u s e d per u n i t o f t i s s u e and t h e m a g n i t u d e o f t i s s u e t r a u m a d u r i n g s u r g e r y were n o t e q u a t e d . U n i l a t e r a l , r a t h e r t h a n b i l a t e r a l , i n f u s i o n s t o t h e MPOA were employed i n E x p e r i m e n t I I I f o r two r e a s o n s . F i r s t , t h i s s t r u c t u r e s u r r o u n d s t h e t h i r d v e n t r i c l e v e r y c l o s e t o t h e m i d l i n e ; however , u s i n g t h e a t l a s o f P e l l e g r i n o e t a l . (1979) t h e 137 d o r s a l p o r t i o n o f t h e MPOA i s n o t b i s e c t e d by t h e t h i r d v e n t r i c l e b u t r a t h e r fo rms a n a r r o w and c o n t i n u o u s b i l a t e r a l m i d l i n e n u c l e u s . The d i f f e r e n c e between b i l a t e r a l and u n i l a t e r a l i n f u s i o n s t o t h i s a r e a i n t e r m s o f t h e amount o f d r u g a c c u m u l a t i n g i n t h e t i s s u e s h o u l d have been m i n i m a l g i v e n t h e n a r r o w n e s s o f t h e s t r u c t u r e . I n a d d i t i o n , b i l a t e r a l i m p l a n t a t i o n wou ld have r e q u i r e d t h e c a n n u l a e t o be p l a c e d i n t o t h e b r a i n a t e x t r e m e l y a c u t e a n g l e s because t h e c a n n u l a e were much t o o l a r g e t o be p l a c e d p a r a l l e l t o one a n o t h e r . T h i s c o u l d have i n c r e a s e d t h e l i k l i h o o d o f m i s p l a c e m e n t . The second r e a s o n f o r c h o o s i n g u n i l a t e r a l c a n n u l a i m p l a n t a t i o n s t o t h e MPOA was t o r e p l i c a t e t h e method used by Pehek e t a l . ( 1 9 8 8 ) , so t h a t a d i r e c t c o m p a r i s o n c o u l d be made between t h e e f f e c t s o f c i s - f l u p e n t h i x o l i n t h a t s t u d y and h a l o p e r i d o l l n E x p e r i m e n t I I I . However, a l t h o u g h b i l a t e r a l i m p l a n t a t i o n 'wou ld have equa ted t h e amount o f t i s s u e t r a u m a i n c u r r e d d u r i n g s u r g e r y , t h e i n f u s i o n o f s i m i l a r doses o f h a l o p e r i d o l wou ld n o t have equa ted t h e r a t i o o f d r u g t o s u r f a c e a r e a because t h e n u c l e u s accumbens, s t r i a t u m , and MPOA v a r y g r e a t l y i n s i z e . I n s t e a d , t h e method employed i n E x p e r i m e n t I I I e q u a t e d t h e o v e r a l l amount o f d r u g r e c e i v e d by each r a t ; 20 ug o f h a l o p e r i d o l d e l i v e r e d u n i l a t e r a l l y t o t h e MPOA was v i e w e d as r e l a t i v e l y e q u i v a l e n t t o 10 u g / s i d e d e l i v e r e d b i l a t e r a l l y t o t h e n u c l e u s accumbens. N e v e r t h e l e s s , c a u t i o n must be t a k e n when c o m p a r i n g t h e e f f e c t s o f h a l o p e r i d o l i n each o f t h e s e s t r u c t u r e s . A l t h o u g h t h e r e s u l t s o f E x p e r i m e n t I I I s u g g e s t t h a t h a l o p e r i d o l a c t s i n t h e n u c l e u s accumbens and MPOA t o d e c r e a s e 138 a n t i c i p a t o r y s e x u a l b e h a v i o r , and i n t h e MPOA or o t h e r d i e n c e p h a l i c s t r u c t u r e s t o d i s r u p t c e r t a i n consummatory a s p e c t s o f c o p u l a t i o n , an a c t i o n on o t h e r DA t e r m i n a l s c a n n o t be r u l e d o u t . I n p a r t i c u l a r , m e s o l i m b i c t e r m i n a l s o t h e r t h a n t h e n u c l e u s accumbens may p l a y a r o l e i n a n t i c i p a t o r y s e x u a l b e h a v i o r . As n o t e d a b o v e , b i l a t e r a l e x c i t o t o x i c l e s i o n s o f t h e b a s o l a t e r a l amygda la r e d u c e r a t e s o f o p e r a n t r e s p o n d i n g i n s e x u a l l y a c t i v e male r a t s f o r a s e c o n d a r y s t i m u l u s a s s o c i a t e d w i t h t h e p r e s e n t a t i o n o f a s e x u a l l y r e c e p t i v e f e m a l e w i t h o u t a f f e c t i n g consummatory measures o f c o p u l a t i o n ( E v e r i t t e t a l . , 1 9 8 9 ) . A l t h o u g h t h e n e a r b y c o r t i c o m e d i a l amygdala r e c e i v e s a l a r g e p r o j e c t i o n o f DA f i b e r s f r o m t h e VTA, DA r e c e p t o r s have been d e m o n s t r a t e d i n t h e b a s o l a t e r a l amygdala ( r e v i e w e d i n Herkenham, 1 9 8 7 ) . The o l f a c t o r y t u b e r c l e a l s o r e c e i v e s a ma jo r DA p r o j e c t i o n f r o m t h e VTA. A l t h o u g h l e s i o n s o f t h e o l f a c t o r y t u b e r c l e do n o t a f f e c t consummatory measures o f c o p u l a t i o n i n male r a t s ( P e r k i n s e t a l . , 1 9 8 0 ) , i t i s n o t known w h e t h e r l e s i o n s o f t h i s s t r u c t u r e a f f e c t a n t i c i p a t o r y s e x u a l b e h a v i o r . An e x h a u s t i v e s t u d y o f d i e n c e p h a l i c DA t e r m i n a l s i s a l s o n e e d e d . A l t h o u g h DA t e r m i n a l s i n t h e MPOA and s u p r a c h i a s m a t i c n u c l e u s have been i m p l i c a t e d i n t h e c o n t r o l o f p e n i l e r e f l e x e s and c e r t a i n consummatory measures o f c o p u l a t i o n , l i t t l e has been done t o examine t h e r o l e o f o t h e r d i e n c e p h a l i c DA t e r m i n a l s . For e x a m p l e , t h e median eminence r e c e i v e s a DA p r o j e c t i o n f r o m t h e A13 c e l l b o d i e s i n t h e m e d i o b a s a l and a r c u a t e n u c l e i o f t h e h y p o t h a l a m u s (Moore , 1 9 8 7 ) , and t h i s s t r u c t u r e has been 139 i m p l i c a t e d i n t h e d i s r u p t i o n o f male s e x u a l b e h a v i o r by h y p e r p r o l a c t i n e m i a ( B a r t k e e t a l . , 1 9 8 3 ) . I n f a c t , DA i s h y p o t h e s i z e d t o a c t as a " p r o l a c t i n i n h i b i t i n g f a c t o r " i n t h e median eminence , w h i c h p a r t i a l l y e x p l a i n s t h e a b i l i t y o f DA a g o n i s t s such as b r o m o c r i p t i n e t o r e d u c e c i r c u l a t i n g l e v e l s o f p r o l a c t i n and t o r e s t o r e s e x u a l b e h a v i o r t o h y p e r p r o l a c t i n e m i c m a l e s . The r e s u l t s o f E x p e r i m e n t I I I i n d i c a t e t h a t t h e a n t a g o n i s m o f DA r e c e p t o r s i n t h e n u c l e u s accumbens and MPOA by h a l o p e r i d o l a r e s u f f i c i e n t t o a c c o u n t f o r most o f t h e e f f e c t s o f s y s t e m i c a d m i n i s t r a t i o n o f h a l o p e r i d o l . The a p p a r e n t b e h a v i o r a l s e l e c t i v i t y o f s y s t e m i c a d m i n i s t r a t i o n s o f h a l o p e r i d o l i n r e d u c i n g l e v e l c h a n g i n g a t doses t h a t d i d n o t s i g n i f i c a n t l y a f f e c t consummatory measures o f c o p u l a t i o n i n E x p e r i m e n t I I may be due t o i t s a c t i o n a t m u l t i p l e s i t e s , i n t h i s case t h e n u c l e u s accumbens and MPOA, whereas i t s a b i l i t y t o d i s r u p t consummatory measures o f c o p u l a t i o n may be due t o a s e l e c t i v e a n t a g o n i s m o f DA r e c e p t o r s i n t h e MPOA. However , a l t h o u g h h a l o p e r i d o l b i n d s w i t h h i g h e s t a f f i n i t y t o D2 r e c e p t o r s , i t has a l ow a f f i n i t y f o r D I , 2 , and 5-HT2 r e c e p t o r s (Tamminga & G e r l a c h , 1 9 8 7 ) . A c o m p a r i s o n o f t h e e f f e c t s o f h i g h a f f i n i t y D I , D2, oil, and 5-HT2 r e c p e t o r a n t a g o n i s t s i n t h e n u c l e u s accumbens and MPOA on a n t i c i p a t o r y and consummatory measures o f s e x u a l b e h a v i o r i n male r a t s wou ld h e l p r e s o l v e t h e i s s u e o f p h a r m a c o l o g i c a l s e l e c t i v i t y . 140 EXPERIMENT IV: ELECTROCHEMICAL DETECTION OF CENTRAL DOPAMINE EFFLUX DURING SEXUAL BEHAVIOR IN THE MALE RAT The r e s u l t s of Experiments II and III confirm that c e n t r a l DA systems play an important r o l e in a n t i c i p a t o r y sexual behavior and i n the i n i t i a t i o n and rate of copulatory behavior in male ra t s . Experiment II demonstrated that the systemic administration of low-to-moderate doses of several c e n t r a l l y -active DA receptor antagonists reduce the number of l e v e l changes, increase the mount and intromission l a t e n c i e s , increase the postejaculatory i n t e r v a l , and/or decrease the number of intromissions and ejacula t i o n s . Experiment III demonstrated that the t y p i c a l DA receptor antagonist haloperidol s e l e c t i v e l y decreases the number of l e v e l changes when infused to the nucleus accumbens, s e l e c t i v e l y increases the number of ejaculations when infused to the striatum, and a f f e c t s both a n t i c i p a t o r y and consummatory measures of sexual behavior in a manner s i m i l a r to systemic administration when infused to the MPOA. These data suggest that aspects of the an t i c i p a t o r y and consummatory sexual behavior of male rats are regulated d i f f e r e n t i a l l y by mesotelencephalic and diencephalic DA terminals, and that the combined antagonism of DA receptors in at least two of these regions (the nucleus accumbens and MPOA) is s u f f i c i e n t to produce the di s r u p t i o n of a n t i c i p a t o r y and consummatory sexual behavior observed following systemic administration of haloperidol. 141 Having established that DA receptors in these terminals d i f f e r e n t i a l l y regulate the sexual behavior of male r a t s , the next question concerned the dynamics of such regulation: What kind of a c t i v i t y do these DA systems exhibit during sexual behavior? Although the r e s u l t s of Experiments II and III provide a basis for onSy the most general inferences, an i n d i r e c t answer has recently been provided by three studies using ex vivo electrochemical assessments of DA and i t s metabolites following periods of sexual a c t i v i t y . To r e i t e r a t e b r i e f l y from the Introduction, Ahlenius et a l . (1987) examined the accumulation of DOPA in the nucleus accumbens, striatum, septum, and anterior hypothalamus following either 10 min of sexual a c t i v i t y (at least one ejaculation) with a receptive female, 25 min of treadmill locomotion, or 10 min in the home cage. Sexual a c t i v i t y increased DOPA accumulation s i g n i f i c a n t l y in the striatum and nucleus accumbens, but not in the septum or anterior hypothalamus, in comparison with c o n t r o l rats l e f t in the home cage. Treadmill locomotion increased DOPA accumulation s i g n i f i c a n t l y in the striatum, but not in the other three regions, suggesting that catecholamine synthesis increases in the nucleus accumbens as a s p e c i f i c function of sexual a c t i v i t y and in the striatum as a nonspecific function of either sexual a c t i v i t y or treadmill locomotion. Levels of DA and DOPAC in the p a r i e t a l cortex, preoptic region, mediobasal hypothalamus, and lumbrosacral cord have been examined in rats that achieved either one ejaculation or 142 i n t r o m i s s i o n s w i t h o u t e j a c u l a t i o n , compared t o s e x u a l l y i n a c t i v e r a t s t h a t d i d n o t i n i t i a t e c o p u l a t i o n w i t h r e c e p t i v e f e m a l e s (Mas e t a l . , 1 9 8 7 ) . Bo th DA and DOPAC l e v e l s i n t h e p r e o p t i c r e g i o n were e l e v a t e d s i g n i f i c a n t l y a f t e r e j a c u l a t i o n , whereas DOPAC a l o n e was e l e v a t e d s i g n i f i c a n t l y a f t e r i n t r o m i s s i o n . DA l e v e l s i n t h e l u m b r o s a c r a l c o r d were a l s o e l e v a t e d s i g n i f i c a n t l y a f t e r i n t r o m i s s i o n , b u t n o t a f t e r e j a c u l a t i o n , s u g g e s t i n g t h a t DA mechanisms i n t h i s r e g i o n o f t h e c o r d may c o n t r i b u t e t o t h e d e s c e n d i n g i n h i b i t i o n o f e j a c u l a t o r y r e f l e x e s d u r i n g i n t r o m i s s i o n . Changes i n DA or DOPAC l e v e l s d i d n o t o c c u r i n e i t h e r t h e m e d i o b a s a l h y p o t h a l a m u s or p a r i e t a l c o r t e x . These r e s u l t s s u g g e s t e d t h a t DA r e l e a s e and u t i l i z a t i o n i s i n c r e a s e d f o l l o w i n g e j a c u l a t i o n . I n t r o m i s s i o n a l o n e i n c r e a s e d DA u t i l i z a t i o n b u t n o t r e l e a s e i n t h e p r e o p t i c a r e a . F i n a l l y , Hof fman e t a l . (1987) examined DA and DOPAC l e v e l s i n t h e MPOA, a r c u a t e n u c l e u s / m e d i a n em inence , or m e d i a l f o r e b r a i n b u n d l e o f i n t a c t , s e x u a l l y a c t i v e r a t s t h a t had e i t h e r c o p u l a t e d t o s e x u a l e x h a u s t i o n o r were r u n i n a m o t o r - d r i v e n w h e e l . Each r a t i n t h e w h e e l - r u n n i n g c o n d i t i o n was yoked t o a r a t i n t h e s e x u a l e x h a u s t i o n c o n d i t i o n such t h a t t h e whee l s t a r t e d r o t a t i n g when mounts were i n i t i a t e d and s t o p p e d r o t a t i n g a f t e r each e j a c u l a t i o n . DA l e v e l s i n t h e MPOA, b u t n o t t h e a r c u a t e n u c l e u s or m e d i a l f o r e b r a i n b u n d l e , were e l e v a t e d s i g n i f i c a n t l y i n b o t h s e x u a l l y e x h a u s t e d and a c t i v e r a t s . However , no d i f f e r e n c e s i n DOPAC c o n c e n t r a t i o n s were d e t e c t e d among g r o u p s i n t h e t h r e e b r a i n r e g i o n s , s u g g e s t i n g t h a t DA u t i l i z a t i o n may have been attenuated in the MPOA following lengthly bouts of locomotor a c t i v i t y , the manipulation common to both the sexual exhaustion and forced a c t i v i t y groups. Taken together, the r e s u l t s of these three studies suggest that DA synthesis, release, and/or u t l i l i z a t i o n increase in the nucleus accumbens, striatum, and MPOA during copulation. However, in the two studies that c o n t r o l l e d for locomotor a c t i v i t y (Ahlenius et a l . , 1987; Hoffman et a l . , 1987), the increases observed in the striatum and MPOA were not s p e c i f i c to copulatory behavior. Unfortunately, ex vivo analyses do not permit DA a c t i v i t y to be observed d i r e c t l y during sexual behavior, thus the p a r t i c u l a r aspects of sexual behavior that correspond to those increases in DA a c t i v i t y cannot be determined. A more d i r e c t way to assess DA a c t i v i t y during sexual behavior i s use electrochemical detection in vivo. This can be accomplished two ways, using voltammetry (Lane & Blaha, 1986) or microdialysis (Imperato & Di Chiara, 1984; Zetterstrom, Sharp, Marsden, & Ungerstedt, 1983). Voltammetry involves the oxidation of e l e c t r o a c t i v e substances within brain e x t r a c e l l u l a r f l u i d by passing a voltage (e.g., -100 to +250 mV) s e l e c t i v e for those substances through a graphite electrode. The r e s u l t i n g oxidation reaction produces current that i s d i r e c t l y proportional to the amount of el e c t r o a c t i v e substance oxidized at the t i p of the electrode. This current can be detected by the graphite electrode. M i c r o d i a l y s i s involves the extraction of e x t r a c e l l u l a r f l u i d w i t h a m i c r o d i a l y s i s p robe and s u b s e q u e n t o x i d a t i o n and e l e c t r o c h e m i c a l d e t e c t i o n o f e l e c t r o a c t i v e s u b s t a n c e s w i t h HPLC. B o t h i n v i v o t e c h n i q u e s have s t r e n g t h s and weaknesses . An i m p o r t a n t s t r e n g t h o f v o l t a m m e t r y i s i t s t e m p o r a l r e s o l u t i o n . E l e c t r o a c t i v e s u b s t a n c e s may be o x i d i z e d a t 1-sec I n t e r v a l s , a l l o w i n g b e h a v i o r a l e v e n t s t o be c o r r e l a t e d w i t h changes i n t h e o x i d a t i o n s i g n a l . U n f o r t u n a t e l y , s e l e c t i v i t y i s a r e c u r r i n g p r o b l e m w i t h v o l t a m m e t r y because s e v e r a l s u b s t a n c e s can be o x i d i z e d a t t h e same p o t e n t i a l s . For e x a m p l e , DA, DOPAC, a s c o r b i c a c i d , and n o r e p i n e p h r i n e a r e a l l o x i d i z e d a t a p p r o x i m a t e l y +250 mV. However , t h e c o n t r i b u t i o n o f t h e a n i o n s DOPAC and a s c o r b i c a c i d t o t h e c a t e c h o l a m i n e o x i d a t i o n s i g n a l can be e l i m i n a t e d e i t h e r by c o a t i n g t h e g r a p h i t e e l e c t r o d e w i t h an a n i o n i c po lymer such as N a t i o n ( G e r h a r d t , Oke, Nagy, Moghaddam, & Adams, 1984) or m i x i n g an a n i o n such as s t e a r i c a c i d w i t h t h e g r a p h i t e p a s t e a t t h e t i p o f t h e e l e c t r o d e ( B l a h a & L a n e , 1 9 8 3 ) . A l t h o u g h i t i s n o t p o s s i b l e c h e m i c a l l y t o d i s t i n g u i s h n o r e p i n e p h r i n e f r o m DA, as b o t h a r e c a t i o n s , t h e c o n t r i b u t i o n o f n o r e p i n e p h r i n e t o t h e c a t e c h o l a m i n e o x i d a t i o n c u r r e n t can be d e t e r m i n e d i n a g i v e n t i s s u e w i t h t h e a p p r o p r i a t e p h a r m a c o l o g i c a l t r e a t m e n t , e . g . , by u s i n g t h e dopamine - h y d r o x y l a s e i n h i b i t o r FLA-63 t o i n h i b i t t h e c o n v e r s i o n o f DA i n t o n o r e p i n e p h r i n e . S t u d i e s such as t h e s e u s i n g s t e a r a t e - m o d i f i e d g r a p h i t e p a s t e e l e c t r o d e s have i n d i c a t e d t h a t n o r e p i n e p h r i n e does n o t c o n t r i b u t e t o t h e c a t e c h o l a m i n e o x i d a t i o n s i g n a l i n t h e n u c l e u s accumbens or s t r i a t u m ( B l a h a & L a n e , 1 9 8 3 ) . The o p p o s i t e i s t r u e f o r m i c r o d i a l y s i s . I t s ma jo r s t r e n g t h i s s e l e c t i v i t y whereas i t s ma jo r weakness i s poor t e m p o r a l r e s o l u t i o n . S e l e c t i v i t y i s r e l a t i v e l y a s s u r e d w i t h m i c r o d i a l y s i s because e l e c t r o a c t i v e s u b s t a n c e s a r e s e p a r a t e d by d i f f e r e n t e l u t i o n r a t e s o f f t h e HPLC c o l u m n , g i v i n g r i s e t o c h a r a c t e r i s t i c peaks i n t h e c h r o m a t o g r a m . However, t h e e x t r a c e l l u l a r f l u i d must be e x t r a c t e d f r o m t h e b r a i n a t a s l o w r a t e ( e . g . , 5 u l / m i n ) and a n a l y z e d w i t h HPLC once e v e r y 10 or 20 min t o a l l o w enough o f t h e d i a l y s a t e t o be p r e s e n t i n t h e d e t e c t o r . A l t h o u g h assessments o f e x t r a c e l l u l a r l e v e l s o f DA and i t s m e t a b o l i t e s once e v e r y 10 or 20 min i s s u f f i c i e n t t o examine d r u g e f f e c t s on DA r e l e a s e , t h e t e m p o r a l r e s o l u t i o n i s n o t s u f f i c i e n t t o p e r f o r m f i n e l y g r a i n e d b e h a v i o r a l a n a l y s e s . For e x a m p l e , w i t h r e s p e c t t o s e x u a l b e h a v i o r , i t i s t y p i c a l f o r a s e x u a l l y a c t i v e r a t t o i n i t i a t e c o p u l a t i o n , e j a c u l a t e , and resume c o p u l a t i o n w i t h i n a 1 0 - m i n p e r i o d . Any i n c r e a s e i n e x t r a c e l l u l a r DA l e v e l s c o u l d have o c c u r r e d d u r i n g one or many o f t h e phases o f c o p u l a t i o n . As w i t h ex v i v o a n a l y s e s , m i c r o d i a l y s i s w i t h HPLC a l l o w s o n l y t h e most g e n e r a l b e h a v i o r a l o b s e r v a t i o n s t o be c o r r e l a t e d w i t h changes i n DA a c t i v i t y . However, t h i s t e c h n i q u e can be used i n a g e n e r a l way t o c o n f i r m t h e s e l e c t i v i t y o f v o l t a m m e t r i c changes i n e x t r a c e l l u l a r DA c o n c e n t r a t i o n s . I n E x p e r i m e n t I V a , i n v i v o v o l t a m m e t r y was used t o assess DA e f f l u x i n t h e n u c l e u s accumbens and s t r i a t u m , and c a t e c h o l a m i n e e f f l u x i n t h e MPOA, b e f o r e , d u r i n g , and a f t e r 30 -m in p e r i o d s o f 146 copulatory a c t i v i t y in sexually active male r a t s . In Experiment IVb, voltammetry was used to assess DA or catecholamine e f f l u x in these regions while sexually active male rats were exposed to other males, nonreceptive females, a s l i d e containing estrous vaginal secretions, or receptive females behind a wire-mesh p a r t i t i o n . In Experiment IVc, in vivo m i c r o d i a l y s i s was used to confirm the r e s u l t s observed in Experiment IVa in the nucleus accumbens and striatum. EXPERIMENT IVa The r e s u l t s of ex vivo studies suggest that DA synthesis, release, and/or u t i l i z a t i o n increases within mesotelencephalic and diencephalic DA terminals following periods of copulation in sexually active male r a t s . To examine t h i s increase in more behavioral d e t a i l , the f i r s t experiment of t h i s s e r i e s used chronoamperometry with a 1-sec interpulse i n t e r v a l to assess DA e f f l u x in the nucleus accumbens and striatum, and catecholamine e f f l u x in the MPOA, before and during a 30-min test of copulation. Method Subjects and Surgery The female and male Long-Evans rats used in Experiment IVa were purchased from Charles River Canada and housed as in the previous experiments. The females were b i l a t e r a l l y ovariectomized under sodium pentobarbital anesthesia one month 147 p r i o r t o t h i s e x p e r i m e n t . Sexua l r e c e p t i v i t y was i n d u c e d i n t h e s e f e m a l e s as i n t h e p r e v i o u s e x p e r i m e n t s . A g r o u p o f 15 male r a t s (450 t o 700 g) was g i v e n a t l e a s t 10 t e s t s o f s e x u a l b e h a v i o r i n t h e b i l e v e l chambers p r i o r t o s u r g e r y . A l l had a c h i e v e d t h e c r i t e r i a f o r s e x u a l e x p e r i e n c e o u t l i n e d i n E x p e r i m e n t I (Page 5 9 ) . The males were a n e s t h e t i z e d w i t h sod ium p e n t o b a r b i t a l ( S o m n i t o l , 60 mg/kg) and a t h r e e -e l e c t r o d e assemb ly c o n s i s t i n g o f a s t a i n l e s s - s t e e l a u x i l i a r y e l e c t r o d e a t t a c h e d t o a s k u l l s c r e w , a Ag/AgCl r e f e r e n c e e l e c t r o d e embedded i n c o r t e x , and a s t e a r a t e - m o d i f l e d g r a p h i t e p a s t e i n d i c a t o r e l e c t r o d e aimed a t e i t h e r t h e n u c l e u s accumbens (n = 5 ) , s t r i a t u m (n = 5 ) , o r MPOA (n = 5) was i m p l a n t e d s t e r e o t a x i c a l l y . The assemb ly was a t t a c h e d f i r m l y t o t h e s k u l l w i t h d e n t a l a c r y l i c . C o o r d i n a t e s f o r t h e p l a c e m e n t o f e l e c t r o d e s and s u r g i c a l p r o c e d u r e s f o r t h e i r i m p l a n t a t i o n were i d e n t i c a l t o t h o s e used i n E x p e r i m e n t I I I , e x c e p t t h a t MPOA p l a c e m e n t s were made a c c o r d i n g t o t h e a t l a s o f P a x i n o s and Watson ( 1 9 8 2 ) . A p o s t s u r g i c a l t e s t o f e x t r a c e l l u l a r DA ( n u c l e u s accumbens and s t r i a t u m ) or c a t e c h o l a m i n e (MPOA) o x i d a t i o n s i g n a l s was c o n d u c t e d 2 days a f t e r s u r g e r y i n an e l e c t r i c a l l y s h i e l d e d , P l e x i g l a s t e s t i n g chamber . A l l r a t s d i s p l a y e d measureab le o x i d a t i o n c u r r e n t s d u r i n g t h i s t e s t . E l e c t r o c h e m i c a l Measurements Measurements o f e x t r a c e l l u l a r DA or c a t e c h o l a m i n e c o n c e n t r a t i o n s were o b t a i n e d u s i n g 1-sec p u l s e c h r o n o a m p e r o m e t r y (Lane & B l a h a , 1 9 8 6 ) . O x i d a t i o n c u r r e n t s were measured by 148 a p p l y i n g a p o t e n t i a l p u l s e o f a p p r o x i m a t e l y -100 mV t o +250 mV ( v s . t h e Ag /AgC l r e f e r e n c e e l e c t r o d e ) and sampled a t 2 0 - s e c i n t e r v a l s . B e h a v i o r a l T e s t i n g P r o c e d u r e s The male r a t s were t e s t e d f o r s e x u a l b e h a v i o r 1 week a f t e r e l e c t r o d e i m p l a n t a t i o n . T e s t s were c o n d u c t e d i n an e l e c t r i c a l l y s h i e l d e d 29 x 29 x 45 cm u n i l e v e l P l e x i g l a s t e s t i n g chamber w i t h a w i r e - m e s h f l o o r and w i r e s c r e e n t h a t d i v i d e d t h e chamber i n t o two s i d e s . Each male was p l a c e d i n one s i d e o f t h e chamber . A s t a b l e c h r o n o a m p e r o m e t r i c b a s e l i n e was e s t a b l i s h e d f o r a t l e a s t 30 m i n , a f t e r w h i c h a s e x u a l l y r e c e p t i v e f e m a l e was p l a c e d i n t h e o t h e r s i d e o f t h e chamber . F i v e min a f t e r t h e i n t r o d u c t i o n o f t h e f e m a l e , t h e s c r e e n was removed t o a l l o w p h y s i c a l c o n t a c t between b o t h a n i m a l s . The measures o f c o p u l a t o r y b e h a v i o r a n a l y z e d i n E x p e r i m e n t I (Page 59) were r e c o r d e d f o r 30 m i n , a f t e r w h i c h t h e f e m a l e was removed. H i s t o l o g y H i s t o l o g i c a l v e r i f i c a t i o n o f i n d i c a t o r e l e c t r o d e p l a c e m e n t s was made a f t e r E x p e r i m e n t I V b . The males were a n e s t h e t i z e d w i t h sod ium p e n t o b a r b i t o l (60 mg /kg )and d e c a p i t a t e d , and t h e i r b r a i n s were removed and s t o r e d i n a 40% f o r m a l i n / s u c r o s e s o l u t i o n . The b r a i n s were s u b s e q u e n t l y f r o z e n i n a c r y o s t a t and 40-um s e c t i o n s were c u t , mounted on g l a s s s l i d e s , and examined under a m i c r o s c o p e . A l l r a t s i n each g r o u p had i n d i c a t o r e l e c t r o d e s e n d i n g i n t h e t a r g e t s t r u c t u r e s . The e l e c t r o d e p l a c e m e n t s a r e shown i n F i g u r e s 19 , 2 0 , and 2 1 . 1 4 9 150 F i g u r e 20. Electrode placements (n = 5) d i r e c t e d at the striatum i n Experiment IVa. . 2 mm 151 152 S t a t i s t i c a l A n a l y s e s The c h r o n o a m p e r o m e t r i c samples f o r each r a t d u r i n g t h e 1 0 -min p e r i o d p r i o r t o t h e i n t r o d u c t i o n o f t h e f e m a l e were d i v i d e d i n t o two b i n s o f 5 min e a c h . A mean c h r o n o a m p e r o m e t r i c v a l u e was c a l c u l a t e d f o r each 5 -m in b i n . B a s e l i n e c h r o n o a m p e r o m e t r i c d i f f e r e n c e s c o r e s wera e s t a b l i s h e d by s u b t r a c t i n g t h e second 5 min v a l u e f r o m t h e f i r s t . The c h r o n o a m p e r o m e t r i c r e c o r d o f each r a t was t h e n compared t o i t s r e c o r d o f s e x u a l b e h a v i o r . D i f f e r e n c e s c o r e s were c a l c u l a t e d f o r n i n e b e h a v i o r a l l y r e l e v a n t e v e n t s by s u b t r a c t i n g t h e c h r o n o a m p e r o m e t r i c v a l u e s f o r each e v e n t f r o m t h e b a s e l i n e d i f f e r e n c e s c o r e . These e v e n t s were 1) t h e 5 - m i n p e r i o d d u r i n g w h i c h t h e f e m a l e was b e h i n d t h e s c r e e n ; 2) t h e p o i n t a t w h i c h t h e s c r e e n was removed ; 3) t h e p o i n t a t w h i c h t h e f i r s t i n t r o m i s s i o n o c c u r r e d ; 4) t h e p o i n t a t w h i c h t h e f i r s t e j a c u l a t i o n o c c u r r e d ; 5) t h e m i d p o i n t be tween t h e f i r s t e j a c u l a t i o n and t h e n e x t i n t r o m i s s i o n ; 6) t h e p o i n t a t w h i c h t h e second c o p u l a t o r y s e r i e s began ( d e f i n e d as t h e f i r s t i n t r o m i s s i o n f o l l o w i n g t h e f i r s t e j a c u l a t i o n ) ; 7) t h e p o i n t a t w h i c h t h e second e j a c u l a t i o n o c c u r r e d ; 8) t h e m i d p o i n t between t h e second e j a c u l a t i o n and t h e n e x t i n t r o m i s s i o n ; and 9) t h e p o i n t a t w h i c h t h e t h i r d c o p u l a t o r y s e r i e s began ( d e f i n e d as t h e f i r s t i n t r o m i s s i o n f o l l o w i n g t h e second e j a c u l a t i o n ) . Mean d i f f e r e n c e s c o r e s were t h e n c a l c u l a t e d f o r t h e 5 r a t s i n each g r o u p f o r each e v e n t and a n a l y z e d u s i n g a w i t h i n - s u b j e c t s ANOVA f o r r e p e a t e d measures . The B o n f e r r o n i method was used t o c o r r e c t t h e e l e v a t e d e x p e r i m e n t - w i s e e r r o r p r o d u c e d by a l a r g e number o f r e p e a t e d 153 measures . The c o r r e c t e d e r r o r r a t e was p_<.005 because 10 e v e n t s ( i n c l u d i n g t h e b a s e l i n e s c o r e ) were a n a l y z e d . For each s i g n i f i c a n t ANOVA, p o s t - h o c c o m p a r i s o n s among t h e e v e n t s were made u s i n g t h e Tukey m e t h o d , p_<.05. R e s u l t s A l l 15 r a t s showed an immed ia te i n t e r e s t i n t h e r e c e p t i v e f e m a l e when she was p l a c e d b e h i n d t h e s c r e e n . T h i s i n t e r e s t was marked by an immed ia te o r i e n t a t i o n t o w a r d t h e s c r e e n , b i t i n g t h e s c r e e n or p r o b i n g t h e i r s n o u t s t h r o u g h t h e o p e n i n g s i n t h e s c r e e n , and e n g a g i n g i n e x t e n d e d p e r i o d s o f g r o o m i n g . S e v e r a l r a t s t r i e d t o g r a b t h e f e m a l e w i t h t h e i r f o r e p a w s and some even a t t e m p t e d t o c l i m b t h e s c r e e n . A l l r a t s i n i t i a t e d c o p u l a t i o n w i t h i n 20 s o f t h e r e m o v a l o f t h e s c r e e n and a l l d i s p l a y e d a c t i v e c o p u l a t i o n d u r i n g t h e 3 0 - m i n t e s t . Nuc leus Accumbens A r e p r e s e n t a t i v e c h r o n o a m p e r o m e t r i c r e c o r d i s d e p i c t e d i n F i g u r e 22A w i t h b e h a v i o r a l e v e n t s shown i n r e a l t i m e . R e a d i l y a p p a r e n t a r e s e v e r a l dynamic changes i n DA e f f l u x a s s o c i a t e d w i t h p a r t i c u l a r e l e m e n t s o f s e x u a l b e h a v i o r . An immed ia te i n c r e a s e i n t h e DA o x i d a t i o n s i g n a l o c c u r r e d i n t h i s r a t when t h e r e c e p t i v e f e m a l e was p l a c e d b e h i n d t h e s c r e e n . The s i g n a l began t o d r i f t back t o b a s e l i n e b e f o r e t h e s c r e e n was removed . A f u r t h e r i n c r e a s e was o b s e r v e d when t h e s c r e e n was removed and t h e r a t i n i t i a t e d t h e f i r s t c o p u l a t o r y s e r i e s . T h i s i n c r e a s e was m a i n t a i n e d u n t i l t h e r a t a c h i e v e d e j a c u l a t i o n . Each e j a c u l a t i o n 154 Figure 22. Changes in DA oxidation current in the nucleus accumbens during phases of sexual behavior in Experiment IVa. A: A representative chronoampero-metric record from a singl e male r a t . Symbols: I = intromission; E = e j a c u l a t i o n . B: Changes in DA oxidation current in the nucleus accumbens (n = 5) during phases of sexual behavior in Experiment IVa. Values are means + SE. Symbols: FEM IN, female in chamber behind the screen; SCR OUT, screen removed to permit contact between the male and female; 1-1, f i r s t intromission of the f i r s t copulatory s e r i e s ; E - l , f i r s t e j a c u l a t i o n ; PEI-1, midpoint of the f i r s t postejaculatory i n t e r v a l ; 1-2, f i r s t intromission of the second copulatory s e r i e s ; E-2, second eja c u l a t i o n ; PEI-2, midpoint of second post-ejaculatory i n t e r v a l ; 1-3, f i r s t intromission of the t h i r d copulatory s e r i e s . Chronoamperometric records were obtained from a stearate-modified carbon paste electrode with a 20-sec sampling rate. Current values represent the sum of both background current and DA oxidation current. * * p_<.05, * p_<.01, from the baseline difference score. NUCLEUS ACCUMBENS 155 156 was f o l l o w e d by a r e d u c t i o n i n t h e DA o x i d a t i o n s i g n a l , however , t h e s i g n a l r o s e b e f o r e each r e i n i t i a t i o n o f c o p u l a t i o n . A s i m i l a r p a t t e r n was o b s e r v e d i n t h e o t h e r f o u r r a t s , a l t h o u g h two o f t h e f o u r showed much l a r g e r mean i n c r e a s e s i n t h e DA o x i d a t i o n s i g n a l ( 3 . 4 and 6 .2 nA, r e s p e c t i v e l y ) d u r i n g t h e 5-min p e r i o d t h a t t h e f e m a l e was b e h i n d t h e s c r e e n . A l t h o u g h t h e DA o x i d a t i o n s i g n a l s o f t h o s e two r a t s began t o d r i f t back t o w a r d b a s e l i n e d u r i n g t h e 5 -m in p e r i o d t h e s i g n a l s d i d n o t i n c r e a s e f u r t h e r when t h e s c r e e n was removed . The o v e r a l l p a t t e r n o f DA o x i d a t i o n s i g n a l s d u r i n g s e x u a l b e h a v i o r i s shown c l e a r l y by t h e mean d i f f e r e n c e s c o r e s d e p i c t e d i n F i g u r e 22b . The ANOVA d e t e c t e d a s i g n i f i c a n t o v e r a l l e f f e c t f o r t h o s e s c o r e s , F ( 9 , 3 6 ) = 6 . 1 1 , p_<.0001. P o s t - h o c c o m p a r i s o n s o f each s c o r e r e v e a l e d t h a t a l l o f t h e d i f f e r e n c e s c o r e s were s i g n i f i c a n t l y h i g h e r t h a n t h e b a s e l i n e d i f f e r e n c e s c o r e ; however , t h e s c o r e s f o r t h e m i d p o i n t s be tween each e j a c u l a t i o n and t h e n e x t i n t r o m i s s i o n were s i g n i f i c a n t l y l o w e r t h a n t h e o t h e r s c o r e s . I t i s i n t e r e s t i n g t o n o t e t h a t , a l t h o u g h t h e y were n o t s i g n i f i c a n t l y d i f f e r e n t f r o m one a n o t h e r , t h e m a g n i t u d e o f t h e d i f f e r e n c e s c o r e s f o r each i n t r o m i s s i o n g o t s m a l l e r as t h e t e s t p r o g r e s s e d . S t r l a t u m A r e p r e s e n t a t i v e c h r o n o a m p e r o m e t r i c r e c o r d i s d e p i c t e d i n F i g u r e 23a w i t h b e h a v i o r a l e v e n t s i n r e a l t i m e . A g r a d u a l r i s e i n t h e DA o x i d a t i o n s i g n a l was o b s e r v e d t h r o u g h o u t t h e t e s t , b u t no b e h a v i o r a l e v e n t was c o n s i s t e n t l y a s s o c i a t e d w i t h a r i s e or f a l l i n t h e DA o x i d a t i o n s i g n a l . The s i g n a l d i d n o t r i s e d u r i n g 157 Figure 23. Changes in DA oxidation current in the striatum during phases of sexual behavior in Experiment IVa. A: A representative chronoamperometric record from a single male r a t . Symbols: I = intromission; E = ejaculation. B: Changes in DA oxidation in the striatum (n = 5) during phases of sexual behavior in Experiment IVa. Values are means + SE. Symbols: FEM IN, female in chamber behind the screen; SCR OUT, screen removed to permit contact between the male and female; 1-1, f i r s t intromission of the f i r s t copulatory se r i e s ; E - l , f i r s t ejaculation; PEI-1, midpoint between the f i r s t postejaculatory i n t e r v a l ; 1-2, f i r s t intromission of the second copulatory ser i e s ; E-2, second ejaculation; PEI-2, midpoint between the second postejaculatory i n t e r v a l ; 1-3, f i r s t intromission of the t h i r d copulatory s e r i e s . Chronoamperometric records were obtained from a stearate-modified carbon paste electrode with a 20-sec sampling rate. Current values represent the sum of both background current and DA oxidation current. * * p_<.05, * p_<.01, from the baseline difference score. 159 t h e 5 -min p e r i o d w i t h t h e f e m a l e b e h i n d t h e s c r e e n , nor d i d i t r i s e a p p r e c i a b l y d u r i n g t h e f i r s t c o p u l a t o r y s e r i e s . A s i m i l a r g r a d u a l i n c l i n e i n t h e OA o x i d a t i o n s i g n a l was o b s e r v e d i n t h e o t h e r f o u r r a t s d u r i n g t h e t e s t . T h i s o v e r a l l p a t t e r n i s shown by t h e mean d i f f e r e n c e s c o r e s d e p i c t e d i n F i g u r e 22b . The ANOVA d e t e c t e d a s i g n i f i c a n t o v e r a l l e f f e c t f o r t h o s e s c o r e s , F ( 9 , 3 6 ) - 6 . 1 7 , p_<.0001. P o s t - h o c c o m p a r i s o n s o f each s c o r e r e v e a l e d t h a t t h e mean d i f f e r e n c e s c o r e s were n o t e l e v a t e d s i g n i f i c a n t l y f r o m the b a s e l i n e d i f f e r e n c e s c o r e u n t i l t h e f i r s t e j a c u l a t i o n . None o f t h e s u b s e q u e n t s c o r e s were s i g n i f i c a n t l y d i f f e r e n t f r o m one a n o t h e r e x c e p t t h e s c o r e f o r t h e m i d p o i n t be tween t h e second e j a c u l a t i o n and t h e t h i r d c o p u l a t o r y s e r i e s , w h i c h was s i g n i f i c a n t l y g r e a t e r t h a n t h e o t h e r 9 s c o r e s . M e d i a l P r e o p t i c Area A r e p r e s e n t a t i v e c h r o n o a m p e r o m e t r i c r e c o r d i s d e p i c t e d i n F i g u r e 24a w i t h b e h a v i o r a l e v e n t s shown i n r e a l t i m e . The p a t t e r n o f c a t e c h o l a m i n e e f f l u x was s t r i k i n g l y s i m i l a r t o t h a t o b s e r v e d f o r DA e f f l u x i n t h e n u c l e u s accumbens. An immed ia te i n c r e a s e i n t h e c a t e c h o l a m i n e o x i d a t i o n s i g n a l o c c u r r e d when t h e f e m a l e was p l a c e d b e h i n d t h e s c r e e n . The s i g n a l began t o d r i f t back t o b a s e l i n e b e f o r e t h e s c r e e n was removed . A f u r t h e r i n c r e a s e was o b s e r v e d when t h e s c r e e n was removed and t h e r a t i n i t i a t e d t h e f i r s t c o p u l a t o r y s e r i e s . Each e j a c u l a t i o n was f o l l o w e d by a d e c r e a s e i n t h e c a t e c h o l a m i n e o x i d a t i o n s i g n a l , however , t h e s i g n a l r o s e b e f o r e each r e i n i t i a t i o n o f c o p u l a t i o n . S i m i l a r p a t t e r n s o f c a t e c h o l a m i n e o x i d a t i o n were o b s e r v e d i n 160 Figure 24. Changes i n catecholamine oxidation current in the medial preoptic area during phases of sexual behavior in Experiment IVa. A: A representative chronoampero-metr i c record from a si n g l e r a t . Symbols: I = i n t r o -mission; E = e j a c u l a t i o n . B: Changes in oxidation current in the medial preoptic area (n = 5) during phases of sexual behavior in Experiment IVa. Values are means + SE. Symbols: FEM IN, female i n behind the screen; SCR OUT, screen removed to permit contact between the male and female; 1-1, f i r s t intromission of the f i r s t copulatory s e r i e s ; E - l , f i r s t e j a c u lation; PEI-1, midpoint between the f i r s t postejaculatory i n t e r v a l ; 1-2, f i r s t intromission of the second copulatory s e r i e s ; E-2; second eja c u l a t i o n ; PEI-2, midpoint between the second postejaculatory i n t e r v a l ; 1-3, f i r s t intromission of the t h i r d copulatory s e r i e s . Chronoamperometric records were obtained from a stearate-modified carbon paste electrode with a 20-sec sampling rate. Current values represent the sum of both background current and DA oxidation current. * * p_<.05, * pjC.CLl, from the baseline d i f f e r e n c e score. MEDIAL PREOPTIC AREA FEM. IN SCR. OUT 1-1 E - 1 P B - 1 1-2 E - 2 P B - 2 1-3 162 the other four r a t s . This o v e r a l l pattern is shown by the mean difference scores depicted i n Figure 24b. Although the magnitude of the catecholamine oxidation signals was generally smaller than that observed for DA oxidation signals in the nucleus accumbens, the ANOVA detected a s i g n i f i c a n t e f f e c t for those scores, F( 9, 36 ) =25 .68, p_<.0001. Post-hoc comparisons of each score revealed that a l l d i f f e r e n c e scores except the midpoints between ejaculation and subsequent r e i n i t i a t i o n of copulation were elevated s i g n i f i c a n t l y from the baselinedifference score. As with the nucleus accumbens, although these scores did not d i f f e r s i g n i f i c a n t l y from one another, the magnitude of the dif f e r e n c e scores for each intromission got smaller as the test progressed. Discussion This experiment provides the f i r s t demonstration that DA e f f l u x in the nucleus accumbens and striatum, and catecholamine e f f l u x in the MPOA, increases in male rats during sexual behavior. However, the pattern and magnitude of the increase d i f f e r e d among these regions. In the nucleus accumbens, DA oxidation signals increased immediately when a receptive female was placed behind the screen. The elevated signals were maintained throughout the f i r s t copulatory s e r i e s . Although those signals decreased af t e r each eja c u l a t i o n , they were s t i l l elevated s i g n i f i c a n t l y above baseline values. Each r e i n i t i a t i o n of copulation was preceded by a r i s e in the DA oxidation s i g n a l s , however, the magnitude of the mean DA oxidation signals that 163 coincided with the beginning of each copulatory s e r i e s got progressively smaller throughout the 30-min test of copulation. In contrast, the DA oxidation signals in the striatum were not affected by the placement of a receptive female behind the screen. However, those signals increased gradually throughout the t e s t but did not correspond to any p a r t i c u l a r aspect of sexual behavior. F i n a l l y , catecholamine oxidation signals in the MPOA revealed a smaller, but e s s e n t i a l l y i d e n t i c a l , pattern to that observed for DA oxidation signals in the nucleus accumbens. Together, these r e s u l t s confirm e a r l i e r ex vivo demonstrations that DA synthesis, release, or u t i l i z a t i o n increase during copulation (Ahlenius et a l . , 1987; Hoffman et a l . , 1987; Mas et a l . , 1987). The r e s u l t s of Experiment IVa are consistent with evidence in Experiment III that DA terminals in the nucleus accumbens and MPOA form part of the neural basis of an t i c i p a t o r y sexual motivation in male r a t s . Oxidation signals in both regions increased immediately and dramatically upon presentation of a receptive female behind the screen, i n d i c a t i n g that DA e f f l u x in the nucleus accumbens and catecholamine e f f l u x in the MPOA i s associated with the presentation of a natural sexual incentive. In most rats there was a further increase in the oxidation signals when the screen was removed. S i m i l a r l y , an increase in the oxidation signals preceded each r e i n i t i a t i o n of copulation. This indicates that the i n i t i a t i o n of a copulatory s e r i e s i s preceded by an increase in DA or catecholamine e f f l u x in these regions. Although t h i s i s consistent with evidence in Experiment III that haloperidol infusions to the MPOA increased intromission l a t e n c i e s , i t i s not e n t i r e l y consistent with the lack of e f f e c t of haloperidol infusions to the nucleus accumbens on mount or intromission l a t e n c i e s . It i s possible, however, that the r i s e in DA e f f l u x i n the nucleus accumbens that precedes the i n i t i a t i o n of copulation i s an epiphenomenon of MPOA a c t i v a t i o n . As mentioned previously, the MPOA sends afferents to DA c e l l bodies in the VTA v i a the medial forebrain bundle. A c t i v a t i o n of these afferents could lead to increased DA release in the nucleus accumbens. The lack of an increase in s t r i a t a l DA e f f l u x during the presentation of the female behind the screen, the point at which the screen was removed, and the point at which the f i r s t intromission occurred, suggests that DA e f f l u x in the striatum i s not involved i n a n t i c i p a t o r y sexual motivation or the i n i t i a t i o n of copulation. This i s consistent with evidence in Experiment III that antagonism of DA terminals in the striatum does not af f e c t l e v e l changing or the i n i t i a t i o n of mounts or intromissions. However, s i m i l a r to the resul.ts of Experiment II I , these data are not consistent with previous reports that e l e c t r o l y t i c lesions of the substantia nigra pars compacta (the source of DA projections to the striatum) increase mount and intromission latencies (Mcintosh & B a r f i e l d , 1984) or decrease the number of ejaculations (Brackett et a l . , 1986). Thus, i t would appear that DA depletion in the striatum i s not s u f f i c i e n t 165 to disrupt the i n i t i a t i o n of copulation or decrease the number of ejaculations. In contrast, the progressive r i s e i n the s t r i a t a l DA s i g n a l throughout the copulatory test suggests that s t r i a t a l DA release may contribute to c e r t a i n e f f e c t s observed in the l a t e r phases of copulation. It i s tempting to speculate that increases in s t r i a t a l DA release serve to suppress ejaculatory mechanisms as a male rat engages in multiple ejaculations, e s p e c i a l l y in l i g h t of evidence in Experiment III that haloperidol infusions to the striatum increase the t o t a l number of ejaculations. This suggestion could be tested formally using penile reflexes as the dependent measure. EXPERIMENT IVb The r e s u l t s of Experiment IVa suggest that DA e f f l u x in the nucleus accumbens and catecholamine e f f l u x in the MPOA are associated with the presentation of a natural sexual incentive to male r a t s . However, several control conditions need to be evaluated before t h i s suggestion can be accepted; An important consideration i s the s p e c i f i c i t y of the e l i c i t i n g stimulus. It is possible that merely presenting a conspe c i f i c behind the screen, regardless of i t s sexual incentive value, i s s u f f i c i e n t to increase DA and catecholamine oxidation signals in the nucleus accumbens and MPOA, res p e c t i v e l y . Experiment IVb examined t h i s p o s s i b i l i t y by analyzing oxidation currents in males presented with either another male, a sexually nonreceptive female, a s l i d e 166 smeared with estrous vaginal secretions, or a receptive female behind the screen. Method Subjects and Stimuli The 15 males used in Experiment IVa were used as subjects in t h i s . Details of th e i r surgery and the housing conditions for a l l animals can be found in Experiment IVa (Page 147). The females used in Experiment IVa were used as sexually receptive stimulus females in t h i s experiment. Sexual r e c e p t i v i t y was induced as in the previous experiments, and these females were presented to the males approximately 5 h a f t e r progesterone administration. A group of 6 ovariectomized females that had not received estrogen or progesterone treatment for at le a s t 4 months prior to t h i s experiment were used as sexually nonreceptive female c o n s p e c i f i c s . A group of 6 i n t a c t , sexually active males were used as male c o n s p e c i f i c s . Estrous vaginal secretions were taken from sexually receptive females by swabbing the vagina gently with a cotton-tipped applicator dampened with d i s t i l l e d water. These secretions were applied to a microscope s l i d e and presented immediately to the males by placing the s l i d e adjacent to the screen. Electrochemical Measurements Measurement of e x t r a c e l l u l a r DA or catecholamine concentrations were made as in Experiment IVa using 1-sec pulse chronoamperometry. 167 B e h a v i o r a l T e s t i n g P r o c e d u r e s T e s t s were c o n d u c t e d 4 days a f t e r E x p e r i m e n t IVa i n t h e same e l e c t r i c a l l y s h i e l d e d P l e x i g l a s chamber used i n t h a t e x p e r i m e n t . As i n E x p e r i m e n t I V a , a s t a b l e c h r o n o a m p e r o m e t r i c b a s e l i n e was e s t a b l i s h e d i n each male f o r a t l e a s t 30 m i n , a f t e r w h i c h t h e s t i m u l i were p r e s e n t e d b e h i n d t h e s c r e e n . Each s t i m u l u s was p r e s e n t e d f o r 5 m i n , t h e n removed . A 2 0 - m i n p e r i o d s e p a r a t e d t h e p r e s e n t a t i o n o f each s t i m u l u s . A l l males r e c e i v e d t h e same o r d e r o f p r e s e n t a t i o n : t h e m a l e , t h e n o n r e c e p t i v e f e m a l e , t h e s l i d e smeared w i t h e s t r o u s v a g i n a l s e c r e t i o n s , and f i n a l l y t h e r e c e p t i v e f e m a l e . T h i s o r d e r o f p r e s e n t a t i o n was b e l i e v e d t o r e f l e c t an a s c e n d i n g o r d e r o f s t i m u l u s s a l i e n c e . I t was hoped t h a t any change i n o x i d a t i o n c u r r e n t p r o d u c e d by s t i m u l i o f p o t e n t i a l l y s m a l l e r s a l i e n c e , e . g . , t h e m a l e , wou ld n o t be overshadowed by t h o s e o f p o t e n t i a l l y l a r g e r s a l i e n c e , e . g . , t h e r e c e p t i v e f e m a l e . F o l l o w i n g t h e p r e s e n t a t i o n o f t h e r e c e p t i v e f e m a l e , t h e s c r e e n was removed and t h e males were a l l o w e d t o c o p u l a t e f o r 30 m i n . T h i s was done t o c o n f i r m t h e r e s u l t s o f E x p e r i m e n t I V a . H i s t o l o g i c a l a n a l y s e s were p e r f o r m e d f o l l o w i n g t h e p r e s e n t e x p e r i m e n t . S t a t i s t i c a l A n a l y s i s B a s e l i n e c h r o n o a m p e r o m e t r i c d i f f e r e n c e s c o r e s were d e t e r m i n e d as i n E x p e r i m e n t I V a . D i f f e r e n c e s c o r e s were c a l c u l a t e d f r o m t h e c h r o n o a m p e r o m e t r i c r e c o r d o f each r a t f o r each 5 -m in p e r i o d t h a t t h e s t i m u l i were p r e s e n t e d , as was done f o r t h e p r e s e n t a t i o n o f t h e r e c e p t i v e f e m a l e i n E x p e r i m e n t I V a . 168 Mean d i f f e r e n c e s c o r e s were c a l c u l a t e d f o r t h e 5 r a t s i n each g r o u p f o r each s t i m u l u s and a n a l y z e d u s i n g a w i t h i n - s u b j e c t s ANOVA f o r r e p e a t e d measures . The B o n f e r r o n i method was used t o c o r r e c t f o r t h e e l e v a t e d e x p e r i m e n t - w i s e e r r o r p r o d u c e d by a l a r g e number o f r e p e a t e d measu res . The c o r r e c t e d e r r o r r a t e was p_<.01 because 5 e v e n t s ( i n c l u d i n g t h e b a s e l i n e s c o r e ) were a n a l y z e d . For each s i g n i f i c a n t ANOVA, p o s t - h o c c o m p a r i s o n s were made u s i n g t h e Tukey m e t h o d , p_<.05. R e s u l t s A g r a d u a l i n c r e a s e i n a c t i v i t y was o b s e r v e d i n each male when t h e s t i m u l i were p r e s e n t e d b e h i n d t h e s c r e e n . T y p i c a l l y , t h e males wou ld d i r e c t t h e i r a t t e n t i o n t o w a r d t h e s c r e e n , move a d j a c e n t t o i t , and p robe t h e i r s n o u t s t h r o u g h t h e o p e n i n g s i n t h e w i r e mesh. A l l b u t one o f t h e males were o b s e r v e d t o l i c k t h e s l i d e smeared w i t h e s t r o u s v a g i n a l s e c r e t i o n s . P r e s e n t a t i o n o f t h e r e c e p t i v e f e m a l e , h o w e v e r , evoked more i n t e r e s t t h a n t h e o t h e r s t i m u l i . As i n E x p e r i m e n t I V a , a l l males a t t e m p t e d t o g r a b t h e r e c e p t i v e f e m a l e t h r o u g h t h e s c r e e n w i t h t h e i r f o r e p a w s and some (2 w i t h n u c l e u s accumbens e l e c t r o d e s ; 2 w i t h s t r i a t a l e l e c t r o d e s ; and 1 w i t h MPOA e l e c t r o d e s ) a t t e m p t e d t o c l i m b t h e s c r e e n . N u c l e u s Accumbens A l l males showed immed ia te i n c r e a s e s i n DA o x i d a t i o n s i g n a l s when each s t i m u l u s was p r e s e n t e d . A l t h o u g h a l l o f t h e s t i m u l i i n c r e a s e d t h e DA o x i d a t i o n s i g n a l s ove r b a s e l i n e , p r e s e n t a t i o n o f 169 t h e r e c e p t i v e fema le had t h e l a r g e s t e f f e c t . T h i s i s shown c l e a r l y by t h e mean d i f f e r e n c e s c o r e s d e p i c t e d i n F i g u r e 25 ( P a n e l A ) . The ANOVA d e t e c t e d a s i g n i f i c a n t o v e r a l l e f f e c t f o r t h e s e s c o r e s , F ( 4 , 1 6 ) = 8 . 3 3 , p jC .001 . P o s t - h o c c o m p a r i s o n s o f each s c o r e r e v e a l e d t h a t t h e y were a l l s i g n i f i c a n t l y g r e a t e r t h a n t h e b a s e l i n e d i f f e r e n c e s c o r e , however , t h e mean d i f f e r e n c e s c o r e f o r t h e p r e s e n t a t i o n o f t h e r e c e p t i v e f e m a l e was s i g n i f i c a n t l y g r e a t e r t h a n t h e s c o r e s f o r t h e p r e s e n t a t i o n o f t h e m a l e , t h e n o n r e c e p t i v e f e m a l e , and t h e s l i d e c o n t a i n i n g e s t r o u s v a g i n a l s e c r e t i o n s . I n t e r e s t i n g l y , t h e two males t h a t c l i m b e d t h e s c r e e n d u r i n g t h e p r e s e n t a t i o n o f t h e r e c e p t i v e f e m a l e d i d n o t have t h e l a r g e s t d i f f e r e n c e s c o r e s f o r t h i s e v e n t . A l l males c o p u l a t e d when t h e s c r e e n was removed , and a l l showed a dynamic p a t t e r n o f DA o x i d a t i o n s i g n a l s v i r t u a l l y i d e n t i c a l t o t h o s e o b s e r v e d i n E x p e r i m e n t IVa ( d a t a n o t s h o w n ) . S t r i a t u m None o f t h e s t i m u l i i n c r e a s e d t h e DA o x i d a t i o n s i g n a l s a p p r e c i a b l y . T h i s i s shown by t h e mean d i f f e r e n c e s c o r e s d e p i c t e d i n F i g u r e 25 ( P a n e l B ) . The ANOVA d i d n o t d e t e c t a s i g n i f i c a n t e f f e c t f o r t h e s e s c o r e s , F ( 4 ,16 ) =0 . 9 4 , p_>.35. A l l males c o p u l a t e d when t h e s c r e e n was removed a n d , as i n E x p e r i m e n t I V a , a l l showed a p r o g r e s s i v e i n c r e a s e i n t h e DA o x i d a t i o n s i g n a l s t h r o u g h o u t t h e t e s t ( d a t a n o t s h o w n ) . M e d i a l P r e o p t i c A rea \ A l l males showed immed ia te i n c r e a s e s i n c a t e c h o l a m i n e o x i d a t i o n s i g n a l s when t h e s l i d e or t h e r e c e p t i v e f e m a l e was 170 F i g u r e 25 . Changes i n DA o x i d a t i o n c u r r e n t f r o m b a s e l i n e i n t h e n u c l e u s accumbens (n = 5) and s t r i a t u m (n = 5 ) , and mean changes i n c a t e c h o l a m i n e o x i d a t i o n c u r r e n t i n t h e m e d i a l p r e o p t i c a r e a (n = 5 ) , o b s e r v e d d u r i n g a 5 -min t e s t i n w h i c h e i t h e r a male r a t (MALE), a n o n r e c e p t i v e f e m a l e (NR FEM), a g l a s s s l i d e c o n t a i n i n g e s t r o u s v a g i n a l s e c r e t i o n s ( S L I D E ) , or a r e c e p t i v e f e m a l e (R FEM) was p l a c e d b e h i n d a w i r e -mesh s c r e e n i n t h e same chamber as t h e e x p e r i m e n t a l male r a t . V a l u e s a r e means + SE. * p_<.05, * p_<.01, f r o m t h e b a s e l i n e d i f f e r e n c e s c o r e . NUCLEUS ACCUMBENS STRIATUM s - i * I MALE NR FEM SUD€ R FEM MALE NR FEM SLIDE R FEM MEDIAL PREOPTIC AREA MALE NR FEM SUOE R FEM p r e s e n t e d . I n c o n t r a s t , c a t e c h o l a m i n e o x i d a t i o n s i g n a l s d i d n o t i n c r e a s e a p p r e c i a b l y when t h e male or t h e n o n r e c e p t i v e f e m a l e was p r e s e n t e d . T h i s i s shown by t h e mean d i f f e r e n c e s c o r e s d e p i c t e d i n F i g u r e 25 ( P a n e l C ) . The ANOVA d e t e c t e d a s i g n i f i c a n t o v e r a l l e f f e c t f o r t h e s e s c o r e s , F( 4 ,16 ) =19 . 2 6 , p_<.0001. P o s t - h o c c o m p a r i s o n s o f each s c o r e r e v e a l e d t h a t n e i t h e r t h e male nor t h e n o n r e c e p t i v e f e m a l e i n c r e a s e d t h e d i f f e r e n c e s c o r e s s i g n i f i c a n t l y ove r t h e b a s e l i n e d i f f e r e n c e s c o r e , whereas b o t h t h e s l i d e and t h e r e c e p t i v e f e m a l e d i d . A l t h o u g h t h e mean d i f f e r e n c e s c o r e f o r t h e r e c e p t i v e f e m a l e was g r e a t e r t h a n t h a t f o r t h e s l i d e , t h e s e two s c o r e s were n o t s i g n i f i c a n t l y d i f f e r e n t f r o m one a n o t h e r . The one male i n t h i s g r o u p t h a t c l i m b e d t h e s c r e e n d u r i n g t h e p r e s e n t a t i o n o f t h e r e c e p t i v e f e m a l e had t h e l a r g e s t d i f f e r e n c e s c o r e f o r t h i s e v e n t ; however , t h i s s c o r e was o n l y 0 . 1 nA l a r g e r t h a n t h e n e x t h i g h e s t s c o r e . A l l males c o p u l a t e d when t h e s c r e e n was removed , and a l l showed a dynamic p a t t e r n o f c a t e c h o l a m i n e o x i d a t i o n s i g n a l s v i r t u a l l y i d e n t i c a l t o t h o s e o b s e r v e d i n E x p e r i m e n t IVa ( d a t a n o t s h o w n ) . D i s c u s s i o n E x p e r i m e n t IVb r e p l i c a t e s and e x t e n d s t h e r e s u l t s o f E x p e r i m e n t IVa by d e m o n s t r a t i n g t h a t t h e immed ia te i n c r e a s e s i n DA and c a t e c h o l a m i n e o x i d a t i o n s i g n a l s i n t h e n u c l e u s accumbens and MPOA o f male r a t s , r e s p e c t i v e l y , a r e r e l a t i v e l y s p e c i f i c t o t h e p r e s e n t a t i o n o f a s e x u a l I n c e n t i v e . As i n E x p e r i m e n t I V a , however , t h e p a t t e r n o f t h e i n c r e a s e s d i f f e r e d among t h e s e two 173 regions. Although small but s i g n i f i c a n t elevations in DA oxidation signals were observed in the nucleus accumbens during the presentation of a male, a nonreceptive female, or a s l i d e smeared with estrous vaginal secretions, the presentation of a sexually receptive female produced a much larger r i s e in DA oxidation s i g n a l s . In contrast, the presentation of either a male or nonreceptive female did not s i g n i f i c a n t l y increase catecholamine oxidation signals in the MPOA, whereas the presentation of either the s l i d e or the receptive female d i d . Consistent with the r e s u l t s of Experiment IVa, none of the st i m u l i affected DA oxidation signals in the striatum. Although the presence of a sexually receptive female i s a p a r t i c u l a r l y s a l i e n t stimulus for evoking an increase in DA ef f l u x in the nucleus accumbens, the r e l a t i v e l y smaller but s i g n i f i c a n t increases in DA oxidation signals during the presentation of the male, the nonreceptive female, or the s l i d e , suggest that DA release in t h i s structure may play a general r o l e in processing incentive cues. This suggestion i s consistent with previous hypotheses concerning the rol e of mesolimbic DA systems in behavior (e.g, Crow, 1973; Fibiger & P h i l l i p s , 1986; Mogenson & P h i l l i p s , 1976). Previous studies that have examined l e v e l s of DA or i t s metabolites ex vivo following periods of copulation have questioned the s p e c i f i c i t y of DA synthesis or release in the striatum or MPOA to copulatory behavior. Ahlenius et a l . (1987) demonstrated that 10 min of copulation increased DOPA synthesis 174 i n b o t h t h e n u c l e u s accumbens and s t r i a t u m . However, f o r c e d t r e a d m i l l l o c o m o t i o n a l s o i n c r e a s e d DOPA s y n t h e s i s i n t h e s t r i a t u m , s u g g e s t i n g t h a t motor a c t i v i t y a l o n e was s u f f i c i e n t t o i n c r e a s e c a t e c h o l a m i n e s y n t h e s i s i n t h e s t r i a t u m b u t n o t t h e n u c l e u s accumbens. S i m i l a r l y , Hof fman e t a l . (1987) d e m o n s t r a t e d t h a t b o t h c o p u l a t i o n t o s e x u a l e x h a u s t i o n and whee l r u n n i n g yoked t o such c o p u l a t i o n i n c r e a s e d DA b u t n o t DOPAC l e v e l s i n t h e MPOA, s u g g e s t i n g t h a t l e n g t h y b o u t s o f motor a c t i v i t y i n c r e a s e d DA r e l e a s e b u t n o t u t i l i z a t i o n i n t h e MPOA. G e n e r a l l o c o m o t o r a c t i v i t y was n o t r e c o r d e d i n e i t h e r E x p e r i m e n t s IVa or I V b ; however , s e v e r a l o b s e r v a t i o n s a r e i n c o n s i s t e n t w i t h t h e i d e a t h a t n o n s p e c i f i c i n c r e a s e s i n moto r a c t i v i t y c o u l d a c c o u n t f o r t h e i n c r e a s e s i n DA e f f l u x . A l t h o u g h t h e males appeared more e x c i t e d and a t t e n t i v e d u r i n g t h e p r e s e n t a t i o n o f t h e r e c e p t i v e fema le t h a n d u r i n g t h e p r e s e n t a t i o n o f t h e o t h e r s t i m u l i , t h e r e was no o b v i o u s r e l a t i o n between t h e l e v e l o f b e h a v i o r a l e x c i t a t i o n and t h e m a g n i t u d e o f i n d i v i d u a l DA o x i d a t i o n s i g n a l s d u r i n g t h e p r e s e n t a t i o n o f t h e r e c e p t i v e f e m a l e . The two males w i t h e l e c t r o d e s i n t h e n u c l e u s accumbens t h a t c l i m b e d t h e s c r e e n d u r i n g t h e p r e s e n t a t i o n o f t h e r e c e p t i v e f e m a l e had mean d i f f e r e n c e s c o r e s t h a t were l e s s t h a n t h o s e o f t h e o t h e r males i n t h i s g r o u p , w h i c h d i d n o t d i s p l a y such b e h a v i o r a l e x c i t a t i o n . The p r e s e n t a t i o n o f t h e r e c e p t i v e f e m a l e d i d n o t i n c r e a s e t h e d i f f e r e n c e s c o r e s o f males w i t h e l e c t r o d e s i n t h e s t r i a t u m , d e s p i t e o b v i o u s i n c r e a s e s i n b e h a v i o r a l e x c i t a t i o n . F i n a l l y , a l t h o u g h t h e one male i n t h e MPOA g r o u p that climbed the screen during the presentation of the receptive female had the highest mean difference score, i t was only 0.1 nA higher than the next highest score. It i s impossible to rul e out a general locomotor e f f e c t on DA e f f l u x in the nucleus accumbens and striatum, or catecholamine e f f l u x in the MPOA, despite the lack of obvious evidence in Experiments IVa or IVb. However, i t i s d i f f i c u l t to design an appropriate control for the locomotor e f f e c t s of copulatory behavior. Although the yoked control used by Hoffman et a l . (1987).was perhaps the best attempt to equate the amount of time in forced a c t i v i t y with the amount of time in copulation, i t did not provide an adequate control for the type of motor a c t i v i t y engaged in during copulation, nor did i t completely equate the t o t a l amount of time each rat was engaged in motor a c t i v i t y , e.g., the wheel did not stop during each yoked rat's inter intromission I n t e r v a l . Nevertheless, a study of DA or catecholamine e f f l u x in these regions during forced a c t i v i t y needs to be conducted before the sexual s p e c i f i c i t y of the present r e s u l t s can be accepted. EXPERIMENT IVc Experiments IVa and IVb provide evidence for several dynamic changes in DA or catecholamine e f f l u x in the nucleus accumbens, striatum, or MPOA during a n t i c i p a t o r y and consummatory aspects of sexual behavior in the male r a t . Placing a sexually receptive female rat behind a screen produced an immediate increase in DA or catecholamine e f f l u x in the nucleus accumbens and MPOA, resp e c t i v e l y . The i n i t i a t i o n of copulation produced a further increase in most of these r a t s , whereas ejaculation was followed immediately by a decrease in DA or catecholamine oxidation signals in every r a t . Each r e i n i t i a t i o n of copulation was preceded by an increase in the oxidation s i g n a l s . In contrast, placement of a receptive female behind the screen had no e f f e c t on DA oxidation signals in the striatum; however, there was a progressive increase in the oxidation signals during the copulatory t e s t that was not associated with any p a r t i c u l a r aspect of copulatory a c t i v i t y . Although Experiment IVb demonstrated that the i n i t i a l increase in DA or catecholamine oxidation signals ln the nucleus accumbens or MPOA was r e l a t i v e l y s p e c i f i c to the presentation of a sexual incentive, neither experiment ruled out the p o s s i b i l i t y that goal-directed locomotor a c t i v i t y , rather than sensory processing of incentive cues alone, increased the oxidation signals in each of the areas. Another p o t e n t i a l problem in in t e r p r e t i n g the r e s u l t s of Experiments IVa and IVb stems from the contr o v e r s i a l nature of the stearate-modified electrode used in those experiments. As noted above, several e l e c t r o a c t i v e substances are oxidized at the same po t e n t i a l as DA. The addition of s t e a r i c acid to the graphite paste separates the anions ascorbate and DOPAC from DA by increasing t h e i r oxidation p o t e n t i a l s , but i t does not f a c i l i t a t e the a b i l i t y of the electrode to d i s t i n g u i s h between DA and norepinephrine. Although there i s pharmacological evidence t h a t n o r e p i n e p h r i n e does n o t c o n t r i b u t e t o t h e o x i d a t i o n s i g n a l s r e c o r d e d by t h i s e l e c t r o d e i n t h e n u c l e u s accumbens or s t r i a t u m ( B l a h a & Lane , 1 9 8 3 ) , t h e r e i s g r o w i n g e v i d e n c e t h a t t h e s e n s i t i v i t y o f t h e e l e c t r o d e t o DA i s i n c r e a s e d d r a m a t i c a l l y f o l l o w i n g e x p o s u r e t o b r a i n t i s s u e ( B l a h a , J u n g , & P h i l l i p s , i n p r e p a r a t i o n ) . However , t h e mechanisms by w h i c h e x p o s u r e t o b r a i n t i s s u e i n c r e a s e s t h e s e n s i t i v i t y have n o t been d e t e r m i n e d . Because t h e n a t u r e o f t h e o x i d a t i o n s i g n a l s p r o d u c e d by t h e s t e a r a t e - m o d i f i e d e l e c t r o d e r e m a i n s c o n t r o v e r s i a l , an i n d e p e n d e n t c o n f i r m a t i o n o f t h e g e n e r a l i n c r e a s e s i n DA e f f l u x o b s e r v e d i n t h e n u c l e u s accumbens and s t r i a t u m d u r i n g t h e p r e s e n t a t i o n o f a r e c e p t i v e f e m a l e and d u r i n g c o p u l a t i o n i n E x p e r i m e n t IVa was a t t e m p t e d u s i n g i n v i v o m i c r o d i a l y s i s . U n f o r t u n a t e l y , a m i c r o d i a l y s i s p robe c a p a b l e o f s a m p l i n g DA or i t s m e t a b o l i t e s i n t h e MPOA has y e t t o be d e s i g n e d , t h e r e f o r e no a t t e m p t was made i n t h i s e x p e r i m e n t t o assess DA or i t s m e t a b o l i t e s i n t h i s r e g i o n . Method S u b j e c t s and S u r g e r y The male Long-Evans r a t s used i n t h i s e x p e r i m e n t were p u r c h a s e d f r o m C h a r l e s R i v e r Canada and housed as i n t h e p r e v i o u s e x p e r i m e n t s . The f e m a l e s used i n t h i s e x p e r i m e n t were used as s e x u a l l y r e c e p t i v e s t i m u l u s f e m a l e s i n E x p e r i m e n t s IVa and I V b . S e x u a l r e c e p t i v i t y was i n d u c e d i n t h e s e f e m a l e s as i n t h e p r e v i o u s e x p e r i m e n t s . A g r o u p o f 10 males was g i v e n a t l e a s t 10 t e s t s o f s e x u a l 178 b e h a v i o r i n t h e b i l e v e l chambers p r i o r t o s u r g e r y . These males had r e a c h e d t h e c r i t e r i a f o r s e x u a l e x p e r i e n c e o u t l i n e d i n E x p e r i m e n t I (Page 5 9 ) . The males were a n e s t h e t i z e d w i t h s o d i u m p e n t o b a r b i t a l (60 mg/kg) and m i c r o d i a l y s i s p r o b e s aimed a t t h e n u c l e u s accumbens (N=5) or t h e s t r i a t u m (N=5) were i m p l a n t e d s t e r e o t a x i c a l l y u s i n g t h e a t l a s o f P e l l e g r i n o e t a l . (1979) f o r t h e n u c l e u s accumbens and t h e a t l a s o f P a x i n o s and Watson (1982) f o r t h e s t r i a t u m . The p r o b e s were c o n s t r u c t e d o f a s e m i p e r m e a b l e h o l l o w f i b e r membrane c l o s e d a t one end w i t h epoxy ( s a p o n i f i e d c e l l u l o s e e s t e r , S p e c t r a P r o d u c t s ) w i t h an o u t s i d e d i a m e t e r o f 250 um. Two s t r a n d s o f f u s e d s i l i c a t u b i n g were i n s e r t e d t h r o u g h t h e o t h e r end and t h e assemb ly was g l u e d t o t h e i n s i d e o f an 8 mm Y-shaped 22 g s t a i n l e s s s t e e l c a n n u l a . The membrane e x t e n d e d e i t h e r 2 mm ( n u c l e u s accumbens) o r 4 mm ( s t r i a t u m ) beyond t h e s i n g l e end o f t h e c a n n u l a . Epoxy was i n s e r t e d a round t h e two s t r a n d s o f s i l i c a t u b i n g t h a t e x t e n d e d o u t o f t h e d o u b l e end o f t h e c a n n u l a . Excess s i l i c a t u b i n g was t h e n s t r i p p e d away f r o m t h e s e ends f l u s h w i t h t h e s u r f a c e o f t h e c a n n u l a . The s i n g l e end was i m p l a n t e d i n t o t h e d e s i r e d l o c a t i o n i n t h e b r a i n w i t h t h e r e s t o f t h e c a n n u l a a n c h o r e d t o t h e s u r f a c e o f t h e s k u l l u s i n g d e n t a l a c r y l i c and s k u l l s c r e w s . The d o u b l e end o f t h e c a n n u l a p r o t r u d e d above t h e d e n t a l a c r y l i c and s e r v e d as an i n l e t and o u t l e t f o r p e r f u s i o n and e x t r a c t i o n o f t h e d i a l y s a t e . E l e c t r o c h e m i c a l A n a l y s i s M i c r o d i a l y s i s and s u b s e q u e n t e l e c t r o c h e m i c a l a n a l y s i s was p e r f o r m e d u s i n g an au tomated o n - l i n e sample i n j e c t i o n s y s t e m 179 (Damsma e t a l . , 1989; W e s t e r i n k & T u i n t e , 1 9 8 6 ) . A p e r f u s i o n s o l u t i o n c o n s i s t i n g o f 147 mM N a C l , 3 mM KC1, 1.3 mM CaCl , 1 mM MgCl , and 1 mM NaPO (pH 7 . 3 ) was pumped t h r o u g h t h e d i a l y s i s t u b e a t a r a t e o f 5 u l / m i n . The p e r f u s a t e was l o a d e d d i r e c t l y i n t o a 100 u l sample l o o p o f t h e i n j e c t o r ( V a l c o ) and a u t o m a t i c a l l y i n j e c t e d i n t o t h e a n a l y t i c a l s y s t e m e v e r y 10 m i n . The q u a n t i f i c a t i o n o f DA, i t s m e t a b o l i t e s DOPAC and h o m o v a n i l l i c a c i d (HVA) , and t h e i n d o l e m e t a b o l i t e 5 - h y d r o x y i n d o l e a c e t i c a c i d ( 5 -HIAA) was p e r f o r m e d as d e s c r i b e d by W e s t e r i n k and Mou lde r ( 1 9 8 1 ) . S e l e c t i v e r e t e n t i o n o f t h e s e compounds was a c h i e v e d u s i n g r e v e r s e phase l i q u i d c h r o m o t o g r a p h y ( 1 5 0 x 4 . 8 mm, N u c l e o s i l 5C 18) w i t h a m o b i l e phase c o n s i s t i n g o f 0 . 1 M a c e t i c a c i d (pH 4 . 1 , a d j u s t e d w i t h s o l i d sod ium a c e t a t e ) w i t h 0 .4 t o 0 .6 mM o c t a n o s u l f o n i c a c i d , 0 . 0 1 mM Na EDTA, and 80 m l / 1 m e t h a n o l a t a f l o w r a t e o f 1.5 m l / m i n . E l e c t r o c h e m i c a l d e t e c t i o n was a c c o m p l i s h e d u s i n g a LC4B a m p e r o m e t r i c d e t e c t o r ( B i o a n a l y t i c a l Systems) w i t h a g l a s s y c a r b o n e l e c t r o d e (+700 mV v s . a Ag/AgCl r e f e r e n c e e l e c t r o d e ) . Chromatograms were r e g i s t e r e d on a two pen c h a r t r e c o r d e r ( K i p p ) . B e h a v i o r a l T e s t i n g P r o c e d u r e s The male r a t s were t e s t e d f o r s e x u a l b e h a v i o r a p p r o x i m a t e l y 48 h r a f t e r t h e i m p l a n t a t i o n o f m i c r o d i a l y s i s p r o b e s . The p r o c e d u r e f o r t e s t i n g s e x u a l b e h a v i o r was n e a r l y i d e n t i c a l t o t h a t used i n E x p e r i m e n t I V a , e x c e p t t h a t a) b a s e l i n e l e v e l s o f DA and i t s m e t a b o l i t e s were t a k e n i n each r a t ' s home cage f o r 40 m i n ; and b) t h e r a t s were t h e n t r a n s f e r r e d t o t h e t e s t i n g chamber used i n E x p e r i m e n t s IVa and IVb ( w h i c h was n o v e l t o them) f o r an 180 a d d i t i o n a l 40 m i n , a f t e r w h i c h a s e x u a l l y r e c e p t i v e f e m a l e was p l a c e d b e h i n d t h e s c r e e n f o r 10 m i n . As b e f o r e , r e m o v a l o f t h e s c r e e n i n i t i a t e d a 3 0 - m i n b o u t o f c o p u l a t o r y b e h a v i o r w h i c h was t e r m i n a t e d by t h e r e m o v a l o f t h e f e m a l e . However , u n l i k e t h e p r e v i o u s two e x p e r i m e n t s , t h e males r e m a i n e d i n t h e t e s t i n g chamber f o r an a d d i t i o n a l 80 min a f t e r r e m o v a l o f t h e f e m a l e . H i s t o l o g y H i s t o l o g i c a l v e r i f i c a t i o n o f m i c r o d i a l y s i s p r o b e s was made u s i n g t h e p r o c e d u r e s o u t l i n e d i n E x p e r i m e n t I V a . E x a m i n a t i o n o f t h e s l i d e s r e v e a l e d t h a t a l l r a t s i n b o t h . g r o u p s had p r o b e t r a c k s e n d i n g w i t h i n t h e t a r g e t s t r u c t u r e s . The p l a c e m e n t o f m i c r o d i a l y s i s p r o b e s i s shown i n F i g u r e s 26 and 27 . S t a t i s t i c a l A n a l y s i s Peak h e i g h t s o f DA, DOPAC, HVA, and 5-HIAA f r o m each r a t were measured f r o m t h e chromatograms and compared t o peak h e i g h t s o b t a i n e d f r o m a s t a n d a r d s o l u t i o n c o n t a i n i n g t h e s e compounds t h a t had been r u n t h r o u g h t h e HPLC p r i o r t o each t e s t . T h i s p r o c e d u r e a l l o w e d a c t u a l c o n c e n t r a t i o n s o f t h e s e compounds t o be d e t e r m i n e d i n t h e d i a l y s a t e s o f each r a t . B a s e l i n e v a l u e s f o r each compound were c a l c u l a t e d as t h e mean c o n c e n t r a t i o n ove r t h e f o u r 1 0 - m i n samples t a k e n b e f o r e each r a t was p l a c e d i n t o t h e t e s t i n g chamber . The p e r c e n t a g e o f b a s e l i n e was t h e n c a l c u l a t e d f o r each 1 0 - m i n sample t h r o u g h o u t t h e t e s t f o r each r a t . Mean p e r c e n t a g e s o f b a s e l i n e were c a l c u l a t e d f o r each sample a c r o s s t h e 5 r a t s i n each g r o u p . S i x samples were s u b j e c t e d t o s t a t i s t i c a l a n a l y s i s : 1) t h e f i r s t 10 min o f b a s e l i n e ; 2) t h e f i r s t 10 min i n t h e 181 182 183 t e s t i n g chamber ; 3) t h e 10 min w i t h t h e r e c e p t i v e f e m a l e b e h i n d t h e s c r e e n ; 4) t h e f i r s t 10 min o f c o p u l a t i o n ; 5) t h e second 10 min o f c o p u l a t i o n ; and 6) t h e t h i r d 10 min o f c o p u l a t i o n . A w i t h i n - s u b j e c t s ANOVA f o r r e p e a t e d measures was c o n d u c t e d f o r each compound a c r o s s t h e seven s a m p l e s . The B o n f e r r o n i method was used t o c o r r e c t t h e e l e v a t e d e x p e r i m e n t -w i s e e r r o r t h a t o c c u r s w i t h a l a r g e number o f r e p e a t e d m e a s u r e s . The c o r r e c t e d e r r o r r a t e was p_<.0083 because s i x r e p e a t e d samples f o r each compound were s u b j e c t e d t o s t a t i s t i c a l a n a l y s i s . For each s i g n i f i c a n t ANOVA, p o s t - h o c c o m p a r i s o n s were made u s i n g t h e Tukey m e t h o d , p_<.05. R e s u l t s D e s p i t e h a v i n g o n l y 48 h t o r e c o v e r f r o m t h e s u r g i c a l i m p l a n t a t i o n o f d i a l y s i s p r o b e s , a l l 10 r a t s showed an i m m e d i a t e i n t e r e s t i n t h e r e c e p t i v e f e m a l e b e h i n d t h e s c r e e n t h a t was i d e n t i c a l t o t h e i n t e r e s t d i s p l a y e d by r a t s i n t h e p r e v i o u s e x p e r i m e n t s . A l l r a t s i n i t i a t e d c o p u l a t i o n w i t h i n 20 s o f t h e r e m o v a l o f t h e s c r e e n and a l l d i s p l a y e d n o r m a l p a t t e r n s o f c o p u l a t i o n d u r i n g t h e t e s t . Most r a t s went t o s l e e p w i t h i n 30 min o f t h e r e m o v a l o f t h e f e m a l e . Nuc leus Accumbens The mean p e r c e n t a g e o f b a s e l i n e DA r e l e a s e f o r each o f t h e 10 -m in samples i s d e p i c t e d i n F i g u r e 28 ( P a n e l A ) . C l e a r l y a p p a r e n t a r e s e v e r a l i m p o r t a n t changes i n DA r e l e a s e . T r a n s f e r r i n g each male f r o m t h e home cage t o t h e t e s t i n g chamber 184 i n c r e a s e d DA l e v e l s an a v e r a g e o f 28% d u r i n g t h e f i r s t 1 0 - m i n sample i n t h e t e s t i n g chamber . A l t h o u g h DA l e v e l s i n c r e a s e d s l i g h t l y over t h e n e x t two s a m p l e s , i t began t o d r i f t back t o w a r d b a s e l i n e d u r i n g t h e f o u r t h s a m p l e . DA l e v e l s i n c r e a s e d an a d d i t i o n a l 10% d u r i n g t h e 1 0 - m i n sample d u r i n g w h i c h t h e f e m a l e was p l a c e d b e h i n d t h e s c r e e n . The sample t a k e n d u r i n g t h e f i r s t 10 min o f c o p u l a t i o n was a s s o c i a t e d w i t h an a d d i t i o n a l 46% i n c r e a s e i n DA l e v e l s . DA l e v e l s i n c r e a s e d an a d d i t i o n a l 8% and 16% ( t o a maximum o f 96% ove r b a s e l i n e ) d u r i n g t h e second and t h i r d 1 0 - m i n samples t a k e n d u r i n g c o p u l a t i o n , r e s p e c t i v e l y . A l t h o u g h t h e r e m o v a l o f t h e f e m a l e r e s u l t e d i n a s t e a d y d e c l i n e i n DA l e v e l s , t h o s e l e v e l s r e m a i n e d above b a s e l i n e t h r o u g h o u t t h e 8 0 - m l n p e r i o d f o l l o w i n g t h e r e m o v a l o f t h e f e m a l e . The ANOVA d e t e c t e d a s i g n i f i c a n t e f f e c t f o r DA r e l e a s e ove r t h e seven samples t e s t e d , P ( 5 , 2 0 ) = 1 6 . 8 8 , pK.OOOl. P o s t - h o c c o m p a r i s o n s r e v e a l e d t h a t a l l o f t h e samples were s i g n i f i c a n t l y i n c r e a s e d f r o m t h e b a s e l i n e s a m p l e . A l t h o u g h DA l e v e l s i n c r e a s e d i n 4 o f t h e 5 r a t s when t h e fema le was p l a c e d b e h i n d t h e s c r e e n , t h i s sample was n o t s i g n i f i c a n t l y d i f f e r e n t f r o m t h e f i r s t 1 0 - m i n sample w i t h t h e males a l o n e i n t h e t e s t i n g chamber (p_<.08 b u t > . 0 5 ) . The f i r s t two samples o f c o p u l a t i o n were n o t s i g n i f i c a n t l y d i f f e r e n t f r o m t h e sample w i t h t h e f e m a l e b e h i n d t h e s c r e e n , a l t h o u g h t h e t h i r d sample o f c o p u l a t i o n was. However , none o f t h e samples o f c o p u l a t i o n d i f f e r e d f r o m one a n o t h e r s i g n i f i c a n t l y . The mean p e r c e n t a g e o f b a s e l i n e DOPAC, HVA, and 5-HIAA 185 release i s depicted in Figure 28 (Panel B). Smaller and delayed patterns of release were observed for each of these metabolites compared to the pattern of DA release. Generally, l e v e l s of HVA were higher throughout the t e s t than l e v e l s of DOPAC, which in turn were higher than l e v e l s of 5-HIAA. The l e v e l s of each metabolite increased gradually when the males were transferred from t h e i r home cage to the t e s t i n g chamber. Very small increases in metabolite l e v e l s accompanied the placement of the female behind the screen. Levels of each metabolite increased further during the three samples of copulation. As with DA, athough the l e v e l s of each metabolite decreased during the 80 min that followed the removal of the female, a l l remained above the baseline. The ANOVA detected s i g n i f i c a n t e f f e c t s across the s i x samples for DOPAC, F ( 5, 20 ) =16 . 58, p_<.0001; HVA, F( 5, 20 ) =8 . 68, p_<.0004; and 5-HIAA, F( 5, 20) =12 . 24, p_<.0001. Post-hoc comparisons revealed that l e v e l s of a l l metabolites were elevated s i g n i f i c a n t l y from baseline during the sample that the female was placed behind the screen and during the three samples of copulation, but not in the f i r s t 10-min sample that the males were placed in the t e s t i n g chamber. However, only l e v e l s of DOPAC were increased s i g n i f i c a n t l y during the f i r s t 10 min of copulation compared to lev e l s during the placement of the female behind the screen. HVA and 5-HIAA l e v e l s increased s i g n i f i c a n t l y in the t h i r d 10-min sample during copulation compared to l e v e l s during the placement of the female behind the screen. 186 F i g u r e 28 . L e v e l s o f DA and i t ' s m e t a b o l i t e s i n d i a l y s a t e s f r o m t h e n u c l e u s accumbens d u r i n g phases o f s e x u a l b e h a v i o r i n E x p e r i m e n t IVc (n = 5 ) . V a l u e s a r e means + SE. A: Chromatogram d e p i c t i n g changes i n DA l e v e l s f r o m b a s e l i n e b e f o r e , d u r i n g , and a f t e r a 3 0 -min t e s t o f c o p u l a t i o n . B: Chromatogram d e p i c t i n g changes f r o m b a s e l i n e i n t h e l e v e l s o f DOPAC, HVA, and 5-HIAA b e f o r e , d u r i n g , and a f t e r t h e 3 0 - m i n t e s t o f c o p u l a t i o n . M i c r o d i a l y s i s and s u b s e q u e n t e l e c t r o -c h e m i c a l a n a l y s i s was p e r f o r m e d u s i n g an a u t o m a t e d o n - l i n e sample i n j e c t i o n s y s t e m . D i a l y s a t e s were sampled e v e r y 10 m i n . The q u a n t i f i c a t i o n o f DA, DOPAC, HVA, and 5-HIAA was p e r f o r m e d u s i n g r e v e r s e -phase l i q u i d c h r o m a t o g r a p h y . Mean c o n c e n t r a t i o n s + SE ( f m o l / m i n ) : DA: 3.09 + 0 . 6 2 ; DOPAC: 7 7 2 . 9 5 + 1 0 2 . 9 4 ; HVA: 444 .30 + 6 5 . 8 5 ; 5 -HIAA: 425.24 + 4 8 . 5 4 . NUCLEUS ACCUMBENS DOPAMINE 187 240 -i 220 -188 S t r i a t u m The mean p e r c e n t a g e o f b a s e l i n e DA r e l e a s e i s d e p i c t e d i n F i g u r e 29 ( P a n e l A ) . I n g e n e r a l , t h e p a t t e r n o f DA r e l e a s e was l e s s marked i n t h e s t r i a t u m t h a n i n t h e n u c l e u s accumbens d u r i n g t h e t e s t . T r a n s f e r r i n g each male f r o m t h e home cage t o t h e t e s t i n g chamber p r o d u c e d a 9% i n c r e a s e i n DA r e l e a s e d u r i n g t h e f i r s t 1 0 - m i n sample i n t h e t e s t i n g chamber . L e v e l s o f DA d i d n o t i n c r e a s e a p p r e c i a b l y w h i l e t h e males were i n t h e t e s t i n g chamber . P l a c i n g a r e c e p t i v e f e m a l e b e h i n d t h e s c r e e n i n c r e a s e d DA l e v e l s a n o t h e r 10%. DA l e v e l s i n c r e a s e d an a d d i t i o n a l 7%, 9%, and 24% ( t o a maximum o f 44% above b a s e l i n e ) d u r i n g t h e f i r s t , s e c o n d , and t h i r d samples o f c o p u l a t i o n , r e s p e c t i v e l y . L e v e l s o f DA d e c r e a s e d i n t h e 80 min f o l l o w i n g t h e r e m o v a l o f t h e f e m a l e , h o w e v e r , as w i t h t h e n u c l e u s accumbens, t h e s e l e v e l s r e m a i n e d above b a s e l i n e . The ANOVA d e t e c t e d a s i g n i f i c a n t e f f e c t f o r DA over t h e s i x samples t e s t e d , F( 5 , 20 ) =13 . 2 9 , p_<.0001 . P o s t - h o c c o m p a r i s o n s r e v e a l e d t h a t o n l y t h e t h r e e samples d u r i n g c o p u l a t i o n were s i g n i f i c a n t l y i n c r e a s e d i n c o m p a r i s o n w i t h t h e b a s e l i n e s a m p l e . None o f t h e o t h e r samples t e s t e d was s i g n i f i c a n t l y d i f f e r e n t f r o m one a n o t h e r . The mean p e r c e n t a g e o f b a s e l i n e DOPAC, HVA, and 5-HIAA i s d e p i c t e d i n F i g u r e 29 ( P a n e l B ) . As w i t h t h e n u c l e u s accumbens, i n c r e a s e s i n t h e l e v e l s o f t h e s e m e t a b o l i t e s were d e l a y e d compared t o i n c r e a s e s i n t h e l e v e l s o f DA, and l e v e l s o f HVA were g e n e r a l l y h i g h e r t h a n l e v e l s o f DOPAC, w h i c h i n t u r n were h i g h e r 189 t h a n l e v e l s o f 5-HIAA. However , b o t h DOPAC and HVA i n c r e a s e d t o l e v e l s comparab le t o DA, an e f f e c t n o t o b s e r v e d i n t h e n u c l e u s accumbens. The l e v e l s o f each m e t a b o l i t e i n c r e a s e d g r a d u a l l y f o l l o w i n g p l a c m e n t o f t h e males i n t o t h e t e s t i n g chamber . P lacement o f t h e f e m a l e b e h i n d t h e s c r e e n p r o d u c e d a s l i g h t i n c r e a s e i n m e t a b o l i t e l e v e l s . M e t a b o l i t e l e v e l s i n c r e a s e d s t e a d i l y t h r o u g h o u t t h e t e s t o f c o p u l a t i o n . L e v e l s o f DOPAC and HVA d e c r e a s e d a p p r e c i a b l y i n t h e 80 min f o l l o w i n g r e m o v a l o f t h e f e m a l e whereas l e v e l s o f 5-HIAA d i d n o t . The ANOVA d e t e c t e d s i g n i f i c a n t e f f e c t s a c r o s s t h e s i x samples f o r DOPAC, F( 5 , 20 ) =17 . 49 , p_<.0001; HVA, F( 5, 20 ) =60 . 04 , p_<.0001; and 5-HIAA, F( 5 , 20 ) =12 . 7 9 , p_<.0001. P o s t - h o c c o m p a r i s o n s r e v e a l e d t h a t l e v e l s o f HVA, b u t n o t DOPAC or 5 -HIAA, were i n c r e a s e d s i g n i f i c a n t l y f r o m b a s e l i n e d u r i n g t h e f i r s t 1 0 -min sample i n t h e t e s t i n g chamber . L e v e l s o f a l l m e t a b o l i t e s were i n c r e a s e d s i g n f i c a n t l y f r o m b o t h b a s e l i n e and t h e sample i n t h e t e s t i n g chamber when t h e f e m a l e was p l a c e d b e h i n d t h e s c r e e n and d u r i n g t h e t h r e e samples o f c o p u l a t i o n . A s i g n i f i c a n t i n c r e a s e d u r i n g t h e f i r s t sample o f c o p u l a t i o n compared t o t h e sample w i t h t h e f e m a l e b e h i n d t h e s c r e e n was d e t e c t e d f o r DOPAC b u t n o t f o r HVA or 5-HIAA. L e v e l s o f HVA i n c r e a s e d s i g n i f i c a n t l y d u r i n g t h e t h i r d sample o f c o p u l a t i o n i n c o n t r a s t w i t h t h e two p r e v i o u s s a m p l e s . However , f o r DOPAC and 5-HIAA, none o f t h e samples d u r i n g c o p u l a t i o n were s i g n i f i c a n t l y d i f f e r e n t f r o m one a n o t h e r . 190 F i g u r e 29 . L e v e l s o f DA and i t s m e t a b o l i t e s i n d i a l y s a t e s f r o m t h e s t r i a t u m d u r i n g phases o f s e x u a l b e h a v i o r i n E x p e r i m e n t IVc (n = 5 ) . Va lues a r e means + SE. A: Chromatogram d e p i c t i n g changes i n DA l e v e l s f r o m b a s e l i n e b e f o r e , d u r i n g , and a f t e r a 3 0 - m i n t e s t o f c o p u l a t i o n . B: Chromatogram d e p i c t i n g changes f r o m b a s e l i n e i n t h e l e v e l s o f DOPAC, HVA, and 5-HIAA b e f o r e , d u r i n g , and a f t e r t h e 3 0 - m i n t e s t o f c o p u l a t i o n . M i c r o d i a l y s i s and s u b s e q u e n t e l e c t r o -c h e m i c a l a n a l y s i s was p e r f o r m e d u s i n g an a u t o m a t e d o n - l i n e sample i n j e c t i o n s y s t e m . D i a l y s a t e s were sampled e v e r y 10 m i n . The q u a n t i f i c a t i o n o f DA, DOPAC, HVA, and 5-HIAA was p e r f o r m e d u s i n g r e v e r s e -phase l i q u i d c h r o m a t o g r a p h y . Mean c o n c e n t r a t i o n s + SE ( f m o l / m i n ) : DA: 5 .90 + 1 . 6 2 ; DOPAC: 709 .73 + 1 9 3 . 5 2 ; HVA: 670 .34 + 9 9 . 8 6 ; 5-HIAA: 447.39 + 3 1 . 0 9 . A U Z U l i u. o o s B 3 u. o u K U l a. STRIATUM DOPAMINE 240 -220 -200 -180 -160 -140 -120 -100 -80 -60 - • 191 IN HOME CAGE SCREEN REMOVED I FEMALE IN FEMALE OUT T 1 1 1 1 — I — T 2 0 40 60 8 0 T 1 1 1 — 100 120 - I 1 1 1 1 1 1 140 160 180 200 METABOLITES 240 -220 -200 -180 -160 -140 -120 -100 -80 -60 • DOPAC • HVA •5-HIAA IN SEX BOX - IN HOME CAGE |SCREEN REMOVED I FEMALE IN FEMALE OUT ~i—r~ 20 T" 40 60 8 0 — 1 1 1 1 1 — 100 120 140 —I 1 1 — 160 180 —I 200 TIME (min) 192 D i s c u s s i o n T h i s e x p e r i m e n t has d e m o n s t r a t e d t h a t l e v e l s o f DA and i t s m e t a b o l i t e s i n c r e a s e i n t h e n u c l e u s accumbens d u r i n g a n t i c i p a t o r y and consummatory a s p e c t s o f male s e x u a l b e h a v i o r and i n t h e s t r i a t u m d u r i n g consummatory a s p e c t s o f male s e x u a l b e h a v i o r . However , t h e p a t t e r n s o f r e l e a s e d i f f e r e d i n t h e s e r e g i o n s . B i o c h e m i c a l a n a l y s e s o f DA i n d i a l y s a t e s f r o m t h e n u c l e u s accumbens r e v e a l e d t h r e e d i s t i n c t p a t t e r n s o f change d u r i n g t h i s e x p e r i m e n t . F i r s t , DA l e v e l s i n c r e a s e d s i g n i f i c a n t l y when r a t s were t r a n s f e r r e d f r o m t h e i r home cages t o t h e t e s t i n g chamber . A l t h o u g h DA l e v e l s r o s e an a d d i t i o n a l 10% i n 4 o f t h e 5 r a t s when t h e f e m a l e was p l a c e d b e h i n d t h e s c r e e n , t h i s i n c r e a s e was n o t s t a t i s t i c a l l y s i g n i f i c a n t . A second s i g n i f i c a n t i n c r e a s e o c c u r r e d d u r i n g c o p u l a t i o n when DA l e v e l s r o s e s t e a d i l y , r e a c h i n g a peak o f 96% above b a s e l i n e d u r i n g t h e t h i r d 10 -m in s a m p l e . F i n a l l y , DA l e v e l s d e c r e a s e d d u r i n g t h e 80 min f o l l o w i n g t h e r e m o v a l o f t h e f e m a l e b u t rema ined e l e v a t e d f r o m b a s e l i n e l e v e l s . I n c o n t r a s t , b i o c h e m i c a l a n a l y s e s o f DA i n d i a l y s a t e s f r o m t h e s t r i a t u m r e v e a l e d a s m a l l b u t s i g n i f i c a n t r i s e i n DA l e v e l s o n l y d u r i n g c o p u l a t i o n . DA l e v e l s i n c r e a s e d g r a d u a l l y d u r i n g c o p u l a t i o n , r e a c h i n g a peak o f 44% d u r i n g t h e t h i r d 1 0 - m i n s a m p l e . U n l i k e t h e n u c l e u s accumbens, s t r i a t a l DA l e v e l s were n o t e l e v a t e d s i g n i f i c a n t l y f r o m b a s e l i n e l e v e l s when t h e males were t r a n s f e r r e d f r o m t h e i r home cage t o t h e t e s t i n g chamber , nor was t h e r e any s i g n i f i c a n t i n c r e a s e when t h e r e c e p t i v e f e m a l e was p l a c e d b e h i n d t h e s c r e e n . M o r e o v e r , s t r i a t a l DA l e v e l s d i d n o t 193 remain elevated from baseline following the removal of the female. These r e s u l t s provide an important confirmation of the previous r e s u l t s using voltammetry. The dramatic increase in DA l e v e l s during copulation i s consistent with the pattern of DA oxidation signals observed in the nucleus accumbens during Experiment IVa. Likewise, the lack of any increase in s t r i a t a l DA release during the presentation of the receptive female, but the small and gradual r i s e i n DA release during copulation, are both consistent with the pattern of DA oxidation signals observed in the striatum during Experiment IVa. This general confirmation of the r e s u l t s of Experiment IVa suggests that the use of stearate-modified graphite paste electrodes provided an accurate account of DA e f f l u x in the nucleus accumbens and striatum during sexual behavior. At f i r s t glance, the lack of a s i g n i f i c a n t increase in DA lev e l s in the nucleus accumbens during the presentation of the female behind the screen appears somewhat inconsistent with the re s u l t s of the voltammetry experiments. However, i t must be remembered that the paradigm used in the microdialysis experiments was d i f f e r e n t . During the micr o d i a l y s i s experiments, the males were given 40 min in the t e s t i n g chamber before the presentation of the female, whereas during the voltammetry experiments the males were placed in the t e s t i n g chamber for at least 2 hr prior to the presentation of the female. This inconsistency was unplanned but fortunate in that i t revealed two 194 p o t e n t i a l l y important increases in DA release: one when the male was placed i n the t e s t i n g chamber and another when the female was introduced. The lack of a further s i g n i f i c a n t r i s e in DA l e v e l s during the placement of the female behind the screen in Experiment IVc may r e f l e c t the fact that these lev e l s were s t i l l elevated following placement of the males in the t e s t i n g chamber. The chamber was not cleaned between tests in t h i s experiment and the odor of previous copulations may have contributed to the elevated DA l e v e l s . In addition, the chamber was a novel environment for the males. However, as shown in Figure 28 (Panel A), a s l i g h t downward trend developed in the l a s t 10-min sample while the males were alone in the t e s t i n g chamber. It i s possible that DA le v e l s would have returned to baseline i f the males had spent more time alone in the t e s t i n g chamber, as the males in the voltammetry experiments did prior to the presentation of a female behind the screen. Thus, i t seems plausable that the r e l a t i v e l y extended time the males spent in the t e s t i n g chamber p r i o r to the presentation of the.female during the voltammetry experiments may have permitted DA l e v e l s to return to baseline values which, in turn, allowed the presentation of the female to elevate DA le v e l s s i g n i f i c a n t l y . This hypothesis requires further examination, as do the e f f e c t s of novel environments and o l f a c t o r y cues from receptive females. The r e s u l t s of Experiment IVc extend the previous findings by demonstrating that DA u t i l i z a t i o n and possibly synthesis are increased in both the nucleus accumbens and striatum during sexual behavior. Although the temporal r e s o l u t i o n of microd i a l y s i s i s not s u f f i c i e n t to d i s t i n g u i s h the dynamic changes in DA e f f l u x following ejaculation or preceding the i n i t i a t i o n of a copulatory s e r i e s , t h i s technique allows several compounds to be analyzed at once. In the nucleus accumbens, l e v e l s of HVA and DOPAC showed d i s t i n c t patterns of change during the t e s t . In general, l e v e l s of HVA were higher than l e v e l s of DOPAC throughout the t e s t , although both were smaller in magnitude than l e v e l s of DA. In addition, the pattern of both metabolites was delayed r e l a t i v e to that of DA. Levels of HVA had increased s i g n i f i c a n t l y from baseline when the female was placed behind the screen and further during the t h i r d 10-min sample of copulation. However, although l e v e l s of HVA decreased aft e r the tes t of copulation, they did not return to baseline. Levels of DOPAC had increased from baseline when the female was placed behind the screen, and increased further during the f i r s t 10-min sample of copulation. Unlike HVA, le v e l s of DOPAC returned to baseline by the end of the t e s t . As in the nucleus accumbens, s t r i a t a l l e v e l s of HVA were generally higher than le v e l s of DOPAC throughout the t e s t . However, l e v e l s of HVA increased s i g n i f i c a n t l y when the males were transferred to the te s t i n g chamber, further when the female was placed behind the screen, and again during the t h i r d 10-min sample of copulation. Following the test of copulation, l e v e l s of HVA decreased s l i g h t l y but did not reach baseline l e v e l s . DOPAC le v e l s increased s i g n i f i c a n t l y from baseline when the female was placed 196 b e h i n d t h e s c r e e n and f u r t h e r d u r i n g t h e f i r s t 1 0 - m i n sample o f c o p u l a t i o n . However , u n l i k e HVA, l e v e l s o f DOPAC d e c r e a s e d back t o b a s e l i n e f o l l o w i n g c o p u l a t i o n . HVA and DOPAC can r e f l e c t t h e p o s t s y n a p t i c u t i l i z a t i o n and p r e s y n a p t i c s y n t h e s i s o f DA, r e s p e c t i v e l y . T h i s i s because c a t e c h o l - o - m e t h y l - t r a n s f e r a s e (COMT; t h e enzyme t h a t c o n v e r t s DA t o 3 - m e t h o x y t y r a m i n e w h i c h i s c o n v e r t e d s u b s e q u e n t l y t o HVA) i s f o u n d i n h i g h e s t c o n c e n t r a t i o n s i n t h e p o s t s y n a p t i c c l e f t whereas monoamine o x i d a s e ( t h e enzyme t h a t c o n v e r t s DA t o 3 , 4 -d i h y d r o x y p h e n y l a c e t a l d e h y d e w h i c h i s c o n v e r t e d s u b s e q u e n t l y t o DOPAC) i s f o u n d i n h i g h e s t c o n c e n t r a t i o n i n m i t o c h o n d r i a w i t h i n p r e s y n a p t i c n e r v e t e r m i n a l s (see e . g . , Cooper , Bloom & R o t h , 1 9 8 6 ) . A l t h o u g h DOPAC i s s u b s e q u e n t l y c o n v e r t e d t o HVA by COMT, l e v e l s o f DOPAC i n e x t r a c e l l u l a r f l u i d may r e f l e c t t h e m e t a b o l i s m o f n o n r e l e a s e d p o o l s o f DA w i t h i n t h e n e r v e t e r m i n a l , and t h u s may s e r v e as a measure o f DA s y n t h e s i s and u t i l i z a t i o n . The i n c r e a s e s i n l e v e l s o f HVA and DOPAC t h r o u g h o u t t h e t e s t p r o v i d e c o m p e l l i n g e v i d e n c e t h a t t h e s e x u a l b e h a v i o r o f male r a t s i s accompanied by i n c r e a s e s i n DA s y n t h e s i s and u t i l i z a t i o n i n b o t h t h e n u c l e u s accumbens and s t r i a t u m . T h i s i s c o n s i s t e n t w i t h p r e v i o u s ex v i v o r e s u l t s t h a t DOPA a c c u m u l a t i o n i n c r e a s e s i n t h e s e s t r u c t u r e s d u r i n g t h e c o p u l a t o r y b e h a v i o r o f male r a t s ( A h l e n i u s e t a l . , 1 9 8 7 ) . Taken t o g e t h e r , t h e r e s u l t s o f E x p e r i m e n t s I V a , I V b , and IVc p r o v i d e t h e f i r s t d i r e c t e v i d e n c e t h a t DA r e l e a s e i n m e s o l i m b i c and m e s o s t r i a t a l t e r m i n a l s , and c a t e c h o l a m i n e r e l e a s e i n 197 diencephalic DA terminals, increases during sexual behavior in the male r a t . However, these systems appear to be activated d i f f e r e n t i a l l y . Increased DA release in the nucleus accumbens and increased catecholamine release in the MPOA were both associated with the presentation of a sexual incentive, and the i n i t i a t i o n of copulation. In contrast, DA release did not increase in the striatum during the presentation of a sexual incentive but increased gradually during copulation. These r e s u l t s give tentative support to the hypotheses generated in Experiments II and III that mesolimbic and diencephalic DA systems play a comparable r o l e in a n t i c i p a t o r y aspects of sexual behavior whereas mesolimbic, mesostriatal, and diencephalic DA systems play a role in d i f f e r e n t aspects of consummatory sexual behavior. 198 GENERAL DISCUSSION The experiments reported in t h i s thesis were undertaken to accomplish two objectives. The f i r s t was to describe the ro l e of brain DA systems in a n t i c i p a t o r y and consummatory aspects of sexual behavior in male r a t s . The second was to r e l a t e t h i s r o l e to the more general one played by brain DA systems in the regulation of incentive motivation. These objectives were accomplished using an integrated approach comprising behavioral, pharmacological, and electrochemical techniques. Accordingly, t h i s f i n a l section begins with a summary of the major fi n d i n g s . It was necessary f i r s t to e s t a b l i s h a standard behavioral framework within which to view the components of male sexual behavior and, with both objectives in mind, to provide a clear conceptual and behavioral d i s t i n c t i o n between an t i c i p a t o r y and consummatory aspects of male sexual behavior. This was accomplished in Experiment I using the b i l e v e l chambers designed by Mendelson and Gorzalka (1987). These chambers allowed a measure of a n t i c i p a t o r y sexual behavior, l e v e l changing (Mendelson & Pfaus, 1989), to be analyzed immediately before the introduction of a sexually receptive female and the s t a r t of a 20-min test of consummatory copulatory behavior. Normative data from a standard t e s t of sexual behavior in the b i l e v e l chambers were gathered from sexually experienced male rats and subjected to multiple c o r r e l a t i o n and factor analyses in Experiment I. The c o r r e l a t i o n a l analyses r e p l i c a t e d the r e s u l t s of a previous study 199 by Sachs ( 1 9 7 8 ) , and c o n f i r m e d t h a t s e v e r a l measures o f c o p u l a t o r y b e h a v i o r were r e l a t e d s t a t i s t i c a l l y . However , l e v e l c h a n g i n g was s t a t i s t i c a l l y i n d e p e n d e n t o f t h e n i n e measures o f c o p u l a t o r y b e h a v i o r a n a l y z e d d u r i n g t h e consummatory phase o f t h e t e s t . F a c t o r a n a l y s i s u s i n g o r t h o g o n a l r o t a t i o n o f t h e axes r e v e a l e d t h e e x i s t e n c e o f f i v e f a c t o r s : C o p u l a t o r y R a t e , I n i t i a t i o n , H i t R a t e , Mount C o u n t , and A n t i c i p a t i o n . These f a c t o r s a c c o u n t e d f o r over 80% o f t h e i n t e r s u b j e c t v a r i a n c e f o r a l l measures and were n e a r l y i d e n t i c a l t o t h o s e f o u n d by Sachs ( 1 9 7 8 ) , w i t h t h e a d d i t i o n o f an A n t i c i p a t i o n f a c t o r a s s o c i a t e d w i t h l e v e l c h a n g i n g . T o g e t h e r , t h e s e r e s u l t s i n d i c a t e d t h a t a t l e a s t f i v e c o n c e p t u a l mechanisms were r e q u i r e d i n any t h e o r e t i c a l a n a l y s i s o f male s e x u a l b e h a v i o r i n t h e b i l e v e l chambers , and e s t a b l i s h e d t h a t l e v e l c h a n g i n g , as a measure o f a n t i c i p a t o r y s e x u a l b e h a v i o r , was s t a t i s t i c a l l y i n d e p e n d e n t o f consummatory measures o f s e x u a l b e h a v i o r . The s t a t i s t i c a l s e p a r a t i o n o f a n t i c i p a t o r y and consummatory measures o f s e x u a l b e h a v i o r f u r t h e r s u p p o r t e d t h e g e n e r a l d i s t i n c t i o n be tween t h e s e c l a s s e s o f b e h a v i o r , and p r o v i d e d an i m p o r t a n t r a t i o n a l e t o use l e v e l c h a n g i n g i n c o n j u n c t i o n w i t h t r a d i t i o n a l measures o f consummatory s e x u a l b e h a v i o r t o assess t r e a t m e n t s t h a t a f f e c t DA t r a n s m i s s i o n . E x p e r i m e n t I I r e v e a l e d s e v e r a l s t r i k i n g e f f e c t s o f DA r e c e p t o r a n t a g o n i s t s on a n t i c i p a t o r y and consummatory measures o f s e x u a l b e h a v i o r . S y s t e m i c a d m i n i s t r a t i o n o f t h e t y p i c a l n e u r o l e p t i c s h a l o p e r i d o l and p i m o z i d e , and t h e D l - s e l e c t i v e a n t a g o n i s t SCH 23390, d o s e - d e p e n d e n t l y d e c r e a s e d t h e number o f 200 l e v e l c h a n g e s , i n c r e a s e d t h e i n t r o m i s s i o n l a t e n c i e s , and d e c r e a s e d t h e number o f i n t r o m i s s i o n s and t h e t o t a l number o f e j a c u l a t i o n s . The a t y p i c a l n e u r o l e p t i c c l o z a p i n e and t h e D2-s e l e c t i v e a n t a g o n i s t s u l p i r i d e r e d u c e d t h e number o f l e v e l changes and i n c r e a s e d t h e i n t r o m i s s i o n l a t e n c i e s , b u t d i d n o t a f f e c t t h e number o f i n t r o m i s s i o n s or e j a c u l a t i o n s . I n a l m o s t e v e r y c a s e , t h e doses r e q u i r e d t o d e c r e a s e l e v e l c h a n g i n g s i g n i f i c a n t l y were l o w e r t h a n t h o s e r e q u i r e d t o s i g n i f i c a n t l y i n c r e a s e t h e i n t r o m i s s i o n l a t e n c i e s or d e c r e a s e t h e number o f i n t r o m i s s i o n s or e j a c u l a t i o n s , i n d i c a t i n g t h a t t h e measure o f a n t i c i p a t o r y s e x u a l b e h a v i o r was more s e n s i t i v e t o t h e d i s r u p t i v e e f f e c t s o f DA a n t a g o n i s t s t h a n were consummatory measures o f s e x u a l b e h a v i o r . The a n t i e m e t i c a g e n t m e t o c l o p r a m i d e r e d u c e d t h e number o f i n t r o m i s s i o n s b u t d i d n o t a f f e c t o t h e r consummatory or a n t i c i p a t o r y measures o f s e x u a l b e h a v i o r . H i g h e r doses o f h a l o p e r i d o l , p i m o z i d e , o r c l o z a p i n e d e l a y e d or a b o l i s h e d l e v e l c h a n g i n g and t h e i n i t i a t i o n o f c o p u l a t o r y b e h a v i o r . These r e s u l t s r e p l i c a t e d p r e v i o u s f i n d i n g s t h a t DA r e c e p t o r a n t a g o n i s t s d i f f e r e n t i a l l y d i s r u p t measures o f c o p u l a t o r y b e h a v i o r i n s e x u a l l y a c t i v e male r a t s ( P f a u s & P h i l l i p s , 1 9 8 9 ) , and d e m o n s t r a t e d t h a t l e v e l c h a n g i n g was more s e n s i t i v e t o such d i s r u p t i o n t h a n were consummatory measures t h a t r e f l e c t e d t h e i n i t i a t i o n or r a t e o f c o p u l a t i o n . I n a d d i t i o n , c o n s i s t e n t w i t h r e p o r t s o f s y n e r g i s t i c a c t i o n s o f D I - and D 2 - s e l e c t i v e compounds, t h e s e r e s u l t s i n d i c a t e d t h a t i t he r e l a t i v e l y s e l e c t i v e a n t a g o n i s m o f D l o r D2 r e c e p t o r s had s i m i l a r e f f e c t s on a n t i c i p a t o r y and 201 consummatory measures o f male s e x u a l b e h a v i o r . E x p e r i m e n t I I I p r o v i d e d t h e f i r s t e v i d e n c e t h a t h a l o p e r i d o l a f f e c t s a n t i c i p a t o r y and consummatory measures o f male s e x u a l b e h a v i o r s e l e c t i v e l y i n d i f f e r e n t DA t e r m i n a l r e g i o n s . Th ree f o r e b r a i n DA t e r m i n a l s , t h e n u c l e u s accumbens, s t r i a t u m , and MPOA, were chosen f o r s t u d y on t h e b a s i s o f p r e v i o u s e v i d e n c e t h a t t h e s e r e g i o n s a r e i n v o l v e d i n t h e c o n t r o l o f consummatory a s p e c t s o f male s e x u a l b e h a v i o r . B i l a t e r a l i n f u s i o n s o f h a l o p e r i d o l t o t h e n u c l e u s accumbens, a ma jo r t e r m i n a l o f t h e m e s o l i m b i c A10 DA p a t h w a y , a t t e n u a t e d l e v e l c h a n g i n g w i t h o u t a f f e c t i n g t h e i n i t i a t i o n o f c o p u l a t i o n or o t h e r consummatory measu res . B i l a t e r a l i n f u s i o n s o f h a l o p e r i d o l t o t h e s t r i a t u m , a ma jo r t e r m i n a l o f t h e m e s o s t r i a t a l A9 DA p a t h w a y , i n c r e a s e d t h e t o t a l number o f e j a c u l a t i o n s b u t d i d n o t a f f e c t o t h e r measures o f a n t i c i p a t o r y or consummatory s e x u a l b e h a v i o r . U n i l a t e r a l i n f u s i o n s o f h a l o p e r i d o l t o t h e MPOA, a ma jo r t e r m i n a l o f t h e i n c e r t o h y p o t h a l a m i c A14 DA p a t h w a y , p r o d u c e d n e a r l y a l l o f t h e e f f e c t s o f s y s t e m i c a d m i n i s t r a t i o n , i n c l u d i n g a d e c r e a s e d number o f l e v e l c h a n g e s , i n c r e a s e d i n t r o m i s s i o n l a t e n c i e s , and a d e c r e a s e d number o f i n t r o m i s s i o n s and e j a c u l a t i o n s . These r e s u l t s s u g g e s t e d t h a t DA i n t h e n u c l e u s accumbens and s t r i a t u m a r e i n v o l v e d i n t h e d i s p l a y o f a n t i c i p a t o r y s e x u a l b e h a v i o r and c o p u l a t o r y r a t e , r e s p e c t i v e l y , whereas DA i n t h e MPOA i s i n v o l v e d i n t h e d i s p l a y o f a n t i c i p a t o r y s e x u a l b e h a v i o r , t h e i n i t i a t i o n o f c o p u l a t i o n , c o p u l a t o r y r a t e , and h i t r a t e . F i n a l l y , two i n v i v o e l e c t r o c h e m i c a l t e c h n i q u e s , v o l t a m m e t r y 202 and m i c r o d i a l y s i s , were used in Experiment IV to examine DA ef f l u x in the nucleus accumbens and striatum, and catecholamine e f f l u x in the MPOA, during a n t i c i p a t o r y and consummatory phases of sexual behavior in sexually active male r a t s . A u n i l e v e l t e s t i n g chamber was used in these experiments because the pa r t i c u l a r construction of the b i l e v e l chambers precluded the free movement of rats with voltammetry or micro d i a l y s i s assemblies protruding from t h e i r heads. However, a new protocol was used in these experiments that comprised an an t i c i p a t o r y phase, in which the males were placed into the chamber and given access to a sexually receptive female behind a screen for 5 min, and a consummatory phase, in which removal of the screen allowed the animals to engage in copulatory behavior. In the f i r s t of these experiments, chronoamperometry revealed that DA e f f l u x in the nucleus accumbens and striatum, and catecholamine e f f l u x in the MPOA, increased d i f f e r e n t i a l l y during the two phases of sexual behavior. In the nucleus accumbens, DA oxidation signals increased when the receptive female was placed behind the screen, and increased further in most rats p r i o r to the i n i t i a t i o n of copulation. These increased signals were maintained throughout the f i r s t copulatory s e r i e s . E j a c u l a t i o n was accompanied by an immediate decrease in DA oxidation s i g n a l s ; however, these signals remained elevated from baseline l e v e l s . Each r e i n i t i a t i o n of copulation was preceded by an increase in the DA oxidation s i g n a l s . In contrast, the DA oxidation signals i n the striatum were not affected s i g n i f i c a n t l y by the placement of a receptive female behind the screen. However, those signals increased gradually throughout the consummatory phase but did not correspond to any p a r t i c u l a r aspect of copulatory behavior. Catecholamine oxidation signals in the MPOA revealed a smaller, but nearly i d e n t i c a l pattern to that observed for DA oxidation signals in the nucleus accumbens. These r e s u l t s indicated that increased DA e f f l u x in the nucleus accumbens and catecholamine e f f l u x in the MPOA were associated with the presentation of a natural sexual incentive and with the i n i t i a t i o n of copulation, whereas DA e f f l u x in the striatum increased n o n s p e c i f i c a l l y during copulation. The second experiment of t h i s s e r i e s examined the s p e c i f i c i t y of the e l i c i t i n g stimulus by analyzing oxidation signals in the nucleus accumbens, striatum, and MPOA during the presentation of either a male, a nonreceptive female, a s l i d e smeared with estrous vaginal secretions, or a receptive female behind the screen. Oxidation signals increased s l i g h t l y but s i g n i f i c a n t l y i n the nucleus accumbens during the presentation of the male, the nonreceptive female, or the s l i d e , but increased dramatically during the presentation of the receptive female. Oxidation signals in the MPOA increased s i g n i f i c a n t l y during the presentation of both the s l i d e and receptive female, but not during the presentation of the male or nonreceptive female. None of the st i m u l i increased oxidation signals s i g n i f i c a n t l y in the striatum. These r e s u l t s suggested that the increases in oxidation signals observed in the nucleus accumbens and MPOA 204 d u r i n g t h e p r e s e n t a t i o n o f a r e c e p t i v e f e m a l e i n t h e p r e v i o u s e x p e r i m e n t may have been s p e c i f i c t o t h e p r e s e n t a t i o n o f a s e x u a l i n c e n t i v e . However , t h e r e l a t i v e l y s m a l l e r b u t s i g n i f i c a n t i n c r e a s e s i n DA o x i d a t i o n s i g n a l s i n t h e n u c l e u s accumbens d u r i n g t h e p r e s e n t a t i o n o f t h e male and n o n r e c e p t i v e f e m a l e l e n d s u p p o r t t o t h e i d e a t h a t DA i n t h i s s t r u c t u r e p l a y s a g e n e r a l r o l e i n t h e p r o c e s s i n g o f i n c e n t i v e c u e s . I n t h e f i n a l e x p e r i m e n t o f t h i s s e r i e s , m i c r o d i a l y s i s was used t o examine l e v e l s o f DA and i t s m e t a b o l i t e s i n t h e n u c l e u s accumbens and s t r i a t u m a t 1 0 - m i n i n t e r v a l s d u r i n g a n t i c i p a t o r y and consummatory phases o f s e x u a l b e h a v i o r . B i o c h e m i c a l a n a l y s i s o f DA and m e t a b o l i t e l e v e l s i n d i a l y s a t e s f r o m t h e n u c l e u s accumbens r e v e a l e d a s i g n i f i c a n t i n c r e a s e i n DA r e l e a s e when males were p l a c e d i n t o a chamber c o n t a i n i n g c o p u l a t o r y o d o r s , a t r e n d t o w a r d a f u r t h e r s i g n i f i c a n t i n c r e a s e d u r i n g t h e p r e s e n t a t i o n o f t h e r e c e p t i v e f e m a l e b e h i n d t h e s c r e e n , and a f u r t h e r s i g n i f i c a n t i n c r e a s e i n DA r e l e a s e , s y n t h e s i s , and u t i l i z a t i o n d u r i n g c o p u l a t i o n . A l t h o u g h DA l e v e l s d e c r e a s e d i n t h e 80 min f o l l o w i n g c o p u l a t i o n , t h e y d i d n o t d e c r e a s e back t o b a s e l i n e l e v e l s . I n c o n t r a s t , b i o c h e m i c a l a n a l y s i s o f DA and m e t a b o l i t e l e v e l s i n d i a l y s a t e s f r o m t h e s t r i a t u m r e v e a l e d a s m a l l e r g r a d u a l i n c r e a s e i n DA r e l e a s e , s y n t h e s i s , and u t i l i z a t i o n d u r i n g c o p u l a t i o n , b u t no s i g n i f i c a n t i n c r e a s e i n DA r e l e a s e or m e t a b o l i s m d u r i n g t h e p l a c e m e n t o f t h e t h e male i n t h e chamber or d u r i n g t h e p l a c e m e n t o f t h e fema le b e h i n d t h e s c r e e n . DA l e v e l s d e c r e a s e d back t o b a s e l i n e i n t h e 80 min f o l l o w i n g 205 c o p u l a t i o n . These r e s u l t s p r o v i d e d a g e n e r a l c o n f i r m a t i o n o f t h e i n c r e a s e s i n DA e f f l u x i n t h e n u c l e u s accumbens and s t r i a t u m o b s e r v e d w i t h v o l t a m m e t r y i n t h e f i r s t e x p e r i m e n t and e x t e n d e d t h o s e r e s u l t s by d e m o n s t r a t i n g t h a t i n c r e a s e s i n DA u t i l i z a t i o n and p o s s i b l y s y n t h e s i s accompany t h e i n c r e a s e s i n DA r e l e a s e d u r i n g s e x u a l b e h a v i o r . These f i n d i n g s have i m p o r t a n t i m p l i c a t i o n s f o r models t h a t c o n s i d e r t h e r o l e o f b r a i n DA sys tems i n t h e c o n t r o l o f male s e x u a l b e h a v i o r and i n t h e more g e n e r a l r e g u l a t i o n o f i n c e n t i v e m o t i v a t i o n . These i m p l i c a t i o n s a r e d i s c u s s e d b e l o w . The Ro le o f B r a i n DA Systems i n Male S e x u a l B e h a v i o r I t i s c l e a r f r o m t h e p r e s e n t r e s u l t s t h a t b r a i n DA sys tems p l a y a complex r o l e i n t h e s e x u a l b e h a v i o r o f male r a t s t h a t appears t o depend as much on t h e p a r t i c u l a r measure o f s e x u a l b e h a v i o r b e i n g a n a l y z e d as on t h e p a r t i c u l a r DA s y s t e m under i n v e s t i g a t i o n . However, c e r t a i n a s p e c t s o f s e x u a l b e h a v i o r a r e more s e n s i t i v e t o t h e g e n e r a l d i s r u p t i o n o f b r a i n DA sys tems t h a n o t h e r s . A n t i c i p a t o r y Sexua l B e h a v i o r One o f t h e most i m p o r t a n t f i n d i n g s i n E x p e r i m e n t I I was t h e p ronounced s e n s i t i v i t y o f t h e a n t i c i p a t o r y measure , l e v e l c h a n g i n g , t o d i s r u p t i o n by t y p i c a l and a t y p i c a l DA a n t a g o n i s t s . H a l o p e r i d o l , p i m o z i d e , c l o z a p i n e , SCH 23390, and s u l p i r i d e s i g n i f i c a n t l y d e c r e a s e d r a t e s o f l e v e l c h a n g i n g a t doses t h a t d i d n o t s i g n i f i c a n t l y i n c r e a s e t h e l a t e n c y t o i n i t i a t e l e v e l c h a n g i n g 206 and t h a t , w i t h few e x c e p t i o n s , d i d n o t a f f e c t consummatory measures o f s e x u a l b e h a v i o r s i g n i f i c a n t l y . C e n t r a l i n f u s i o n s o f h a l . o p e r i d o l t o t h e n u c l e u s accumbens and MPOA i n E x p e r i m e n t I I I a l s o d e c r e a s e d r a t e s o f l e v e l c h a n g i n g whereas i n f u s i o n s t o t h e s t r i a t u m d i d n o t . As w i t h f e e d i n g ( e . g . , B l a c k b u r n e t a l . , 1987 ; B l u n d e l l e t a l . , 1977 ; F i b i g e r e t a l . , 1974 ; K e l l e y & S t i n u s , 1 9 8 5 ) , t h e s e r e s u l t s s u g g e s t t h a t c e n t r a l DA sys tems p l a y a p r e f e r e n t i a l r o l e i n a n t i c i p a t o r y o r p r e p a r a t o r y a s p e c t s o f s e x u a l b e h a v i o r , and i n d i c a t e t h a t a t l e a s t two f o r e b r a i n DA t e r m i n a l s , t h e n u c l e u s accumbens and MPOA, f o r m p a r t o f t h e n e u r a l c i r c u i t r y o f l e v e l c h a n g i n g . A l t h o u g h t h e r e s u l t s o f E x p e r i m e n t s I I and I I I p r o v i d e d e v i d e n c e o f a n e c e s s a r y r o l e o f DA sys tems i n t h e n u c l e u s accumbens and MPOA i n t h e c o n t r o l o f a n t i c i p a t o r y s e x u a l b e h a v i o r , t h e y d i d n o t s p e c i f y how t h o s e sys tems o p e r a t e . However , i n l i g h t o f e v i d e n c e t h a t DA a g o n i s t s can s t i m u l a t e c o p u l a t o r y b e h a v i o r i n s e x u a l l y s l u g g i s h males ( D a l l o e t a l . , 1986 ; Hansen e t a l . , 1982; Malmnas, 1973; T a g l i a m o n t e e t a l . , 1 9 7 4 ) , t h e most o b v i o u s i n f e r e n c e was t h a t DA a c t i v i t y i n c r e a s e s i n t h o s e r e g i o n s when a male r a t a n t i c i p a t e s t h e o p p o r t u n i t y t o c o p u l a t e . T h i s i n f e r e n c e was c o n f i r m e d i n E x p e r i m e n t I V u s i n g two i n v i v o t e c h n i q u e s , v o l t a m m e t r y and m i c r o d i a l y s i s . V o l t a m m e t r y r e v e a l e d t h a t DA and c a t e c h o l a m i n e e f f l u x i n t h e n u c l e u s accumbens and MPOA, r e s p e c t i v e l y , i n c r e a s e s d r a m a t i c a l l y i n male r a t s when a s e x u a l l y r e c e p t i v e f e m a l e was p l a c e d b e h i n d a s c r e e n and d u r i n g t h e i n i t i a t i o n o f c o p u l a t i o n . S i m i l a r l y , 207 m i c r o d i a l y s i s confirmed a s i g n i f i c a n t increase in DA release in the nucleus accumbens when the male was transferred to a chamber containing copulatory odors and a trend toward a s i g n i f i c a n t increase during the presentation of a receptive female. The increase in DA l e v e l s in the nucleus accumbens that accompanied the placement of the males i n the t e s t i n g chamber i s i n t e r e s t i n g in l i g h t of the finding that haloperidol decreased rates of l e v e l changing following infusion to the nucleus accumbens in Experiment I I I . In both cases, males were placed in a t e s t i n g chamber that contained odors from previous tests of copulation. To the extent that these conditions are comparable, i t would seem l i k e l y that a dynamic increase in DA release potentiates l e v e l changing and perhaps other forms of a n t i c i p a t o r y sexual behavior. Consistent with the r e s u l t s of Experiment I I I , there was no increase in DA e f f l u x in the striatum during the presentation of the receptive female, thus i t would seem that mesostriatal DA systems are not involved in the control of a n t i c i p a t o r y sexual behavior. I n t e r e s t i n g l y , oxidation currents in the nucleus accumbens and MPOA displayed a d i f f e r e n t pattern of increase during the placement of either a male, a nonreceptive female, a s l i d e smeared with estrous vaginal secretions, or a receptive female behind the screen. A l l of these s t i m u l i increased the oxidation signals s i g n i f i c a n t l y in the nucleus accumbens, although placement of the receptive female induced a s i g n i f i c a n t l y greater increase in the oxidation s i g n a l s . In contrast, only the placement of s l i d e or the eceptive female 208 increased the oxidation signals s i g n i f i c a n t l y in the MPOA. Moreover, the magnitude of the oxidation signals during the placement of the receptive female was not s i g n i f i c a n t l y d i f f e r e n t from those observed during the during the placement of the s l i d e . Although these data indicate that the increase in oxidation signals observed i n both of these regions i s r e l a t i v e l y s p e c i f i c to the presentation of a sexual incentive, they suggest that the nucleus accumbens and MPOA process cues from a receptive female d i f f e r e n t l y . Differences between mesolimbic and diencephalic nuclei in the control of an t i c i p a t o r y aspects of male sexual behavior are not new. E v e r i t t et a l . (1987) reported that ibotenic acid lesions of the MPOA had no e f f e c t on rates of bar pressing by male rats for a secondary sexual incentive (a stimulus l i g h t associated with the presentation of a sexually receptive female). In contrast, E v e r i t t et a l . (1989) showed that b i l a t e r a l N-methyl-D-aspartate lesions of the basolateral amygdala, a structure that contains DA receptors and that l i e s close to a major mesolimbic DA terminal, the corticomedial amygdala, dramatically reduced rates of bar pressing for the secondary sexual incentive. I n t e r e s t i n g l y , the basolateral amygdala sends afferent projections to the nucleus accumbens and infusions of d-amphetamine to the nucleus accumbens of rats with those lesions restored rates of bar pressing. Assuming that lesions of the MPOA in the e a r l i e r study by E v e r i t t et a l . (1987) reduced DA input from the zona incerta, a 209 treatment that should have been s i m i l a r to infusions of a DA antagonist, i t must be concluded that the MPOA, and i t s DA innervation, does not contribute to the neural c i r c u i t r y involved in bar pressing for a secondary sexual incentive. Although at f i r s t glance, those r e s u l t s appear inconsistent with the effectiveness of haloperidol infusions to the MPOA in reducing rates of l e v e l changing, there are important differences between the types of s t i m u l i responded to by rats in the two paradigms. The chambers used in the present experiments were not cleaned between te s t s of sexual behavior, thus i t i s conceivable that the odor of previous copulations may contribute to the displ a y of l e v e l changing. Those odors may provide unconditioned o l f a c t o r y cues and may have d i r e c t and r e l a t i v e l y s e l e c t i v e access to hormone s e n s i t i v e MPOA neurons. The MPOA receives a large efferent projection from the corticomedial amygdala v i a the s t r i a terminalis (Krettek & Pr i c e , 1978). The corticomedial amygdala, in turn, receives efferent projections from both the vomeronasal organ and the o l f a c t o r y bulbs (Lehman & Winans, 1982). It i s int e r e s t i n g to note that o l f a c t o r y s t i m u l i from a female rat w i l l evoke e l e c t r i c a l a c t i v i t y in the MPOA. of i n t a c t , but not castrated male rats (Pfaff & Pfaffmann, 1969). In contrast, i t is u n l i k e l y that odor cues contribute to the rates of bar-pressing assessed by E v e r i t t et a l . , as such cues were not present in the chamber. Although l i t t l e i s known about the function of the incertohypothalamic DA neurons that project to the MPOA, the c e l l bodies within the zona incerta that give r i s e 210 t o t h i s p r o j e c t i o n r e c e i v e d i f f u s e i n n e r v a t i o n f r o m o t h e r i n t r i n s i c h y p o t h a l a m i c n e u r o n s (Moore , 1 9 8 7 ) . G iven t h e r e s u l t s o f E x p e r i m e n t I I I , i t wou ld be s u r p r i s i n g i f t h e s e neurons d i d n o t c o n t r i b u t e t o t h e p r o c e s s i n g o f s e n s o r y i n f o r m a t i o n by t h e MPOA. Taken t o g e t h e r , t h e r e s u l t s o f E v e r i t t e t a l . ( 1 9 8 7 ; 1989) and t h o s e o f t h e p r e s e n t e x p e r i m e n t s s u g g e s t t h a t DA i n t h e MPOA may be i n v o l v e d i n t h e e x p r e s s i o n o f o l f a c t o r y - d e p e n d e n t fo rms o f a n t i c i p a t o r y s e x u a l b e h a v i o r whereas DA i n t h e n u c l e u s accumbens may by i n v o l v e d i n t h e e x p r e s s i o n o f b o t h o l f a c t o r y - d e p e n d e n t and i n t e p e n d e n t fo rms o f a n t i c i p a t o r y s e x u a l b e h a v i o r . Consummatory S e x u a l B e h a v i o r A l t h o u g h l e v e l c h a n g i n g was g e n e r a l l y more s e n s i t i v e t h a n consummatory measures o f c o p u l a t i o n t o d i s r u p t i o n by s m a l l doses o f DA a n t a g o n i s t s , s e v e r a l consummatory measures were a f f e c t e d by modera te doses o f t h e s e d r u g s t h a t d i d n o t a f f e c t o t h e r a s p e c t s o f c o p u l a t o r y b e h a v i o r or e l i m i n a t e i t a l t o g e t h e r . The i n i t i a t i o n o f c o p u l a t i o n ( e . g . , t h e i n t r o m i s s i o n l a t e n c y ) , c o p u l a t o r y r a t e ( e . g . , t h e number o f e j a c u l a t i o n s ) , and mount c o u n t ( e . g . , t h e number o f i n t r o m i s s i o n s ) were a f f e c t e d by t r e a t m e n t w i t h DA a n t a g o n i s t s . H a l o p e r i d o l , p i m o z i d e , and t h e D l - s e l e c t i v e a n t a g o n i s t SCH 23390 i n c r e a s e d t h e i n t r o m i s s i o n l a t e n c i e s and d e c r e a s e d t h e number o f i n t r o m i s s i o n s and e j a c u l a t i o n s . C l o z a p i n e and t h e D 2 - s e l e c t i v e a n t a g o n i s t s u l p i r i d e b o t h i n c r e a s e d t h e i n t r o m i s s i o n l a t e n c i e s b u t d i d n o t a f f e c t measures o f c o p u l a t o r y r a t e o r mount c o u n t . I n c o n t r a s t , m e t o c l o p r a m i d e d e c r e a s e d t h e number o f i n t r o m i s s i o n s b u t d i d n o t 211 a f f e c t t h e i n i t i a t i o n o f c o p u l a t i o n or c o p u l a t o r y r a t e . H i g h e r doses o f h a l o p e r i d o l , p i m o z i d e , and c l o z a p i n e s i g n f i c a n t l y d e c r e a s e d t h e p r o p o r t i o n o f r a t s t h a t i n i t i a t e d c o p u l a t i o n . C e n t r a l i n f u s i o n s o f h a l o p e r i d o l t o t h e n u c l e u s accumbens d i d n o t a f f e c t consummatory measures o f s e x u a l b e h a v i o r . I n f u s i o n s o f t h a l o p e r i d o l t o t h e MPOA p r o d u c e d n e a r l y a l l t h e e f f e c t s o f s y s t e m i c a d m i n i s t r a t i o n , i n c l u d i n g i n c r e a s e d i n t r o m i s s i o n l a t e n c i e s and a d e c r e a s e d number o f i n t r o m i s s i o n s and e j a c u l a t i o n s . S u r p r i s i n g l y , i n f u s i o n s o f h a l o p e r i d o l t o t h e s t r i a t u m i n c r e a s e d , r a t h e r t h a n d e c r e a s e d , t h e number o f e j a c u l a t i o n s . U n l i k e d a t a f r o m t h e f e e d i n g l i t e r a t u r e , t h e s e r e s u l t s i n d i c a t e t h a t c e n t r a l DA sys tems p l a y an i m p o r t a n t r o l e i n c e r t a i n e l e m e n t s o f consummatory s e x u a l b e h a v i o r i n t h e male r a t , i n c l u d i n g t h e i n i t i a t i o n o f i n t r o m i s s i o n s , t h e number o f i n t r o m i s s i o n s , and t h e number o f e j a c u l a t i o n s . As n o t e d p r e v i o u s l y , i t i s d i f f i c u l t t o r e c o n c i l e t h e s e r e s u l t s w i t h a s i m p l e e f f e c t o f DA a n t a g o n i s t s on consummatory s e x u a l m o t i v a t i o n . I n d e e d , some o f t h e e f f e c t s a r e p a r a d o x i c a l . For examp le , an i n c r e a s e i n t h e i n t r o m i s s i o n l a t e n c y o r a d e c r e a s e i n t h e number o f e j a c u l a t i o n s can be i n t e r p r e t e d as a d i s r u p t i o n o f consummatory s e x u a l m o t i v a t i o n whereas a d e c r e a s e i n t h e number o f i n t r o m i s s i o n s can be i n t e r p r e t e d as a f a c i l i t a t i o n ( e . g . , Sachs & B a r f i e l d , 1 9 7 6 ) . However, a c r i t i c a l s e r i e s o f e x p e r i m e n t s by Pehek e t a l . (1988a) d e m o n s t r a t e d t h a t h a l o p e r i d o l d e l a y s s e m i n a l e m i s s i o n and d e c r e a s e s t h e number o f p e n i l e e r e c t i o n s d i s p l a y e d by i n t a c t , s e x u a l l y a c t i v e male r a t s . 212 These f i n d i n g s o f f e r a p a r s i m o n i o u s e x p l a n a t i o n t o n e a r l y a l l o f t h e e f f e c t s o f h a l o p e r i d o l on consummatory s e x u a l b e h a v i o r . The d e c r e a s e d a b i l i t y o f a r a t t o g a i n or m a i n t a i n e r e c t i o n f o l l o w i n g t r e a t m e n t w i t h h a l o p e r i d o l s h o u l d i n c r e a s e t h e i n t r o m i s s i o n l a t e n c i e s and d e c r e a s e t h e number o f i n t r o m i s s i o n s ; t h e d e l a y e d s e m i n a l e m i s s i o n s h o u l d l e a d t o fewer e j a c u l a t i o n s d u r i n g a s t a n d a r d t e s t o f c o p u l a t o r y b e h a v i o r . I n c i r c u m s t a n c e s where p e n i l e r e f l e x e s a r e d i s r u p t e d by d r u g t r e a t m e n t s i t may be more a p p r o p r i a t e t o use mount l a t e n c i e s w i t h or w i t h o u t i n t r o m i s s i o n , i n a d d i t i o n t o t h e i n t r o m i s s i o n l a t e n c i e s , as an i n d e x o f t h e m o t i v a t i o n t o i n i t i a t e c o p u l a t i o n . I n t e r e s t i n g l y , h a l o p e r i d o l , c l o z a p i n e , SCH 23390, and s u l p i r i d e a l l i n c r e a s e d t h e mount l a t e n c i e s i n E x p e r i m e n t I I . I n f u s i o n s o f h a l o p e r i d o l t o t h e MPOA a l s o i n c r e a s e d t h e mount l a t e n c i e s i n E x p e r i m e n t I I I . Thus , i t may be c o n c l u d e d t h a t b r a i n DA sys tems p l a y a r o l e i n t h e i n i t i a t i o n o f c o p u l a t i o n and i n t h e c o n t r o l o f p e n i l e r e f l e x e s . As w i t h a n t i c i p a t o r y s e x u a l b e h a v i o r , s e v e r a l i n f e r e n c e s abou t DA f u n c t i o n i n t h e n u c l e u s accumbens, s t r i a t u m , and MPOA c o u l d be made based on t h e r e s u l t s o f E x p e r i m e n t I I I . Because h a l o p e r i d o l i n f u s i o n s t o t h e MPOA had n e a r l y t h e same e f f e c t as s y s t e m i c a d m i n i s t r a t i o n s , i t c o u l d be i n f e r r e d t h a t i n c r e a s e d DA a c t i v i t y i n t h e MPOA f a c i l i t a t e s t h e i n i t i a t i o n o f c o p u l a t i o n and p e n i l e e r e c t i o n . Such a r o l e f o r d i e n c e p h a l i c DA sys tems has been s u g g e s t e d p r e v i o u s l y on t h e b a s i s o f , e v i d e n c e t h a t i n f u s i o n s o f apomorph ine t o e i t h e r t h e MPOA or p a r a v e n t r i c u l a r n u c l e u s 213 f a c i l i t a t e b o t h t h e i n i t i a t i o n o f c o p u l a t i o n and p e n i l e e r e c t i o n s (Pehek e t a l . , 1 9 8 8 b ) . C o n s i s t e n t w i t h t h i s s u g g e s t i o n , an i n c r e a s e i n c a t e c h o l a m i n e e f f l u x was o b s e r v e d i n t h e MPOA p r i o r t o t h e i n i t i a t i o n o f c o p u l a t i o n i n E x p e r i m e n t I V . E j a c u l a t i o n was a s s o c i a t e d w i t h an immed ia te d e c r e a s e i n t h e o x i d a t i o n s i g n a l s i n t h e MPOA, s u g g e s t i n g t h a t p a r t o f t h e s e x u a l q u i e s c e n c e o f male r a t s f o l l o w i n g e j a c u l a t i o n may, i n p a r t , be due t o an i n h i b i t i o n o f c a t e c h o l a m i n e e f f l u x i n t h e MPOA. Each r e i n i t i a t i o n o f c o p u l a t i o n a f t e r t h e p o s t e j a c u l a t o r y i n t e r v a l was p r e c e d e d by an i n c r e a s e i n t h e o x i d a t i o n s i g n a l s . However , t h e r e i s e v i d e n c e t h a t male r a t s w i t h e l e c t r o l y t i c l e s i o n s o f t h e MPOA c o n t i n u e t o d i s p l a y an i n t e r e s t i n s e x u a l l y r e c e p t i v e f e m a l e s d e s p i t e t h e f a c t t h a t t h e y do n o t c o p u l a t e . Such males w i l l o f t e n i n v e s t i g a t e t h e a n o g e n i t a l r e g i o n s o f t h e f e m a l e s and o c c a s i o n a l l y d i s p l a y mounts w i t h p e l v i c t h r u s t i n g b u t w i t h o u t i n t r o m i s s i o n ( B r a c k e t t & Edwards , 1984; Hansen, 1982; Heimer & L a r s s o n , 1 9 6 6 ) . Taken t o g e t h e r , t h e s e r e s u l t s s u g g e s t t h a t DA r e l e a s e i n t h e MPOA s e r v e s t o f a c i l i t a t e p e n i l e e r e c t i o n and m o u n t i n g . The l a c k o f c o p u l a t i o n i n r a t s w i t h l e s i o n s o f t h e MPOA may t h u s r e f l e c t a f a i l u r e t o g a i n p e n i l e e r e c t i o n . The l a c k o f e f f e c t o f h a l o p e r i d o l i n t h e n u c l e u s accumbens on c o p u l a t i o n i n E x p e r i m e n t I I I s u g g e s t e d t h a t DA a c t i v i t y i n t h i s s t r u c t u r e was n o t r e q u i r e d f o r consummatory measures o f s e x u a l b e h a v i o r . T h i s was c o n s i s t e n t w i t h p r e v i o u s r e p o r t s t h a t t h e DA a g o n i s t apomorph ine f a i l e d t o a f f e c t c o p u l a t o r y b e h a v i o r f o l l o w i n g i n f u s i o n s t o t h e n u c l e u s accumbens ( H u l l e t a l . , 1 9 8 6 ) . 214 However, E v e r i t t e t a l . (1989) r e p o r t e d t h a t i n f u s i o n s o f d -amphetamine t o t h e n u c l e u s accumbens d e c r e a s e d t h e mount and i n t r o m i s s i o n l a t e n c i e s o f s e x u a l l y a c t i v e L i s t e r r a t s , s u g g e s t i n g t h a t i n c r e a s e d DA a c t i v i t y i n t h e n u c l e u s accumbens c o u l d f a c i l i t a t e t h e i n i t i a t i o n o f c o p u l a t i o n . I n E x p e r i m e n t I V , b o t h v o l t a m m e t r y and m i c r o d i a l y s i s r e v e a l e d a dynamic p a t t e r n o f DA e f f l u x i n t h e n u c l e u s accumbens d u r i n g c o p u l a t i o n t h a t was i d e n t i c a l t o c a t e c h o l a m i n e e f f l u x i n t h e MPOA b u t l a r g e r i n m a g n i t u d e . DA e f f l u x i n c r e a s e d p r i o r t o t h e i n i t i a t i o n o f each c o p u l a t o r y s e r i e s and d e c r e a s e d f o l l o w i n g each e j a c u l a t i o n . The e l e c t r o c h e m i c a l d a t a s u g g e s t s e v e r a l p o s s i b i l i t i e s a b o u t DA f u n c t i o n i n t h e n u c l e u s accumbens d u r i n g c o p u l a t i o n . F i r s t , DA r e l e a s e i n t h i s s t r u c t u r e may be n e c e s s a r y f o r t h e i n i t i a t i o n o f c o p u l a t i o n . I t i s c o n c e i v a b l e t h a t t h e h i g h e s t dose o f h a l o p e r i d o l used i n E x p e r i m e n t I I I (10 u g / s i d e ) was n o t s u f f i c i e n t t o i n c r e a s e mount o r i n t r o m i s s i o n l a t e n c i e s . The r e s u l t s r e p o r t e d by E v e r i t t e t a l . (1989) wou ld t e n d t o s u p p o r t t h i s h y p o t h e s i s . Second, t h e p a t t e r n o f DA e f f l u x o b s e r v e d i n t h e n u c l e u s accumbens d u r i n g c o p u l a t i o n i n E x p e r i m e n t I V c o u l d be an epiphenomenon o f i n c r e a s e d a c t i v i t y i n t h e MPOA. Because c e l l b o d i e s i n t h e MPOA send axons t h r o u g h t h e m e d i a l f o r e b r a i n b u n d l e t o t h e VTA (Conrad & P f a f f , 1976 ; Swanson, 1 9 7 6 ) , i t i s p o s s i b l e t h a t a c t i v a t i o n o f t h e MPOA l e a d s t o a c t i v a t i o n o f t h e VTA a n d , h e n c e , a c t i v a t i o n o f DA t e r m i n a l s i n t h e n u c l e u s accumbens. However, g i v e n t h e g e n e r a l i m p o r t a n c e o f t h e n u c l e u s accumbens i n b e h a v i o r , i t seems u n l i k e l y t h a t t h e dynamic changes o b s e r v e d i n 215 E x p e r i m e n t I V were r e s i d u a l e f f e c t s o f s i m i l a r a c t i v a t i o n o f t h e MPOA. I t m i g h t be u s e f u l t o c o n s i d e r an h y p o t h e s i s t h a t p r e c o p u l a t o r y s e x u a l a r o u s a l i s "summed" ( B e a c h , 1956) or " g a t e d " (Sachs & B a r f i e l d , 1976) i n t o t h e i n i t i a t i o n o f c o p u l a t i o n . To t h e e x t e n t t h a t DA r e l e a s e i n t h e n u c l e u s accumbens i s n e c e s s a r y f o r t h e e x p r e s s i o n o f a n t i c i p a t o r y a s p e c t s o f s e x u a l b e h a v i o r , i t may s e r v e t o s e n s i t i z e motor p rograms f o r c o p u l a t i o n and t h u s a c t as p a r t o f a " g a t i n g " mechan ism. I n t h i s way, DA r e l e a s e i n t h e n u c l e u s accumbens c o u l d be s u f f i c i e n t , b u t n o t n e c e s s a r y , f o r t h e i n i t i a t i o n o f c o p u l a t i o n . C l e a r l y , t h e e f f e c t s o f i n f u s i o n o f h i g h e r doses o f h a l o p e r i d o l , o r pe rhaps more s e l e c t i v e DA r e c e p t o r a n t a g o n i s t s , need t o be examined i n t h e n u c l e u s accumbens d u r i n g c o p u l a t i o n b e f o r e any o f t h e s e p o s s i b i l i t i e s can be r e j e c t e d . The r o l e o f s t r i a t a l DA i n consummatory a s p e c t s o f s e x u a l b e h a v i o r i s d i f f i c u l t t o e s t a b l i s h . As n o t e d a b o v e , h a l o p e r i d o l i n f u s i o n s t o t h e s t r i a t u m i n E x p e r i m e n t I I I i n c r e a s e d , r a t h e r t h a n d e c r e a s e d t h e t o t a l number o f e j a c u l a t i o n s , s u g g e s t i n g t h a t i n c r e a s e d DA a c t i v i t y i n t h e s t r i a t u m s e r v e s t o i n h i b i t e j a c u l a t i o n . The mechanisms o f such i n h i b i t i o n , however , a r e u n c l e a r . An i n h i b i t o r y e f f e c t on p e n i l e r e f l e x e s , as can be e n v i s i o n e d f o r t h e a n t a g o n i s m o f DA a c t i v i t y i n t h e MPOA, i s p o s s i b l e , a l t h o u g h h a l o p e r i d o l d i d n o t a f f e c t t h e number o f i n t r o m i s s i o n s o r t h e e j a c u l a t i o n l a t e n c y . V o l t a m m e t r y and m i c r o d i a l y s i s b o t h r e v e a l e d t h a t DA e f f l u x i n c r e a s e s p r o g r e s s i v e l y i n t h e s t r i a t u m d u r i n g c o p u l a t i o n b u t , u n l i k e 216 e f f l u x i n t h e n u c l e u s accumbens o r MPOA, i s n o t a s s o c i a t e d w i t h any p a r t i c u l a r a s p e c t o f c o p u l a t i o n . The i n c r e a s e d r e l e a s e o f DA i n t h e s t r i a t u m d u r i n g c o p u l a t i o n c o u l d be an a r t i f a c t o f g e n e r a l moto r a c t i v i t y . A h l e n i u s e t a l . (1987) n o t e d t h a t b o t h 10 min o f c o p u l a t i o n and 25 min o f t r e a d m i l l l o c o m o t i o n l e d t o s i g n i f i c a n t i n c r e a s e s i n DOPA s y n t h e s i s i n t h e s t r i a t u m o f male r a t s . I n l i g h t o f t h e e f f e c t o f h a l o p e r i d o l i n f u s i o n s t o t h e s t r i a t u m i n E x p e r i m e n t I I I , t o g e t h e r w i t h t h e d i s r u p t i o n s i n i n i t i a t i o n and r a t e o f c o p u l a t i o n i n d u c e d by e i t h e r e l e c t r o l y t i c or 6-OHDA l e s i o n s o f t h e s t r i a t u m ( B r a c k e t t e t a l . , 1986 ; Robb ins e t a l . , 1 9 8 9 ) , i t i s t e m p t i n g t o s u g g e s t t h a t i n c r e a s e d DA a c t i v i t y i n t h e s t r i a t u m s e r v e s t o r e g u l a t e c e r t a i n motor components o f c o p u l a t i o n , such as m o u n t i n g or p e l v i c t h r u s t i n g , t h a t t e m p o r a r i l y a n t a g o n i z e e j a c u l a t o r y mechan isms. A l t h o u g h t h e n e r v o u s s y s t e m m i g h t be e x p e c t e d t o e s t a b l i s h m u t u a l i n h i b i t i o n between such i n c o m p a t i b l e p r o c e s s e s ( K o n o r s k i , 1 9 6 7 ) , t h i s s u g g e s t i o n seems somewhat i n c o m p a t i b l e w i t h t h e i d e a o r i g i n a l l y p r o p o s e d by Beach (1956) and r e i t e r a t e d by o t h e r s ( e . g . , B i t r a n & H u l l , 1988 ; C r o w l e y & Zemlan , 1 9 8 1 ; Sachs & B a r f i e l d , 1976; Sachs & M e i s e l , 1988) t h a t m o u n t i n g and i n t r o m i t t i n g s e r v e t o s e n s i t i z e an e j a c u l a t o r y mechanism. However, i t i s c o n c e i v a b l e t h a t t h e m u t u a l i n h i b i t i o n and s e n s i t i z a t i o n c o u l d o c c u r s i m u l t a n e o u s l y i n d i f f e r e n t b r a i n a r e a s and t h a t s e n s i t i z a t i o n p r o c e s s e s e v e n t u a l l y s u p e r s e d e t h o s e o f i n h i b i t i o n . C l e a r l y , i t w i l l be n e c e s s a r y t o examine t h e e f f e c t s t r i a t a l i n f u s i o n s o f h a l o p e r i d o l o r more s e l e c t i v e DA a n t a g o n i s t s i n g r e a t e r d e t a i l . 217 Brain DA Systems and Male Sexual Behavior: A Synthesis The foregoing discussion i l l u s t r a t e s how brain DA systems may control a n t i c i p a t o r y and consummatory aspects of male sexual behavior at d i f f e r e n t l e v e l s of neural processing. What appears as a natural cascade of events, from a n t i c i p a t i o n to i n i t i a t i o n to e j a c u l a t i o n , i s dependent on the successful switching of motor programs as the topography of the sexual incentive changes from a t t r a c t i v i t y to p r o c e p t i v i t y to r e c e p t i v i t y . Two brain areas in which DA appears to modulate male sexual behavior, the MPOA and nucleus accumbens, figure prominently in the neurally-based model system for the execution of motivated behavior o r i g i n a l l y proposed by Mogenson, Jones, and Yim (1980) and modified subsequently by Toates (1986) and Sachs and Meisel (1988). B r i e f l y , forebrain structures serve as an interface between an animal's motivational state and the motor systems that allow the animal to act on external incentive cues. The MPOA receives afferents from a v a r i e t y of sources, including the o l f a c t o r y bulbs, amygdala, and hypothalamus. The MPOA and i t s efferents thus form a common pathway for the integration of an animal's hormonal state, the presence of an estrous female, the environmental context, and previous experience. This information is transmitted v i a the medial forebrain bundle to the dorsal and ventral tegmentum, where i t i s relayed in part to the nucleus accumbens. The nucleus accumbens also receives inputs from several other sources, most notably the amygdala. By vi r t u e of i t s d i f f u s e connections, with the basal ganglia, the nucleus 218 accumbens i s viewed as an interface between motivation and action. The present r e s u l t s suggest that the presentation of a sexual incentive, such as the odor or presence of an estrous female behind a screen, increases DA release and metabolism in diencephalic and mesolimbic DA terminals. This increased release s e n s i t i z e s both the MPOA and the nucleus accumbens simultaneously and stimulates the hypothalamus to f a c i l i t a t e penile erections and the basal ganglia to f a c i l i t a t e the motor programs necessary for the di s p l a y of a n t i c i p a t o r y sexual behaviors and mounting. Disruption of DA a c t i v i t y in the MPOA or nucleus accumbens progressively decreases the l i k e l i h o o d of a complete t r a n s i t i o n from sexual motivation to an t i c i p a t o r y or consummatory forms of male sexual behavior. The present r e s u l t s are also compatible with Toates' (1986) model of sexual motivation, which recognizes a complex i n t e r a c t i o n between external incentive s t i m u l i and int e r n a l hormonal state in determining sexual arousal and the s e n s i t i z a t i o n of an ejac u l a t i o n mechanism. The increase in DA leve l s e l i c i t e d by cues from a receptive female may be an ess e n t i a l neural substrate for processes of sexual arousal. Toates also postulates that e j a c u l a t i o n , in turn, leads to the des e n s i t i z a t i o n of sexual arousal. The clear and dramatic drop in both the DA oxidation s i g n a l in the nucleus accumbens and the catecholamine oxidation s i g n a l in the MPOA following e j a c u l a t i o n i s e n t i r e l y consistent with t h i s postulation. However, i t must be remembered that DA terminals exist e l s e w h e r e i n t h e b r a i n . No s t u d i e s have y e t d e t e r m i n e d a r o l e i n male s e x u a l b e h a v i o r o f DA t e r m i n a l s i n t h e f r o n t a l c o r t e x , c . o r t i c o m e d i a l a m y g d a l a , or o l f a c t o r y b u l b s . S i m i l a r l y , t h e r o l e i n male s e x u a l b e h a v i o r o f o t h e r d i e n c e p h a l i c DA t e r m i n a l s , such as t h o s e i n t h e median em inence , i s unknown. F i n a l l y , t h e r o l e o f DA i n the* s t r i a t u m needs t o be examined i n more d e t a i l . U n t i l such t i m e as t h e s e gaps i n knowledge a r e f i l l e d , t h e d e s c r i p t i o n o f DA f u n c t i o n p r e s e n t e d above w i l l r e m a i n l i t t l e more t h a n e d u c a t e d s p e c u l a t i o n . C l i n i c a l I m p l i c a t i o n s I t i s i m p o r t a n t t o c o n s i d e r t h e r e s u l t s o f t h e p r e s e n t e x p e r i m e n t s i n t e r m s o f t h e o r g a n i z a t i o n o f human s e x u a l b e h a v i o r and t h e c l i n i c a l impac t o f t r e a t m e n t s t h a t a f f e c t b r a i n DA s y s t e m s . As n o t e d i n t h e I n t r o d u c t i o n , t h e human s e x u a l r e s p o n s e c y c l e can be d i v i d e d i n t o f o u r p h a s e s , a p p e t i t i v e , e x c i t e m e n t , o rgasm, and r e s o l u t i o n ( e . g . , A m e r i c a n P s y c h i a t r i c A s s o c i a t i o n , 1987; K a p l a n , 1974; M a s t e r s & J o h n s o n , 1 9 6 6 ) . W i t h i n t h e f i r s t two p h a s e s , t h e r e i s good r e a s o n t o d i s t i n g u i s h between p r o c e s s e s o f s e x u a l d e s i r e , c o n s i s t i n g o f f a n t a s i e s a b o u t , or a d e s i r e t o engage i n , s e x u a l a c t i v i t y ; and s e x u a l a r o u s a l , c o n s i s t i n g o f t h e s u b j e c t i v e and p h y s i o l o g i c a l changes t h a t accompany s e x u a l e x c i t e m e n t b e f o r e and d u r i n g c o p u l a t o r y a c t i v i t y ( A m e r i c a n P s y c h i a t r i c A s s o c i a t i o n , 1 9 8 7 ) . T h i s c l i n i c a l d i s t i n c t i o n i s r e m i n i s c e n t o f t h e g e n e r a l d i s t i n c t i o n between a n t i c i p a t o r y and consummatory a s p e c t s o f b e h a v i o r used i n t h e p r e s e n t e x p e r i m e n t s . 220 To the extent that such homologies are v a l i d , the present r e s u l t s o f f e r some hypotheses about the e f f e c t of DA agonists and antagonists on the sexual behavior of human males. Typical and a t y p i c a l DA antagonists are used in p s y c h i a t r i c medicine as major t r a n q u i l i z e r s and antipsychotic agents. They have also been used rather innapropriately as sedatives and antianxiety drugs. Certain DA antagonists that lack antipsychotic e f f i c a c y , e.g., metoclopramide, are also used as antiemetic agents. Among the lesser "side e f f e c t s " of many of these drugs are disorders of sexual behavior that include i n h i b i t e d sexual desire, delayed or in h i b i t e d sexual arousal, and delayed orgasm (Kotin et a l . , 1977; P e t r i e , 1985; Segraves, 1988). The r e s u l t s of Experiment II are generally consistent with these c l i n i c a l impressions. It would be predicted that sexual desire i s extremely s e n s i t i v e to disruption by DA antagonists, followed by sexual arousal. The l a t t e r of these may involve an e f f e c t of DA antagonists on the neuroendocrine regulation of penile erection. D i f f i c u l t i e s achieving orgasm can also stem from the i n a b i l i t y to achieve or maintain erection. C l i n i c i a n s attempting to treat sexual disorders or dysfunctions should be concerned about the widespread use of these drugs, and they should attempt to rule out a " p h y s i o l o g i c a l " e t i o l o g y that stems from concurrent treatment with DA antagonists. In addition, the impact of sexual disorders or dysfunctions that are induced by treatment with DA antagonists should be assessed on therapeutic e f f i c a c y . Obviously the a b i l i t y to manage one set of 221 symptoms must be we ighed a g a i n s t t h e i n d u c t i o n o f a n o t h e r s e t o f symptoms, e s p e c i a l l y when t h e o t h e r s e t i n v o l v e s a d i s r u p t i o n o f one o f t h e most i m p o r t a n t s o u r c e s o f p l e a s u r e and i n t i m a c y . To t h i s e n d , i t i s i m p e r a t i v e t h a t w e l l - c o n t r o l l e d e x p e r i m e n t s t h a t u t i l i z e d o u b l e - b l i n d d r u g a d m i n i s t r a t i o n p r o c e d u r e s , and t h a t f r a c t i o n a t e s e x u a l b e h a v i o r a l o n g t h e t h e o r e t i c a l l y u s e f u l l i n e s m e n t i o n e d a b o v e , be c o n d u c t e d t o examine t h e e f f e c t s o f DA a n t a g o n i s t s on t h e s e x u a l b e h a v i o r o f human m a l e s . C o n v e r s e l y , t h e s t i m u l a t i o n o f s e x u a l d e s i r e or a r o u s a l has been r e p o r t e d by r e c r e a t i o n a l u s e r s o f d r u g s t h a t s t i m u l a t e DA pa thways or r e c e p t o r s , such as d - a m p h e t a m i n e , c o c a i n e , or apomorph ine ( B u r r o u g h s , 1959 ; C a r t e r & D a v i s , 1976; H o l l i s t e r , 1975; Schne iden & Rees, 1985; Waud, 1 9 3 3 ) . Such r e p o r t s have g e n e r a t e d a l o n g - s t a n d i n g i n t e r p r e t a t i o n t h a t DA a g o n i s t s a r e a p h r o d i s i a c s . T h i s i n t e r p r e t a t i o n has been s t r e n g t h e n e d by c l i n i c a l e v i d e n c e t h a t DA a g o n i s t s a r e e f f e c t i v e i n t h e t r e a t m e n t o f c e r t a i n s e x u a l d i s o r d e r s and d y s f u n c t i o n s . For e x a m p l e , c o n s i s t e n t w i t h t h e e f f e c t s o f DA a n t a g o n i s t s on t h e s e x u a l b e h a v i o r o f human m a l e s , t h e l o s s o f s e x u a l d e s i r e and a r o u s a l a s s o c i a t e d w i t h c e r t a i n m e d i c a l c o n d i t i o n s , such as P a r k i n s o n ' s d i s e a s e , h y p e r p r o l a c t i n e m i a , d i a b e t e s , and r e n a l f a i l u r e , has been c o u n t e r a c t e d w i t h t h e DA p r e c u r s o r 1-DOPA or t h e DA r e c e p t o r a g o n i s t s l i s u r i d e , a p o m o r p h i n e , or b r o m o c r i p t i n e ( B a r t k e e t a l . , 1983 ; B a r w i n , 1985; Bowers & Van W o e r t , 1972 ; P i e r i n i & N u s i m o v i c h , 1 9 8 1 ; R u i l o p e e t a l . , 1 9 8 5 ) . S i m i l a r l y , apomorph ine i s e f f e c t i v e i n t h e t r e a t m e n t o f e r e c t i l e d y s f u n c t i o n ( e . g . , L a i 222 et a l . , 1987). The DA receptor agonist quinpirole is also undergoing c l i n i c a l t r i a l s as a general treatment for sexual desire and arousal disorders (M. Foreman, personal communication). The effectiveness of DA agonists in stimulating sexual desire or arousal suggests that disrupted DA a c t i v i t y contributes to sexual desire and arousal disorders. Based on the r e s u l t s of Experiment IV, such disru p t i o n may occur in mesolimbic or diencephalic DA terminals. However, although there i s corresponding evidence that DA agonists stimulate copulation in sexually inactive or sluggish male r a t s , these drugs can also delay the i n i t i a t i o n of copulation and reduce the number of intromissions in sexually active r a t s . Thus, the u t i l i t y of these drugs as a treatment for sexual desire or arousal disorders may be lim i t e d to in d i v i d u a l s possessing hypoactive DA systems. It has been argued that the sexual behavior of male rats does not constitute a v a l i d model of the sexual behavior of human males because rats lack the "cognitive c o n t r o l " that is assumed to mediate human sexual behavior (e.g., Wilson, 1977). The fact •that rats are r e a d i l y able to respond v i a c l a s s i c a l and operant conditioning for primary and secondary sexual incentives ( E v e r i t t et a l . , 1987; Mendelson & Pfaus, 1989; Zamble, M i t c h e l l , & Findlay, 1986), and capable of i n h i b i t i n g t h e i r sexual responses with sexually nonreceptive females (Pfaus & P i n e l , 1989), indicates that higher-order learning accompanies the sexual responding of male r a t s . Moreover, many drug e f f e c t s on the 223 s e x u a l b e h a v i o r o f male r a t s r e s e m b l e d r u g e f f e c t s on t h e s e x u a l b e h a v i o r o f human m a l e s , as d e m o n s t r a t e d amply i n E x p e r i m e n t I I . These r e s u l t s c h a l l e n g e W i l s o n ' s c o n t e n t i o n and u n d e r s c o r e t h e u t i l i t y o f t h e c o m p a r a t i v e a p p r o a c h i n t h e s t u d y o f d r u g e f f e c t s on male s e x u a l b e h a v i o r . C l i n i c a l r e s e a r c h e r s can t h u s t a k e a d v a n t a g e o f t h e r i c h l i t e r a t u r e on t h e s e x u a l b e h a v i o r o f male r a t s t o g e n e r a t e t e s t a b l e h y p o t h e s e s c o n c e r n i n g t h e e t i o l o g y and t r e a t m e n t o f s e x u a l d i s o r d e r s and d y s f u n c t i o n s i n human m a l e s . Male S e x u a l B e h a v i o r as a Form o f M o t i v a t e d B e h a v i o r The second o b j e c t i v e o f t h i s t h e s i s was t o r e l a t e t h e r o l e o f DA i n male s e x u a l b e h a v i o r t o t h e more g e n e r a l r o l e o f DA i n i n c e n t i v e m o t i v a t i o n . T h i s was a c c o m p l i s h e d two ways , f i r s t by d e m o n s t r a t i n g t h a t a n t i c i p a t o r y and consummatory a s p e c t s o f male s e x u a l b e h a v i o r a r e r e g u l a t e d d i f f e r e n t l y by b r a i n DA sys tems and second by p r o v i d i n g e v i d e n c e t h a t i n c r e a s e s i n e x t r a c e l l u l a r DA r e l e a s e a r e e l i c i t e d by i n c e n t i v e c u e s . I t i s c l e a r t h a t a n t i c i p a t o r y b e h a v i o r s a r e more s e n s i t i v e t h a n consummatory b e h a v i o r s t o d i s r u p t i o n by DA a n t a g o n i s t s . T h i s was shown r e p e a t e d l y i n t h e p r e s e n t e x p e r i m e n t s and has been d e m o n s t r a t e d f o r o t h e r fo rms o f a n t i c i p a t o r y r e s p o n d i n g , such as h o a r d i n g ( B l u n d e l l e t a l . , 1 9 7 7 ) , c o n d i t i o n e d p r e p a r a t o r y r e s p o n s e s t o a CS+ t h a t s i g n a l s t h e d e l i v e r y o f a meal ( B l a c k b u r n e t a l . , 1 9 8 7 ) , c o n d i t i o n e d i n s t r u m e n t a l r e s p o n s e s f o r f o o d ( F i b i g e r e t a l . , 1 9 7 4 ) , and c o n d i t i o n e d p r e p a r a t o r y r e s p o n s e s t o a CS+ t h a t s i g n a l s shock ( B l a c k b u r n , 1 9 8 9 ) . L i k e w i s e , t h e 224 p r e s e n c e o f an e s t r o u s fema le b e h i n d t h e s c r e e n was a p a r t i c u l a r l y s a l i e n t s t i m u l u s f o r e v o k i n g an i n c r e a s e i n DA and c a t e c h o l a m i n e r e l e a s e i n t h e n u c l e u s accumbens and MPOA. T h i s i s s i m i l a r t o t h e i n c r e a s e d r e l e a s e o f DA i n t h e n u c l e u s accumbens t h a t accompanies t h e p r e s e n t a t i o n o f a p r e p a r a t o r y CS+ f o r f o o d ( B l a c k b u r n e t a l . , 1989 ; P h i l l i p s , P f a u s , & B l a h a , 1 9 9 0 ) . T o g e t h e r , t h e s e r e s u l t s s u g g e s t t h a t i n c r e a s e d DA a c t i v i t y fo rms an i m p o r t a n t p a r t o f t h e m o t i v a t i o n a l s t a t e i n d u c e d by i n c e n t i v e c u e s . The g e n e r a l i t y o f t h e s e f i n d i n g s l e n d s s u p p o r t t o t h e i d e a t h a t male s e x u a l b e h a v i o r and o t h e r fo rms o f m o t i v a t e d b e h a v i o r s h a r e common n e u r o a n a t o m i c a l and n e u r o c h e m i c a l n e t w o r k s f o r t h e p r o c e s s i n g o f i n c e n t i v e c u e s . However , d e s p i t e t h e s i m i l a r i t i e s , t h e r e a r e i m p o r t a n t d i f f e r e n c e s be tween s e x u a l b e h a v i o r and o t h e r fo rms o f m o t i v a t e d b e h a v i o r . The most o b v i o u s i n t h e p r e s e n t e x p e r i m e n t s i s t h e r o l e o f b r a i n DA sys tems i n consummatory a s p e c t s o f b e h a v i o r . As i n d i c a t e d a b o v e , c e r t a i n consummatory a s p e c t s o f f e e d i n g or a v o i d i n g do n o t appear t o i n v o l v e b r a i n DA sys tems because t h e i n i t i a t i o n and d i s p l a y o f t h o s e b e h a v i o r s a r e n o t a f f e c t e d by t r e a t m e n t w i t h DA a n t a g o n i s t s or l e s i o n s o f m e s o t e l e n c e p h a l i c DA p a t h w a y s . I n c o n t r a s t , b o t h t h e i n i t i a t i o n and r a t e o f c o p u l a t i o n were a f f e c t e d by t r e a t m e n t w i t h modera te doses o f DA a n t a g o n i s t s t h a t d i d n o t p roduce g e n e r a l motor d e f i c i t s . M o r e o v e r , dynamic changes i n DA and c a t e c h o l a m i n e r e l e a s e i n t h e n u c l e u s accumbens and MPOA were o b s e r v e d d u r i n g t h e i n i t i a t i o n o f c o p u l a t i o n and e j a c u l a t i o n ; a p r o g r e s s i v e r i s e 225 i n s t r i a t a l DA r e l e a s e o c c u r r e d t h r o u g h o u t c o p u l a t i o n . A n o t h e r i m p o r t a n t d i f f e r e n c e between male s e x u a l b e h a v i o r and f e e d i n g o r a v o i d i n g i n v o l v e s t h e r o l e o f i n t e r n a l c u e s . B l a c k b u r n (1989) has a rgued t h a t DA does n o t p l a y a r o l e i n t h e p r o c e s s i n g o f i n t e r n a l or p r o x i m a l cues because w e l l - t r a i n e d r a t s t r e a t e d w i t h DA a n t a g o n i s t s i n h i s s t u d y were c a p a b l e o f p e r c e i v i n g t h e shock and e s c a p i n g s u c c e s s f u l l y once i t was d e l i v e r e d . However , b o t h a n t i c i p a t o r y and consummatory a s p e c t s o f male s e x u a l b e h a v i o r a r e dependen t on t h e b i n d i n g o f and rogens t o c e r t a i n b r a i n a r e a s , most n o t a b l y t h e MPOA. Androgens may f a c i l i t a t e s e x u a l a r o u s a b i l i t y and p e n i l e r e f l e x e s i n p a r t by a c t i v a t i n g DA t e r m i n a l s w i t h i n t h e MPOA or p a r a v e n t r i c u l a r n u c l e u s . T h u s , c o n s i s t e n t w i t h t h e i n t e r p r e t a t i o n i n t h e p r e v i o u s s e c t i o n , d i e n c e p h a l i c DA sys tems may p l a y an i m p o r t a n t r o l e i n t h e p r o c e s s i n g o f i n t e r n a l ho rmona l c u e s . I n c o n c l u s i o n , c a u t i o n must be e x e r c i s e d when a t t e m p t i n g t o i n f e r a g e n e r a l r o l e o f a n e u r o t r a n s m i t t e r i n m o t i v a t e d b e h a v i o r based on t h e s t u d y o f a s i n g l e m o t i v a t i o n a l s y s t e m . Comparable b e h a v i o r a l a s p e c t s o f d i f f e r e n t m o t i v a t i o n a l sys tems may be a f f e c t e d d i f f e r e n t l y by l e s i o n s or d r u g t r e a t m e n t s . A l t h o u g h n e u r o t r a n s m i t t e r pa thways may f i g u r e p r o m i n e n t l y i n t h e c o n t r o l o f c e r t a i n a s p e c t s o f b e h a v i o r , i t i s i n c o r r e c t t o t h i n k o f n e u r o t r a n s m i t t e r s as h a v i n g a s i n g l e r o l e i n b e h a v i o r . S i m i l a r l y , a l t h o u g h l e s i o n s o f t h e MPOA d i s r u p t m a t e r n a l b e h a v i o r , f e e d i n g , and t h e r m o r e g u l a t i o n , i n a d d i t i o n t o s e x u a l b e h a v i o r (Mogenson e t a l . , 1980 ; V a l e n s t e i n e t a l . , 1 9 7 0 ) , t h e 2 2 6 role of diencephalic DA systems in the control of neuroendocrine processes that underlie the di s p l a y of penile r e f l e x e s , and hence c e r t a i n aspects of copulatory behavior, may be s p e c i f i c to male sexual behavior. Obviously i t i s unwise to base a theory of neurotransmitter function in motivation on a single aspect of motivated behavior derived from a si n g l e motivational system. However, should comparative analyses reveal a common thread among d i f f e r e n t motivational systems, as i s becoming apparent for the general role of mesolimbic DA pathways in a n t i c i p a t o r y aspects of behavior, then the goal of generating coherent and comprehensive theory about neurotransmitters in behavior w i l l begin to be r e a l i z e d . Summary and Conclusions The sexual behavior of male rats depends upon the a c t i v i t y of a v a r i e t y of c e n t r a l and peripheral neural systems that integrate the animal's i n t e r n a l motivational state with the external environment. The ro l e of both diencephalic and mesotelencephalic DA systems in t h i s regard can be viewed as an interface between motivation and action. Increased DA release in these systems in response to a sexual incentive may constitute a necessary neural component of a n t i c i p a t o r y sexual desire and arousal that s e n s i t i z e s penile r e f l e x mechanisms in the hypothalamus and motor programs for copulation in the basal ganglia. This is consistent with the general theory that brain DA systems form an important component of incentive motivation. 227 There is s t i l l much to be done. The role of other brain DA terminals in male sexual behavior needs to be addressed, as they do in other forms of motivated behavior. The impact of other drugs or neurotransmitters on diencephalic and mesotelencephalic DA systems in male sexual behavior also needs to be assessed. Moreover, before a general r o l e can be assigned to brain DA systems in sexual behavior, the r o l e of these systems in female sexual behavior needs to be studied in d e t a i l . The experiments reported in t h i s thesis combined behavioral, pharmacological, and electrochemical techniques in the study of the role of DA in male sexual behavior. This combined approach provided a systematic way to examine DA function at several levels of a n a l y s i s . Hopefully, t h i s approach w i l l prove useful in future experiments with sexual behavior or with other classes of motivated behavior. 228 REFERENCES Agmo, A. & F e r n a n d e z , H. ( 1 9 8 9 ) . Dopamine and s e x u a l b e h a v i o r i n t h e male r a t : A r e e v a l u a t i o n . J o u r n a l o f N e u r a l  T r a n s m i s s i o n . 77 , 2 1 - 3 7 . A h l e n i u s , S . , C a r l s s o n , A . , H i l l e g a a r t , V . , H j o r t h , S . , & L a r s s o n , K. ( 1 9 8 7 ) . R e g i o n - s e l e c t i v e a c t i v a t i o n o f b r a i n monoamine s y n t h e s i s by s e x u a l a c t i v i t y i n t h e male r a t . European J o u r n a l o f P h a r m a c o l o g y , 144 , 7 7 - 8 2 . 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I n h i b i t i o n o f s e x u a l b e h a v i o r by dopamine a n t a g o n i s t or s e r o t o n i n a g o n i s t d r u g s i n c a s t r a t e d male r a t s g i v e n e s t r a d i o l or d i h y d r o t e s t o s t e r o n e . Pharmaco logy B i o c h e m i s t r y & B e h a v i o r , 13 , 5 7 - 6 7 . Beach , F .A. ( 1 9 5 6 ) . C h a r a c t e r i s t i c s o f m a s c u l i n e " s e x d r i v e " . Nebraska Symposium on M o t i v a t i o n , 4_, 1 -32 . Beach , F .A . & J o r d a n , L. ( 1 9 5 6 ) . S e x u a l e x h a u s t i o n and r e c o v e r y i n t h e male r a t . Q u a r t e r l y J o u r n a l o f E x p e r i m e n t a l  P s y c h o l o g y . 8., 1 2 1 - 1 3 3 . B e n a s s i - B e n e l l i , A. & F e r r a r i , F. ( 1 9 7 9 ) . A c t i v a t i o n w i t h N - n -p r o p y l n o r a p o m o r p h i n e (NPA) o f t h e male r a t c o p u l a t o r y b e h a v i o r . E x p e r e n t i a , 35 , 6 4 5 - 6 4 6 . B e n i n g e r , R . J . ( 1 9 8 3 ) . 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M e d i c a l A s p e c t s o f  Human S e x u a l i t y , 6., 8 8 - 9 8 . B r a c k e t , N .L . & Edwards , D.A. ( 1 9 8 4 ) . M e d i a l p r e o p t i c c o n n e c t i o n s w i t h t h e m i d b r a i n tegmentum a r e e s s e n t i a l f o r male s e x u a l b e h a v i o r . P h y s i o l o g y and B e h a v i o r , 3 2 , 7 9 - 8 4 . B r a c k e t t , N . L . , I u v o n e , P . M . , & Edwards , D.A. ( 1 9 8 6 ) . M i d b r a i n l e s i o n s , d o p a m i n e , and male s e x u a l b e h a v i o r . B e h a v i o u r a l  B r a i n R e s e a r c h , 20 , 2 3 1 - 2 4 0 . B u r r o u g h s , W.S. ( 1 9 5 9 ) . Naked l u n c h . New Y o r k : Grove P r e s s . C a g g i u l a , A . R . , Shaw, D . H . , A n t e l m a n , S . M . , & Edwards , D.A. ( 1 9 7 6 ) . I n t e r a c t i v e e f f e c t s o f b r a i n c a t e c h o l a m i n e s and v a r i a t i o n s i n s e x u a l and n o n s e x u a l a r o u s a l on c o p u l a t o r y b e h a v i o r o f male r a t s . B r a i n R e s e a r c h , 1 1 1 , 3 2 1 - 3 3 6 . C a g i a n o , R . , B a r f i e l d , R . J . , W h i t e , N . R . , P l e i m , E . T . , & Cuomo, V. ( 1 9 8 8 ) . D o p a m i n e r g i c (D2) m e d i a t i o n o f r a t 22kHz p o s t e j a c u l a t o r y u l t r a s o n i c v o c a l i z a t i o n . S o c i e t y f o r  N e u r o s c i e n c e A b s t r a c t s , 13 , 3 1 . C a l h o u n , J . B . ( 1 9 6 2 ) . The e c o l o g y and s o c i o l o g y o f t h e Norway  r a t ( U . S . P u b l i c H e a l t h S e r v i c e P u b l i c a t i o n No. 1 0 0 8 ) . W a s h i n g t o n , D . C : U.S. Government P r i n t i n g O f f i c e . C a r l i , M . , Evenden, J . L . , & R o b b i n s , T.W. ( 1 9 8 5 ) . D e p l e t i o n o f u n i l a t e r a l s t r i a t a l dopamine i m p a i r s i n i t i a t i o n o f c o n t r a l a t e r a l a c t i o n s and n o t s e n s o r y a t t e n t i o n . N a t u r e , 313, 6 7 9 - 6 8 2 . C a r l s o n , J . H . , B e r g s t r o m , D . A . , Demo, S . D . , & W a l t e r s , J . R . ( 1 9 8 8 ) . A c u t e r e d u c t i o n o f dopamine l e v e l s a l t e r s r e s p o n s e s o f b a s a l g a n g l i a neurons t o s e l e c t i v e D - l and D-2 dopamine r e c e p t o r s t i m u l a t i o n . European J o u r n a l o f P h a r m a c o l o g y , 152 , 2 8 9 - 3 0 0 . C a r l s s o n , A. ( 1 9 6 3 ) . E f f e c t o f c h l o r p r o m a z i n e or h a l o p e r i d o l on f o r m a t i o n o f 3 - m e t h o x y t y r a m i n e and n o r m e t a n e p h r i n e i n mouse b r a i n . A c t a P h a r m a c o l o g i a & T o x i c o l o g i a , 20 , 1 4 0 - 1 7 6 . C a r l s s o n , A. ( 1 9 5 9 ) . O c c u r r e n c e , d i s t r i b u t i o n , and p h y s i o l o g i c a l r o l e o f c a t e c h o l a m i n e s i n t h e n e r v o u s s y s t e m . P h a r m a c o l o g i c a l R e v i e w s . 1 1 . 4 3 1 - 4 5 5 . C a r l s s o n , A . , L i n d q v i s t , M . , Magnusson, T . , & Wa ldeck , B. ( 1 9 5 8 ) . On t h e p r e s e n c e o f 3 - h y d r o x y t y r a m i n e i n b r a i n . S c i e n c e ,  127 , 4 7 1 - 4 7 4 . C a r t e r , C S . & D a v i s , J . M . ( 1 9 7 6 ) . E f f e c t s o f d r u g s on s e x u a l 232 a r o u s a l and p e r f o r m a n c e . I n J . Myer ( E d . ) , C l i n i c a l  management o f s e x u a l d i s o r d e r s ( p p . 1 9 5 - 2 0 5 ) . B a l t i m o r e : W i l l i a m s & W i l k i n s . C h e r n e y , E . F . & B e r m a n t , G. ( 1 9 7 0 ) . The r o l e o f s t i m u l u s f e m a l e n o v e l t y i n t h e r e a r o u s a l o f c o p u l a t i o n i n male l a b o r a t o r y r a t s ( R a t t u s N o r v e g i c u s ) . A n i m a l B e h a v i o u r , 1 8 , 5 6 7 - 5 7 4 . C h i o d o , L . A . & Bunney, B .S . ( 1 9 8 4 ) . E f f e c t s o f dopamine a n t a g o n i s t s on m i d b r a i n dopamine c e l l a c t i v i t y . I n E. U s d i n , A. C a r l s s o n , A. D a h l s t r o m , & J . E n g e l ( E d s . ) , C a t e c h o l a m i n e s : n e u r o p h a r m a c o l o g y and c e n t r a l n e r v o u s s y s t e m  t h e o r e t i c a l a s p e c t s ( p p . 2 6 9 - 2 9 1 ) . New Y o r k : L i s s . C l a r k , J . T . & S m i t h , E .R. ( 1 9 8 6 ) . F a i l u r e o f p i m o z i d e and m e t e r g o l i n e t o a n t a g o n i z e t h e RDS-127 - induced f a c i l i t a t i o n o f e j a c u l a t o r y b e h a v i o r . P h y s i o l o g y and B e h a v i o r , 37 , 4 7 -5 2 . C l a r k , J . T . , S m i t h , E . R . , & D a v i d s o n , J . M . ( 1 9 8 5 ) . E v i d e n c e f o r t h e m o d u l a t i o n o f s e x u a l b e h a v i o r by - a d r e n o c e p t o r s i n male r a t s . N e u r o e n d o c r i n o l o g y , 4 1 , 3 6 - 4 3 . C l a r k , J . T . , S t e f a n i c k , M . L . , S m i t h , E . R . , & D a v i d s o n , J . M . ( 1 9 8 3 ) . F u r t h e r s t u d i e s on a l t e r a t i o n s i n male r a t c o p u l a t o r y b e h a v i o r i n d u c e d by t h e d o p a m i n e - r e c e p t o r a g o n i s t RDS-127. Pharmaco logy B i o c h e m i s t r y & B e h a v i o r , 19., 7 8 1 - 7 8 6 . C l a r k , T . K . , C a g g i u l a , A . R . , M c C o n n e l l , R . A . , & A n t e l m a n , S.M. ( 1 9 7 5 ) . Sexua l i n h i b i t i o n i s r e d u c e d by r o s t r a l m i d b r a i n l e s i o n s i n t h e male r a t . S c i e n c e , 190 , 1 6 9 - 1 7 1 . C o n r a d , L . C . A . & P f a f f , D.W. ( 1 9 7 6 ) . E f f e r e n t s f r o m m e d i a l b a s a l f o r e b r a i n and h y p o t h a l a m u s i n t h e r a t . I . An a u t o r a d i o -g r a p h i c s t u d y o f t h e m e d i a l p r e o p t i c a r e a . J o u r n a l o f  C o m p a r a t i v e N e u r o l o g y , 169 , 1 8 5 - 2 2 0 . Cooper , J . R . , B loom, F . E . , & R o t h , R.H. ( 1 9 8 6 ) . The b i o c h e m i c a l  b a s i s o f n e u r o p h a r m a c o l o g y . New Y o r k : O x f o r d . C r a i g , W. ( 1 9 1 8 ) . A p p e t i t e s and a v e r s i o n s as c o n s t i t u e n t s o f i n s t i n c t s . B i o l o g i c a l B u l l e t i n o f Woods H o l e . 34., 9 1 - 1 0 7 . C r e e s e , I . ( 1 9 8 5 ) . Dopamine r e c e p t o r s e x p l a i n e d . T rends i n  P h a r m a c o l o g i c a l S c i e n c e s , 5 , 4 3 5 - 4 4 1 . C r e e s e , I . ( 1 9 8 3 ) . The c l a s s i f i c a t i o n o f dopamine r e c e p t o r s : R e l a t i o n s h i p t o r a d i o l i g a n d b i n d i n g . Annua l Rev iew o f  N e u r o s c i e n c e , £ , 4 3 - 5 3 . C r e e s e , I . , B u r t , D . , & S n y d e r , S. ( 1 9 7 6 ) . Dopamine r e c e p t o r b i n d i n g : D i f f e r e n t i a t i o n o f a g o n i s t and a n t a g o n i s t s t a t e s 233 w i t h [ 3 ] H - d o p a m i n e and [ 3 J H - h a l o p e r i d o l . L i f e S c i e n c e s , 17 , 9 9 3 - 9 9 8 . Crow, T . J . ( 1 9 7 3 ) . C a t e c h o l a m i n e - c o n t a i n i n g neu rons and e l e c t r i c a l s e l f - s t i m u l a t i o n : 2 . A t h e o r e t i c a l i n t e r p r e t a t i o n and some p s y c h i a t r i c i m p l i c a t i o n s . P s y c h o l o g i c a l M e d i c i n e , 1, 6 6 - 7 3 . C r o w l e y , W.R. & Zemlan , F . P . ( 1 9 8 1 ) . The n e u r o c h e m i c a l c o n t r o l o f m a t i n g b e h a v i o r . I n N.T. A d l e r ( E d . ) , N e u r o e n d o c r i n o l o g y  o f r e p r o d u c t i o n ( p p . 4 5 1 - 4 8 2 ) . New Y o r k : Plenum P r e s s . D a h l s t r o m , A. & F u x e , K. ( 1 9 6 4 ) . E v i d e n c e f o r t h e e x i s t e n c e o f monoamine neurons i n t h e c e n t r a l n e r v o u s s y s t e m . I . D e m o n s t r a t i o n o f monoamines i n c e l l b o d i e s o f b r a i n s t e m n e u r o n s . ACTA P h y s i o l o g i c a l S c a n d i n a v i c a , 64 ( S u p p l . ) , 2 3 2 -278. D a l l o , J . , L e k k a , N . , & K n o l l , J . ( 1 9 8 6 ) . The e j a c u l a t o r y b e h a v i o r o f s e x u a l l y s l u g g i s h male r a t s t r e a t e d w i t h ( - ) d e p r e n y l , a p o m o r p h i n e , b r o m o c r i p t i n e , and amphetamine . P o l i s h J o u r n a l o f Pharmaco logy and Pharmacy, 38 , 2 5 1 - 2 5 5 . Damsma, G . , Y o s h i d a , M . , W e n k s t e r n , D . , Nomikos , G . G . , P h i l l i p s , A . G . , & F i b i g e r , H.C. ( 1 9 8 9 ) . Dopamine t r a n s m i s s i o n i n t h e r a t s t r i a t u m , n u c l e u s accumbens and p r e f r o n t a l c o r t e x i s d i f f e r e n t i a l l y a f f e c t e d by f e e d i n g , t a i l p i n c h , and i m m o b i l i z a t i o n . S o c i e t y f o r N e u r o s c i e n c e A b s t r a c t s , 15 , 557. D a v i d s o n , J . M . ( 1 9 6 6 ) . A c t i v a t i o n o f t h e male r a t ' s s e x u a l b e h a v i o r by i n t r a c e r e b r a l i m p l a n t a t i o n o f a n d r o g e n . E n d o c r i n o l o g y , 7 9 , 7 8 3 - 7 9 4 . D o r s a , D. & S m i t h , E .R. ( 1 9 8 0 ) . F a c i l i t a t i o n o f m o u n t i n g b e h a v i o r o f male r a t s by i n t r a c r a n i a l i n j e c t i o n s o f l u t e i n i z i n g h o r m o n e - r e l e a s i n g hormone. R e g u l a t o r y P e p t i d e s , I , 1 4 7 - 1 5 4 . Edwards , D.A. & E i n h o r n , L . C . ( 1 9 8 6 ) . P r e o p t i c and m i d b r a i n c o n t r o l o f s e x u a l m o t i v a t i o n . P h y s i o l o g y and B e h a v i o r , 37 , 3 2 9 - 3 3 5 . E l l i s , H. ( 1 9 3 8 ) . P s y c h o l o g y o f s e x . New Y o r k : Emerson. E v e r i t t , B . J . , Cador , M . , & R o b b i n s , T.W. ( 1 9 8 9 ) . I n t e r a c t i o n s between t h e amygdala and v e n t r a l s t r i a t u m i n s t i m u l u s - r e w a r d a s s o c i a t i o n s : S t u d i e s u s i n g a s e c o n d - o r d e r s c h e d u l e o f s e x u a l r e i n f o r c e m e n t . N e u r o s c i e n c e , 2 0 , 6 3 - 7 5 . E v e r i t t , B . J . , F r a y , P . , K o s t a r c z y k , E . , T a y l o r , S . , & S t a c e y , P. ( 1 9 8 7 ) . S t u d i e s o f i n s t r u m e n t a l b e h a v i o r w i t h s e x u a l 234 r e i n f o r c e m e n t i n male r a t s ( r a t t u s n o r v e g i c u s ) : I . C o n t r o l by b r i e f v i s u a l s t i m u l i p a i r e d w i t h a r e c e p t i v e f e m a l e . J o u r n a l o f C o m p a r a t i v e P s y c h o l o g y , 1 0 1 , 3 9 5 - 4 0 6 . E v e r i t t , B . J . & S t a c e y , P. ( 1 9 8 7 ) . S t u d i e s o f i n s t r u m e n t a l b e h a v i o r w i t h s e x u a l r e i n f o r c e m e n t i n male r a t s ( r a t t u s  n o r v e g i c u s ) : I I . E f f e c t s o f p r e o p t i c a r e a l e s i o n s , c a s t r a t i o n , and t e s t o s t e r o n e . J o u r n a l o f C o m p a r a t i v e  P s y c h o l o g y , 1 0 1 . 4 0 7 - 4 1 9 . F a g e , D. & S c a t t o n , B. ( 1 9 8 6 ) . Oppos ing e f f e c t s o f D - l and D-2 r e c e p t o r a g o n i s t s on a c e t y l c h o l i n e l e v e l s i n t h e r a t s t r i a t u m . European J o u r n a l o f P h a r m a c o l o g y , 129 , 3 5 9 - 3 6 2 . F a l a s c h i , P . , Rocco , A . , De G i o r g i o , G . , F r a j e s e , G . , F r a t t a , W., & Gessa, G . L . ( 1 9 8 1 ) . B r a i n dopamine and p r e m a t u r e e j a c u l a t i o n : R e s u l t s o f t r e a t m e n t w i t h dopamine a n t a g o n i s t s . I n G .L . Gessa & G.U. C o r s i n i ( E d s . ) , Apomorphine and o t h e r  d o p a m i n o m l m e t i c s . V o l . 1 : B a s i c p h a r m a c o l o g y ( p p . 1 1 7 - 1 2 1 ) . New Y o r k : Raven P r e s s . F e r n a n d e z - G u a s t i , A . , L a r s s o n , K . , & B e y e r , C. ( 1 9 8 6 ) . E f f e c t o f b i c u c u l l i n e on s e x u a l a c t i v i t y i n c a s t r a t e d male r a t s . P h y s i o l o g y & B e h a v i o r , 3 6 , 2 3 5 - 2 3 7 . F e r r a r i , F . , B a g g i o , G . , & M a n g i a f i c o , V. ( 1 9 8 5 ) . The dopamine a u t o r e c e p t o r a g o n i s t B-HT 920 m a r k e d l y s t i m u l a t e s s e x u a l b e h a v i o r i n male r a t s . E x p e r e n t i a , 4 1 , 6 3 6 - 6 3 8 . F i b i g e r , H.C. & P h i l l i p s , A . G . ( 1 9 8 6 ) . B e h a v i o r a l p h a r m a c o l o g y o f n e u r o l e p t i c d r u g s : P o s s i b l e mechanisms o f a c t i o n . I n S . L . Se iden & R . L . B a l s t e r ( E d s . ) , B e h a v i o r a l p h a r m a c o l o g y :  The c u r r e n t s t a t u s ( p p . 2 4 3 - 2 5 9 ) . New Y o r k : A l a n L i s s . F i b i g e r , H . C , Z i s , A . P . , & P h i l l i p s , A . G . ( 1 9 7 5 ) . H a l o p e r i d o l -i n d u c e d d i s r u p t i o n o f c o n d i t i o n e d a v o i d a n c e r e s p o n d i n g : A t t e n u a t i o n by p r i o r t r a i n i n g or by a n t i c h o l i n e r g i c d r u g s . European J o u r n a l o f P h a r m a c o l o g y , 30 , 3 0 9 - 3 1 4 . Foreman, M.M. & H a l l , J . L . ( 1 9 8 7 ) . E f f e c t s o f D 2 - d o p a m i n e r g i c r e c e p t o r s t i m u l a t i o n on male r a t s e x u a l b e h a v i o r . J o u r n a l  o f N e u r a l T r a n s m i s s i o n , 6 8 , 1 5 3 - 1 7 0 . F r e e d , W . J . & Zee, R .F . ( 1 9 8 2 ) . C r i t e r i a f o r r u l i n g o u t s e d a t i o n as an i n t e r p r e t a t i o n f o r n e u r o l e p t i c e f f e c t s . B e h a v i o r a l  and B r a i n S c i e n c e s , 5_, 5 7 - 5 9 . G e r h a r d t , G . A . , Oke, A . F . , Nagy, G . , Moghaddam, B . , & Adams, R.N. ( 1 9 8 4 ) . N a f i o n - c o a t e d e l e c t r o d e s w i t h h i g h s e l e c t i v i t y f o r CNS e l e c t r o c h e m i s t r y . B r a i n R e s e a r c h , 290 , 3 9 0 - 3 9 5 . Gessa, G .L . & T a g l i a m o n t e , A. ( 1 9 7 5 ) . Ro le o f b r a i n s e r o t o n i n 235 and dopamine i n male s e x u a l b e h a v i o r . I n M. S a n d l e r & G .L . Gessa ( E d s . ) , S e x u a l b e h a v i o r : Pha rmaco logy and b i o c h e m i s t r y ( p p . 1 1 7 - 1 2 8 ) . New Y o r k : Raven P r e s s . G i a n t o n i o , G.W., L u n d , N . L . , & G e r a l l , A . A . ( 1 9 7 0 ) . E f f e c t o f d i e n c e p h a l i c and r h i n e n c e p h a l i c l e s i o n s on t h e male r a t ' s s e x u a l b e h a v i o r . 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