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Isolation-induced facilitation of male sexual behavior in mice De Catanzaro, Denys Anthony 1979

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ISOLATION-INDUCED FACILITATION OF MALE SEXUAL BEHAVIOR IN MICE by DENYS ANTHONY DE CATANZARO B.A. (Hons,), C a r l e t o n U n i v e r s i t y , 1975 M.A., C a r l e t o n U n i v e r s i t y , 1977 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR'THE DEGREE OF DOCTOR OF PHILOSOPHY i n ' • THE FACULTY OF GRADUATE STUDIES Department o f P s y c h o l o g y We a c c e p t t h i s t h e s i s as conforming to the r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA J u l y , 1979 (c) Denys Anthony de C a t a n z a r o , 1979 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 representatives. It is understood that copying or publication of this thesis"for financial gain shall not be allowed without my written permission. Department Of P s y c h o l o g y The University of British Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 D a t e August 2, 1979 B P 75-5 1 1 E i i A b s t r a c t The p r e s e n t study examined the e f f e c t s o f h o u s i n g and s o c i a l c o n d i t i o n s on the s e x u a l performance of male house mice (Mus m u s c u l u s ) • S p e c i f i c a l l y , mice housed p o s t p u b e r t a l l y i n s o c i a l i s o l a t i o n were compared to o t h e r s housed i n a l l - m a l e groups. F o l l o w i n g p e r i o d s o f d i f f e r e n t i a l h o u s i n g , males were t e s t e d i n the p r e s e n c e of o v a r i e c t o m i z e d females made r e c e p t i v e with•exogenous, e s t r o g e n and p r o g e s t e r o n e . In f i v e s e r i e s o f experiments, e f f e c t s o f i s o l a t i o n / g r o u p i n g and r e l a t e d parameters were d e l i n e a t e d , and p h y s i o l o g i c a l and s o c i a l mechanisms u n d e r l y i n g t h e se e f f e c t s , probed, I n the f i r s t s e r i e s o f experiments, the b a s i c e f f e c t s o f i s o l a t i o n and g r o u p i n g were•• examined, In Experiment 1A, a n i m a l s housed 1, 3, o r 12 per cage were g i v e n r e p e a t e d weekly t e s t s w i t h f e m a l e s , ' Performance i n i s o l a t e s - w a s - c o n s i s t e n t l y s u p e r i o r and reached an asymptote t w i c e t h a t o f grouped a n i m a l s , In Experiment IB, r e v e r s a l o f h o u s i n g c o n d i t i o n s , r e v e r s e d performance. Experiment 2 v a r i e d i n t e r v a l s , o f i s o l a t i o n Between s u b j e c t s , f i n d i n g f a c i l i t a t i o n a t s e v e r a l i n t e r v a l s . Experiment 3 compared a n i m a l s under' d i f f e r e n t p o p u l a t i o n d e n s i t i e s . ' D e n s i t y d i d not a l t e r the e f f e c t s o f i s o l a t i o n and g r o u p i n g . In a l l experiments-, a d d i t i o n a l t e s t s w i t h t a r g e t males i n d i c a t e d t h a t a g g r e s s i v e and s e x u a l performance were m o d e r a t e l y c o r r e l a t e d and responded s i m i l a r l y to p a r a m e t r i c m a n i p u l a t i o n s . In the second s e r i e s , the s t r a i n and s p e c i e s g e n e r a l i t y o f i s o l a t i o n / g r o u p i n g d i f f e r e n c e s i n s e x u a l a c t i v i t y was s t u d i e d . Experiment 4 examined male Swiss-Webster, C57, and DBA mice housed i n d i v i d u a l l y or grouped f o r 2 weeks. W i t h i n each s t r a i n , s o c i a l i s o l a t e s showed more mounts, i i i 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 and s h o r t e r l a t e n c i e s to f i r s t mount and i n t r o m i s s i o n . Experiment 5 i n v o l v e d a s i m i l a r comparison o f i s o l a t e d and grouped male r a t s , hamsters, and g e r b i l s . I s o l a t i o n produced no major e f f e c t i n hamsters but reduced performance i n r a t s and g e r b i l s . R e s u l t s suggest t h a t f a c i l i t a t i o n o f s e x u a l a c t i v i t y by i s o l a t i o n i s c h a r a c t e r i s t i c o f the mouse s p e c i e s . Decrements accompanying p o s t p u b e r t a l i s o l a t i o n i n the r a t resemble e f f e c t s o f p r e p u b e r t a l i s o l a t i o n i n t h i s s p e c i e s . These s p e c i e s d i f f e r e n c e s may p a r a l l e l d i f f e r e n c e s i n p h y s i o l o g y and s o c i a l b e h a v i o r . I n the t h i r d s e r i e s , the minimum p e r i o d o f i s o l a t i o n r e q u i r e d to produce i s o l a t i o n / g r o u p i n g d i f f e r e n c e s was e s t a b l i s h e d . Experiment 6 compared s e x u a l performance of male mice i s o l a t e d o r grouped f o r p e r i o d s of 1 day or 2 weeks. I s o l a t i o n f a c i l i t a t e d performance e q u a l l y a t b o t h i n t e r v a l s ; t h i s d i f f e r s from e f f e c t s o f i s o l a t i o n oh o t h e r b e h a v i o r a l and p h y s i o l o g i c a l v a r i a b l e s . Experiment 7 examined a n i m a l s i s o l a t e d f o r i n t e r v a l s r a n g i n g from 1 hour to 1 week. I s o l a t e s showed g r e a t e r p e r f o r -mance a t a l l i n t e r v a l s e x c e e d i n g 12 h o u r s . Simple c l e a n i n g o f grouped a n i m a l ' s cages i n c r e a s e d t h e i r performance a t 1- and 4-hour i n t e r v a l s . In Experiment 8, grouped males were observed c o n t i n u o u s l y f o r 24 hours p r e c e d i n g t e s t i n g . I n t e r m a l e mounting was r a r e and n e i t h e r i t nor a g g r e s s i o n c o r r e l a t e d w i t h subsequent s e x u a l performance. In the f o u r t h and f i f t h s e r i e s , some p o s s i b l e p h y s i o l o g i c a l m e d i a t o r s o f i s o l a t i o n / g r o u p i n g e f f e c t s were s t u d i e d . In Experiment 9A, a d r e n a l e c t o m i z e d and n o n - a d r e n a l e c t o m i z e d mice were compared. F o l l o w i n g a drenalectomy, grouped mice showed e l e v a t e d s e x u a l a c t i v i t y w h i l e i s o l a t e s d e c l i n e d . In Experiment 9B, c o r t i c o s t e r o n e treatment f a i l e d t o r e v e r s e e f f e c t s o f adrenalectomy. In Experiment 10, ACTH treatment r e s t o r e s mating i v a c t i v i t y to p r e a d r e n a l e c t o m y l e v e l s i n a d r e n a l e c t o m i z e d i s o l a t e s but had l i t t l e e f f e c t on i n t a c t i s o l a t e s . R e s u l t s suggest an a d r e n a l involvement i n i s o l a t i o n e f f e c t s but do not s p e c i f y i t s n a t u r e . I n Experiment 11, c a s t r a t e d males g i v e n replacement t e s t o s t e r o n e were compared to i n t a c t males. I s o l a t i o n / g r o u p i n g d i f f e r e n c e s were p r e s e n t i n i n t a c t but not t e s t o s t e r o n e t r e a t e d mice, s u g g e s t i n g gonadal hormone in v o l v e m e n t i n the phenomenon. S o c i a l i n t e r a c t i o n s among grouped male mice appear to suppress t h e i r subsequent s e x u a l a c t i v i t y w i t h f e m a l e s , ' I n t e r m a l e a g g r e s s i o n , p a r t i c u l a r l y , may s t r e s s group members, p r o d u c i n g p h y s i o l o g i c a l changes c o n d u c i v e to low s e x u a l a c t i v i t y . Furthermore, the p r e s e n t a t i o n of stimulus' f e m a l e s .may Be r e l a t i v e l y - m o r e n o v e l f o r i s o l a t e s and c o n s e q u e n t l y produce >higher level's o f g e n e r a l a r o u s a l i n t h e s e mice, T a b l e o f Contents page A b s t r a c t ,. i i T a b l e o f Contents , . , ..... v L i s t o f T a b l e s , , v i i i L i s t o f F i g u r e s x Acknowledgements x i i I n t r o d u c t i o n 1 E f f e c t s o f I s o l a t i o n on B e h a v i o r and P h y s i o l o g y . . . 2 R e l a t i o n s h i p o f I s o l a t i o n to S t r e s s , Dominance, D e f e a t , and T e r r i t o r i a l i t y . .5 I s o l a t i o n and Male S e x u a l B e h a v i o r . , . . , 9 S e c t i o n I : E f f e c t s o f B a s i c I s o l a t i o n / G r o u p i n g Parameters on S e x u a l and A g g r e s s i v e B e h a v i o r 14 Experiment IA 15 Method 15 Subj e c t s • .15 P r e p a r a t i o n of s t i m u l u s f e m a l e s . . . 16 P r o c e d u r e 16 R e s u l t s and D i s c u s s i o n , 17 Experiment IB .22 Method.. .. ,,. 22 R e s u l t s and D i s c u s s i o n , 2 3 v i E xperiment 2 24 Method 25 R e s u l t s and D i s c u s s i o n 26 Experiment 3 31 Method. .31 R e s u l t s and D i s c u s s i o n 33 G e n e r a l D i s c u s s i o n , 38 S e c t i o n I I : S t r a i n and S p e c i e s G e n e r a l i t y . . . . . . . 46 Experiment 4 47 Method. 47 R e s u l t s and D i s c u s s i o n . 49 Experiment 5 ...53 Method. , 55 Subj e c t s , 55 S t i m u l u s f e m a l e s 5 5 P r o c e d u r e . . . . ... . .. ,.. . ............ . ........ 56 R e s u l t s and D i s c u s s i o n . 56 G e n e r a l D i s c u s s i o n 61 S e c t i o n I I I : B r i e f P e r i o d s o f I s o l a t i o n o r Grouping 65 Experiment 6 67 Method ..' 67 R e s u l t s and D i s c u s s i o n 68 Experiment 7 70 Method 70 R e s u l t s and D i s c u s s i o n . 71 v i i E xperiment 8 75 Method 76 R e s u l t s and D i s c u s s i o n . .76 G e n e r a l D i s c u s s i o n 80 S e c t i o n IV: P i t u i t a r y - A d r e n a l M e d i a t i o n , ..85 Experiment 9A. ............................ , 86 Method. f ......87 R e s u l t s and D i s c u s s i o n . , 8 8 Experiment 9 B , . 9 2 Method t.......... , 93 R e s u l t s and D i s c u s s i o n . .93 Experiment 10,.,...,.,.........., , .95 M e t h o d , , t - 1 . . . . . . . . . . , , . . , , , , . , .96 R e s u l t s and D i s c u s s i o n . . . , , . , , . , , . , , 9 7 G e n e r a l D i s c u s s i o n 101 S e c t i o n V: P i t u i t a r y - G o n a d a l M e d i a t i o n 106 Experiment 11 • • .106 Method 107 R e s u l t s 107 D i s c u s s i o n . . , • .112 O v e r a l l D i s c u s s i o n and C o n c l u s i o n s ,, 117 The Nature o f I s o l a t i o n E f f e c t s on Sex u a l Behavior...117 The M e d i a t i o n o f I s o l a t i o n E f f e c t s , 120 G e n e r a l I m p l i c a t i o n s 126 R e f e r e n c e s 132 v i i i L i s t o f T a b l e s T a b l e T i t l e " Page I: Mean Scor e s i n Weekly Repeated Measures o f S e x u a l and 21 A g g r e s s i v e Responses to S t i m u l u s Females and Males i n Experiment 1 I I : Mean Scores on Sexu a l and A g g r e s s i v e Measures w i t h . 29 St i m u l u s Females and Males a t I n t e r v a l s from I s o l a t i o n / Grouping i n Experiment 2 I I I : Mean Scores on Measures of Sexu a l and A g g r e s s i v e Responses 37 to S t i m u l u s Females and Males Under D i f f e r e n t D e n s i t i e s i n Experiment 3 I V : Means and Standard E r r o r s of Response L a t e n c i e s ( i n sec) 52 and C o p u l a t o r y E f f i c i e n c y , and P e r c e n t Responding i n Experiment 4 V: Means and Standard E r r o r s o f Response L a t e n c i e s ( i n sec) 59 and C o p u l a t o r y E f f i c i e n c y , and P e r c e n t Responding i n Experiment 5 VI: Means and Standard E r r o r s of Measures of Male M i c e "; 69 I s o l a t e d or Grouped i n 3 or 12 f o r 24 Hours o r 2 Weeks i n Experiment 6 V I I : Means and Standard E r r o r s o f Measures o f Male M i c e 74 I s o l a t e d or Grouped f o r D i f f e r e n t I n t e r v a l s i n Experiment 7 VIII.: S e x u a l Performance and Stepwise R e g r e s s i o n Between 77 I n t e r m a l e A g g r e s s i o n and Mounting and Subsequent Se x u a l Measures i n Experiment 8 i x IX: Means and Standard E r r o r s o f Measures o f I n t e r m a l e 78 A g g r e s s i o n and Mounting i n Experiment 8 X: Means and Standard E r r o r s o f Measures o f S e x u a l 91 Performance i n A d r e n a l e c t o m i z e d or Sham-Adrenalectomized, I s o l a t e d or Grouped Male M i c e i n Experiment 9A XI: Means and Standard E r r o r s of Measures o f S e x u a l 94 Performance o f A d r e n a l e c t o m i z e d C o r t i c o s t e r o n e - T r e a t e d and Sham-Adrenalectomized O i l - T r e a t e d M i c e i n Experiment 9B X I I : Means and Standard E r r o r s o f Sex u a l Performance o f 100 A d r e n a l e c t o m i z e d and Sham-Adrenalectomized M i c e T r e a t e d w i t h ACTH o r S a l i n e i n Experiment 10 X I I I : Means and Standard E r r o r s o f S e x u a l Performance o f I n t a c t 110 or C a s t r a t e d Male M i c e T r e a t e d w i t h O i l or T e s t o s t e r o n e P r o p i o n a t e i n Experiment 11 X L i s t o f F i g u r e s F i g u r e T i t l e Page 1: The Mean T o t a l D u r a t i o n o f Mounting, w i t h o f w i t h o u t 19 I n t r o m i s s i o n , i n Weekly Repeated Measures of Animals i n Experiment 1 2: The Mean T o t a l D u r a t i o n of Mounting, w i t h or w i t h o u t 28 I n t r o m i s s i o n , i n Between-Group T e s t s a t D i f f e r e n t I n t e r v a l s f o l l o w i n g I s o l a t i o n or Grouping i n Experiment 2 3: The Mean T o t a l D u r a t i o n o f Mounting, w i t h or w i t h o u t 35 I n t r o m i s s i o n , o f Animals Housed w i t h D i f f e r e n t Volumes of Space per Animal i n Each Cage i n Experiment 3 4: Mean Performance o f I s o l a t e d and Grouped Swiss-Webster 51 ( S w i s s ) , C57Bl/GCrlBR (C57), and DBA/2NG1BR (DBA) Male M i c e on Measures o f Sex u a l B e h a v i o r i n the P r e s e n c e o f R e c e p t i v e Females i n Experiment 4 5; Mean Performance of I s o l a t e d and Grouped Male R a t s , 58 Hamsters, and G e r b i l s on Measures of Sex u a l B e h a v i o r i n the P r e s e n c e of R e c e p t i v e C o n s p e c i f i c Females i n Experiment 5 6: The Mean T o t a l D u r a t i o n o f Mounting, w i t h or w i t h o u t 73 I n t r o m i s s i o n , i n M i c e I s o l a t e d o r Grouped f o r D i f f e r e n t I n t e r v a l s i n Experiment 7 The Mean T o t a l D u r a t i o n o f Mounting, 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 r e n a l e c t o m i z e d (Adx) or Sham-A d r e n a l e c t o m i z e d (Sham) , I s o l a t e d ( I s o l ) o r Grouped (Gp) M i c e i n Experiment 9A 5 The Mean T o t a l D u r a t i o n o f Mounting^ 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 r e n a l e c t o m i z e d (Adx) or Sham-A d r e n a l e c t o m i z e d (Sham) I s o l a t e d M i c e G i v e n D a i l y S a l i n e ( S a l ) or ACT1I i n Experiment 10 The Mean T o t a l D u r a t i o n of Mounting, with, o r w i t h o u t I n t r o m i s s i o n , i n I n t a c t O i l - T r e a t e d and C a s t r a t e d T e s t o s t e r o n e - T r e a t e d M i c e i n Experiment 11 x i i Acknowledgements T h i s r e s e a r c h was su p p o r t e d by N a t i o n a l R e s e a r c h C o u n c i l o f Canada Grant AG277 and a N a t u r a l , A p p l i e d , and H e a l t h S c i e n c e s Grant from the U n i v e r s i t y o f B r i t i s h Columbia, b o t h awarded to Dr. B o r i s B. G o r z a l k a . I t was pursued d u r i n g the a u t h o r ' s t e n u r e of a N a t i o n a l R e s earch C o u n c i l o f Canada P o s t g r a d u a t e S c h o l a r s h i p and an NIMR Type B Supplementary S c h o l a r s h i p . I would l i k e to thank Dr. B o r i s B. G o r z a l k a f o r h i s i n v a l u a b l e a d v i c e and a s s i s t a n c e throughout the c o u r s e of t h i s r e s e a r c h . I would a l s o l i k e to thank E l l e n Beaumont, A z i z T h obani, and B a r r y B a y l i s f o r t h e i r a b l e a s s i s t a n c e i n implementing some of the e x p e r i m e n t a l p r o c e d u r e s , e s p e c i a l l y those of Experiments 4, 7, and 9A, 1 .INTRODUCTION There i s growing e v i d e n c e t h a t the b i o l o g y and b e h a v i o r o f male house mice (Mus musculus) a r e s t r o n g l y a f f e c t e d by m a n i p u l a t i o n s o f s o c i a l v a r i a b l e s and h o u s i n g c o n d i t i o n s . One major f o c u s of i n v e s t i g a t i o n has i n v o l v e d a comparison o f a d u l t male mice housed e i t h e r i n s o c i a l i s o l a t i o n o r i n a l l - m a l e groups. T h i s i n v e s t i g a t i o n has produced a c o n s i d e r a b l e amount of d a t a i n d i c a t i n g the e x i s t e n c e of major p h y s i o l o g i c a l and b e h a v i o r a l d i f f e r e n c e s between i s o l a t e d and grouped mice. The e x p e r i m e n t a t i o n d e s c r i b e d h e r e i n v o l v e d an e x a m i n a t i o n o f male s e x u a l b e h a v i o r w i t h i n the i s o l a t i o n / g r o u p i n g paradigm. While t h e r e have been numerous r e p o r t s of e f f e c t s of i s o l a t i o n and g r o u p i n g on subsequent i n t e r m a l e i n t e r a c t i o n s and on a s s o c i a t e d p h y s i o l o g i c a l v a r i a b l e s , t h e r e a r e no comparable r e p o r t s i n v o l v i n g male-female i n t e r -a c t i o n s . In the p r e s e n t s t u d y male mice t h a t were housed d i f f e r e n t i a l l y d u r i n g p o s t p u b e r t a l development were measured f o r s e x u a l a c t i v i t y . Measurement o c c u r r e d i n the p r e s e n c e o f females made s e x u a l l y r e c e p t i v e t hrough o v a r i e c t o m y and treatment w i t h e s t r o g e n and p r o g e s t e r o n e . The e f f e c t s o f the b a s i c i s o l a t i o n / g r o u p i n g and r e l a t e d parameters were 2 probed. Subse q u e n t l y , p h y s i o l o g i c a l and s o c i a l m e d i a t o r s of t h e s e e f f e c t s were examined through t e c h n i q u e s i n v o l v i n g g l a n d u l a r e x t r a c t i o n , treatment w i t h exogenous hormones, and s y s t e m a t i c o b s e r v a t i o n of i n t e r -male i n t e r a c t i o n s . E f f e c t s o f I s o l a t i o n on B e h a v i o r and P h y s i o l o g y The most f r e q u e n t l y s t u d i e d e f f e c t o f s o c i a l i s o l a t i o n upon male mice i s i s o l a t i o n - i n d u c e d a g g r e s s i o n ( S c o t t , 1966; V a l z e l l i , 1969). Mice i s o l a t e d f o r s e v e r a l days i n a d u l t h o o d f r e q u e n t l y show i n t e n s e l e v e l s o f a g g r e s s i o n when s u b s e q u e n t l y p l a c e d w i t h t a r g e t mice. I s o l a -t i o n - i n d u c e d a g g r e s s i o n i s found almost e x c l u s i v e l y i n males of the s p e c i e s and i s u s u a l l y d i r e c t e d o n l y toward o t h e r males. The e f f e c t s o f i s o l a t i o n on i n t e r m a l e a g g r e s s i o n a r e known to be p r o g r e s s i v e ; they i n c r e a s e w i t h time i n i s o l a t i o n ( B r a i n & N o w e l l , 1970; V a l z e l l i , 1969). Some i n b r e d g e n e t i c s t r a i n s o f mice show h i g h e r l e v e l s o f a g g r e s s i o n than do o t h e r s t r a i n s (Karczmar & Scudder, 1969; LeDouarec & Broussy, 1969). I s o l a t i o n - i n d u c e d a g g r e s s i o n may o c c u r i n a r e l a t i v e l y m i l d and a t t e n u a t e d form i n some o t h e r r o d e n t s p e c i e s ( B l a n c h a r d & B l a n c h a r d , 1977; Conner, 1972; Edwards & Rowe, 1975; T h i e s s e n & Yahr, 1977). In mice, however, i t i s g e n e r a l l y q u i t e i n t e n s e ; mice may b i t e and a t t a c k one another q u i t e v i g o r o u s l y , i n f l i c t i n g l a r g e l a c e r a t i o n s and o c c a s i o n a l l y c a u s i n g d e a t h , when p l a c e d t o g e t h e r f o l l o w i n g l o n g p e r i o d s o f i s o l a t i o n . G e n e r a l a c t i v i t y l e v e l s may a l s o be a f f e c t e d i n male mice by s o c i a l i s o l a t i o n . Essman (1968) and B r a i n , H a l e y , and Nowell (1971) have found t h a t i s o l a t e s show more locomotor a c t i v i t y than do grouped an i m a l s upon exposure to a n o v e l environment. However, i s o l a t e d mice a r e u s u a l l y l e s s a c t i v e than grouped mice w h i l e i n t h e i r home cages 3 w i t h o u t d i s t u r b a n c e (Welch & Welch, 1969a; 1969b). There i s c o n s i d e r a b l e e v i d e n c e t h a t the p i t u i t a r y - a d r e n o c o r t i c a l system i s a f f e c t e d by s o c i a l i s o l a t i o n , a l t h o u g h the r e p o r t e d r e s u l t s and i n t e r p r e t a t i o n s a r e o f t e n a t v a r i a n c e . I s o l a t e d male mice g e n e r a l l y show lower a d r e n a l w e i g h t s than do grouped males when n e i t h e r have been sub-j e c t e d to s t r e s s o r s ( e .g., Benton, G o l d s m i t h , Gamal-El-Din, B r a i n , & H u c k l e b r i d g e , 1978; B r a i n & N o w e l l , 1971; Bronson, 1967; C h r i s t i a n , 1959). Experiments r e p o r t i n g h i g h e r a d r e n a l w e i g h t s f o r i s o l a t e s (e.g., S i g g , 1969) tend to be t h o s e i n which the animals a r e s u b j e c t e d t o s t r e s s f u l e x p e r i e n c e s such as f i g h t i n g b e f o r e the g l a n d weights a r e o b t a i n e d . Assays of c i r c u l a t i n g c o r t i c o s t e r o n e l e v e l s have i n d i c a t e d a l a c k o f d i f f e r e n c e between u n s t r e s s e d i s o l a t e d and grouped mice (Benton e t a l . , 1978; G o l d s m i t h , Brain,& Benton, 1976). However, i s o l a t e s may show h i g h e r l e v e l s o f c i r -c u l a t i n g . c o r t i c o s t e r o n e when s t r e s s e d by f i g h t i n g or o t h e r means (Goldsmith e t a l . , 1976; S i g g , 1969). R e s u l t s from a s t u d y by B r a i n and Nowell (1971) ar e somewhat i n c o n s i s t e n t w i t h t h i s p i c t u r e . B r a i n and Nowell found t h a t b o t h b a s a l and s t r e s s c o r t i c o s t e r o n e l e v e l s were lower i n i s o l a t e d mice, however, t h e i r group s i z e (16 mice) was somewhat l a r g e r than i n most s t u d i e s . A d r e n o c o r t i c o t r o p i c hormone, which i s more d i f f i c u l t to assay because i t i s r e l a t i v e l y u n s t a b l e and i t s l e v e l s may change r a p i d l y , appears to be i n v o l v e d i n c o n t r o l o f i s o l a t i o n - i n d u c e d a g g r e s s i o n ( B r a i n & P o o l e , 1974; L e s h n e r , Walker, Johnson, K e l l i n g , K r e i s l e r , & Svare, 1973) and may a l s o d i f f e r between i s o l a t e d and grouped mice. A d r e n a l m e d u l l a r y f u n c t i o n i s a l s o a f f e c t e d . There a r e a number of r e p o r t s (Anton, 1969; Anton, Schwartz, and Kramer, 1968; Benton e t a l . , 1978; Welch & Welch, 1968) t h a t t h e r e a r e no s i g n i f i c a n t d i f f e r e n c e s i n a d r e n a l c a t e c h o l a m i n e l e v e l s between i s o l a t e d and grouped mice. However, 4 one study (Welch, 1965) has r e p o r t e d t h a t grouped mice have h i g h e r m e d u l l a r y l e v e l s of e p i n e p h r i n e . I t a l s o appears t h a t the t u r n o v e r o f e p i n e p h r i n e i s g r e a t e r i n grouped a n i m a l s (Welch & Welch, 1968; 1971). The p e r c e n t a g e o f t o t a l a d r e n a l c a t e c h o l a m i n e c o n s t i t u t e d by n o r e p i n e -p h r i n e has been r e p o r t e d b o t h t o be h i g h e r i n i s o l a t e s (Welch, 1965) and not t o d i f f e r between i s o l a t e d and grouped male mice (Anton, 1969; Anton e t a l . , 1968). Many s t u d i e s o f mice r e p o r t an i n c r e a s e i n gonadal a c t i v i t y as a consequence o f i s o l a t i o n . S t u d i e s c o n t r a s t i n g i s o l a t e d and group-housed males have i n d i c a t e d t h a t the former have h e a v i e r sex a c c e s s o r i e s t h a n the l a t t e r (Benton e t a l . , 1978; B r a i n , 1971; B r a i n & N o w e l l , 1971; C h r i s t i a n , 1955; Vandenbergh, 1960). S i z e s o f t e s t e s , p r e p u t i a l s , p r o s -t a t e s , and s e m i n a l v e s i c a l s , may a l l be i n c r e a s e d by s o c i a l i s o l a t i o n . D i f f e r e n c e s between i s o l a t e d and grouped a n i m a l s i n gonadal a c t i v i t y may r e l a t e t o d i f f e r e n c e s i n p i t u i t a r y - a d r e n o c o r t i c a l a c t i v i t y because l e v e l s o f t e s t o s t e r o n e a r e known to d e c r e a s e as a consequence o f p i t u i -t a r y - a d r e n o c o r t i c a l a c t i v a t i o n ( B u l l o c k & New, 1971; D e s j a r d i n s & Ewing, 1971). N e u r o t r a n s m i t t e r systems a l s o appear t o be a f f e c t e d by s o c i a l i s o l a t i o n and group h o u s i n g . Marked e f f e c t s have been o b s e r v e d i n the l e v e l s and t u r n o v e r r a t e s o f many o f the p u t a t i v e n e u t r o t r a n s m i t t e r s and t h e i r p r e c u r s o r s and m e t a b o l i t e s i n the c e n t r a l nervous system. I s o l a t e d mice have been r e p o r t e d to show lower l e v e l s o f the b r a i n c a t e -c h o l a m i n e s , n o r e p i n e p h r i n e and dopamine, w h i l e s e r o t o n i n l e v e l s a r e g e n e r a l l y n ot a f f e c t e d ( G a r a t t i n i , G i a c a l o n e , & V a l z e l l i , 1969; Welch & Welch, 1969a; 1969b). Decreased l e v e l s o f n e u r a l N - a c e t y l - L - a s p a r t i c 5 a c i d have a l s o been observed i n i s o l a t e s ( M a r c u c c i , M u s s i n i , V a l z e l l i , & G a r a t t i n i , 1968). Turnover o r u t i l i z a t i o n r a t e s o f n o r e p i n e p h r i n e , dopamine, and s e r o t o n i n may a l l be h i g h e r i n i s o l a t e d than i n grouped mice when these a n i m a l s a r e exposed to s t r e s s f u l or n o v e l s t i m u l i ( G a r a t t i n i e t a l . , 1969; Welch & Welch, 1969a; 1969b). I n c r e a s e d neuro-t r a n s m i t t e r t u r n o v e r may r e l a t e to h i g h e r l e v e l s o f a g g r e s s i v e b e h a v i o r and g e n e r a l a c t i v i t y o b s erved i n i s o l a t e s (Essman, 1968; Welch & Welch, 1971). D i f f e r e n c e s i n n e u r o t r a n s m i t t e r l e v e l s and u t i l i z a t i o n between i s o l a t e d and grouped a n i m a l s may a l s o r e l a t e t o d i f f e r e n c e s i n p i t u i t a r y -a d r e n o c o r t i c a l a c t i v i t y ; f o r example, i n c r e a s e d ACTH l e v e l s may produce i n c r e a s e d t u r n o v e r o f c a t e c h o l a m i n e s and s e r o t o n i n (Dunn & G i s p e n , 1977). In summary so f a r , t h e r e i s e v i d e n c e t h a t i s o l a t e s - a r e l e s s a c t i v e i n t h e i r home cage, but more a c t i v e and prone t o be a g g r e s s i v e when exposed to n o v e l o r s t r e s s f u l environments. A l s o , i s o l a t e s show lower b a s e l i n e p i t u i t a r y - a d r e n a l and ca-techolaminergic a c t i v i t y , but h i g h e r a c t i v i t y o f t h e s e systems when s t r e s s e d . B a s e l i n e gonadal a c t i v i t y i s i n c r e a s e d i n i s o l a t e s . R e l a t i o n s h i p o f I s o l a t i o n to S t r e s s , Dominance, D e f e a t , and T e r r i t o r i a l i t y The p h y s i o l o g i c a l d i f f e r e n c e s between i s o l a t e d and group-housed mice can be i n t e r p r e t e d as i n d i c a t i n g g r e a t e r " s t r e s s " i n the grouped a n i m a l s . " S t r e s s " i s g e n e r a l l y d e f i n e d p h y s i o l o g i c a l l y as i n v o l v i n g p i t u i t a r y - a d r e n o c o r t i c a l and a d r e n a l m e d u l l a r y f u n c t i o n i n g , w i t h i n c r e a s e d a c t i v a t i o n o f t h e s e systems i n d i c a t i n g i n c r e a s e d s t r e s s ( L e v i n e , 1976; S e l y e , 1956). A v a r i e t y of p h y s i o l o g i c a l and p s y c h o l o g i c a l s t i m u l i , which u s u a l l y a r e a v e r s i v e and t a x the organism's a b i l i t y to cope, w i l l a c t i v a t e t h e s e p h y s i o l o g i c a l systems; such s t i m u l i a r e commonly c a l l e d s t r e s s o r s . 6 A d r e n a l a c t i v a t i o n adapts the organism to"demanding s i t u a t i o n s through a number of b i o c h e m i c a l and v i s c e r a l changes t h a t i n c r e a s e the organism's energy l e v e l s . P r o l o n g e d a d r e n a l a c t i v a t i o n i s u s u a l l y a s s o c i a t e d w i t h r e d u c t i o n s i n o t h e r p h y s i o l o g i c a l a c t i v i t y , such as i m munological and r e p r o d u c t i v e a c t i v i t y . R e c e n t . e v i d e n c e i n d i c a t e s t h a t changes i n n e u r o -c h e m i c a l systems o c c u r concomitant w i t h s t r e s s - r e l a t e d p i t u i t a r y - a d r e n a l change. B r i e f s t r e s s o r s may produce immediate i n c r e a s e s i n c e n t r a l c a t e -c h o l a m i n e r g i c a c t i v i t y , f o l l o w e d by a d e c r e a s e i n c a t e c h o l a m i n e r g i c a c t i v i t y below b a s e l i n e and an i n c r e a s e i n c h o l i n e r g i c a c t i v i t y (Anisman, 1978). D u r i n g more p r o l o n g e d s t r e s s t h e r e may be an i n c r e a s e i n s y n t h e s i s of c a t e c h o l a m i n e s , a slowdown i n u t i l i z a t i o n o f c a t e c h o l a m i n e s , or b o t h , w h i l e v e r y s e v e r e s t r e s s may produce v e r y low l e v e l s o f b r a i n c a t e c h o l a -mines (Weil-Maherbe, 1972; Y u w i l e r , 1971). The i n d i c a t i o n s , d i s c u s s e d above, o f i n c r e a s e d p i t u i t a r y -a d r e n o c o r t i c a l , a d r e n a l m e d u l l a r y , and c e n t r a l c a t e c h o l a m i n e r g i c a c t i v i t y , and d e c r e a s e d gonadal a c t i v i t y i n grouped male mice a r e thus i n d i c a t i v e o f g r e a t e r s t r e s s l e v e l s i n t h e s e a n i m a l s (see B r a i n , 1975 f o r f u r t h e r d i s c u s s i o n o f t h i s p o i n t ) . T h i s s t r e s s presumably a r i s e s from i n t e r m a l e a g g r e s s i o n and c o m p e t i t i o n f o r common r e s o u r c e s among grouped a n i m a l s . P a r a d o x i c a l l y , however, i s o l a t e s may show g r e a t e r immediate s t r e s s r e a c t i o n s to n o v e l s t i m u l i . T h i s i n c r e a s e d p h y s i o l o g i c a l r e a c t i v i t y i s accompanied by i n c r e a s e d b e h a v i o r a l a c t i v a t i o n . Male mice i n l o n g e s t a b l i s h e d groups u s u a l l y demonstrate c o n s i -derable, v a r i a n c e i n i n t e r m a l e i n t e r a c t i o n s and b e h a v i o r a l response to a number of e x p e r i m e n t a l t a s k s . Such i n t e r - i r i d i v i d u a l d i f f e r e n c e s have f r e q u e n t l y been i n t e r p r e t e d as i n d i c a t i n g the p r e s e n c e of dominance 7 h i e r a r c h i e s . "Dominance" l e v e l has been r a t e d through o b s e r v a t i o n of r e l a t i v e s u c c e s s o f group members i n o b t a i n i n g r e i n f o r c e r s , such as f o o d , when they must compete f o r a s i n g l e s o u r c e (e.g., M e s s e r i , E l e f t h e r i o u , & O l i v e r i o , 1975). The o c c u r r e n c e of s u b m i s s i v e p o s t u r e s has a l s o been used; t h e s e a r e c h a r a c t e r i z e d by u p r i g h t s t a n c e s w i t h eyes open, e a r s e r e c t , and o c c a s i o n a l v o c a l i z a t i o n ( e . g., Benton e t a l . , 1978). Animals t h a t a r e more a g g r e s s i v e a r e a l s o g e n e r a l l y c o n s i d e r e d more dominant, and the o c c u r r e n c e of s c a r s on the f l a n k s and h i n d q u a r t e r s , i n f l i c t e d by o t h e r a g g r e s s i v e males, i s c o n s i d e r e d an e s p e c i a l l y r e l i a b l e s i g n of s u b o r d i n a t i o n (Benton e t a l . , 1978; D e F r i e s & M c C l e a r n , 1970; 1972; McKinney & D e s j a r d i n s , 1973a; 1973b). There i s a s u b s t a n t i a l amount of e v i d e n c e i n d i c a t i n g t h a t i s o l a t e d male mice a r e s i m i l a r i n terms o f b o t h p h y s i o l o g y and b e h a v i o r to more dominant and t e r r i t o r i a l grouped males. L i k e i s o l a t e s , dominant grouped males show g l a n d u l a r and hormonal i n d i c a -t i o n s o f r e l a t i v e l y low a d r e n a l m e d u l l a r y and p i t u i t a r y - a d r e n o c o r t i c a l a c t i v i t y , and r e l a t i v e l y h i g h gonadal a c t i v i t y (Benton, e_t a l . , 1978; B r a i n , 1975; McKinney & D e s j a r d i n s , 1973a; 1973b). Among grouped mice, then, dominants may be l e s s s t r e s s e d than s u b o r d i n a t e s . The major d e f i n i n g f e a t u r e o f dominance, a g g r e s s i v e n e s s , i s a l s o an a t t r i b u t e o f i s o l a t e s . B r a i n (1975) has r e c e n t l y s u g g e s t e d t h a t b o t h i s o l a t e s and dominants a r e t e r r i t o r i a l a n i m a l s and t h a t t h e i r a g g r e s s i v e n e s s r e f l e c t s t h i s . These dominance s t u d i e s a r e complemented by s t u d i e s o f b i o -c h e m i c a l and b e h a v i o r a l e f f e c t s o f d e f e a t i n f i g h t i n g b o u t s . S u b j e c t i n g mice to d e f e a t i n c r e a s e s a d r e n o c o r t i c a l a c t i v i t y ( B r a i n & N o w e l l , 1970; Bronson & E l e f t h e r i o u , 1965) as does g r o u p i n g . D e f e a t a l s o a l t e r s whole b r a i n , h y p o t h a l a m i c , amygdaloid, and f r o n t a l c o r t i c a l l e v e l s o f n o r e p i n e -8 p h r i n e and s e r o t o n i n ( E l e f t h e r i o u & Church, 1968; Welch & Welch, 1971). Changes i n h y p o t h a l a m i c l e v e l s o f l u t e i n i z i n g hormone a l s o f o l l o w d e f e a t ( E l e f t h e r i o u & Church, 1967; 1968), w h i l e p r o l o n g e d a g g r e s s i v e i n t e r -a c t i o n s may suppress w e i g h t s o f sex a c c e s s o r y g l a n d s and d e c r e a s e produc-t i o n of t e s t i c u l a r androgens i n s u b o r d i n a t e but not dominant mice (McKinney & D e s j a r d i n s , 1973a; 1973b). S u b j e c t i n g mice to d e f e a t may a l s o e l e v a t e a d r e n a l m e d u l l a r y t y r o s i n e h y d r o x y l a s e and phenyl-ethanolamine-N-methyl t r a n s f e r a s e a c t i v i t y (Maengwyn-Davies, Johnson, Thoa, Weise, & Kopi n , 1973) and a d r e n a l and plasma l e v e l s o f e p i n e p h r i n e and n o r e p h i n e p h r i n e ( H u c k l e -b r i d g e , N o w e l l , & D i l k s , 1973; Welch & Welch, 1971). P i t u i t a r y - t h y r o i d a l a c t i v i t y may a l s o be i n f l u e n c e d by d e f e a t i n mice ( E l e f t h e r i o u , Church, Norman, P a t t i n s o n , & Z o l o v i c k , 1968). S i n c e i n t e r m a l e f i g h t i n g i s common among grouped male mice, t h e s e s t u d i e s o f d e f e a t and dominance may h e l p e x p l a i n the c o n d i t i o n o f grouped a n i m a l s . As i n c r e a s i n g numbers o f male mice a r e housed p e r cage, the number o f d e f e a t e d o r s u b o r d i n a t e mice may i n c r e a s e ( B r a i n , 1975), t h e r e b y i n c r e a s i n g the number o f s t r e s s e d a n i m a l s . I s o l a t e d a n i m a l s may be r e l a t i v e l y u n s t r e s s e d because they remain unexposed to d e f e a t and o t h e r s o c i a l s t r e s s o r s . D i f f e r e n t i a l s t r e s s and o t h e r i s o l a t i o n / g r o u p i n g e f f e c t s may a l s o be e x p l a i n e d by the r e l a t i o n s h i p o f t h e s e h o u s i n g c o n d i t i o n s to the n a t u r a l s o c i a l s t r u c t u r e o f the s p e c i e s . House mice g e n e r a l l y l i v e i n s m a l l demes, w i t h one dominant male d e f e n d i n g a t e r r i t o r y ( C r o w c r o f t & Rowe, 1963; M a c i n t o s h , 1970; Reimer & P e t r a s , 1967; Rowe & R e d f e r n , 1969). I n d i v i d u a l h o u s i n g i n the l a b o r a t o r y may b e t t e r approximate n a t u r a l e n v i r o n m e n t a l and s o c i a l c o n d i t i o n s than does the confinement o f s e v e r a l males t o g e t h e r i n a l i m i t e d space. Each i n d i v i d u a l l y housed mouse may 9 c o n s t i t u t e a t e r r i t o r i a l and dominant a n i m a l . However, Reimer & P e t r a s (1967) r e p o r t t h a t some s u b o r d i n a t e males may be found l i v i n g i n p r o x i m i t y w i t h more dominant males i n n a t u r a l demes of house mice; thus i t i s not y e t c l e a r t h a t l a b o r a t o r y grouped-mouse s o c i a l s t r u c t u r e s are u n n a t u r a l . N o n e t h e l e s s , s u b o r d i n a t e grouped animals i n the l a b o r a t o r y may be p a r t i -c u l a r l y s t r e s s e d because they cannot escape the a g g r e s s i o n o f dominant males as they might under more n a t u r a l c o n d i t i o n s . I s o l a t i o n and Male Sexual B e h a v i o r The p r e s e n t s t u d y extends the i s o l a t i o n / g r o u p i n g l i t e r a t u r e through an e x a m i n a t i o n o f the e f f e c t s o f t h i s parameter on male s e x u a l b e h a v i o r . As d i s c u s s e d above, t h e r e have been numerous exami n a t i o n s of e f f e c t s o f p o s t p u b e r t a l s o c i a l i s o l a t i o n and g r o u p i n g on subsequent i n t e r -male i n t e r a c t i o n s (see r e v i e w s by B r a i n , 1975; S c o t t , 1966; V a l z e l l i , 1969). In c o n t r a s t , t h e r e a r e v e r y few r e p o r t s o f e f f e c t s of i s o l a t i o n on male-female i n t e r a c t i o n s . K i n g (1956) r e p o r t e d t h a t i s o l a t i o n e x t e n d i n g from weaning-age w e l l i n t o a d u l t h o o d d i d not a f f e c t male s e x u a l b e h a v i o r i n mice; h i s s t u d y d i f f e r s , however, from the i s o l a t i o n s t u d i e s d i s c u s s e d above, where i s o l a t i o n b e g i n s i n a d u l t h o o d . A number of s t u d i e s i n o t h e r s p e c i e s have concerned e f f e c t s o f postweaning, p r e p u b e r t a l i s o l a t i o n . Such i s o l a t i o n has been r e p o r t e d to i m p a i r a d u l t s e x u a l performance i n r a t s (Folman & D r o r i , 1965; G e r a l l , Ward, & G e r a l l , 1967; Gruendel & A r n o l d , 1974) and g u i n e a p i g s ( V a l e n s t e i n , R i s s , & Young, 1955), a l t h o u g h Beach (1958) r e p o r t e d an o p p o s i t e e f f e c t i n r a t s . The d i f f e r e n c e s i n s p e c i e s and the d e v e l o p m e n t a l s t a g e a t which i s o l a t i o n i s i n t r o d u c e d , however, make t h e s e s t u d i e s incomparable t o those concerned w i t h p o s t p u b e r t a l i s o l a t i o n i n mice. 10 The p r e s e n t s t u d y i s concerned w i t h the e f f e c t s o f p o s t p u b e r t a l s o c i a l i s o l a t i o n and g r o u p i n g on male s e x u a l b e h a v i o r d i r e c t e d toward e s t r o u s f e m a l e s . A l t h o u g h e f f e c t s o f t h i s parameter on s e x u a l b e h a v i o r have not p r e v i o u s l y been r e p o r t e d , t h e r e a r e r e l a t e d r e p o r t s t h a t i n d i r e c t l y suggest, t h a t such e f f e c t s might o c c u r . As d i s c u s s e d above, b o t h locomotor and a g g r e s s i v e a c t i v i t y a r e h i g h e r i n i s o l a t e s when animals a r e exposed t o n o v e l s i t u a t i o n s ; t h i s t r e n d might a l s o o c c u r w i t h s e x u a l a c t i v i t y . A l s o d i s c u s s e d above, t e s t i c u l a r . f u n c t i o n , which e x e r t s some c o n t r o l over male s e x u a l b e h a v i o r ( G o r z a l k a & Mogenson, 1977), may be su p p r e s s e d by p r o l o n g e d g r o u p i n g . Numerous s t u d i e s (see C h r i s t i a n , 1971) i n d i c a t e t h a t h i g h popu-l a t i o n d e n s i t y and g r o u p i n g d e c r e a s e n a t a l i t y ; t h i s may i n p a r t be due to ind u c e d low l e v e l s o f s e x u a l a c t i v i t y . In female mice, g r o u p i n g may sup-p r e s s e s t r u s and l e n g t h e n d i e s t r u s (Whitten, 1959), e f f e c t s which would reduce s e x u a l r e c e p t i v i t y and which might be p a r a l l e l e d i n males. When females a r e p l a c e d w i t h grouped males, dominants may s i r e the m a j o r i t y o f o f f s p r i n g ( D e F r i e s & M c C l e a r n , 1970; 1972); these e f f e c t s may r e l a t e t o d i f f e r e n t i a l s e x u a l a c t i v i t y , and i f i s o l a t e s resemble dominants, may suggest h i g h l e v e l s o f s e x u a l a c t i v i t y i n i s o l a t e s . F i n a l l y , male mice s u b j e c t e d to d e f e a t may show poor s e x u a l a c t i v i t y (Kahn, 1961); s i n c e grouped males a r e exposed t o a g g r e s s i o n they may show s e x u a l a c t i v i t y d e f i c i t s . A l l o f t h e s e f i n d i n g s suggest t h a t i s o l a t e s might show h i g h e r l e v e l s o f s e x u a l a c t i v i t y than do grouped mice. Male s e x u a l b e h a v i o r i n mice has been d e s c r i b e d by M c G i l l (1965) and more r e c e n t l y by Mosig and Dewsbury (1976). T h i s b e h a v i o r i s comprised o f t h r e e b a s i c elements: mounts, 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 . When a male mouse i s p r e s e n t e d w i t h an e s t r o u s female he u s u a l l y b e g i n s i n v e s t i -g a t o r y b e h a v i o r , c o n s i s t i n g o f nudging and s n i f f i n g the female's body, 11 p a r t i c u l a r l y her g e n i t a l a r e a . T h i s u s u a l l y c u l m i n a t e s i n mounting b e h a v i o r . A mount i s s c o r e d when the male s t r a d d l e s the female's back w i t h h i s f o r e l i m b s . The male may t e r m i n a t e a mount w i t h i n a few seconds o f i t s i n c e p t i o n , o r he may b e g i n to p a l p a t e the female's s i d e s w i t h h i s forepaws, s i m u l t a n e o u s l y e x e c u t i n g a s e r i e s o f r a p i d , p r o b i n g p e l v i c t h r u s t s . An i n t r o m i s s i o n i s s c o r e d when the male g a i n s v a g i n a l p e n e t r a -t i o n . The male's s u c c e s s i n a c h i e v i n g mounts and i n t r o m i s s i o n s i s h i g h l y dependent on female r e c e p t i v i t y . A f u l l y r e c e p t i v e female r a i s e s her h i n d q u a r t e r s and t a i l and m a i n t a i n s a r i g i d p o s t u r e u n t i l the male d i s -mounts. When an i n t r o m i s s i o n i s t e r m i n a t e d b o t h a n i m a l s engage i n c l e a n i n g of t h e i r own g e n i t a l i a . A f t e r from one t o more than 100 i n t r o m i s s i o n s t h e male may e j a c u l a t e . D u r i n g the e j a c u l a t o r y i n t r o m i s s i o n the tempo of p e l v i c t h r u s t i n g may i n c r e a s e u n t i l the male d i s p l a y s a c o n v u l s i v e q u i v e r i n g of t h e h i n d q u a r t e r s , c l u t c h i n g the female w i t h h i s f o r e l i m b s . O f t e n the male w i l l f a l l to one s i d e , c a r r y i n g the female w i t h him. The e j a c u l a t o r y i n t r o -m i s s i o n may t e r m i n a t e w i t h the female s t r u g g l i n g to r e l e a s e h e r s e l f and v o c a l i z i n g . O c c a s i o n a l l y the male may a t t a c k and b i t e the female immediate-l y f o l l o w i n g an e j a c u l a t i o n . The i n i t i a l e j a c u l a t i o n u s u a l l y t e r m i n a t e s a l l s e x u a l b e h a v i o r f o r a t l e a s t 15 minutes. A l t h o u g h many males may be c a p a b l e o f a second e j a c u l a t i o n w i t h i n one hour, r e c o v e r y from a second e j a c u l a t i o n u s u a l l y r e q u i r e s c o n s i d e r a b l y l o n g e r than one hour. The time r e q u i r e d to r e c o v e r mounting b e h a v i o r a f t e r an e j a c u l a t i o n , l i k e many o t h e r a s p e c t s of s e x u a l b e h a v i o r i n mice, i s dependent on g e n e t i c s t r a i n ( L e v i n e , B a r s e l , & Diakow, 1966; M c G i l l , 1965). An e x a m i n a t i o n of the e f f e c t s of s o c i a l i s o l a t i o n and a l l - m a l e g r o u p i n g on s e x u a l b e h a v i o r might be of s c i e n t i f i c v a l u e f o r s e v e r a l r e a -sons. S i n c e a c o n s i d e r a b l e amount o f e v i d e n c e s p e c i f i e s the p h y s i o l o g i c a l 12 and b e h a v i o r a l e f f e c t s o f the i s o l a t i o n / g r o u p i n g parameter, such an exami-n a t i o n might improve u n d e r s t a n d i n g o f the r e l a t i o n s h i p between s e x u a l b e h a v i o r and s e v e r a l o t h e r p h y s i o l o g i c a l and b e h a v i o r a l v a r i a b l e s . W hile the e f f e c t s of i s o l a t i o n on many o t h e r v a r i a b l e s a r e w e l l d e l i n e a t e d , the r e l a t i o n s h i p o f s e x u a l b e h a v i o r to t h i s p r o f i l e o f e f f e c t s i s not known. The s t u d y of i s o l a t i o n and g r o u p i n g e f f e c t s on s e x u a l b e h a v i o r might p a r t i c u l a r l y e l u c i d a t e an h y p o t h e s i z e d s t r e s s - s e x antagonism. There have been a l l u s i o n s to such an antagonism i n b o t h the human c l i n i c a l and the b e h a v i o r a l - e c o l o g i c a l l i t e r a t u r e s , but t h e r e have been a few r e l e v a n t e x p e r i m e n t a l e x a m i n a t i o n s . There are a number of human c l i n i c a l o b s e r v a -t i o n s t h a t p h y s i c a l and m e n t a l f a t i g u e , as w e l l as any o t h e r type of s t r e s s f u l e x p e r i e n c e , d i m i n i s h e s s e x u a l d e s i r e and may i n d u c e temporary impotence ( S e l y e , 1961). I t has a l s o been suggested t h a t p o p u l a t i o n r e g u l a t o r y mechanisms may reduce r e p r o d u c t i v e a c t i v i t y i n times o f h i g h d e n s i t y , and t h a t t h e s e mechanisms may o p e r a t e s p e c i f i c a l l y by r e d u c i n g the r e p r o d u c t i v e a c t i v i t y o f s t r e s s e d members of the p o p u l a t i o n ( C h r i s t i a n , 1971; Gray, 1971). L i t t l e i s known r e g a r d i n g the mechanisms t h a t might u n d e r l i e t h e se phenomena. Because group-housing produces s t r e s s - c h a r a c -t e r i s t i c hormonal and n e u r o c h e m i c a l c o n d i t i o n s , i s o l a t i o n / g r o u p i n g com-p a r i s o n s might p r o v i d e a model f o r the study o f a s t r e s s - s e x antagonism. The comparison o f a n i m a l s d i f f e r i n g i h endogenous hormonal and n e u r o c h e m i c a l l e v e l s may have advantages, f o r the s t u d y o f s t r e s s e f f e c t s , over o t h e r methods such as t h o se a t t e m p t i n g to mimic s t r e s s s t a t e s through exogenous hormones and d r ugs. The study of a n i m a l s exposed to d i f f e r e n t l e v e l s o f s o c i a l s t r e s s , as a r e i s o l a t e d and grouped male mice, may e l u c i d a t e complex n a t u r a l i n t e r a c t i o n s among p h y s i o l o g i c a l and b e h a v i o r a l r e s ponse to s t r e s s . I s o l a t e d and grouped mice a l s o p r o v i d e two d i f f e r i n g 13 b a s e l i n e p h y s i o l o g i c a l p r e p a r a t i o n s f o r e x a m i n a t i o n of b e h a v i o r a l e f f e c t s o f a v a r i e t y o f hormonal, p h a r m a c o l o g i c a l , and o t h e r p h y s i o l o g i c a l mani-p u l a t i o n s . The comparison o f s e x u a l performance o f i s o l a t e d and grouped mice might a l s o p r o v i d e i n f o r m a t i o n r e g a r d i n g an h y p o t h e s i z e d r e l a t i o n s h i p between sex and a g g r e s s i o n . B i n d r a (1959) has s u g g e s t e d t h a t sex and a g g r e s s i o n c o v a r y i n s o f a r as they b o t h respond to changes i n the l e v e l o f a r o u s a l . In s e a s o n a l l y p o l y e s t r o u s o r monestrous mammals, f i g h t i n g among males i n c r e a s e s d r a m a t i c a l l y d u r i n g the b r e e d i n g season (Bermant & D a vidson, 1974). T a y l o r (1976), L a g e r s p e t z & H a u t o j a r v i . (1967), and Kahn (1961) a l l r e p o r t e d i n t e r a c t i o n s between s e x u a l and a g g r e s s i v e b e h a v i o r i n the l a b o r a t o r y . In males o f many mammalian s p e c i e s , b o t h sex and a g g r e s s i o n a r e dependent on p r e n a t a l and c i r c u l a t i n g l e v e l s o f androgens (Quadagno, B r i s c o e & Quadagno, 1977). There i s a c o n s i d e r a b l e amount of e v i d e n c e r e g a r d i n g p h y s i o l o g i c a l , s o c i a l , and e n v i r o n m e n t a l c o n t r o l of a g g r e s s i v e b e h a v i o r i n mice, and most o f i t i s d e r i v e d from s t u d i e s w i t h i n the i s o l a -t i o n / g r o u p i n g paradigm (see r e v i e w s by B r a i n , 1975; S c o t t , 1966; V a l z e l l i , 1969). P a r a l l e l m a n i p u l a t i o n s o f i s o l a t i o n / g r o u p i n g e f f e c t s on s e x u a l b e h a v i o r and comparisons w i t h r e s u l t s i n a g g r e s s i o n s t u d i e s might p r o v i d e i n f o r m a t i o n r e g a r d i n g common or d i f f e r e n t i a l c o n t r o l of sex and a g g r e s s i o n . An e x a m i n a t i o n o f i s o l a t i o n / g r o u p i n g d i f f e r e n c e s i n s e x u a l b e h a v i o r might a l s o e l u c i d a t e the s o c i o b i o l o g y of the mouse s p e c i e s . An e x a m i n a t i o n of the r e sponse o f s e x u a l a c t i v i t y to the p r e s e n c e or absence o f c o n s p e c i f i c males may c l a r i f y the n e c e s s a r y c o n d i t i o n s f o r r e p r o d u c t i v e s u c c e s s i n t h i s s p e c i e s . I t might a l s o p r o v i d e i n f o r m a t i o n about the r e l a t i o n s h i p o f s o c i a l s t r u c t u r e , s o c i a l s t a t u s , and p o p u l a t i o n d e n s i t y to r e p r o d u c t i v e b e h a v i o r . 14 SECTION I : EFFECTS OF BASIC ISOLATION/GROUPING  PARAMETERS ON SEXUAL AND AGGRESSIVE BEHAVIOR W i t h i n t h e i s o l a t i o n / g r o u p i n g paradigm, c o n s i d e r a b l e a t t e n t i o n has been p a i d t o the e f f e c t s o f p r i o r h o u s i n g upon b e h a v i o r i n i n t e r m a l e e n c o u n t e r s . S p e c i f i c a l l y , i t has been demonstrated t h a t mice i s o l a t e d f o r s e v e r a l days i n a d u l t h o o d show i n t e n s e l e v e l s o f a g g r e s s i o n when s u b s e q u e n t l y p l a c e d w i t h t a r g e t mice (e.g., S c o t t , 1966; V a l z e l l i , 1969). I s o l a t i o n - i n d u c e d a g g r e s s i o n i s found almost e x c l u s i v e l y i n male mice and i s u s u a l l y d i r e c t e d o n l y toward o t h e r male mice ( S c o t t , 1966). S e v e r a l p h y s i o l o g i c a l systems a r e known to be a l t e r e d by i s o l a t i o n and a s s o c i a t e d w i t h i s o l a t i o n - i n d u c e d a g g r e s s i o n . These i n c l u d e , among o t h e r s , p i t u i t a r y -g o nadal, p i t u i t a r y - a d r e n o c o r t i c a l , and b r a i n b i o g e n i c amine systems (see r e v i e w by B r a i n , 1975). While b e h a v i o r a l i n v e s t i g a t i o n s have d e l i n e a t e d the e f f e c t s o f i s o l a t i o n v e r s u s g r o u p i n g upon i n t e r m a l e i n t e r a c t i o n s , l i t t l e a t t e n t i o n has been g i v e n to the e f f e c t s o f t h i s parameter upon male-female i n t e r -a c t i o n s . A few s t u d i e s o f male r a t s (e.g., G e r a l l e t a l . , 1967; G r u e n d e l & A r n o l d , 1974) have i n d i c a t e d t h a t p r e a d o l e s c e n t s o c i a l i s o l a t i o n can reduce subsequent s e x u a l b e h a v i o r , a l t h o u g h e f f e c t s of p e r i o d s o f i s o l a t i o n 15 i n a d u l t h o o d were not r e p o r t e d . K i n g (1956) r e p o r t e d t h a t i s o l a t i o n a t weaning d i d not a f f e c t s e x u a l performance of male mice i n a d u l t h o o d , but d i d not i n v e s t i g a t e the e f f e c t s of p o s t p u b e r t a l i s o l a t i o n and g r o u p i n g . The p r e s e n t s e r i e s o f s t u d i e s i n v e s t i g a t e d male s e x u a l b e h a v i o r i n mice t h a t were e i t h e r i s o l a t e d o r housed i n groups i n a d u l t h o o d . Sexual b e h a v i o r was compared as a f u n c t i o n of number of a n i m a l s per cage, l e n g t h of time i n p a r t i c u l a r h o u s i n g c o n d i t i o n s , and p o p u l a t i o n d e n s i t y . S i n c e a g g r e s s i v e b e h a v i o r has been e x t e n s i v e l y examined w i t h i n t h i s paradigm and i s r e l a t i v e l y w e l l u n d e r s t o o d , the degree o f c o r r e l a t i o n between s e x u a l and a g g r e s s i v e r e s p o n s e s w i t h i n t h i s c o n t e x t was a l s o examined. Experiment IA The f i r s t experiment was d e s i g n e d to examine development of s e x u a l b e h a v i o r i n s e x u a l l y - n a i v e males housed w i t h d i f f e r e n t numbers of c o n s p e c i f i c males. Because s e x u a l performance might a l s o v a r y w i t h e x p e r i e n c e and m a t u r a t i o n , b e h a v i o r was measured weekly u n t i l i t reached an asymptote. Method S u b j e c t s - T h i r t y - s i x male CD-I mice, o b t a i n e d from Canadian B r e e d i n g Farms, St . Constant,Que.,served as e x p e r i m e n t a l s u b j e c t s . A f t e r r e c e i p t from the b r e e d e r and b e f o r e commencement of the e x p e r i m e n t a l h o u s i n g c o n d i t i o n s , a l l a n i m a l s were housed f o r 3 days i n groups of 6 i n cages measuring 28 x 16 x 11 cm. A l s o , o b t a i n e d from the same b r e e d e r , were two groups o f 9 CD-I s t i m u l u s females each and one group o f 6 CD-I s t i m u l u s males, each group b e i n g housed i n a cage measuring 26 x 47 x 14 cm. A l l a n i m a l s were m a i n t a i n e d under a r e v e r s e d 12-hr dark/12-hr l i g h t c y c l e a t 21 + 1°C. Animals were t e s t e d 5-8 h r a f t e r commencement o f t h e i r dark phase i n an 16 i l l u m i n a t e d room. . . . P r e p a r a t i o n o f s t i m u l u s females - S t i m u l u s females were p r e p a r e d so as to in d u c e maximum r e c e p t i v i t y a c c o r d i n g to a pr o c e d u r e adapted from s t u d i e s by G o r z a l k a and Whalen (1974, 1976). These females were b i l a t e r a l l y o v a r i e c t o m i z e d a t a p p r o x i m a t e l y 60 days o f age. Two weeks f o l l o w i n g s u r g e r y an i n j e c t i o n s c h e d u l e was begun i n which each female r e c e i v e d 10 yg of e s t r a d i o l benzoate i n .05 cc o f peanut o i l sc f o l l o w e d 48 h r l a t e r by 500 yg o f p r o g e s t e r o n e i n .05 cc o i l s c . T h i s i n j e c t i o n s c h e d u l e was r e p e a t e d weekly. F o r t h e f i r s t f i v e weeks, s t i m u l u s females were p r e s e n t e d i n groups o f 6 f o r one hour to a group o f 6 . group-housed males 6 h r s f o l l o w i n g p r o g e s t e r o n e t r e a t m e n t . On the s i x t h and subsequent weeks, females were p r e s e n t e d to t h e e x p e r i m e n t a l animals 6 h r s f o l l o w i n g p r o g e s -t e r o n e , each group of females b e i n g used f o r 3 s u c c e s s i v e h o u r l y t e s t s w i t h e x p e r i m e n t a l males. Pro c e d u r e - At 50 days o f age, e x p e r i m e n t a l males were s e p a r a t e d i n t o 3 group c o n d i t i o n s . These c o n s i s t e d o f one group o f 12, 4 groups o f 3, and 12 an i m a l s housed i n d i v i d u a l l y . These were housed i n s t a n d a r d p o l y p r o p y -l e n e cages, manufactured by Carworth Lab Cages and measuring a p p r o x i m a t e l y 28 cm x 16 cm x 11 cm w i t h s t r a i g h t - w i r e tops each c o n t a i n i n g a b u i l t - i n 3 f e e d e r and water d i s p e n s e r which t o g e t h e r d i s p l a c e d 952 cm . Each cage c o n t a i n e d one l i t e r o f commercial b e d d i n g m a t e r i a l ( S a n - i - c e l ) and one 24 x 24 cm paper t o w e l t o r n i n t o s e v e r a l p i e c e s . T h i s b e d d i n g was changed as r e q u i r e d t o m a i n t a i n a l l cages a t an a p p r o x i m a t e l y e q u i v a l e n t l e v e l o f c l e a n l i n e s s . At 7-day i n t e r v a l s b e g i n n i n g one week f o l l o w i n g the i n t r o d u c t i o n o f the d i f f e r e n t i a l h o u s i n g c o n d i t i o n s , a n i m a l s were p r e s e n t e d w i t h r e c e p -t i v e females f o r 1-hr s e s s i o n s . D u r i n g each s e s s i o n , 6 males were observed 17 s i m u l t a n e o u s l y i n a d j a c e n t P l e x i g l a s e n c l o s u r e s measuring 23 cm x 12 cm x 22 cm ( h e i g h t ) . Each e n c l o s u r e c o n t a i n e d 0.5 l i t e r b e d d i n g m a t e r i a l . I n t e r n a l w a l l s of the e n c l o s u r e s were c o v e r e d so t h a t an a n i m a l c o u l d not see e v e n t s i n a d j a c e n t e n c l o s u r e s . T e s t i n g times were c o u n t e r b a l a n c e d so t h a t each h o u s i n g c o n d i t i o n was r e p r e s e n t e d e q u a l l y i n each s e t of a n i m a l s observed s i m u l t a n e o u s l y . S t i m u l u s females were r o t a t e d among the e n c l o s u r e s e v e r y 10 min of each hour s e s s i o n so t h a t a n i m a l s r e p r e s e n t i n g each c o n d i -t i o n r e c e i v e d each female f o r an e q u a l p e r i o d of time. D u r i n g s e s s i o n s , t h e f r e q u e n c y and d u r a t i o n o f mounts w i t h o u t i n t r o m i s s i o n (mounts) and mounts w i t h i n t r o m i s s i o n and p e l v i c t h r u s t i n g ( i n t r o m i s s i o n s ) , and the o c c u r r e n c e of any t a i l - r a t t l e s , b i t e s , and n o n - b i t i n g a t t a c k s were r e c o r d e d v i a an E s t e r l i n e - A n g u s event r e c o r d e r . Three days f o l l o w i n g each s e s s i o n w i t h r e c e p t i v e f e m a l e s , e x p e r i -m e n t a l males were each p r e s e n t e d w i t h a s i n g l e group-housed t a r g e t male i n an e x p e r i m e n t a l e n c l o s u r e of the same dimensions as those used i n t e s t s w i t h females. S e s s i o n s w i t h males were l i m i t e d t o 15 min to p r e v e n t s e v e r e damage t o t a r g e t males. A composite a g g r e s s i o n s c o r e , adapted from Leshner et a l . . (1973) was c a l c u l a t e d , w e i g h t i n g t a i l r a t t l e s by 1 and b i t e s and a t t a c k s each by 2. The number and d u r a t i o n of any mounts o r i e n t e d toward t a r g e t males were a l s o measured. In the event of a death of an e x p e r i m e n t a l group-housed a n i m a l , t h a t a n i m a l would be removed and r e p l a c e d w i t h a s u r r o -gate t h a t would not be i n c l u d e d i n t e s t i n g . R e s u l t s and D i s c u s s i o n F i g u r e 1 shows the mean t o t a l d u r a t i o n of mounting per hour s e s s i o n f o r a l l c o n d i t i o n s . T h i s measure i s c a l c u l a t e d by summing, f o r each a n i m a l , the d u r a t i o n o f a l l 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 , 18 F i g u r e 1: The mean t o t a l d u r a t i o n o f mounting, w i t h o r w i t h o u t i n t r o m i s s i o n , i n weekly r e p e a t e d measures o f a n i m a l s i n Experiment 1. The squares r e p r e s e n t mice i n d i v i d u a l l y housed i n p a r t IA, then grouped i n 3 r s i n p a r t IB. The open c i r c l e s r e p r e s e n t mice housed i n 3's f o r p a r t IA, then i s o l a t e d i n p a r t IB. The c l o s e d c i r c l e s r e p r e s e n t mice grouped i n 12 f o r p a r t IA, then i s o l a t e d i n p a r t IB, -20 and p r o v i d e s a summary s t a t i s t i c f o r male murine s e x u a l b e h a v i o r i n t h a t i t c o n t a i n s i n f o r m a t i o n about b o t h mounts and i n t r o m i s s i o n s and d u r a t i o n of t h e s e r e s p o n s e s . A f t e r one week i n the h o u s i n g c o n d i t i o n s about t w i c e as much a c t i v i t y was e v i d e n t i n i s o l a t e d a nimals as i n an i m a l s i n groups of 3 or 12. T h i s p a t t e r n c o n t i n u e d i n s u c c e s s i v e weekly t e s t s , w i t h a c t i v i t y i n c r e a s i n g i n p a r a l l e l u n t i l i t reached an apparent asymptote a t weeks 7 and 8. A t w o - f a c t o r a n a l y s i s o f v a r i a n c e i n d i c a t e d a s i g n i f i c a n t e f f e c t of number of an i m a l s per cage (F = 7.37, df_ = 2/231, £ = .002). Subsequent Newman-Keuls comparisons (p_<:05) i n d i c a t e d two homogeneous s u b s e t s : the groups o f 3 and 12 v e r s u s the i s o l a t e s . The w i t h i n - s u b j e c t s f a c t o r , weeks, was a l s o s i g n i f i c a n t (F = 6.85, df_ = 7/231, p_<.001) w h i l e the i n t e r a c t i o n f a c t o r was not s i g n i f i c a n t . T a b l e I g i v e s the r e s u l t s f o r a l l r e m a i n i n g measures i n E x p e r i -ment 1. Trends i n the numbers o f mounts and i n t r o m i s s i o n s were i d e n t i c a l to t h o se i n the d u r a t i o n measure. There was a s i g n i f i c a n t e f f e c t o f number of a n i m a l s p e r cage w i t h b o t h mounts (F = 9.56, df_ = 2/231, p_ <.001) and i n t r o m i s s i o n s (F = 6.98, df_ = 2/231, p_ = .004), w h i l e b o t h mounts (F = 5.53, df = 7/231, £ <.001) and i n t r o m i s s i o n s (F = 7.36, df = 7/231, £ <.001) i n c r e a s e d over weeks. In b o t h measures subsequent comparisons i n d i c a t e d t h a t the i s o l a t e s d i f f e r e d from grouped a n i m a l s w h i l e t h e r e were no d i f f e r e n c e s between the groups o f 3 and 12. A few an i m a l s showed some a g g r e s s i v e r e s p o n s e s toward r e c e p t i v e f emales. D e s p i t e a low l e v e l o f such r e s p o n s e s i n a l l groups, t h e r e was a s i g n i f i c a n t e f f e c t o f number of a n i m a l s per cage (F_ = 3.56, df_ = 2/231, £ = .039), w i t h comparisons i n d i c a t i n g t h a t the d i f f e r e n c e l a y between i s o l a t e s and grouped a n i m a l s . In the 15-min t e s t s w i t h s t i m u l u s males, more a g g r e s s i o n was e v i d e n t i n i s o l a t e s t h a n i n e i t h e r s e t of grouped a n i m a l s . Composite TABLE I Mean Scores i n Weekly Repeated Measures of Sexual and Aggressive Responses to Stimulus Females and Males i n Experiment 1. EXPERIMENT 1A W e e k EXPERIMENT IB W e e k Measure n per • n per cage ] 2 i 4 5 6 7 8 cage 9 i 10 11 1Z 1 15. .83 22. 92 28, ,00 32. ,33 34. 00 36. ,08 42. 33 40 .00 3 28. 42b 10. 40b 16. 3°b 17. Mounts 3 6. .42 5. 84 9, .50 8. .58 14. ,50 12, .75 14. 58 10 .92 1 24. 3 6b 20. 8 2b 37. 09h 33. 6 4b 12 3. 42 6. 33 14. .16 16. ,67 9. 45 7. .09 21. 18 8 .82 1 35. 18b 46. 27b 47. 73b 45. 64° Intromission s 1 8. .00 13. 60 22, ,00 25. .42 33. .92 32, .92 33. 67 25 .84 3_ 15. 92b 14. 10b 8. 9°b 10. 9°b 3 3. .42 4. 75 8, .42 10. ,84 13. .75 17. .60 13. 33 11 .75 1 13. 5 5b 21. 5 5b 15. 5 5b 18. Stimulus 12 3. .02 6. 42 5. ,08 9. .33 12. ,64 8. .27 13. 27 7 .00 1 43. 96b 22. 09b 21. 36b 24. ,55° Females Aggression 1 9. ,08 3. ,33 1. ,00 0, .17 1, .00 2, .17 1. 33 0 .33 3 0. 00b 0. oob 0. 0°b 0. °s Score 3 0. .33 0. ,67 0, ,00 0. ,00 0. .17 1, .33 0. 50 0 .00 1 4. 0. 3 6b 0. 7 3b 0. 1 8b 12 0, .83 0. ,00 0. ,50 0. .00 0. .00 2, .00 0. 00 1 .45 1 0. 33b 0. 18 0. ,00 0. ,00° Aggression 1 21, .75 35. ,16 39; .08 29, .00 40. .33 52 .33 41. 84 a 3 11. 83b 10. 40b 12. < 6. , 9 0h Score 3 0, .00 1. ,00 1, .30 12, .75 8. .25 6 .50 8. 33 a 1 29. 6\ 42. 4 5b 49. 0 9b 44. '27b Stimulus 12 0 .00 0. ,67 0. .00 1, .64 0. .18 0 .00 7. 64 a 1 42. 91b 63. 18b 62. ,91b 60. ,73° Duration of 1 0 .58 0, ,75 0, .25 2 .17 0. .25 0 .25 1. 83 a 3 0. 00b 0. 00b 0. 0 0b 0. •*°b Mounting 3 0 .00 0, .25 0, .08 0 .17 0, .00 0 .00 0. 00 a 1 1. 5 5b 1. 6 4b 1. ,09b 0. ' 9 1b (Sec,) 12 0 .00 0, .00 0, .00 0 .00 0, .08 0 .00 0. 64 a 1 5. 09b 0. 73b 0. ,55b 0. ,73b aData not col l e c t e d due to recent introduction of reversal conditions. n = 11 n - 10 a g g r e s s i o n s c o r e s r e v e a l e d s i g n i f i c a n t d i f f e r e n c e s i n the number of animals per cage f a c t o r (F = 7.92, d_f = 2/198, £ = .002), but not i n the weeks and i n t e r a c t i o n f a c t o r s . Comparisons i n d i c a t e d a g a i n t h a t group d i f f e r e n c e s l a y between the i s o l a t e s on the one hand and the groups of 3 and 12 on the o t h e r . V e r y few a n i m a l s mounted s t i m u l u s males; t h i s measure showed no s i g n i f i c a n t d i f f e r e n c e s . A Pearson product-moment c o r r e l a t i o n , c a l c u l a t e d between the t o t a l d u r a t i o n s c o r e w i t h s t i m u l u s females f o r each a n i m a l and the composite a g g r e s s i o n s c o r e w i t h s t i m u l u s males f o r t h a t a n i m a l , i n d i -c a t e d a moderate p o s i t i v e r e l a t i o n s h i p ( r = .33, n = 36, p_ = .023). When the s c o r e s f o r the i n d i v i d u a l g r o u p i n g c o n d i t i o n s were c o r r e l a t e d s e p a r a t e l y (n = 12) no s i g n i f i c a n t c o r r e l a t i o n s were o b t a i n e d . These r e s u l t s i n d i c a t e t h a t i s o l a t i o n i n male mice not o n l y i n c r e a s e s a g g r e s s i v e n e s s , but a l s o produces a marked i n c r e a s e i n the q u a n t i t y o f s e x u a l b e h a v i o r . T h i s e f f e c t i s m a i n t a i n e d d e s p i t e i n c r e a s e s i n s e x u a l b e h a v i o r i n a l l groups w i t h s u c c e s s i v e r e p e a t e d measures o f b e h a v i o r . .Experiment IB I f i s o l a t i o n i s the p r i m a r y f a c t o r r e s p o n s i b l e f o r h i g h e r l e v e l s o f s e x u a l b e h a v i o r observed i n the i n d i v i d u a l l y - h o u s e d a n i m a l s of Experiment IA, then i t s h o u l d be p o s s i b l e to i n c r e a s e b e h a v i o r i n the grouped animals by i s o l a t i n g them and to d e c r e a s e b e h a v i o r i n i s o l a t e s by g r o u p i n g them. P a r t B o f Experiment 1 attempted such a r e v e r s a l . Method Subsequent to the e i g h t h week's measure of b e h a v i o r i n the p r e -sence of r e c e p t i v e f e m a l e s , a n i m a l s t h a t were i s o l a t e d i n Experiment IA were rehoused i n groups o f 3, w h i l e a n i m a l s f o r m e r l y i n groups of 3 and 12 23 were rehoused i n d i v i d u a l l y . B e h a v i o r was measured a c c o r d i n g to the p r o -cedures o f Experiment IA, w i t h weekly 1-hour t e s t s w i t h r e c e p t i v e females and 15-min t e s t s w i t h group-housed t a r g e t males 3 days a f t e r each s e x u a l t e s t . B e h a v i o r was a g a i n t e s t e d weekly u n t i l performance i n a l l c o n d i t i o n s appeared to have s t a b i l i z e d . A l l o t h e r p r o c e d u r e s were i d e n t i c a l t o t hose o f Experiment IA. R e s u l t s and D i s c u s s i o n Weeks 9-12 i n F i g u r e 1 and T a b l e I g i v e r e s u l t s f o r a l l measures f o l l o w i n g r e v e r s a l of c o n d i t i o n s . One week . f o l l o w i n g r e v e r s a l t h e r e were two to t h r e e times as many mounts, i n t r o m i s s i o n s , and seconds spent mount-i n g than found the p r e v i o u s week i n the i s o l a t e d animals t h a t were f o r m e r l y grouped i n 12. T h i s i n c r e a s e was s u s t a i n e d d u r i n g the t h r e e subsequent weekly t e s t s . I s o l a t e d a n i m a l s t h a t were f o r m e r l y grouped i n 3 d i d not show a s i m i l a r immediate i n c r e a s e , but by the t h i r d and f o u r t h week f o l l o w -i n g r e v e r s a l (weeks 11 and 12) these a n i m a l s performed a t l e v e l s s u b s t a n -t i a l l y h i g h e r than any they had p r e v i o u s l y shown. The f o r m e r l y i s o l a t e d a n i m a l s showed a l a r g e d e c r e a s e i n performance one week f o l l o w i n g r e v e r s a l , w i t h f u r t h e r d e c r e a s e s o c c u r r i n g d u r i n g subsequent weeks. Two a n i m a l s i n t h i s c o n d i t i o n d i e d , a p p a r e n t l y as a r e s u l t of wounding i n c u r r e d by o t h e r a n i m a l s . I n d i v i d u a l a n a l y s e s o f v a r i a n c e performed on measures from weeks 11 and 12 i n d i c a t e d d i f f e r e n c e s -between c o n d i t i o n s o f the number o f animals per cage ( d u r a t i o n o f mounting: F_ = 9.84, d_f = 2/29, p_ = .001; mounts: F = 5.23, df = 2/29, p_ = .011; i n t r o m i s s i o n s : F = 3.85, df = 2/29, p = .033). Newman-Keuls comparisons (p_ <.05) i n each case i n d i c a t e d two homogeneous groups: i s o l a t e d v s . grouped a n i m a l s . There were no s i g n i f i c a n t d i f f e r e n c e s i n the composite a g g r e s s i o n s c o r e s toward females. 24 In the a g g r e s s i o n t e s t s w i t h t a r g e t males, a r e v e r s a l i n p e r -formance was e v i d e n t a t the f i r s t t e s t 10 days a f t e r r e v e r s a l o f c o n d i -t i o n s and was m a i n t a i n e d i n subsequent weeks. An a n a l y s i s of v a r i a n c e on d a t a from weeks 11 and 12 i n d i c a t e d d i f f e r e n c e s between c o n d i t i o n s (F = 3.06, d_f = 2/29, _p_ = .044), w h i l e comparisons i n d i c a t e d t h a t b o t h groups o f i s o l a t e s showed more a g g r e s s i o n than d i d grouped a n i m a l s . Only a few a n i m a l s showed s e x u a l b e h a v i o r toward males; t h e r e were no s i g n i f i -c a nt d i f f e r e n c e s i n t h i s measure. A c o r r e l a t i o n c a l c u l a t e d by p a i r i n g the t o t a l d u r a t i o n s c o r e ( w i t h females) from weeks 11 and 12 w i t h the a g g r e s s i o n s c o r e f o r t h a t animal on the subsequent t e s t w i t h males showed a s i g n i f i c a n t r e l a t i o n s h i p ( r = .40, n. = 32, p_ = .002). T h i s r e v e r s a l i n performance pursuant to r e v e r s a l of i s o l a t i o n / g r o u p i n g would appear to i n d i c a t e t h a t the e f f e c t o f d i f f e r e n t i a l h o u s i n g upon s e x u a l performance i s not permanent and i s more dependent upon c u r r e n t h o u s i n g c o n d i t i o n s than upon p r i o r e x p e r i e n c e . Furthermore, i t s u g g e s t s t h a t the performance of s e x u a l l y e x p e r i e n c e d mice i s a f f e c t e d by g r o u p i n g or i s o l a t i o n as much as i s the performance of n a i v e a n i m a l s . I t i s noteworthy t h a t a s i m i l a r r e v e r s a l o c c u r r e d i n a g g r e s s i v e b e h a v i o r . Experiment 2 I t has been r e p o r t e d t h a t i s o l a t i o n - i n d u c e d a g g r e s s i o n ( V a l z e l l i , 1969) and b i o c h e m i c a l changes (see B r a i n , 1975) a r e a f u n c t i o n o f the l e n g t h of time t h a t a nimals have been housed i n d i v i d u a l l y . In g e n e r a l , i t has been found t h a t some changes o c c u r w i t h i n a few days of the i n t r o -d u c t i o n o f i s o l a t i o n and t h a t p r o l o n g e d i s o l a t i o n produces a more marked e f f e c t . While Experiment 1 examined s e x u a l b e h a v i o r w i t h i n s u b j e c t s a t d i f f e r e n t i n t e r v a l s f o l l o w i n g i s o l a t i o n , d i f f e r e n c e s i n performance i n s u c c e s s i v e measures may have been due to e x p e r i e n c e and age. Experiment 2 25 examined whether d i f f e r e n c e s i n s e x u a l performance were a f u n c t i o n o f the l e n g t h o f time i n i s o l a t i o n , t h i s v a r i a b l e b e i n g m a n i p u l a t e d between s u b j e c t s w i t h age a t time o f t e s t i n g h e l d c o n s t a n t a c r o s s c o n d i t i o n s . A l s o , s i n c e e j a c u l a t i o n s were not s y s t e m a t i c a l l y r e c o r d e d i n Experiment 1 and might v a r y between c o n d i t i o n s i n a manner d i s s i m i l a r to those of mounts and i n t r o m i s s i o n s , these r e s p o n s e s were measured i n b o t h t h i s and-sub- . sequent experiments. Murine e j a c u l a t o r y r e s p o n s e s have been d e s c r i b e d by M c G i l l (1965). Method CD-I s t i m u l u s females were p r e p a r e d , housed, and made r e c e p t i v e a c c o r d i n g t o the p r o c e d u r e d e s c r i b e d f o r Experiment IA. E x p e r i m e n t a l males c o n s i s t e d of 144 CD-I males o b t a i n e d a t 50 days o f age and housed i n groups o f 6 u n t i l commencement of the e x p e r i m e n t a l h o u s i n g c o n d i t i o n s . A l l a n i m a l s were w i t h o u t p r e v i o u s s e x u a l e x p e r i e n c e and were t e s t e d a t 77-82 days of age, each age b e i n g e q u a l l y r e p r e s e n t e d i n a l l c o n d i t i o n s . S u b j e c t s were d i v i d e d i n t o 12 c o n d i t i o n s , each o f which c o n t a i n e d 12 sub-j e c t s . C o n d i t i o n s c o n s i s t i n g o f a n i m a l s housed w i t h 1, 3, o r 12 animals per cage were formed at the b e g i n n i n g of each of f o u r i n t e r v a l s p r i o r to t e s t i n g : 3, 7, 14, and 28 days. Cages and b e d d i n g were p r o v i d e d and m a i n t a i n e d a c c o r d i n g to the p r o c e d u r e s of Experiment IA. A 1-hr t e s t s e s s i o n i n the p r e s e n c e o f s t i m u l u s females was g i v e n to each a n i m a l . These s e s s i o n s were conducted as i n Experiment 1, w i t h the o c c u r r e n c e and d u r a t i o n o f mounts, 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 r e c o r d e d on an E s t e r -l i n e - A n g u s event r e c o r d e r . A g g r e s s i v e a t t a c k s , b i t e s , and t a i l - r a t t l e s o r i e n t e d toward s t i m u l u s females were a l s o r e c o r d e d . A 15-min t e s t s e s s i o n i n the p r e s e n c e of a group-housed t a r g e t male was g i v e n to each experimen-26 t a l a n i m a l 3 days f o l l o w i n g i t s s e s s i o n w i t h s t i m u l u s females. D u r i n g these t e s t s , b i t e s , n o n - b i t i n g a t t a c k s , t a i l r a t t l e s , mounts, and d u r a -t i o n o f mounting were r e c o r d e d . R e s u l t s and D i s c u s s i o n F i g u r e 2 p r e s e n t s the mean t o t a l d u r a t i o n o f mounting, w i t h or w i t h o u t i n t r o m i s s i o n , f o r a l l c o n d i t i o n s . At the 3-day i n t e r v a l , i s o l a t e d a n i m a l s showed m a r g i n a l l y more a c t i v i t y than a n i m a l s i n groups of 3, which i n t u r n showed m a r g i n a l l y more a c t i v i t y than animals i n groups o f 12. At the 7, 14, and 28 day i n t e r v a l s , more a c t i v i t y was e v i d e n t i n the i s o l a t e s than a t the 3 day i n t e r v a l . Animals grouped i n 3 and 12 showed s i m i l a r l e v e l s o f performance a t a l l i n t e r v a l s , except a t 7 days when groups o f 3 performed a t a h i g h e r l e v e l , and always e x h i -b i t e d l e s s a c t i v i t y than i s o l a t e s . A t w o - f a c t o r a n a l y s i s o f v a r i a n c e i n d i c a t e d a s i g n i f i c a n t main e f f e c t o f the number o f an i m a l s p e r cage (F = 10.26, d_f = 2/131, p_ <.001), w h i l e o t h e r e f f e c t s were not s i g n i f i c a n t . Subsequent Newman-Keuls comparisons (p_ <.05) i n d i c a t e d t h a t t h i s s i g n i f i -cant e f f e c t was due to d i f f e r e n c e s between the i s o l a t e s and the animals i n groups of 3 and 12. T a b l e I I g i v e s the r e s u l t s f o r a l l r e m a i n i n g measures i n Experiment 2. The p a t t e r n s i n measures of mounts and i n t r o m i s s i o n s were comparable to the p a t t e r n i n the d u r a t i o n measure. There was a s i g n i f i c a n t e f f e c t o f number of animals per cage i n mounts (F = 15.90, d_f = 2/131, p_ <.001) and i n t r o m i s s i o n s (F = 4.67, d_f = 2/131, p_ = .011) w h i l e o t h e r e f f e c t s were not s i g n i f i c a n t . Comparisons i n d i c a t e d t h a t the i s o l a t e s exceeded b o t h s e t s o f grouped a n i m a l s f o r mounts,. w h i l e the i s o l a t e s exceeded the an i m a l s grouped i n 12 f o r i n t r o m i s s i o n s . Only a s m a l l number 27 F i g u r e 2: The mean t o t a l d u r a t i o n o f mounting, w i t h o r w i t h o u t i n t r o m i s s i o n , i n between-^group t e s t s a t d i f f e r e n t i n t e r v a l s f o l l o w i n g i s o l a t i o n o r g r o u p i n g i n Experiment 2, The squares r e p r e s e n t a n i m a l s housed i n d i v i d u a l l y ' , the .open c i r c l e s groups of 3, and the c l o s e d c i r c l e s . . g r o u p s , o f 12, N3 00 29 TABLE I I Mean Scores on Sexual and A g g r e s s i v e Measures w i t h S t i m u l u s Females and Males a t I n t e r v a l s from I s o l a t i o n / G r o uping i n Experiment 2 Days i n C o n d i t i o n Measure n per cage 3 7 14 28 1 18.33 27.75 25.90 3 25.58 Mounts 3 16.50 16.16 9.67 9.50 12 13.92 8.00 8.67 7.16 1 12.58 15.67 15.81 a 9.75 I n t r o m i s s i o n s 3 8.83 15.58 11.25 6.75 12 6.50 8.67 6.00 / 6.83 S t i m u l u s i Females 1 0.08 0.33 0.54 a 0.17 E j a c u l a t i o n s 3 0.17 0.50 0.08 0.08 12 0.17 0.33 0.17 0.08 A g g r e s s i o n 1 0.67 0.07 11.36 3 3.50 Score 3 0.00 6.00 0.33 1.16 12 0.00 7.83 5.00 4.33 6 10 17 31 A g g r e s s i o n 1 33.67 44.92 31.50 3 36.08 Score 3 15.08 20.83 2.58 15.25 firi-miil us 12 6.42 8.58 3.67 0.75 Males D u r a t i o n of 1 0.1.7 4.00 1.36 a 1.00 Mounting 3 0.08 0.00 0.50 0.00 (Sec.) - 12 0.00 0.08 0.00 0.00 a 1 1 n = 11 30 of e j a c u l a t i o n s were obs e r v e d . T h i s appeared to be not so much due to the l e n g t h o f s e s s i o n s as to the f a c t t h a t some an i m a l s showed v e r y l i t t l e s e x u a l b e h a v i o r w h i l e o t h e r s would cease r e s p o n d i n g b e f o r e a c h i e v i n g an e j a c u l a t i o n . There were no s i g n i f i c a n t d i f f e r e n c e s i n t h i s measure. There were a l s o no s i g n i f i c a n t d i f f e r e n c e s i n the com-p o s i t e a g g r e s s i o n s c o r e toward females. In the 15-min t e s t s w i t h s t i m u l u s males, more a g g r e s s i o n was e v i d e n t i n i s o l a t e s than i n e i t h e r s e t of grouped a n i m a l s . S t a t i s t i c a l a n a l y s i s i n d i c a t e d a s i g n i f i c a n t e f f e c t o f number of animals per cage (F = 14.25, df = 2/131, £ <.001) but no s i g n i f i c a n t e f f e c t o f i n t e r v a l nor an i n t e r a c t i o n e f f e c t . There was a l s o a s i g n i f i c a n t e f f e c t of number of a n i m a l s per cage i n the d u r a t i o n of mounting w i t h s t i m u l u s males (F_ = 8.19, d_f = 2/131, p_ <.001), a l t h o u g h o n l y a few a n i m a l s showed such r e s p o n s e s . In b o t h t h e s e l a t t e r measures comparisons i n d i c a t e d t h a t d i f f e r e n c e s were due to h i g h e r performance i n i s o l a t e s but t h a t no d i f f e r -ence o c c u r r e d between the two s e t s of grouped a n i m a l s . A c o r r e l a t i o n c a l -c u l a t e d between each a n i m a l ' s d u r a t i o n of mounting w i t h females s c o r e and i t s a g g r e s s i o n s c o r e w i t h males i n d i c a t e d a moderate r e l a t i o n s h i p (r_ = .25, n = 143, p_ = .001). When i s o l a t e s and a n i m a l s i n groups of 3 were each c o n s i d e r e d s e p a r a t e l y , no s i g n i f i c a n t r e l a t i o n s h i p was o b t a i n e d . However, when ani m a l s i n groups o f 12 were c o n s i d e r e d a p o s i t i v e c o r r e l a t i o n was o b t a i n e d ( r = .28, n = 48, p_ = .027). These r e s u l t s suggest t h a t d i f f e r e n c e s between i n d i v i d u a l l y -and group-housed n a i v e male mice a r e e v i d e n t a t a wide range of i n t e r v a l s between i s o l a t i o n and t e s t i n g . While t h e r e i s some i n d i c a t i o n t h a t d i f f e r -ences may not be f u l l y d e v e l o p e d b e f o r e one week of i s o l a t i o n f t h i s ques-t i o n r e q u i r e s more e x t e n s i v e i n v e s t i g a t i o n . S i m i l a r l y , a study o f i n t e r v a l s e x c e e d i n g 4 weeks may r e v e a l r e s u l t s which d i f f e r from those o b t a i n e d h e r e . 31 N e v e r t h e l e s s , t h e s e r e s u l t s i n d i c a t e t h a t i s o l a t i o n - i n d u c e d f a c i l i t a t i o n o f male s e x u a l b e h a v i o r i s a r o b u s t r a t h e r than a t r a n s i e n t phenomenon and t h a t i t o c c u r s under a f a i r l y wide v a r i e t y o f e x p e r i m e n t a l c o n d i t i o n s . One q u a l i f i c a t i o n i s t h a t r e s u l t s may have been i n f l u e n c e d by the a r b i t r a r y p r e - t r e a t m e n t . h o u s i n g o f a l l a n i m a l s i n groups o f 6. I t seems c o n c e i v a b l e t h a t i f a l l animals had been i s o l a t e d o r housed i n d i f f e r e n t group s i z e s p r i o r to t r e a t m e n t , d i f f e r e n t r e s u l t s may have been o b t a i n e d . Experiment 3 In b o t h o f the p r e v i o u s experiments treatment i n v o l v e d p l a c i n g 1, 3, or 12 animals i n cages of i d e n t i c a l dimensions f o r a l l c o n d i t i o n s . T h i s p r a c t i c e has been common i n s t u d i e s o f the b e h a v i o r a l and p h y s i o l o g i -c a l e f f e c t s o f i s o l a t i o n . These s t u d i e s confound two v a r i a b l e s however: the number o f a n i m a l s per cage and t h e amount of space per a n i m a l . S i n c e e i t h e r f a c t o r might be r e s p o n s i b l e f o r i s o l a t i o n - i n d u c e d f a c i l i t a t i o n o f male s e x u a l b e h a v i o r , the p r e s e n t experiment endeavored to v a r y b o t h p a r a -meters s y s t e m a t i c a l l y . Method S t i m u l u s females employed i n Experiment 2 were m a i n t a i n e d on t h e i r weekly i n j e c t i o n s c h e d u l e and r e - u s e d i n t h i s experiment. E x p e r i -mental males were 108 CD-I males o b t a i n e d a t 55 days of age and housed i n groups o f 6 u n t i l commencement o f the e x p e r i m e n t a l h o u s i n g c o n d i t i o n s . Two weeks p r i o r t o t e s t i n g w i t h r e c e p t i v e females a t 75-80 days of age, males were d i v i d e d i n t o 9 c o n d i t i o n s o f 12 s u b j e c t s each. These c o n d i -t i o n s c o n s i s t e d of 3 group s i z e s (1, 3, o r 12 animals per cage) a t each 3 3 3 o f 3 d i f f e r e n t p o p u l a t i o n d e n s i t i e s (331 cm , 1325 cm , or 3976 cm per a n i m a l ) . These volumes per a n i m a l were e q u i v a l e n t , r e s p e c t i v e l y , t o the volumes per ani m a l i n Experiments 1 and 2 i n the 1, 3, and 12 a n i m a l s per cage c o n d i t i o n s . These volumes i n c l u d e d space f i l l e d w i t h b e d d i n g but not space d i s p l a c e d by the f e e d e r and water d i s p e n s e r . S p e c i a l cages were c o n s t r u c t e d from p o l y p r o p y l e n e and P l e x i g l a s where cages o f the r e q u i r e d dimensions were not a v a i l a b l e . A l l cages were 11 cm h i g h . 3 In t h e 331 cm c o n d i t i o n , the 12-animal group was p l a c e d i n a pre-manufactured cage w i t h f l o o r dimensions 28 x 16 cm, w i t h a f e e d e r d i s -3 p l a c i n g 952 cm and equipped as d e s c r i b e d i n Experiment IA. The 3-animal groups were housed i n an i d e n t i c a l cage t h a t was s u b d i v i d e d i n t o 4 compart-ments o f e q u a l volume by p o l y p r o p y l e n e d i v i d e r s . Each compartment a l l o w e d a c c e s s to the f e e d e r and was equipped w i t h a s e p a r a t e water d i s p e n s e r . The i s o l a t e d a n i m a l s i n t h i s c o n d i t i o n were a l s o housed i n an i d e n t i c a l cage; t h i s was s u b d i v i d e d i n t o 12 compartments and equipped w i t h a s p e c i a l l y -2 c o n s t r u c t e d w i r e - g r i d top w i t h 1 cm h o l e s i n the g r i d . Each compartment a l l o w e d a c c e s s to food through the g r i d and was equipped w i t h i t s own 3 water d i s p e n s e r . A l l 331 cm animals were g i v e n .083 l i t e r b e d d i n g m a t e r i a l and one 4 x 12 cm p i e c e of paper towel per a n i m a l . 3 In the 1325 cm c o n d i t i o n , the 3-animal groups were each housed 3 as d e s c r i b e d f o r Experiment IA ( a l s o i d e n t i c a l to the h o u s i n g of the 331 cm 12-animal group). The 12-animal group was housed i n 4 such cages which had s i d e w a l l s removed and were a d j o i n e d , w h i l e the i s o l a t e d a n i m a l s were 3 housed i n 4 such cages each s u b d i v i d e d i n t o 3 compartments. A l l 1325 cm per a n i m a l cages were p r o v i d e d w i t h .333 l i t e r b e d d i n g m a t e r i a l and one 12 x 12 cm p i e c e o f paper towel per ani m a l i n the cage. 3 In the 3976 cm c o n d i t i o n , the i s o l a t e d a n i m a l s were each housed as d e s c r i b e d f o r Experiment IA. The 3-animal groups were housed i n cages 33 w i t h f l o o r dimensions 47 x 26 cm, each equipped w i t h a l a r g e s t r a i g h t -3 w i r e top w i t h a b u i l t - i n f e e d e r t h a t d i s p l a c e d 1514 cm . The 12-animal group was housed i n a s p e c i a l l y - c o n s t r u c t e d P l e x i g l a s cage w i t h f l o o r d imensions 104 x 47 cm and r o o f e d w i t h 4 l a r g e s t r a i g h t - w i r e tops which 3 3 i n t o t a l d i s p l a c e d 6056 cm . A l l 3976 cm per a n i m a l cages were p r o v i d e d w i t h one l i t e r b e d d i n g m a t e r i a l and one 24 x 24 cm paper towel per a n i m a l . Bedding was changed as r e q u i r e d to m a i n t a i n cages i n a l l c o n d i t i o n s a t an a p p r o x i m a t e l y e q u i v a l e n t l e v e l o f c l e a n l i n e s s . T e s t i n g p r o c e d u r e s w i t h r e c e p t i v e females were the same as i n Experiments 1 and 2, w i t h c o n d i t i o n s c o u n t e r b a l a n c e d a c r o s s times o f t e s t i n g . Number and d u r a t i o n of mounts, 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 , and b i t e s , a t t a c k s , and t a i l r a t t l e s were measured i n a s i n g l e 1-hr t e s t w i t h r e c e p t i v e females two weeks f o l l o w i n g i n t r o d u c t i o n of the h o u s i n g c o n d i t i o n s . A l s o , as i n the p r e v i o u s e x p e r i m e n t s , a 15-min s e s s i o n w i t h a s t i m u l u s male was g i v e n to each a n i m a l 3 days f o l l o w i n g i t s t e s t w i t h f e m a l e s ; d u r i n g t h i s s e s s i o n b i t e s , a t t a c k s , t a i l r a t t l e s , and number and d u r a t i o n of mounts were r e c o r d e d . R e s u l t s and D i s c u s s i o n F i g u r e 3 g i v e s the mean t o t a l d u r a t i o n of mounting, w i t h or w i t h -out i n t r o m i s s i o n , f o r each c o n d i t i o n . Performance i n i s o l a t e s was h i g h e r than t h a t o f e i t h e r s e t of grouped a n i m a l s at a l l volumes of space per a n i m a l . There was a s i g n i f i c a n t main e f f e c t of the number of a n i m a l s per cage (F_ = 5.99, df_ = 2/99, p_ = .004) but no s i g n i f i c a n t e f f e c t of space per a n i m a l and no i n t e r a c t i o n . Newman-Keuls comparisons (p <.05) i n d i c a t e d t h a t the i s o l a t e s d i f f e r e d from the a n i m a l s grouped i n 3 and 12, but t h a t t h e r e was no d i f f e r e n c e between the two s e t s of grouped a n i m a l s . 34 F i g u r e 3: The mean t o t a l - d u r a t i o n o f mounting, w i t h or w i t h o u t i n t r o m i s s i o n , o f a n i m a l s housed w i t h d i f f e r e n t volumes of space per a n i m a l i n each cage i n Experiment 3, The squares i n d i c a t e a n i m a l s housed i n d i v i d u a l l y , the open c i r c l e s groups of 3, and the c l o s e d c i r c l e s groups of 12, 36 T a b l e I I I shows means f o r a l l r e m a i n i n g measures i n Experiment 3. The t r e n d s i n the mounts measure were i d e n t i c a l to those i n the d u r a t i o n measure, w i t h a s i g n i f i c a n t e f f e c t of number of animals per cage (F_ = 9.16, d f = 2/99, £ <•001) and comparisons i n d i c a t i n g a d i f f e r e n c e between i s o l a t e s and grouped a n i m a l s . The i n t r o m i s s i o n s measure a l s o showed a s i g n i f i c a n t e f f e c t o f number o f a n i m a l s per cage (F_ =3.65, df_ = 2/99, £ = .029). Comparisons showed a d i f f e r e n c e between i s o l a t e s and the a n i m a l s grouped i n 12, but no d i f f e r e n c e s between a n i m a l s grouped i n 3 and e i t h e r o f the o t h e r g r o u p i n g c o n d i t i o n s . Only a few a n i m a l s showed e j a c u l a t i o n s ; t h e r e were no s i g n i f i c a n t d i f f e r e n c e s i n t h i s measure. There were a l s o no s i g n i -f i c a n t e f f e c t s i n the composite a g g r e s s i o n s c o r e w i t h females. The composite a g g r e s s i o n s c o r e w i t h males showed a s i g n i f i c a n t i n t e r a c t i o n (F_ = 7.48, df. =' 4/99, £ = .021). Comparisons showed t h a t the 3 t h r e e i n d i v i d u a l l y - h o u s e d groups and the 3976 cm group of 12 formed one homogeneous s u b s e t , w h i l e a l l r e m a i n i n g groups formed a second s u b s e t . There were v e r y few mounts d i r e c t e d toward males, a l t h o u g h t h i s measure showed a s i g n i f i c a n t e f f e c t o f number of animals per cage (J_ = 5.67, d f = 2/99, £ = .005). A c o r r e l a t i o n between the d u r a t i o n o f mounting w i t h females measure and the a g g r e s s i o n s c o r e w i t h males, c a l c u l a t e d by p a i r i n g each a n i m a l ' s s c o r e s on t h e s e measures, i n d i c a t e d a p o s i t i v e r e l a t i o n s h i p (r_ = .32, n = 108, £ = .001). No c o r r e l a t i o n s were e v i d e n t when i s o l a t e s and groups of 3 were each c o n s i d e r e d s e p a r a t e l y , a l t h o u g h a s i g n i f i c a n t c o r r e l a t i o n d i d o c c u r i n the groups o f 12 (_r = .62, n_ = 36, £ = .001). I t a p p e a r s , then, t h a t the p r i m a r y f a c t o r r e s p o n s i b l e f o r d i f ^ f e r e n t i a l s e x u a l performance i s the number of a n i m a l s per cage r a t h e r than T a b l e I I I Mean Scores on Measures of S e x u a l and A g g r e s s i v e Responses to S t i m u l u s Females and Males Under D i f f e r e n t D e n s i t i e s i n Experiment 3 Measure n per Space per a n i m a l (cm ) cage 3 3 1 T 1 3 2 5 3 9 7 6 1 2 7 . 6 7 2 1 . 2 5 2 4 . 9 5 Mounts 3 1 6 . 5 3 1 4 . 0 8 9.67 1 2 6.17 6.00 1 0 . 3 3 1 7.08 9.25 8.42 I n t r o m i s s i o n s 3 6.00 6.00 5.00 1 2 1.25 3.58 5.33 S t i m u l u s . Females 1 0.17 0.08 0.17 E j a c u l a t i o n s 3 0.08 0.17 0.17 1 2 0.00 0.17 0.08 A g g r e s s i o n 1 4.75 1 0 . 7 5 8.50 Score 3 0.00 3.42 1.42 1 2 1.83 0.00 6.42 A g g r e s s i o n 1 1 5 . 5 0 2 3 . 7 5 1 4 . 1 7 Score 3 1.50 2.83 0,00 1 2 0,00 0.00 2 2 , 5 8 S t i m u l u s (  Males D u r a t i o n of 1 Mounting 3 ( s e e l 1 2 0.83 0.00 1.33 0.00 0.00 0.08 0.00 0.00 0,00 38 the amount of space a l l o t t e d per a n i m a l . T h i s must be q u a l i f i e d , however, i n t h a t volumes per a n i m a l o u t s i d e the range s t u d i e d might produce d i f f e r e n t r e s u l t s . Volumes s u f f i c i e n t l y s m a l l as to c o n s t i t u t e s e v e r e r e s t r a i n t s t r e s s might i m p a i r s e x u a l performance d e s p i t e i n d i v i d u a l h o u s i n g , w h i l e e x t r e m e l y l a r g e volumes might reduce c o n t a c t between grouped a n i m a l s to an e x t e n t e q u i v a l e n t to i n d i v i d u a l h o u s i n g . C l e a r l y the r e s u l t s o f Experiments 1 and 2 cannot be a t t r i b u t e d to d i f f e r e n t i a l volume or d e n s i t y . I t i s i n t e r -e s t i n g t h a t an i n t e r a c t i o n o c c u r r e d i n t h e measure of a g g r e s s i o n w i t h males but not i n measures of s e x u a l b e h a v i o r . T h i s i n t e r a c t i o n , which appeared i n p a r t due to h i g h l e v e l s o f a g g r e s s i o n i n the low d e n s i t y group o f 12, may r e f l e c t some d i f f e r e n t i a l c o n t r o l o f sex and a g g r e s s i o n . G e n e r a l D i s c u s s i o n These experiments demonstrate a s u b s t a n t i a l f a c i l i t a t i o n o f male s e x u a l b e h a v i o r i n mice when they a r e housed i n d i v i d u a l l y r a t h e r than i n groups. T h i s f a c i l i t a t i o n i s p o s i t i v e l y c o r r e l a t e d w i t h i s o l a t i o n - i n d u c e d a g g r e s s i o n and responds s i m i l a r l y t o most o f the p a r a m e t r i c m a n i p u l a t i o n s i n v e s t i g a t e d . I s o l a t i o n - i n d u c e d f a c i l i t a t i o n o f male s e x u a l b e h a v i o r o c c u r s i n b o t h n a i v e and e x p e r i e n c e d a n i m a l s , and>can be r e v e r s e d by r e v e r s i n g c o n d i t i o n s . A s t r o n g e f f e c t i s produced w i t h i n one week of i s o l a t i o n , w h i l e the e f f e c t i s p r e s e n t i n n a i v e a n i m a l s a f t e r p e r i o d s o f i s o l a t i o n as p r o l o n g e d as f o u r weeks. W i t h i n l i m i t s , i s o l a t i o n - i n d u c e d f a c i l i t a t i o n o f male s e x u a l b e h a v i o r i s independent of p o p u l a t i o n d e n s i t y and amount of space a l l o t t e d per a n i m a l . S e v e r a l v a r i a b l e s may p l a y a r o l e i n p r o d u c i n g t h i s phenomenon. One p o s s i b i l i t y i s t h a t the p o o r e r performance o f grouped animals i s due to s t r e s s - r e l a t e d v a r i a b l e s . There i s e v i d e n c e t h a t grouped male mice a r e more s t r e s s e d than i n d i v i d u a l l y - h o u s e d mice, i n s o f a r as grouped 39 mice show h i g h b a s e l i n e l e v e l s of p i t u i t a r y - a d r e n o c o r t i c a l a c t i v i t y ( B r a i n , 1975; Leshner e t a l . , 1973). T h i s h i g h e r p i t u i t a r y - a d r e n o c o r t i c a l a c t i v i t y i s thought to be due to c o m p e t i t i o n and i n t e r m a l e f i g h t i n g , and i s p a r t i c u l a r l y e v i d e n t i n r e g u l a r l y d e f e a t e d animals ( B r a i n , 1975; Bronson & E l e f t h e r i o u , 1965). There have been s u g g e s t i o n s , b o t h i n the human c l i n i c a l (e.g., S e l y e , 1961) and b e h a v i o r a l - e c o l o g i c a l (e.g., C h r i s t i a n , 1971) l i t e r a t u r e s t h a t an antagonism e x i s t s between s t r e s s and s e x u a l performance i n mammals. While i t has been demonstrated t h a t s o c i a l s t r e s -s o r s may i n h i b i t o t h e r a s p e c t s of r e p r o d u c t i v e f u n c t i o n i n g (see C h r i s t i a n , 1971), t h e r e has been l i t t l e e x a m i n a t i o n of s e x u a l performance per se w i t h -i n t h i s c o n t e x t . I t may be t h a t i n c r e a s e d p i t u i t a r y - a d r e n o c o r t i c a l a c t i v i t y a c t s through some unknown p h y s i o l o g i c a l mechanism to depress s e x u a l f u n c -t i o n i n g , and t h a t t h i s mechanism ac c o u n t s f o r the p r e s e n t phenomenon. I f t h i s p o s i t i o n h o l d s , t h i s phenomenon might p r o v i d e an e x p e r i m e n t a l paradigm f o r i n v e s t i g a t i o n o f such a mechanism. A second, r e l a t e d p o s s i b i l i t y i n v o l v e s d i f f e r e n t i a l p i t u i t a r y -g onadal f u n c t i o n i n g i n i s o l a t e d and grouped mice. An i n c r e a s e i n gonadal a c t i v i t y , as a consequence o f i s o l a t i o n , has been i n d i c a t e d i n many s t u d i e s of male mice. S t u d i e s c o n t r a s t i n g i s o l a t e d and group-housed males have i n d i c a t e d t h a t i s o l a t e s have h e a v i e r sex a c c e s s o r i e s , such as t e s t e s , s e m i n a l v e s i c l e s , p r o s t a t e g l a n d s , and p r e p u t i a l g l a n d s (e.g., B r a i n & N o w e l l , 1971; C h r i s t i a n , 1955). A l s o , l e v e l s of t e s t o s t e r o n e a r e known to d e c r e a s e as a f u n c t i o n o f p i t u i t a r y - a d r e n o c o r t i c a l a c t i v a t i o n ( B u l l o c k & New, 1971; D e s j a r d i n s & Ewing, 1971), which has been demonstrated, as d i s c u s s e d above, i n grouped a n i m a l s . Thus, i t may be t h a t h i g h e r l e v e l s o f gonadal a c t i v i t y i n i s o l a t e s l e a d to h i g h e r l e v e l s of s e x u a l performance. The mechanism by which such an e f f e c t c o u l d o c c u r i s not as s t r a i g h t f o r w a r d 40 as might be assumed. IThere i s l i t t l e e v i d e n c e , f o r example, to suggest t h a t changes i n mammalian t e s t o s t e r o n e l e v e l s , above a c e r t a i n t h r e s h o l d l e v e l , a r e c o r r e l a t e d w i t h changes i n s e x u a l performance ( G o r z a l k a & Mogenson, 1977). Nor has any means been e s t a b l i s h e d by which d e c r e a s e d g l a n d u l a r weight might e f f e c t n e u r a l o r g a n i z a t i o n o f s e x u a l b e h a v i o r . N o n e t h e l e s s , the p o s s i b i l i t y remains t h a t d e c r e a s e d p i t u i t a r y - g o n a d a l f u n c t i o n i n g might produce s o c i a l s t r e s s - and housing-dependent d e f i c i t s i n s e x u a l performance. A t h i r d p o s s i b i l i t y i s t h a t a h i g h e r l e v e l o f g e n e r a l a c t i v i t y a c c o u n t s f o r b o t h enhanced s e x u a l performance and i n c r e a s e d a g g r e s s i o n i n i s o l a t e s exposed to c o n s p e c i f i c s . In t h i s l i g h t , Essman (1968) and B r a i n , Haley, and Nowell (1971) have found t h a t i s o l a t e s show more locomotor a c t i v i t y t h a n do grouped animals upon exposure to a n o v e l environment. G e n e r a l a c t i v i t y and b e h a v i o r a l a c t i v a t i o n a r e thought to be p a r t i a l l y r e g u l a t e d by l e v e l s and u t i l i z a t i o n r a t e s of b i o g e n i c amines (Bennett^ & ; Rosenzweig, 1971). A l t h o u g h i s o l a t e s may show lower b a s e l i n e l e v e l s and u t i l i z a t i o n o f n o r e p i n e p h r i n e and dopamine, and lower u t i l i z a t i o n o f s e r o t o n i n , they may e x h i b i t v e r y h i g h l e v e l s o f u t i l i z a t i o n o f t h e s e amines i n s t r e s s f u l and n o v e l s i t u a t i o n s ( G a r a t t i n i e t a l . , 1969; Welch & Welch, 1969a; 1969b). I t may be t h a t i n c r e a s e d t u r n o v e r of b i o g e n i c amines mediates enhancement o f s e x u a l performance i n i s o l a t e s , e i t h e r by i n c r e a s -i n g n o n - s p e c i f i c a c t i v i t y l e v e l s o r by d i r e c t l y f a c i l i t a t i n g s e x u a l p e r -formance through some unknown mechanism. Some e v i d e n c e s u g g e s t i n g dopa-m i n e r g i c and s e r o t o n e r g i c i n v o l v e m e n t i n male s e x u a l b e h a v i o r has been p r e s e n t e d by Gessa and T a g l i a m o n t e (1975). A f o u r t h p o s s i b i l i t y i s t h a t the t a c t i l e and o l f a c t o r y s t i m u l i which presumably e l i c i t s e x u a l b e h a v i o r i n mice are more n o v e l to animals 41 t h a t a r e i n d i v i d u a l l y housed and thus may be more p o w e r f u l i n c o n t r o l l i n g t h e i r b e h a v i o r . S i n c e a n i m a l s housed i n groups i n s m a l l e n c l o s u r e s cons-t a n t l y r e c e i v e s t i m u l i a s s o c i a t e d w i t h c o n s p e c i f i c s , s i m i l a r s t i m u l i might be l e s s s a l i e n t when animals a r e exposed to r e c e p t i v e females i n a n o v e l environment. R e c e p t i v e females may be i n s u f f i c i e n t l y d i s t i n c t from o t h e r males to e l i c i t s e x u a l b e h a v i o r from e x p e r i m e n t a l males. S i m i l a r l y , a s u f f i c i e n t l e v e l o f i n t e r m a l e mounting may o c c u r i n grouped a n i m a l s to make t h e s e a n i m a l s s e x u a l l y s a t i a t e d when they ar e exposed to f e m a l e s . I n t e r m a l e mounting i s commonly observed i n mammalian s p e c i e s and was o c c a s i o n a l l y o b served i n the p r e s e n t s t u d y when e x p e r i m e n t a l animals were exposed to t a r g e t males. Such mounting might be u n l i k e l y to l e a d to s e x u a l s a t i e t y , however, s i n c e mounted males might not be s u f f i c i e n t l y r e c e p t i v e to a l l o w r e s p o n s e s analogous t o i n t r o m i s s i o n . In the p r e s e n t s t u d y , the few c a s e s o f i n t e r m a l e mounting were u s u a l l y r e p u l s e d by the mounted male and f r e q u e n t l y evoked an a t t a c k . A f a i r l y h i g h l e v e l o f i n t e r m a l e mounting would presumably be r e q u i r e d to produce the d e f i c i t s i n performance observed A i n group-housed a n i m a l s . F i n a l l y , s o c i a l l e a r n i n g v a r i a b l e s may i n some manner i n h i b i t the o c c u r r e n c e of s e x u a l a c t i o n p a t t e r n s i n group-housed a n i m a l s . For example, s i n c e s e x u a l b e h a v i o r o r i e n t e d towards o t h e r males i n a group may evoke a t t a c k s a g a i n s t the s e x u a l l y aroused a n i m a l , the p r o b a b i l i t y o f mount-i n g b e h a v i o r may be d e c r e a s e d i n the aroused a n i m a l . The e f f e c t s o f p u n i s h -ment o f s e x u a l o v e r t u r e s by evoked a t t a c k s may g e n e r a l i z e to o t h e r s i t u a -t i o n s , i n t h a t the p r o b a b i l i t y o f s e x u a l r e s p o n s e s on the p a r t of group-housed males toward r e c e p t i v e females c o u l d be reduced. 42 One c o n s i d e r a t i o n f o r f u t u r e r e s e a r c h i s t h a t the topography, as w e l l as the q u a n t i t y , of murine s e x u a l b e h a v i o r may be a f f e c t e d by i s o l a -t i o n . F o r example, i t may be t h a t more mounts and i n t r o m i s s i o n s a r e r e q u i r e d f o r each e j a c u l a t i o n on the p a r t of i s o l a t e s . The p r o p o r t i o n s o f e j a c u l a t i o n s t o mounts and i n t r o m i s s i o n s observed i n Experiments 2 and 3 appeared comparable f o r a l l c o n d i t i o n s . More e j a c u l a t i o n s o c c u r r e d i n the i s o l a t e s than i n the groups of 12, and u s u a l l y more i n i s o l a t e s than i n the groups of 3. However, the sample of e j a c u l a t o r y r e s p o n s e s was too s m a l l f o r s t a t i s t i c a l a n a l y s i s t o r e v e a l s i g n i f i c a n t d i f f e r e n c e s . F u t u r e e x a m i n a t i o n might t e s t a n i m a l s under c o n d i t i o n s where a s u f f i c i e n t number o f e j a c u l a t o r y r e s p o n s e s o c c u r to p r o v i d e an a n a l y s i s o f t h i s q u e s t i o n . The moderate p o s i t i v e c o r r e l a t i o n s between s e x u a l performance and a g g r e s s i o n suggest t h a t some v a r i a b l e a f f e c t e d by the m a n i p u l a t i o n s of t h i s s t u d y i n f l u e n c e s t h e s e two response c l a s s e s commonly. S i n c e the c o r -r e l a t i o n was u s u a l l y absent when c o n d i t i o n s were c o n s i d e r e d s e p a r a t e l y , sex and a g g r e s s i o n may o n l y c o v a r y i n s o f a r as they respond s i m i l a r l y to the parameters s t u d i e d . These c o r r e l a t i o n s may n o t , however, e n t i r e l y r e f l e c t the r e l a t i o n s h i p between sex and a g g r e s s i o n . The o r d e r df t e s t i n g , which i n the p r e s e n t s t u d y i n v o l v e d a g g r e s s i o n t e s t s t h r e e days a f t e r sex t e s t s , may have i n f l u e n c e d the o b t a i n e d r e l a t i o n s h i p between these response c l a s s e s . L a g e r s p e t z and Hautoj'arvi (1967) demonstrated t h a t p r i o r a g g r e s -s i v e e x p e r i e n c e s can a f f e c t s e x u a l performance i n mice, and v i c e v e r s a . P r e v i o u s a g g r e s s i v e e x p e r i e n c e w i t h a male was found to d e c r e a s e s e x u a l b e h a v i o r i n male mice, w h i l e p r e v i o u s s e x u a l e x p e r i e n c e was found to d e c r e a s e a g g r e s s i o n toward o t h e r males. T h i s f a c t o r , then, c o u l d have reduced a g g r e s s i v e b e h a v i o r i n a n i m a l s which were s e x u a l l y a c t i v e i n the 43 p r e v i o u s t e s t w i t h females, thus l o w e r i n g the c o r r e l a t i o n v a l u e s o b t a i n e d . T h i s f a c t o r might a l s o have a f f e c t e d the r e s u l t s o f Experiment 1, where s e v e r a l t e s t s o f s e x u a l and a g g r e s s i v e b e h a v i o r were g i v e n to the same an i m a l s . However, i t might be more l i k e l y t o reduce d i f f e r e n c e s i n s e x u a l performance between c o n d i t i o n s than to i n c r e a s e such d i f f e r e n c e s , i n t h a t g r e a t e r a g g r e s s i v e e x p e r i e n c e would a c c o r d i n g l y reduce s e x u a l performance i n i s o l a t e s . A l s o , L a g e r s p e t z and Hautoj'arvi (1967) found t h e i r r e s u l t s were l i m i t e d t o i n e x p e r i e n c e d a n i m a l s and a t t r i b u t e d e f f e c t s to a l a c k of d i f f e r e n t i a t i o n o f r e s p o n s e s to males and females. In Experiment 1 of the p r e s e n t s t u d y r e s p o n s e s to males and females were h i g h l y d i f f e r e n t i a t e d , p a r t i c u l a r l y a f t e r the e x p e r i m e n t a l a n i m a l s had had the e x p e r i e n c e of s e v e r a l s e s s i o n s . In another r e l e v a n t experiment, Kahn (1961) has found t h a t i s o -l a t e d mice t r a i n e d t o be a g g r e s s i v e by a d a n g l i n g t e c h n i q u e were subse-q u e n t l y more a c t i v e s e x u a l l y than o t h e r i s o l a t e d males made s u b m i s s i v e by s u c c e s s i v e d e f e a t s by a t r a i n e d f i g h t e r . A l t h o u g h o n l y a few s u b j e c t s were examined, t h i s study s u g g e s t s a f u r t h e r means by which a g g r e s s i o n may i n t e r a c t w i t h s e x u a l b e h a v i o r . A l s o , these r e s u l t s c o u l d i n d i c a t e a mechanism a c c o u n t i n g f o r f a c i l i t a t i o n o f s e x u a l performance i n i s o l a t e s . S i n c e grouped male mice n o r m a l l y f i g h t f r e q u e n t l y and e s t a b l i s h dominance h i e r a r c h i e s ( D e F r i e s & M c C l e a r n , 1970; M e s s e r i e t a l . , 1975), i t may be t h a t i n d i v i d u a l s a t d i f f e r e n t s t r a t a of a h i e r a r c h y show d i f f e r e n t l e v e l s of s e x u a l performance. R e g u l a r l y d e f e a t e d , more s u b o r d i n a t e males i n a group may show poor performance, w h i l e v i c t o r i o u s , dominant males may show performance comparable to t h a t of i s o l a t e s . Such an i n t e r p r e t a t i o n might be comparable w i t h some o f the b i o c h e m i c a l i n t e r p r e t a t i o n s p r e s e n t e d above, i n s o f a r as d e f e a t e d and s u b o r d i n a t e mice show i n c r e a s e d a d r e n o c o r t i c a l 44 a c t i v i t y (Bronson & E l e f t h e r i o u , 1965), changes i n n e u r o t r a n s m i t t e r l e v e l s (Welch & Welch, 1971; E l e f t h e r i o u , 1971) and de c r e a s e d t e s t o s t e r o n e l e v e l s (McKinney & D e s j a r d i n s , 1973a; 1973b), e f f e c t s which a r e absent i n dominant, v i c t o r i o u s mice. I t i s a l s o c o n s i s t e n t w i t h the i n t e r p r e t a t i o n t h a t s o c i a l l e a r n i n g i s i n v o l v e d , i n t h a t b e h a v i o r o r i e n t e d toward dominant males might be pu n i s h e d and the subsequent s u p p r e s s i o n o f b e h a v i o r g e n e r a l i z e to s i t u a t i o n s i n v o l v i n g r e c e p t i v e f e m a l e s . In t h i s r e g a r d , D e F r i e s and Mc C l e a r n (1970, 1972) have found t h a t dominant male mice i n a group s i r e the m a j o r i t y o f o f f s p r i n g when females a r e i n t r o d u c e d i n t o the group. There have been a number o f p r e v i o u s s u g g e s t i o n s t h a t s e x u a l and a g g r e s s i v e b e h a v i o r may be m o t i v a t i o n a l l y l i n k e d . Both a g g r e s s i v e and s e x u a l b e h a v i o r a r e known to be dependent upon p r e n a t a l and c i r c u l a t i n g l e v e l s o f androgens i n many s p e c i e s i n c l u d i n g mice (Quadagno e t a l . , 1977). A c c o r d -i n g l y , the r e l a t i o n s h i p between sex and a g g r e s s i o n i n the p r e s e n t study might be dependent upon d i v e r g e n c e i n androgen l e v e l s subsequent t o s e p a r a -t i o n i n t o i s o l a t e d and grouped c o l o n i e s . S t u d i e s by Leshner e t a l . (1973) and B r a i n and Po o l e (1974) might c o n t r a d i c t such a p o s i t i o n , however, s i n c e they i n d i c a t e t h a t d i f f e r e n c e s between i s o l a t e d and grouped animals i n a g g r e s s i o n r e s u l t more from l e v e l s o f ACTH than from l e v e l s o f androgens. B i n d r a (1959) has sugg e s t e d t h a t c o v a r i a t i o n o f sex and a g g r e s s i o n i s due to changes i n the l e v e l o f a r o u s a l , i n t h a t b o t h types o f b e h a v i o r a r e n o r m a l l y performed i n a s t a t e of h i g h a r o u s a l and thus a r e more l i k e l y to occ u r when a r o u s a l i s a l r e a d y h i g h . Such a p o s i t i o n might be concordant w i t h an i n t e r p r e t a t i o n t h a t i s o l a t i o n l e a d s t o i n c r e a s e d l e v e l s o f a r o u s a l i n n o v e l s i t u a t i o n s , which c o n s e q u e n t l y i n c r e a s e s a g g r e s s i v e , s e x u a l , and g e n e r a l a c t i v i t y l e v e l s i n these s i t u a t i o n s . Such a r o u s a l might be mediated by i n c r e a s e d u t i l i z a t i o n o f c e n t r a l and p e r i p h e r a l b i o g e n i c amines as d i s -c u ssed above, w i t h i t s o r i e n t a t i o n b e i n g determined by s a l i e n t s t i m u l i i n 45 the n o v e l environment. A number o f n a t u r a l i s t i c s t u d i e s p r o v i d e a f u r t h e r p e r s p e c t i v e t h a t may h e l p to e x p l a i n a m o t i v a t i o n a l l i n k between sex and a g g r e s s i o n . Turner and I v e r s o n (1973) found t h a t a g g r e s s i v e a c t s i n males sampled from n a t u r a l p o p u l a t i o n s o f v o l e s ( M i c r o t u s p e n n s y l v a n i c u s ) i n c r e a s e d i n f r e -quency as males became r e p r o d u c t i v e l y a c t i v e and d e c r e a s e d as the b r e e d i n g season ended. In o t h e r s e a s o n a l l y p o l y e s t r o u s o r monestrous mammals, f i g h t i n g among males i n c r e a s e s d r a m a t i c a l l y d u r i n g the b r e e d i n g season (Bermant & D a v i d s o n , 1974). T a y l o r (1976) has found t h a t , i n r a t s , expo-s u r e to e s t r o u s females has a d i r e c t i n f l u e n c e upon i n t e r m a l e i n t e r a c t i o n s , i n t h a t i t i n c r e a s e s t h e p r o b a b i l i t y t h a t a male w i l l approach o t h e r a g g r e s -s i v e males. These r e s u l t s a r e s i g n i f i c a n t s i n c e they i n d i c a t e t h a t i n c r e a s e d i n t e r m a l e f i g h t i n g a t b r e e d i n g season i s not s i m p l y an i n d i r e c t r e s u l t of the a t t r a c t i o n o f s e v e r a l males t o an a r e a o c c u p i e d by a female. T h i s m o t i v a t i o n a l l i n k may have s u r v i v a l v a l u e i n t h a t a male t h a t i s a g g r e s s i v e d u r i n g the mating season may be more l i k e l y t o pass on h i s genes than would a n o n - a g g r e s s i v e male. 46 SECTION I I : STRAIN AND SPECIES GENERALITY In the p r e v i o u s e x p e r i m e n t s , s o c i a l i s o l a t i o n o f male mice f a c i l i t a t e d t h e i r s e x u a l performance. The experiments of the p r e s e n t s e c t i o n examined the s t r a i n and s p e c i e s g e n e r a l i t y o f i s o l a t i o n / g r o u p i n g d i f f e r e n c e s i n male s e x u a l performance. Because of c r o s s - s p e c i e s v a r i a -t i o n i n s o c i a l s t r u c t u r e , v a r i o u s s o c i a l arrangements may d i f f e r e n t i a l l y a f f e c t t h e b e h a v i o r o f members of d i f f e r e n t s p e c i e s . F urthermore, t h e r e a r e i n d i c a t i o n s t h a t p h y s i o l o g i c a l v a r i a b l e s may be d i f f e r e n t i a l l y a f f e c t e d by s o c i a l i s o l a t i o n i n d i f f e r e n t s p e c i e s (Bennett & Rosenzweig, 1971; Sahakian, Robbins, Morgan, & I v e r s o n , 1975; S t o l k , Conner, & Barchas, 1974), e f f e c t s which may i n t u r n produce d i f f e r e n c e s i n s e x u a l performance. P r e v i o u s i n v e s t i g a t i o n o f i s o l a t i o n - i n d u c e d f a c i l i t a t i o n o f male s e x u a l b e h a v i o r (Experiments 1, 2, & 3) was l i m i t e d to CD-I s t r a i n mice. I t i s thus i m p o r t a n t to examine whether the phenomenon i s c h a r a c t e r i s t i c o f t h i s s t r a i n , o f mice i n g e n e r a l , o r of a number of s p e c i e s . F urthermore, d i f f e r e n t i a l s e x u a l r e s p o n s i v e n e s s to i s o l a t i o n or g r o u p i n g can be com-p a r e d to d i f f e r e n t i a l p h y s i o l o g i c a l r e s p o n s i v e n e s s and s o c i a l d i f f e r e n c e s among s p e c i e s . Such a comparison might p r o v i d e i n d i r e c t i n f o r m a t i o n r e g a r d i n g the r e l a t i o n s h i p o f s e x u a l b e h a v i o r to s o c i a l and p h y s i o l o g i c a l v a r i a b l e s . Experiment 4 There i s c o n s i d e r a b l e e v i d e n c e t h a t i n b r e d s t r a i n s o f house mice may respond d i f f e r e n t i a l l y t o s o c i a l i s o l a t i o n . D i f f e r e n c e s may o c c u r i n a g g r e s s i v e n e s s (Karczmar & Scudder, 1969; LeDouarec & Broussy,' 1969), p i t u i t a r y - a d r e n o c o r t i c a l and p i t u i t a r y - g o n a d a l response (see B r a i n , 1975), and n e u r o c h e m i s t r y (Karczmar & Scudder, 1969). F u r t h e r -more, the d i s t r i b u t i o n and r e l a t i v e f r e q u e n c i e s o f s e x u a l a c t i o n p a t t e r n s may v a r y among s t r a i n s . S e v e r a l r e s e a r c h e r s ( L e v i n e e t a l . , 1966; M c G i l l , 1962; 1965; Mosig & Dewsbury, 1976) have p r o v i d e d d e s c r i p t i o n s o f s t r a i n d i f f e r e n c e s i n s e x u a l performance. On t h i s b a s i s i t becomes n e c e s s a r y t o e s t a b l i s h whether or not a phenomenon found i n one s t r a i n i s c h a r a c t e r i s t i c o f o n l y t h a t s t r a i n . The p r e s e n t experiment examined the e f f e c t s o f i s o l a t i o n and g r o u p i n g upon the s e x u a l performance of t h r e e commonly s t u d i e d s t r a i n s o f mice. Method E x p e r i m e n t a l a n i m a l s c o n s i s t e d o f 24 male C57Bl/6NCrlBRand 24 male DBA/2NCr,lBR/mice o b t a i n e d from Canadian B r e e d i n g Farms, , and 24 male Swiss-Webster mice o b t a i n e d from B i o b r e e d i n g L a b o r a t o r i e s , Ottawa. A l l a n i m a l s were s e x u a l l y n a i v e . A f t e r r e c e i p t from the b r e e d e r s a t 55 days o f age, animals were housed i n groups of 6 of homogeneous s t r a i n u n t i l commencement o f the e x p e r i m e n t a l h o u s i n g c o n d i t i o n s . Each group was caged and m a i n t a i n e d as i n Experiment 1A. Animals were t e s t e d 5-8 h r a f t e r the commencement of t h e i r dark phase i n an i l l u m i n a t e d room. S t i m u l u s a n i m a l s c o n s i s t e d o f 40 group-housed CD-I females o b t a i n e d from Canadian B r e e d i n g Farms. Females from a f o u r t h s t r a i n were employed to a v o i d c o n f o u n d i n g of male s t r a i n d i f f e r e n c e s w i t h s t r a i n d i f f e r e n c e s i n 48 female r e c e p t i v i t y (see G o r z a l k a & Whalen, 1976). S t i m u l u s females were p r e p a r e d a c c o r d i n g to the p r o c e d u r e o u t l i n e d f o r Experiment IA. Females were used f o r no more than two s u c c e s s i v e h o u r l y t e s t s . At 60-65 days o f age, 12 o f the a n i m a l s from each s t r a i n were rehoused i n c l e a n cages i n groups of 6 w h i l e the r e m a i n i n g 12 animals were housed i n d i v i d u a l l y i n c l e a n cages. Groups of 6 were c o n s t i t u t e d by the same an i m a l s as they had been s i n c e r e c e i p t from the b r e e d e r . Cages were those manufactured by Carworth Lab Cages from p o l y p r o p y l e n e d e s c r i b e d f o r Experiment IA. Cages were c l e a n e d as r e q u i r e d t o m a i n t a i n a l l c o n d i -t i o n s a t an a p p r o x i m a t e l y e q u i v a l e n t l e v e l of c l e a n l i n e s s , but under no c i r c u m s t a n c e s were they d i s t u r b e d d u r i n g the 3 days immediately p r e c e d i n g t e s t i n g . A f t e r 2 weeks i n t h e s e c o n d i t i o n s , a p e r i o d p r e v i o u s l y e s t a b l i s h e d as s u f f i c i e n t to produce e f f e c t s i n CD-I mice (Experiment 2 ) , a n i m a l s were t e s t e d f o r s e x u a l performance. T h i s t e s t c o n s i s t e d o f a 1-hr s e s s i o n d u r i n g which each a n i m a l was p r e s e n t e d w i t h r e c e p t i v e females i n the t e s t i n g e n c l o s u r e s d e s c r i b e d f o r the p r e v i o u s e x p e r i m e n t s . S i x a n i m a l s were t e s t e d s i m u l t a n e o u s l y i n a d j a c e n t e n c l o s u r e s , w i t h one a n i m a l from each treatment c o m b i n a t i o n p r e s e n t a t each s e s s i o n . A f t e r 5 min of a d a p t a t i o n to the chamber, a s i n g l e r e c e p t i v e female was p r e s e n t e d to each a n i m a l . At 10-min i n t e r v a l s females were r o t a t e d so t h a t each treatment c o m b i n a t i o n r e c e i v e d each female f o r an e q u i v a l e n t amount of time. D u r i n g s e s s i o n s , the f r e q u e n c y , d u r a t i o n , and l a t e n c y o f mounts w i t h o u t i n t r o m i s s i o n (mounts) and mounts w i t h i n t r o m i s s i o n and p e l v i c t h r u s t i n g ( i n t r o m i s s i o n s ) , and the number and l a t e n c y o f e j a c u l a t i o n s were measured. A l l l a t e n c i e s were measured from the commencement o f the s e s s i o n . Responses were r e c o r d e d v i a an E s t e r l i n e - A n g u s event r e c o r d e r by a t r a i n e d o b s e r v e r who was unaware of the purpose of the experiment. Mounts, 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 49 were d e f i n e d as d e s c r i b e d by M c G i l l (1965). R e s u l t s and D i s c u s s i o n F i g u r e 4 shows the r e s u l t s f o r measures of d u r a t i o n o f mounting, w i t h or w i t h o u t i n t r o m i s s i o n , and number of mounts, 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 a b l e IV r e p o r t s r e m a i n i n g measures of c o p u l a t o r y p e r f o r -mance. The measure of c o p u l a t o r y e f f i c i e n c y i s adapted from P a r r o t t (1975) and i s c a l c u l a t e d u s i n g a l l mounts and i n t r o m i s s i o n s p r e c e d i n g the f i r s t e j a c u l a t i o n or the end of the s e s s i o n as f o l l o w s : i f M + I >0, CE = J L i f M + I = 0, CE = 0 where M = number of mounts, I = number o f i n t r o m i s s i o n s , CE = c o p u l a t o r y e f f i c i e n c y . I n d i v i d u a l l y - h o u s e d mice o f a l l s t r a i n s showed s u b s t a n t i a l l y more mounts, i n t r o m i s s i o n s , and time spent mounting than d i d s a m e - s t r a i n group-housed mice. There were o n l y a few e j a c u l a t i o n s i n any c o n d i t i o n , but t h e s e were a l s o more common i n i s o l a t e d than group-housed mice. L a t e n c i e s t o f i r s t mount and i n t r o m i s s i o n were on the average s h o r t e r i n i s o l a t e d mice, w h i l e the p e r c e n t a g e mounting, i n t r o m i t t i n g , and e j a c u l a t -i n g was i n a l l cases h i g h e r i n i s o l a t e d a n i m a l s w i t h i n each s t r a i n . DBA mice showed s u b s t a n t i a l l y l e s s s e x u a l a c t i v i t y than e i t h e r C57 or Swiss-Webster mice; t h i s may i n p a r t be due to t h e i r s m a l l e r r e l a t i v e s i z e compared to CD-I fe m a l e s . P a r a l l e l t w o - f a c t o r ( h o u s i n g c o n d i t i o n and s t r a i n ) a n a l y s e s o f v a r i a n c e were conducted on a l l measures except p e r c e n t a g e s o f r e s p o n s e s . The i s o l a t i o n / g r o u p i n g f a c t o r was s i g n i f i c a n t i n t o t a l d u r a t i o n (F = 7.54, df = 1/66, p_ = .008), number o f mounts (F = 10.94, df = 1/66, p = .002), number of i n t r o m i s s i o n s (F = 4.62, df = 1/66, p_ = .033), mount l a t e n c y 50 F i g u r e 4: Mean performance of i s o l a t e d and grouped Swiss'-Webster ( S w i s s ) , C57Bl/6NCrlBR(C57), and DBA/2NCr1BR(DBA) male mice on measures of s e x u a l B e h a v i o r i n t h e p r e s e n c e of r e c e p t i v e females i n Experiment 4, L i n e s above the Ba r s i n d i c a t e s t a n d a r d e r r o r s . NUMBER OF INTROMISSIONS o Ul NUMBER OF EJACULATIONS cn b 8 o cn D > J " 1 8 o > c= H "D m m D O DURATION OF MOUNTING (SEC) _i ro CO £ o o o o o o o o o cn 5 C O 8 o cn 5 NUMBER OF MOUNTS J. ro co p o o o cn o IS 52 T a b l e IV Means and Standard E r r o r s of Response L a t e n c i e s ( i n sec) and C o p u l a t o r y E f f i c i e n c y , and P e r c e n t Responding i n Experiment 4 ° Swiss C5/ DBA Mount 1 592+140 344+100 2105+471 L a t e n c y 6 1088+327 1163+356 3315+285 I n t r o m i s s i o n 1 985+247 1265+354 29.86+285 L a t e n c y 6 1664+399 1881+375 3225+275 E j a c u l a t i o n • .1. 3234+224 3304+163 3600+0 L a t e n c y 6 3226+258 3314+151 3600+0 C o p u l a t o r y 1 ,318+, 036 .256+,047 ,119+.048 E f f i c i e n c y 6 ,258+.053 .214+.062 .021+.021 % Mounting 1 100 100 50 6 92 92 8 % I n t r o m i t t i n g 1 100 92 42 6 83 67 8 % E j a c u l a t i n g 1 25 50 0 6 17 25 0 53 (F = 11.25, d_f = 1/66, p_ = .001), and i n t r o m i s s i o n l a t e n c y (F = 4.16, df = 1/66, p_ = .043). There was n o t a s i g n i f i c a n t e f f e c t o f t h i s f a c t o r i n o t h e r measures. There was a s i g n i f i c a n t e f f e c t o f s t r a i n i n a l l measures except e j a c u l a t i o n l a t e n c y : d u r a t i o n (F_ = 16.10, d_f = 2/66, £ <.001), mounts (F = 13.30, df_ = 2/66, £ <.001), i n t r o m i s s i o n s (F = 10.87, df = 2/66, £ <.001), e j a c u l a t i o n s (F = 6.03, df = 2/66, £ = .004), mount l a t e n c y (F_ = 25.87, df_ = 2/66, £ <.001), i n t r o m i s s i o n l a t e n c y (F = 18.44, df = 2/66, £ <-:.001), and c o p u l a t o r y e f f i c i e n c y (F = 12.03, df = 2/66, £ < . 0 0 1 ) . In a l l cases Newman-Keuls t e s t s (p <.05) i n d i c a t e d t h a t the DBA mice showed lower performance than b o t h the C57 and Swiss-Webster mice, but t h a t t h e s e l a t t e r two s t r a i n s d i d not d i f f e r . There were no s i g n i f i c a n t s t r a i n by i s o l a t i o n / g r o u p i n g i n t e r a c t i o n s . These r e s u l t s suggest t h a t f a c i l i t a t i o n o f s e x u a l b e h a v i o r by i s o l a t i o n i s c h a r a c t e r i s t i c o f t h e . s p e c i e s . I s o l a t i o n a f f e c t s s e v e r a l components of s e x u a l b e h a v i o r . An e f f e c t i s e v i d e n t i n a l l measures, a l t h o u g h a few may not 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 under these c o n d i -t i o n s . There i s c o n s i d e r a b l e v a r i a b i l i t y among group a n i m a l s ; some show no s e x u a l r e s p o n s e whatsoever, o t h e r s show performance comparable to t h a t o f i s o l a t e s . In the Swiss-Webster and C57 mice, the major e f f e c t o f i s o l a t i o n appeared to be an i n c r e a s e i n the average amount o f s e x u a l b e h a v i o r , w i t h most grouped a n i m a l s showing some re s p o n s e . In the DBA s t r a i n , the major e f f e c t o f i s o l a t i o n was to i n c r e a s e the number of a n i m a l s showing any response to females. Experiment 5 House mice n o r m a l l y l i v e i n s m a l l demes composed of a dominant male, s e v e r a l f e m a l e s , and a few s u b o r d i n a t e males (Reimer & P e t r a s , 1967). -Male mice may c o n s e q u e n t l y adapt r e a d i l y to i n d i v i d u a l h o u s i n g , but be 54 r e l a t i v e l y s t r e s s e d under group-housing c o n d i t i o n s , an i n t e r p r e t a t i o n t h a t i s s u p p o r t e d by hormonal comparisons of i s o l a t e d and grouped mice (see r e v i e w by B r a i n , 1975). I t has been h y p o t h e s i z e d t h a t s t r e s s may a n t a g o n i z e s e x u a l b e h a v i o r ( C h r i s t i a n , 1971; Gray, 1971; S e l y e , 1961); the f i n d i n g s o f Experiment 1 may s u p p o r t t h i s h y p o t h e s i s . Other r o d e n t s p e c i e s d i f f e r from mice i n s o c i a l o r g a n i z a t i o n . The r a t (Rattus n o r v e g i c u s ) , f o r example,.is a f a i r l y s o c i a l s p e c i e s w i t h i n d i v i d u a l s l i v i n g i n l a r g e c o l o n i e s t h a t share n e s t i n g s i t e s and f e e d i n g grounds ( B a r n e t t , 1975). The g o l d e n hamster ( M e s o c r i c e t u s  a u r a t u s ) i s b e l i e v e d to be s o l i t a r y i n i t s n a t u r a l environment ( E i b l -E i b e s f e l d t , 1953; Johnson, 1975). The M o n g o l i a n g e r b i l (Meriones  u n g u i c u l a t u s ) i s r e p o r t e d to show s m a l l p e r s o n a l d i s t a n c e s and aggregate p e a c e f u l l y i n s e m i n a t u r a l environments ( E i s e n b e r g , 1967; T h i e s s e n & Yahr, 1977). These s p e c i e s may a l s o respond d i f f e r e n t l y t o i s o l a t i o n and h o u s i n g c o n d i t i o n s w i t h r e s p e c t to l e v e l s of a g g r e s s i v e n e s s ( c f . , B l a n c h a r d & B l a n c h a r d , 1971; Conner, 1972, 1972; Edwards & Rowe, 1975; S c o t t , 1966; T h i e s s e n & Yahr, 1977) and p h y s i o l o g y (see Bennett & Rosenzweig, 1971). Moreover, the topography o f male s e x u a l b e h a v i o r d i f f e r s among t h e s e s p e c i e s ( c f . , G o r z a l k a & Mogenson, 1977; Kuehn & Zucker, 1968; L a r s s o n , 1956, M c G i l l , 1965). Because of these s p e c i e s d i f f e r e n c e s , t h e r e i s r e a s o n to s u s p e c t t h a t male s e x u a l b e h a v i o r might respond d i f f e r e n t i a l l y i n d i f f e r e n t s p e c i e s to the i s o l a t i o n / g r o u p i n g m a n i p u l a t i o n . T h e r e f o r e , i n o r d e r to t e s t the g e n e r a l i t y of p r e v i o u s f i n d i n g s , male r a t s , g e r b i l s , and hamsters were examined under c o n d i t i o n s known to produce i s o l a t i o n / g r o u p i n g d i f f e r e n c e s i n mice. 55 Method S u b j e c t s - Twenty-four s e x u a l l y n a i v e male Long-Evans r a t s , o b t a i n e d from Canadian B r e e d i n g Farms, were housed i n groups of 6 i n s t a n d a r d t r i p l e wire-mesh cages u n t i l commencement of the e x p e r i m e n t a l h o u s i n g c o n d i t i o n s a t about 120 days of age. Twenty-four s e x u a l l y n a i v e male g o l d e n hamsters, o b t a i n e d from C h a r l e s R i v e r L a b o r a t o r i e s , N e w f i e l d , N.J., were housed i n groups of 6 i n p o l y c a r b o n a t e cages measuring 46 x 25 x 15 ( h e i g h t ) cm equipped w i t h l a r g e s t r a i g h t - w i r e tops u n t i l commencement of e x p e r i m e n t a l h o u s i n g c o n d i t i o n s a t about 100 days of age. These cages each c o n t a i n e d 2 l i t e r s of bedding m a t e r i a l and one paper t o w e l . Twenty-four s e x u a l l y n a i v e male g e r b i l s , o b t a i n e d from H i g h Oak Ranch, Goodwood, Ont., were housed i n the manner d e s c r i b e d f o r hamsters u n t i l about 120 days of age. These ages were chosen because almost a l l males of t h e s e s p e c i e s s h o u l d be s e x u a l l y mature by t h e s e ages. A l l a n i m a l s were housed under a r e v e r s e d 12-hr dark/12-hr l i g h t c y c l e and kept i n rooms m a i n t a i n e d a t 21 + 1°C. Animals were t e s t e d 5-8 h r a f t e r commencement of " t h e i r dark phase i n an i l l u m i n a t e d room. S t i m u l u s females - A d u l t females of each s p e c i e s were o b t a i n e d and group-housed. These were b i l a t e r a l l y o v a r i e c t o m i z e d a t l e a s t 3 weeks p r i o r to t e s t i n g . On the f i r s t and second days b e f o r e t e s t i n g females were g i v e n 5 e s t r a d i o l benzoate i n .05 cc peanut o i l s c . On the day of t e s t i n g females were g i v e n 500 jug p r o g e s t e r o n e i n .05 cc o i l sc 5 h r p r i o r t o t e s t i n g f o r r a t s and hamsters and 9 hr p r i o r to t e s t i n g f o r g e r b i l s . Females were used f o r no more than two s u c c e s s i v e h o u r l y t e s t s . Procedure - Two weeks p r i o r t o t e s t i n g w i t h r e c e p t i v e c o n s p e c i f i c f e m a l e s , males were p l a c e d i n t o two c o n d i t i o n s , each of which c o n t a i n e d 12 a n i m a l s of each s p e c i e s : animals grouped i n 6 and animals housed' i n d i v i d u a l l y . A l l groups o f 6 were s i m p l y p l a c e d i n c l e a n cages a t t h i s p o i n t w i t h each group b e i n g c o n s t i t u t e d by the same i n d i v i d u a l s as i t had been s i n c e a nimals were r e c e i v e d from the b r e e d e r s . I n d i v i d u a l l y - h o u s e d r a t s were-, each housed i n s t a n d a r d l a b o r a t o r y s i n g l e wire-mesh cages. I n d i v i d u a l l y -housed g e r b i l s and hamsters were each housed i n cages i d e n t i c a l to those d e s c r i b e d f o r mice i n Experiment IA. Animals were t e s t e d f o r 1 h r i n c y l i n d r i c a l Pyrex t e s t i n g j a r s measuring 45 cm i n h e i g h t w i t h a diameter of 29 cm. Each s p e c i e s was t e s t e d a t s e p a r a t e t i m e s . S i x a n i m a l s , t h r e e i s o l a t e s and t h r e e grouped a n i m a l s , were observed s i m u l t a n e o u s l y . A f t e r 5 min a d a p t a t i o n to the j a r , each a n i m a l was p r e s e n t e d w i t h a r e c e p t i v e c o n s p e c i f i c female. Females were t r a n s f e r r e d to a d j a c e n t j a r s e v e r y 10 min so t h a t grouped and i s o l a t e d c o n d i t i o n s r e c e i v e d each female f o r i d e n t i c a l l e n g t h s o f time. D u r i n g these s e s s i o n s the number and l a t e n c i e s of mounts, 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 were r e c o r d e d v i a an E s t e r l i n e -Angus event r e c o r d e r . The s e x u a l r e s p o n s e s o f r a t s were d e f i n e d as des-c r i b e d by L a r s s o n (1956), those o f hamsters as d e s c r i b e d by G o r z a l k a and Mogenson (1977), and those o f g e r b i l s as d e s c r i b e d by Kuehn and Zucker (1968). R e s u l t s and D i s c u s s i o n F i g u r e 5 g i v e s the r e s u l t s f o r measures o f mounts, 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 . Remaining measures a r e g i v e n i n T a b l e V. A d u r a t i o n o f mounting measure i s not r e p o r t e d s i n c e most mounts and i n t r o m i s s i o n s a r e v e r y b r i e f and o f about the same d u r a t i o n w i t h i n each o f these s p e c i e s . 57 F i g u r e 5: Mean performance o f i s o l a t e d and grouped male r a t s , hamsters, and g e r b i l s on measures of s e x u a l b e h a v i o r i n the p r e s e n c e o f r e c e p t i v e c o n s p e c i f i c f emales In Experiment 5, L i n e s above the b a r s i n d i c a t e s t a n d a r d e r r o r s , RATS HAMSTERS GERBILS C/5 3 31 *£. —> LU O or LU CD GROUPED • ISOLATED^ 1 RATS HAMSTERS GERBILS 59 T a b l e V Means , and Standard E r r o r s ? of Response L a t e n c i e s ( i n sec) and C o p u l a t o r y E f f i c i e n c y , and P e r c e n t Responding i n Experiment 5 Measure n per S p e c i e s cage Rats Hamsters G e r b i l s Mount 1 1494+354 207+68 1635+410 L a t e n c y 6 838+370 99+23 1276+388 I n t r o m i s s i o n 1 1801+378 418+130 3018+391 L a t e n c y .6 1079+394 192+48 2198+440 E j a c u l a t i o n 1 2867+293 1808+406 3600+0 L a t e n c y 6 2216+351 1230+373 3600+0 C o p u l a t o r y 1 .338+.070 . .660+.057 .09.4+, 070 E f f i c i e n c y 6 ,529+,076 ,620+,053 .321+,112 % Mounting 1 , 83 100 82 6 92 100 83 % I n t r o m i t t i n g •1 75 100 18 6 92 100 50 % E j a c u l a t i n g 1 50 75 0 6 66 92 0 60 More mounts, 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 were e v i d e n t i n grouped r a t s and more mounts and i n t r o m i s s i o n s e v i d e n t i n grouped g e r b i l s than i n s o c i a l l y i s o l a t e d c o n s p e c i f i c s . There was l i t t l e d i f f e r e n c e i n performance between i s o l a t e d and grouped hamsters, a l t h o u g h t h e r e was a s l i g h t t r e n d i n the same d i r e c t i o n as found i n r a t s and g e r b i l s . G e r b i l s showed r e l a t i v e l y few mounts and i n t r o m i s s i o n s and no e j a c u l a t i o n s . One i s o l a t e d g e r b i l d i e d p r i o r t o t e s t i n g . An a n a l y s i s o f v a r i a n c e on t h e measure of mounts i n d i c a t e d a s i g n i f i c a n t d i f f e r e n c e between grouped and i s o l a t e d a n i m a l s (F = 7.54, df = 1/65, £ - .007). Newman-Keuls t e s t s (p_ <.05) on i n d i v i d u a l s p e c i e s i n d i c a t e d a s i g n i f i c a n t d i f f e r e n c e between the grouped and i s o l a t e d c o n d i -t i o n s i n r a t s and g e r b i l s but not hamsters. A n a l y s e s o f v a r i a n c e i n d i c a t e d t h a t the d i f f e r e n c e between grouped and i s o l a t e d a nimals approached s i g n i -f i c a n c e , but d i d not r e a c h the a c c e p t e d l e v e l , f o r i n t r o m i s s i o n s (F_ = 3.75, ,d | = 1/65, j? = .054) and c o p u l a t o r y e f f i c i e n c y (F = 3.61, df = 1/65, £ = .059), w h i l e a s i m i l a r a n a l y s i s o f i n t r o m i s s i o n l a t e n c y was s i g n i f i c a n t (F = 4.18, d f = 1/65, £ = .042). The i s o l a t i o n / g r o u p i n g f a c t o r was not s i g n i f i c a n t i n o t h e r measures. In a l l a n a l y s e s t h e r e were a l s o s i g n i f i c a n t d i f f e r e n c e s among s p e c i e s : mounts (F_ = 10.37, d_f = 2/65, £ <.001), i n t r o m i s s i o n s (F = 12.06, df_ = 2/65, £ < . 0 0 1 ) , e j a c u l a t i o n s (F = 14.96, df = 2/65, £ < . 0 0 1 ) , mount l a t e n c y (F = 9.68, df_ = 2/65, £ <.001), i n t r o m i s s i o n l a t e n c y (F = 23.66, dT = 2/65, £ <.001), e j a c u l a t i o n l a t e n c y (F = 24.41, df = 2/65, £ <.001), c o p u l a t o r y e f f i c i e n c y (F = 15.68, d_f = 2/65, £ <.001). None of the i n t e r -a c t i o n f a c t o r s was . s i g n i f i c a n t . These r e s u l t s i n d i c a t e t h a t , c o n t r a r y to f i n d i n g s w i t h mice, p o s t -p u b e r t a l s o c i a l i s o l a t i o n may d e c r e a s e s e x u a l performance i n r a t s and g e r b i l s 6 1 and have l i t t l e e f f e c t i n hamsters. The low l e v e l o f performance observed i n g e r b i l s may r e l a t e to the f a c t t h a t a d u l t s of t h i s s p e c i e s f r e q u e n t l y form monogamous p a i r s ( T h e i s s e n & Yahr, 1977). T h i s may l i m i t i n t e r p r e -t a t i o n s o f f i n d i n g s w i t h t h i s s p e c i e s . G e n e r a l D i s c u s s i o n The p r e s e n t r e s u l t s i n d i c a t e t h a t the e f f e c t s o f i s o l a t i o n and group-housing upon male s e x u a l b e h a v i o r v a r y c o n s i d e r a b l y a c r o s s d i f f e r e n t r o d e n t s p e c i e s . The r e s u l t s o f Experiment 4 suggest t h a t f i n d i n g s i n the p r e v i o u s experiments o f f a c i l i t a t i o n o f male s e x u a l p a t t e r n s i n CD-I mice by i s o l a t i o n can be g e n e r a l i z e d t o o t h e r mouse s t r a i n s . W hile the d i f f e r e n t s t r a i n s I n v e s t i g a t e d h e r e showed markedly d i f f e r e n t l e v e l s o f s e x u a l b e h a v i o r , w i t h i n each o f the t h r e e s t r a i n s i s o l a t e d a n i m a l s showed p e r f o r -mance t h a t exceeded t h a t o f group a n i m a l s . By c o n t r a s t , i n Experiment 5, i s o l a t e d male r a t s , g e r b i l s , and hamsters showed p o o r e r performance than group-housed c o n s p e c i f i c s . T h i s l a t t e r e f f e c t was most marked i n r a t s and g e r b i l s and o n l y s l i g h t l y e v i d e n t i n hamsters. In most c a s e s the measures of d u r a t i o n o f mounting, mounts, i n t r o m i s s i o n s , and some of the l a t e n c y measures reached s i g n i f i c a n c e , w h i l e measures o f e j a c u l a t i o n d i d not. I t thus remains p o s s i b l e t h a t s p e c i f i c components of the s e x u a l r e sponse p a t t e r n , r a t h e r than the q u a n t i t y o f a l l r e s p o n s e s , a r e s e n s i t i v e to the p r e s e n c e or absence o f c o n s p e c i f i c males. However, i n a l l c ases where e j a c u l a t i o n s o c c u r r e d t h i s measure r e f l e c t e d a s t r o n g t r e n d i n the same d i r e c t i o n as was found w i t h o t h e r measures. The l a c k o f s i g n i f i c a n c e i n the e j a c u l a t i o n measure was u s u a l l y due to a low number o f such r e s p o n s e s i n a l l c o n d i t i o n s , which reduced s t a t i s t i c a l power. 62 The f i n d i n g i n Experiment 5 o f de c r e a s e d s e x u a l performance i n i s o l a t e d male r a t s and g e r b i l s i s c o n s i s t e n t w i t h many (but not a l l , e.g., Beach, 1958) p r e v i o u s i n v e s t i g a t i o n s o f 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 s o l a t i o n . The l i t e r a t u r e abounds w i t h r e p o r t s of d e f i c i t s i n 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 s o l a t i o n . F o r example, i s o l a t i o n has been r e p o r t e d to i m p a i r s e x u a l performance i n r a t s (Folman & D r o r i , 1965; G e r a l l ej: a l . , 1967; Gruendel & A r n o l d , 1974) and gu i n e a p i g s ( V a l e n s t e i n et a l . , 1955). However, s t u d i e s o f t h i s type have employed postweaning, p r e p u b e r t a l i s o l a t i o n . These d e f i c i t s have been t y p i c a l l y i n t e r p r e t e d as e v i d e n c e t h a t c o n t a c t between c o n s p e c i f i c s p r i o r t o p u b e r t y i s e s s e n t i a l f o r normal a d u l t s e x u a l performance. In the p r e s e n t s t u d y , a n i m a l s were i s o l a t e d d u r i n g a d u l t h o o d a f t e r h a v i n g been group-housed d u r i n g d e v e l o p -ment. The r e s u l t s o f Experiment 5 open the p o s s i b i l i t y t h a t i s o l a t i o n p e r se, r a t h e r than i s o l a t i o n d u r i n g a c r i t i c a l p e r i o d , produces d e f i c i t s i n a d u l t s e x u a l performance. A l t h o u g h these d a t a do not r u l e out the p o t e n t i a l importance o f p r e p u b e r t a l s o c i a l i n t e r a c t i o n s , e a r l i e r s t u d i e s may n e v e r t h e l e s s have confounded the concept o f c r i t i c a l p e r i o d s w i t h the i n t r i n s i c e f f e c t s o f i s o l a t i o n . The s p e c i e s d i f f e r e n c e s observed here a r e c o n s i s t e n t w i t h f i n d -i n g s o f o t h e r d i f f e r e n c e s between these s p e c i e s i n b e h a v i o r a l r e s p o n s e s to s o c i a l i s o l a t i o n . A g g r e s s i v e n e s s i s a l s o i n c r e a s e d i n male mice by i s o l a t i o n ( S c o t t , 1966), w h i l e i s o l a t i o n - i n d u c e d a g g r e s s i o n i s e i t h e r absent (Conner, 1972) or v e r y m i l d and a t t e n u a t e d i n r a t s ( B l a n c h a r d & B l a n c h a r d , 1977) and l e s s pronounced i n hamsters (Edwards & Rowe, 1975) and g e r b i l s (Edwards & Rowe, 1975; T h i e s s e n & Yahr, 1977) than i n mice. Moreover, these e f f e c t s may r e l a t e to the n a t u r a l s o c i a l e c o l o g y o f the d i f f e r e n t s p e c i e s . A l t h o u g h l a b o r a t o r y r a t s and mice have been b r e d under u n n a t u r a l l a b o r a t o r y c o n d i t i o n s through s e v e r a l g e n e r a t i o n s , i t i s l i k e l y t h a t many of t h e i r n a t u r a l s o c i a l p r e d i s p o s i t i o n s s u r v i v e ( c f . , B o i c e , 1977; Boreman & P r i c e , 1972). S i n c e , as d i s c u s s e d above, r a t s a r e n a t u r a l l y found i n l a r g e r g r oupings than a r e mice, i t i s c o n s i s t e n t t h a t they adapt more r e a d i l y to group h o u s i n g . I t may be t h a t the s u p p r e s s i o n of s e x u a l performance i n mice i n the p r e s e n c e o f c o n s p e c i f i c males r e l a t e s to the p o p u l a t i o n dynamics of n a t u r a l house mice. The s p e c i e s d i f f e r e n c e s , a t l e a s t t h o se between mice and r a t s , a r e a l s o c o n s i s t e n t w i t h d i f f e r e n c e s between t h e s e s p e c i e s i n t h e i r p h y s i o l o g i c a l response to s o c i a l i s o l a t i o n . I s o l a t e d mice e x h i b i t l e s s p i t u i t a r y - a d r e n o c o r t i c a l and more p i t u i t a r y - g o n a d a l a c t i v i t y than do grouped mice (Benton e t a l . , 1978; B r a i n , 1975; B r a i n & N o w e l l , 1971; C h r i s t i a n , 1955; 1959; McKinney & D e s j a r d i n s , 1973a; 1973b). I s o l a t e d mice may a l s o show lower b a s e l i n e l e v e l s and u t i l i z a t i o n r a t e s of b r a i n c a t e c h o l a m i n e s , and lower u t i l i z a t i o n o f s e r o t o n i n than grouped mice, but g r e a t e r u t i l i z a t i o n o f t h e se amines i n s t r e s s f u l and n o v e l s i t u a t i o n s ( G a r a t t i n i e t a l . , 1969; Welch & Welch, 1969a; 1969b). There would appear to have been fewer i n v e s t i g a t i o n s o f the e f f e c t s of i s o l a t i o n on p h y s i o -l o g i c a l mechanisms i n r a t s ; t h o se t h a t e x i s t i n d i c a t e e f f e c t s which a r e q u a l i t a t i v e l y d i f f e r e n t of r e l a t i v e l y weaker ( c f . Bennett & Rosenzweig, 1971; Sahakian eit a l . , 1975; S t o l k e t a l , 1974). For example, i s o l a t i o n i n r a t s may produce an i n c r e a s e i n b a s e l i n e t u r n o v e r of c a t e c h o l a m i n e s and m i n i m a l changes i n s e r o t o n i n metabolism r e l a t i v e to grouped s u b j e c t s ( S t o l k tit. al_. , 1974). These d i f f e r e n c e s i n p h y s i o l o g i c a l r e sponse to i s o l a t i o n may be r e l e v a n t i n l i g h t o f e v i d e n c e t h a t p i t u i t a r y - a d r e n a l hormones ( B e r t o l i n i , Gessa, & F e r r a r i , 1975), p i t u i t a r y - g o n a d a l hormones 64 ( G o r z a l k a & Mogenson, 1911), and c e n t r a l c a t e c h o l a m i n e s and s e r o t o n i n (Gessa & T a g l i a m o n t e , 1975) may a l l i n f l u e n c e male s e x u a l b e h a v i o r . The p r e s e n t r e s u l t s s u g g e s t , then, t h a t the m o d u l a t i o n o f male s e x u a l b e h a v i o r by i s o l a t i o n may be dependent on the s o c i a l e c o l o g y o f the s p e c i e s and the p r o f i l e o f p h y s i o l o g i c a l changes accompanying i n d i -v i d u a l h o u s i n g . One p o s s i b i l i t y i s t h a t p h y s i o l o g i c a l d e t e r m i n a n t s of s e x u a l b e h a v i o r a r e c o n s t a n t a c r o s s s p e c i e s but t h a t s o c i a l mechanisms a f f e c t i n g them a r e n o t . The p i t u i t a r y - a d r e n a l and n e u r o c h e m i c a l e f f e c t s o f group-housing i n mice a r e c o n s i s t e n t w i t h the i n t e r p r e t a t i o n t h a t g r o u p i n g may produce some l e v e l o f s t r e s s i n t h i s s p e c i e s ( B r a i n , 1975). In more s o c i a l s p e c i e s , such as the r a t , i s o l a t i o n o f p r e v i o u s l y grouped a n i m a l s may c o n s t i t u t e a s t r e s s o r and t h e r e b y produce s e x u a l performance d e f i c i t s . F u t u r e r e s e a r c h c o r r e l a t i n g p h y s i o l o g i c a l r e s p o n s e s and s o c i a l mechanisms might t h e r e f o r e h e l p to e x p l a i n b e h a v i o r a l e f f e c t s of s o c i a l i s o l a t i o n . 65 SECTION I I I : BRIEF PERIODS OF ISOLATION OR GROUPING As o u t l i n e d i n the G e n e r a l D i s c u s s i o n o f S e c t i o n I, s e v e r a l p h y s i o l o g i c a l and b e h a v i o r a l mechanisms may mediate d i f f e r e n c e s i n s e x u a l performance between i s o l a t e d and grouped mice. I s o l a t e d mice e x h i b i t l e s s p i t u i t a r y - a d r e n o c o r t i c a l and more p i t u i t a r y - g o n a d a l a c t i v i t y than do grouped mice (Benton e t a l . , 1978; B r a i n , 1971; 1975; C h r i s t i a n , 1955, 1959; McKinney & D e s j a r d i n s , 1973a; 1973b). I s o l a t e d and grouped mice a l s o show d i f f e r e n t u t i l i z a t i o n r a t e s and l e v e l s o f the c e n t r a l c a t e c h o l a m i n e s , n o r e -p i n e p h r i n e and dopamine, and s e r o t o n i n ( G a r a t t i n i e t a l . , 1969; Welch & Welch, 1969a; 1969b). Both c a t e c h o l a m i n e r g i c and s e r o t o n e r g i c a c t i v i t y can i n f l u e n c e male s e x u a l b e h a v i o r (Gessa & Ta g l i a m o n t e , 1975). One b e h a v i o r a l p o s s i b i l i t y i s t h a t grouped mice might be r e l a t i v e l y s a t i a t e d when p r e s e n t e d w i t h females i f h i g h l e v e l s o f i n t e r m a l e mounting o c c u r i n the group. A l t e r -n a t i v e l y , i n t e r m a l e f i g h t i n g among grouped a n i m a l s may p u n i s h approach b e h a v i o r o r i e n t e d toward o t h e r group members, w i t h consequent s u p p r e s s i o n of r e s p o n d i n g g e n e r a l i z i n g t o s i t u a t i o n s w i t h females. S i n c e t h ese p o s s i b i l i t i e s c o u l d r e q u i r e d i f f e r e n t time minima to i n f l u e n c e mating b e h a v i o r , an i n v e s t i g a t i o n o f the temporal parameters o f t h i s phenomenon c o u l d p r o v i d e i n f o r m a t i o n about c a u s a t i o n . The g r o s s changes i n wei g h t s o f a d r e n a l s , t e s t e s , s e m i n a l v e s i c l e s , p r o s t a t e s , and 66 p r e p u t i a l s t h a t accompany s o c i a l i s o l a t i o n g e n e r a l l y r e q u i r e s e v e r a l weeks of i n d i v i d u a l h o u s i n g to d e v elop (Benton et_ a l . , 1978; B r a i n , 1971; B r a i n & N owell, 1971; C h r i s t i a n , 1955; 1959; McKinney & D e s j a r d i n s , 1973a; 1973b). N e u r o t r a n s m i t t e r changes, however, can o c c u r w i t h i n one or two days of i s o l a t i o n ( G a r a t t i n i e £ al., 1969; G i a c a l o n e , T a n z e l l a , V a l z e l l i , & G a r a t t i n i , 1968). I n t e r m a l e mounting would have to o c c u r s h o r t l y b e f o r e t e s t i n g t o produce s a t i a t i o n , w h i l e l e a r n e d s u p p r e s s i o n of approach b e h a v i o r might r e q u i r e s e v e r a l t r i a l s and thus l o n g e r p e r i o d s o f g r o u p i n g or i s o l a t i o n . E xperiments 1, 2, and 3 i n d i c a t e d t h a t i s o l a t i o n - i n d u c e d f a c i l i -t a t i o n o f s e x u a l a c t i v i t y i n male-female i n t e r a c t i o n s p a r a l l e l e d i s o l a t i o n -i n d u c e d a g g r e s s i o n i n i n t e r m a l e i n t e r a c t i o n s i n s e v e r a l p a r a m e t r i c mani-p u l a t i o n s . I s o l a t i o n - i n d u c e d a g g r e s s i o n i s a p r o g r e s s i v e phenomenon t h a t u s u a l l y r e q u i r e s p e r i o d s of i s o l a t i o n g r e a t e r than one week to d e velop ( B r a i n , 1975; S c o t t , 1966). An e x a m i n a t i o n o f e f f e c t s of d i f f e r e n t p e r i o d s of i s o l a t i o n on s e x u a l b e h a v i o r might thus a l s o p r o v i d e f u r t h e r i n f o r m a t i o n r e g a r d i n g a p o s s i b l e common c o n t r o l o f sex and a g g r e s s i o n i n mice. In Experiment 2 i t was found t h a t i s o l a t i o n f a c i l i t a t e d s e x u a l b e h a v i o r a t i s o l a t i o n - t e s t i n t e r v a l s of 1-4 weeks, w h i l e r e s u l t s a t a s h o r t e r i n t e r v a l (3 days) were u n c l e a r . The p r e s e n t s e r i e s of experiments i n v e s t i g a t e d b r i e f e r p e r i o d s of i s o l a t i o n than those p r e v i o u s l y examined to e s t a b l i s h the minimum p e r i o d n e c e s s a r y to produce e f f e c t s on mating. Once t h i s p e r i o d was e s t a b l i s h e d , b e h a v i o r o f grouped a n i m a l s d u r i n g t h i s m i n i -mum p e r i o d was examined and c o r r e l a t e d w i t h subsequent s e x u a l performance to e l u c i d a t e p o s s i b l e mechanisms u n d e r l y i n g i s o l a t i o n / g r o u p i n g d i f f e r e n c e s . 67 Experiment 6 Experiment 2 i n d i c a t e d t h a t the maximum e f f e c t o f i s o l a t i o n upon male s e x u a l b e h a v i o r i s e v i d e n t a f t e r about two weeks o f s o c i a l i s o l a t i o n . The p r e s e n t experiment examined a n i m a l s a f t e r one day o f i s o l a t i o n , a p e r i o d much s h o r t e r than those p r e v i o u s l y examined, and compared these to a n i m a l s i s o l a t e d f o r 2 weeks. Method Seventy-two male CD-I mice, o b t a i n e d from Canadian Breeding,Farms^ a t 55 days o f age, were housed u n t i l commencement of the experiment i n groups of 6. S t i m u l u s animals c o n s i s t e d o f CD-I -females, o b t a i n e d from the same b r e e d e r and made r e c e p t i v e a c c o r d i n g t o p r o c e d u r e s o u t l i n e d f o r Experiment 1A. A l l a n i m a l s were housed, m a i n t a i n e d , and t e s t e d under the same c o n d i t i o n s as i n Experiment 1A. At 60 days of age, h a l f o f the e x p e r i m e n t a l males were d i v i d e d i n t o t h r e e c o n d i t i o n s . These c o n s i s t e d of one group o f 12, f o u r groups of t h r e e and 12 i s o l a t e d a n i m a l s . The r e m a i n i n g e x p e r i m e n t a l males were d i v i d e d i n t o t h r e e i d e n t i c a l c o n d i t i o n s a t 73 days of age. A l l cages were those manufactured from p o l y p r o p y l e n e by Carworth Lab Cages equipped as d e s c r i b e d f o r Experiment 1A. At 74 days o f age, a f t e r they had been housed i n t h e s e c o n d i t i o n s f o r 2 weeks or 1 day, animals were p r e s e n t e d w i t h r e c e p t i v e females. T e s t s e s s i o n s were conducted i n the P l e x i g l a s e n c l o s u r e s d e s c r i b e d f o r Experiment 1A. Each e x p e r i m e n t a l male was adapted to the e n c l o s u r e f o r 5 min, p r e s e n t e d w i t h a r e c e p t i v e female, and observed f o r 1 h r . D u r i n g these s e s s i o n s the number, l a t e n c y , and d u r a t i o n o f mounts w i t h o u t i n t r o m i s s i o n (mounts), mounts w i t h i n t r o m i s s i o n and p e l v i c t h r u s t i n g ( 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 were r e c o r d e d v i a an E s t e r l i n e - A n g u s event r e c o r d e r . A l l l a t e n c i e s were taken from the 68 commencement of the s e s s i o n . R e s u l t s and D i s c u s s i o n T a b l e V I g i v e s the r e s u l t s f o r a l l measures. At b o t h i n t e r v a l s (1 day and 2 weeks) i n d i v i d u a l l y - h o u s e d a n i m a l s showed more mounts and i n t r o m i s s i o n s and a l o n g e r d u r a t i o n o f mounting than animals housed i n groups o f 3 or 12. Animals i n groups o f t h r e e showed somewhat more mating than a n i m a l s i n groups o f 12. Mount and i n t r o m i s s i o n l a t e n c i e s ( l a t e n c i e s to t h e f i r s t mount and i n t r o m i s s i o n ) were s h o r t e r i n i s o l a t e s than i n grouped a n i m a l s . I n d i v i d u a l a n a l y s e s o f v a r i a n c e on each measure i n d i c a t e d a s i g n i f i c a n t e f f e c t of number of a n i m a l s per cage f o r d u r a t i o n o f mount-i n g (F = 5.91, df = 2/66, p_ = .004), number of mounts (F = 7.66, d_f = 2/66, p_ = .001), number o f i n t r o m i s s i o n s (F = 3.81, df = 2/66, p_ = .027), mount l a t e n c y (F = 5.62, elf = 2/66, p_ = .006), and i n t r o m i s s i o n l a t e n c y (F = 9.33, df = 2/66, _p <.001). Subsequent Newman-Keuls comparisons (p_ <.05) i n d i c a t e d t h a t 'the i s o l a t e s exceeded b o t h animals grouped i n t h r e e and a n i m a l s grouped i n 12 i n mounts, and t h a t i s o l a t e s exceeded animals grouped i n 12 i n d u r a -t i o n o f mounting and i n t r o m i s s i o n s . Comparisons i n mount l a t e n c y i n d i c a t e d t h a t i s o l a t e s showed s h o r t e r l a t e n c i e s than grouped a n i m a l s . In i n t r o m i s -s i o n l a t e n c y i s o l a t e s showed s h o r t e r l a t e n c i e s than a n i m a l s grouped i n 3 which i n t u r n showed s h o r t e r l a t e n c i e s than animals grouped i n 12. There were no s i g n i f i c a n t e f f e c t s o f i n t e r v a l l e n g t h nor were any of the i n t e r -a c t i o n f a c t o r s s i g n i f i c a n t . There were a l s o no s i g n i f i c a n t e f f e c t s i n measures o f number of e j a c u l a t i o n s o r e j a c u l a t i o n l a t e n c y . The p r e s e n t r e s u l t s extend p r e v i o u s f i n d i n g s i n t h a t they i n d i -c a t e t h a t i s o l a t i o n produces as s t r o n g an e f f e c t a t 1 day as i s found a t 69 T a b l e VI Means and Standard E r r o r s o f Measures o f Male Mice I s o l a t e d o r Grouped i n 3 or 12 f o r 24 Hours o r 2 Weeks i n Experiment 6 Measure n p e r I s o l a t i o n T e s t I n t e r v a l cage 24 Hours 2 Weeks D u r a t i o n of 1 145.08 + 30.48 127.83 + 27.83 Mounting ( sec) 3 77.25 + 35.82 90.25 + 37.13 12 38.42 + 29.13 28.25 + 13.67 1 25.33 + 6.35 24.42 + 6.08 Mounts 3 9.25 + 4.46 14.17 + 5.97 12 5.50 + 3.17 6.08 + 2.57 1 10.33 + 2.64 8.50 + 2.58 I n t r o m i s s i o n s 3 6.00 + 3.63 6.00 + 3.09 12 2.92 + 2.33 1.25 + 0.79 1 0.25 + 0.13 0.17 + 0.11 Ej a c u l a t i o n s 3 0.08 + 0.08 0.17 + 0.11 12 0.08 + 0.08 0.00 + 0.00 Mount 1 1085 + 371 1215 + 302 L a t e n c y ( s ec) 3 2469 + 472 2124 + 435 12 2290 + 399 2303 + 367 I n t r o m i s s i o n 1 1761 + 327 1815 + 361 L a t e n c y ( s ec) 3 2535 + 444 2519 + 380 12 3285 + 275 3251 + 222 E j a c u l a t i o n 1 3314 + 151 3398 + 136 L a t e n c y (s ec) 3 3568 + 110 3226 + 258 12 3575 + 83 3600 + 0 70 the l o n g e r i n t e r v a l s p r e v i o u s l y i n v e s t i g a t e d . These r e s u l t s a r e c o n t r a r y to e x p e c t a t i o n because many of the major p h y s i o l o g i c a l changes accompany-i n g s o c i a l i s o l a t i o n , p a r t i c u l a r l y those i n v o l v i n g gonads and p e r i p h e r a l r e p r o d u c t i v e t i s s u e s , r e q u i r e s e v e r a l days of s o c i a l i s o l a t i o n t o d evelop (Benton e t a l . , 1978; B r a i n , 1971; B r a i n & N o w e l l , 1971; C h r i s t i a n , 1955). Moreover, o t h e r b e h a v i o r a l changes w i t h i s o l a t i o n , such as i n c r e a s e s i n a g g r e s s i v e n e s s , r e q u i r e more p r o l o n g e d p e r i o d s of i s o l a t i o n ( B r a i n , 1975). Experiment 7 The time c o u r s e f o r development o f f a c i l i t a t i o n of s e x u a l beha-v i o r by i s o l a t i o n remains to be determined. The p r e s e n t experiment com-pared the e f f e c t s o f p e r i o d s of i s o l a t i o n r a n g i n g from 1 hour to 1 week. A l s o , because i t i s p o s s i b l e t h a t p r e - t r e a t m e n t g r o u p i n g of a n i m a l s and the p r o v i s i o n o f a c l e a n cage might a f f e c t b e h a v i o r , a comparison s e t of grouped a n i m a l s was p r o v i d e d w i t h c l e a n cages a t each of the times b e f o r e t e s t i n g t h a t animals were i s o l a t e d . Method S u b j e c t s were 216 male .CD-I mice r e c e i v e d a t 55 days of age and housed i n groups of 6 u n t i l commencement of the e x p e r i m e n t a l c o n d i t i o n s . = P r e p a r a t i o n o f females and o t h e r p r e - e x p e r i m e n t a l c o n d i t i o n s were the same as i n Experiment IA. A l l a n i m a l s were t e s t e d a t 72-75 days of age. At i n t e r v a l s p r i o r to t e s t i n g o f 1 h r , 4 h r , 12 h r , 1 day, 3 days, and 7 days, a n i m a l s were housed i n d i v i d u a l l y i n c l e a n cages. At each of these i n t e r -v a l s o t h e r animals w e r e : p l a c e d i n c l e a n cages but remained i n the same groups of 6 as they had been s i n c e r e c e i p t from the b r e e d e r . There was an e q u a l number o f animals i n each treatment c o m b i n a t i o n . One hour t e s t 71 s e s s i o n s i n the p r e s e n c e of r e c e p t i v e females were conducted as d e s c r i b e d f o r Experiment IA. B e h a v i o r was r e c o r d e d v i a an event r e c o r d e r by a t r a i n e d o b s e r v e r who was u n f a m i l i a r w i t h p r e v i o u s f i n d i n g s and the purpose of the experiment. R e s u l t s and D i s c u s s i o n F i g u r e 6 g i v e s r e s u l t s f o r the t o t a l d u r a t i o n of mounting, w i t h or w i t h o u t i n t r o m i s s i o n . T a b l e V I I p r e s e n t s r e s u l t s f o r a l l r e m a i n i n g measures. Most of the measures r e f l e c t the same t r e n d . I n d i v i d u a l l y -housed animals showed m a r g i n a l l y more s e x u a l a c t i v i t y a t i n t e r v a l s of 12 h r or l o n g e r than a t s h o r t e r i n t e r v a l s . Group-housed a n i m a l s showed more s e x u a l a c t i v i t y a t 1 and 4 h r i n t e r v a l s , where they exceeded the i s o l a t e s , than they d i d a t l o n g e r i n t e r v a l s , where they showed p o o r e r performance than t h e i s o l a t e s . S e p a r a t e a n a l y s e s of v a r i a n c e were con-d u c t e d on each measure. There was a s i g n i f i c a n t i n t e r a c t i o n i n d u r a t i o n of mounting (F =3.13, d f = 5/204, £ = .010), number of mounts (F = 2.43, d f =4/204, £ = .036), number of i n t r o m i s s i o n s (F = 3.12, df = 5/204, £ = .010), and i n t r o m i s s i o n l a t e n c y (F = 3.13, df_ = 5/204, £ = .010). Subsequent e x a m i n a t i o n of s i m p l e main e f f e c t s r e v e a l e d a s i g n i f i c a n t e f f e c t o f i n t e r v a l among grouped a n i m a l s f o r each o f t h e s e measures ( d u r a -t i o n : F = 3.73, df = .5/102, £ = .004; mounts: F = 2.'74, df = 5/102, £ = .023; i n t r o m i s s i o n s : F_ = 4.02, d_f = 5/102, £ = .002; i n t r o m i s s i o n l a t e n c y : _F = 3.58, df = 5/102, £ = .005). Newman-Keuls comparisons (p <.05) i n d i c a t e d t h a t 4 h r d i f f e r e d from 12 h r , 1 day, 3 days, and 7 d a y s , i n the d u r a t i o n and i n t r o m i s s i o n measures. 1 h r d i f f e r e d from 3 days i n the mounts measured, w h i l e 1. h r d i f f e r e d from 7 days and 4 h r d i f f e r e d from 3 and 7 days i n the i n t r o m i s s i o n l a t e n c y measure. C o r r e s p o n d i n g a n a l y s e s o f i s o l a t e d a n i m a l s i n d i c a t e d t h a t the t r e n d s over i n t e r v a l s d i d not r e a c h F i g u r e 6: The-mean t o t a l d u r a t i o n of -mounting, w i t h o r w i t h o u t i n t r o m i s s i o n , i n mice i s o l a t e d o r grouped f o r d i f f e r e n t i n t e r v a l s i n Experiment 7, The open squares r e p r e s e n t i s o l a t e d a n i m a l s t h a t were f o r m e r l y i n g r o u p s . o f 6. The c l o s e d c i r c l e s r e p r e s e n t groups of 6 whose cages were .cleaned a t the s p e c i f i e d i n t e r v a l s B e f o r e t e s t i n g . V e r t i c a l l i n e s i n d i c a t e s t a n d a r d e r r o r s . 1 hr 4 hrs 12 hrs 1day 3 days 7 days ISOLATION - TEST INTERVAL Table VII Means and Standard Errors of Measures of Male Mice Isolated or Grouped for Different Intervals in Experiment 1 Measure Isolation-Test Interval 1 hr 4 hrs 12 hrs 1 day 3 days 7 days Mounts 1 16.28+4.23 14.89+3.84 19.72+5.07 23.28+4.95 19.67+3.44 26.61+5.65 6 22.67+4.36 14.83+3.57 14.00+3.78 10.33+2.49 7.06+1.86 10.11+3.04 Intro- 1 6.94+2.17 7.94+2.32 10.72+2.16 10.28+2.81 10.67+2.78 8.67+1.64 missions 6 11.72+2.24 15.56+3.05 6.94+2.25 4.72+1.12 5.06+1.90 5.28+2.27 Ejacula- 1 0.17+0.09 0.11+0.08 0.06+0.06 0.00+0.00 0.00+0.00 0.06+0.06 tions 6 0.17+0.09 0.28+0.11 0.11+0.08 0.00+0.00 0.11+0.08 0.17+0.12 Mount 1 1518+350 990+296 1053+284 1134+269 977+295 810+149 Latency (s.ec) 6 1034+304 928+190 1361+296 1418+321 1636+326 1924+352 Intro- 1 1882+333 2093+330 1519+324 1415+288 1534+320 1646+249 mission 6 1364+306 1089+227 1895+316 1737+313 2312+307 2593+312 Latency (s ec) Ejacula- 1 3374+161 3385+152 3590+10 3600+0 3600+0 35 85+12 tion 6 3302+166 3240+163 3436+152 3600+0 3489+83 3481+105 Latency (s ec) 75 s i g n i f i c a n c e . E x a m i n a t i o n o f the s i m p l e main e f f e c t o f i s o l a t i o n / g r o u p -i n g a t each i n t e r v a l i n d i c a t e d d i f f e r e n c e s a t 4 h r i n i n t r o m i s s i o n l a t e n c y (F = 6.30, df = 1/34, p_ = .016), a t 24 h r i n d u r a t i o n (F = 4.28, df = 1/34, p_ = .044) and mounts (F = 5.47, df = 1/34, p_ = .024), a t 3 days i n mounts (F = 10.41, df_ = 1/34, p_ = .003), and a t 7 days i n mounts (F_ = 6.65, d f = 1/34, £ = .014) and i n t r o m i s s i o n l a t e n c y (F = 5.62, df = 1/34, p_ = .022). T h i s experiment s u g g e s t s t h a t i s o l a t i o n - g r o u p i n g d i f f e r e n c e s r e q u i r e a t l e a s t 12-24 h r to d e v e l o p . I t would thus appear t h a t some b e h a v i o r a l and/or p h y s i o l o g i c a l t r a n s i t i o n o c c u r s i n male mice d u r i n g the 24 h r i n t e r v a l a f t e r they a r e i s o l a t e d from c o n s p e c i f i c s . F u r t h e r -more, t h i s experiment s u g g e s t s a second phenomenon, t h a t s e x u a l b e h a v i o r of grouped a n i m a l s i s f a c i l i t a t e d f o r a few hours f o l l o w i n g p r o v i s i o n o f c l e a n cages. The b e h a v i o r of grouped animals whose cage has r e c e n t l y been c l e a n e d resembles t h a t o f a n i m a l s i s o l a t e d f o r a t l e a s t 24 hr. Experiment 8 I f b e h a v i o r a l events i n grouped animals reduce t h e i r performance r e l a t i v e to i s o l a t e s , t h e s e e v e n t s s h o u l d be o b s e r v a b l e d u r i n g the 24 h r p e r i o d p r e c e d i n g t e s t i n g . Numerous p o s s i b i l i t i e s e x i s t . I f grouped a n i m a l s p a r t i c i p a t e i n i n t e r m a l e mounting, one might expect some degree of s a t i a t i o n which would i n h i b i t subsequent performance w i t h females. Con-v e r s e l y , i n t e r m a l e mounting c o u l d be found i n a n i m a l s t h a t a r e more a c t i v e s e x u a l l y , s i n c e mounts w i t h o u t i n t r o m i s s i o n may i n c r e a s e the p r o b a b i l i t y o f a male a p p r o a c h i n g a female (Bermant & Davidson, 1974), and i n h i b i t i o n i n r e m a i n i n g animals be caused by o t h e r f a c t o r s . A number o f p r e v i o u s s t u d i e s ( D e F r i e s and M c C l e a r n , 1970; Kahn, 1961; L a g e r s p e t z & H a u t o j a r v i , 76 1971) suggest t h a t i n t e r m a l e a g g r e s s i o n and dominance may be c o r r e l a t e d w i t h s e x u a l performance. In the p r e s e n t experiment, the a g g r e s s i v e and s e x u a l b e h a v i o r of group-housed males was c o n t i n u o u s l y r e c o r d e d d u r i n g the 24 h r p r i o r t o t e s t i n g w i t h f e m a l e s . Animals grouped i n 12 were examined because these a n i m a l s have d i s p l a y e d the p o o r e s t performance o f those examined i n p r e v i o u s e x p e r i m e n t s . Method S u b j e c t s c o n s i s t e d of male CD-I mice o b t a i n e d a t 60 days of age. These were housed i n groups o f 6 u n t i l 72 days of age. At t h i s time a s i n g l e group of 12 was formed and housed i n a cage s i m i l a r t o those d e s c r i b e d f o r Experiment 1A. T h i s group was t r a n s f e r r e d to a p a r t i a l l y i l l u m i n a t e d t e s t i n g room and remained t h e r e f o r 24 h r . M i c e w i t h i n the group were l a b e l l e d w i t h c o l o r e d markings on t h e i r t a i l s and observed c o n t i n u o u s l y by the a u t h o r and t h r e e o t h e r e x p e r i m e n t e r s t a k i n g s h i f t s . E x p e r i m e n t e r s were p r e - t r a i n e d to use the same measuring system. T h i s i n v o l v e d r e c o r d i n g the number and d u r a t i o n of mounts, and the number of n o n - b i t i n g a t t a c k s , b i t e s , and t a i l - r a t t l e s . Both the a n i m a l e x h i b i t -i n g and t h e a n i m a l r e c e i v i n g mounts or a g g r e s s i v e r e s p o n s e s were r e c o r d e d . Immediately f o l l o w i n g t h i s 24 h r p e r i o d , a l l a n i m a l s were t e s t e d w i t h r e c e p t i v e females a c c o r d i n g to the p r o c e d u r e s of Experiment 1A. R e s u l t s and D i s c u s s i o n T a b l e V I I I g i v e s the r e s u l t s o f s e x u a l t e s t s w i t h females. R e s u l t s a r e s i m i l a r to those o b t a i n e d f o r the group o f 12 i n Experiment 6. T a b l e IX g i v e s the r e s u l t s f o r measures of i n t e r m a l e mounting and a g g r e s -s i o n d u r i n g the 24 h r p r i o r to t e s t i n g . A g g r e s s i v e r e s p o n s e s were sum-mar i z e d through the composite a g g r e s s i o n s c o r e employed i n Experiments 1, Table VIII Sexual Performance and Stepwise Regression Between Intermale Aggression and Mounting and Subsequent Sexual Measures i n Experiment 8 Measure Variables not i n equation Duration of Mounting (Sec) Mounts Intromissions Ejaculations Mount _ Latency (sec) Intromission Latency (sec) Ejaculation Latency ( sec) Mean + S.E. Regression (Includes only s i g n i f i c a n t measures) Exhibition of Aggression Receipt of Aggression Exhibition of Mounting Receipt of Mounting 40.42 R 2 = .351 P a r t i a l R .177 .075 .227 +15.78 F =5.40 s i g n i f . £ = .041 £ .608 .810 .507 3.50 R 2 = .000 P a r t i a l R .178 .039 .514 .157 + 1.11 £ .584 .871 .085 .629 2.25 R 2 = .000 P a r t i a l R .191 .043 .370 .242 + 0.95 £ .559 .863 .236 .453 0.08 R 2 = .987 P a r t i a l R .109 .307 .100 + 0.08 F = 756.00 s i g n i f . _p_ = .000 .744 .361 .762 2282 R 2 = .000 P a r t i a l R .249 .031 .482 .231 +310 .440 .887 .110 .476 2864 R 2 = .462 P a r t i a l R .189 .202 .248 +291 F = 8.59 s i g n i f . £ = .015 £ .582 .558 .468 3490 R 2 = .987 P a r t i a l R .109 .307 .100 +11 • F = 756.10 s i g n i f . -2 = -000 £ .744 .360 .762 78 T a b l e IX Means and S t a n d a r d E r r o r s of Measures of I n t e r m a l e A g g r e s s i o n and Mounting i n Experiment 8 . E x h i b i t i o n ^ R e c e i p t o f ^ E x h i b i t i o n R e c e i p t of of A g g r e s s i o n A g g r e s s i o n o f Mounting Mounting (sec) (sec) Mean 11.67 11.33 0.50 0.50 1-4 h S.E. 10.13 2.83 0.50 0.29 a n 7 12 1 3 Mean 5.83 5.83 1.25 1.25 5-8 h S,E. 5.12 2.69 0.95 1.25 n a 3 8 2 1 Mean 2.17 2.17 1.25 1.25 9-12 h S.E. 1.03 1.22 1.25 1.25 a n 5 4 1 1 Mean 3.00 3.00 0.00 0.00 13-16 h S.E. 1.90 0.97 0.00 0.00 n a 3 8 0 0 Mean 1.00 1.00 0.00 0.00 17-20 h S.E. 0.83 0.39 0.00 0.00 n a 2 5 0 0 Mean 8.08 7.67 0.25 0.25 21-24 h S.E. 6.56 2.71 0.25 0.25 a n 6 9 1 1 Mean 31.75 31.00 3.25 3.25 T o t a l S.E. 24.72 5.04 2.91 2.90 n a 11 12 2 3 fnumber of animals ( o f 12 t o t a l ) showing response E x h i b i t i o n o f A g g r e s s i o n may exceed R e c e i p t of A g g r e s s i o n because t a i l r a t t l e s o c c u r r e d . 2, and 3. Sex u a l r e s p o n s e s were summarized by t a k i n g a t o t a l d u r a t i o n o f mounting s c o r e . A c o n s i d e r a b l e amount of a g g r e s s i o n o c c u r r e d d u r i n g the i n i t i a l 4-hr p e r i o d i n which the a n i m a l s were obs e r v e d . There were o c c a s i o n a l a g g r e s s i v e r e s p o n s e s d u r i n g the r e m a i n i n g p e r i o d o f o b s e r v a t i o n . Only two a n i m a l s mounted o t h e r males and these r e s p o n s e s were i n f r e q u e n t i n t h e s e a n i m a l s . E x h i b i t i o n o f a g g r e s s i o n , r e c e i p t o f a g g r e s s i o n , e x h i b i -t i o n o f mounts, and r e c e i p t o f mounts were t r e a t e d as p r e d i c t o r v a r i a b l e s i n a s t e p w i s e m u l t i p l e r e g r e s s i o n a n a l y s i s performed on each dependent measure (see K e r l i n g e r & Pedhazur, 1973). The r e s u l t s of t h e s e a n a l y s e s a r e p r e s e n t e d i n T a b l e V I I I . R e g r e s s i o n a n a l y s e s i n d i c a t e d t h a t the e x h i -b i t i o n o f i n t e r m a l e mounting showed a s i g n i f i c a n t r e l a t i o n s h i p t o f o u r measures, n o t a b l y e j a c u l a t i o n number and l a t e n c y . T h i s o c c u r r e d because the one h i g h - s c o r i n g a n i m a l t h a t e j a c u l a t e d was a l s o . t h e o n l y a n i m a l t h a t showed a s u b s t a n t i a l amount of mounting o f males. Other v a r i a b l e s d i d not r e a c h s i g n i f i c a n c e , a l t h o u g h e x h i b i t i o n o f a g g r e s s i o n and r e c e i p t o f mount-i n g each showed s m a l l r e l a t i o n s h i p s to most measures. These r e s u l t s suggest t h a t i n t e r m a l e mounting i s uncommon and i n s u f f i c i e n t to account f o r i s o l a t i o n - g r o u p i n g d i f f e r e n c e s . There i s , how-eve r , some i n d i c a t i o n t h a t e j a c u l a t i o n f r e q u e n c y i n grouped animals r e l a t e s to i n t e r m a l e mounting. T h i s may be because i n t e r m a l e mounts i n c r e a s e the l i k e l i h o o d o f e j a c u l a t i o n o r because some s e x u a l l y a c t i v e males may mount o t h e r males. In n e i t h e r case c o u l d t h i s r e l a t i o n s h i p a ccount f o r the poor performance o f o t h e r males t h a t showed no i n t e r m a l e mounting. While i n t e r m a l e a g g r e s s i o n l e v e l s were r e l a t i v e l y h i g h , none of the r e l a t i o n s h i p s between them and b e h a v i o r w i t h females reached s t a t i s -t i c a l s i g n i f i c a n c e . These r e s u l t s l e a v e open the p o s s i b i l i t y t h a t r e c e n t 80 i n t e r m a l e a g g r e s s i o n reduces the s e x u a l performance of grouped animals as a whole, b u t suggest t h a t any e f f e c t s i t has on i n t r a - g r o u p v a r i a n c e i n s e x u a l performance a r e s m a l l . G e n e r a l D i s c u s s i o n The p r e s e n t f i n d i n g s extend r e s u l t s o f the p r e v i o u s experiments by d e m o n s t r a t i n g t h a t o n l y a b r i e f p e r i o d o f i s o l a t i o n i s n e c e s s a r y t o f a c i l i t a t e mounting and i n t r o m i t t i n g . Males from b o t h r e c e n t l y formed (Experiment 6) and l o n g - e s t a b l i s h e d (Experiment 7) s o c i a l groups show fewer mounts and i n t r o m i s s i o n s than do i s o l a t e s . The e f f e c t s of these m a n i p u l a t i o n s on e j a c u l a t i o n s remain u n c l e a r due to the low i n c i d e n c e o f these r e s p o n s e s . R e s u l t s o f Experiment 8 i n d i c a t e t h a t e f f e c t s o f group-i n g on e j a c u l a t i o n f r e q u e n c y may be c o m p l i c a t e d by e f f e c t s o f i n t e r m a l e mounting on e j a c u l a t i o n s . I t was p r e v i o u s l y suggested ( S e c t i o n I) t h a t s e x u a l and a g g r e s -s i v e p a t t e r n s respond i n p a r a l l e l t o p a r a m e t r i c m a n i p u l a t i o n s o f e n v i r o n -mental and s o c i a l v a r i a b l e s . S i n c e major e f f e c t s of i s o l a t i o n on a g g r e s -s i v e n e s s g e n e r a l l y r e q u i r e s e v e r a l days o f i n d i v i d u a l h o u s i n g t o develop ( B r a i n , 1975; S c o t t , 1966), t h i s study s u g g e s t s some d i f f e r e n t i a l c o n t r o l o f sex and a g g r e s s i o n . These r e s u l t s may narrow the range o f hypotheses t h a t c o u l d account f o r i s o l a t i o n / g r o u p i n g d i f f e r e n c e s i n mating. The f i n d i n g s o f Experiment 8 appear to r u l e out more v i s i b l e a s p e c t s o f i n t e r m a l e s o c i a l i n t e r a c t i o n as d e t e r m i n a n t s o f the poor performance of grouped a n i m a l s . C l e a r l y , i n t e r m a l e mounting o c c u r s much too i n f r e q u e n t l y t o produce r e l a t i v e s e x u a l s a t i a t i o n i n group-housed males. D i f f e r e n t i a l p a r t i c i p a -t i o n i n i n t e r m a l e a g g r e s s i o n does not appear to account f o r i n t r a - g r o u p 81 v a r i a n c e i n subsequent s e x u a l performance. I t remains p o s s i b l e , however, t h a t exposure to or o b s e r v a t i o n o f a t t a c k s from o t h e r males reduces the subsequent s e x u a l performance of a l l group-housed males, and i s thus i n v o l v e d i n the i s o l a t i o n / g r o u p i n g d i f f e r e n c e s . Indeed, e v i d e n c e p r e s e n t e d by Kahn (1961) s u g g e s t s t h a t exposure to a t t a c k does reduce subsequent s e x u a l performance w i t h f e m a l e s . A l a c k o f a s t r o n g r e l a t i o n s h i p between d i f f e r e n t i a l p a r t i c i p a -t i o n i n i n t e r m a l e a g g r e s s i o n and subsequent i n t r a - g r o u p v a r i a t i o n i n s e x u a l performance r a i s e s some i n t e r e s t i n g q u e s t i o n s . I t has been argued (Benton et_ al., 1978; B r a i n , 1975) t h a t i s o l a t e s a r e s i m i l a r t o dominant, t e r r i t o -r i a l grouped males i n s e v e r a l b e h a v i o r a l and p h y s i o l o g i c a l r e s p e c t s . On t h i s b a s i s one would p r e d i c t t h a t more a g g r e s s i v e or dominant grouped males would be more a c t i v e s e x u a l l y than o t h e r grouped males. Indeed, D e F r i e s and M c C l e a r n (1970) have found t h a t dominant males s i r e the v a s t m a j o r i t y o f o f f s p r i n g when females a r e i n t r o d u c e d i n t o a group. Kahn (1961) found t h a t more a g g r e s s i v e males mated more; a l t h o u g h L a g e r s p e t z and H a u t o j a r v i (1967) found a t r a n s i e n t e f f e c t i n the o p p o s i t e d i r e c t i o n . The absence o f a s i g n i f i c a n t c o r r e l a t i o n between a g g r e s s i o n and subsequent i n t r a - g r o u p v a r i a n c e i n mating h e r e would c o n t r a d i c t t h e se s t u d i e s . How-ever, i t i s p o s s i b l e t h a t t h i s l a c k o f s i g n i f i c a n c e r e f l e c t s the s m a l l sample s i z e o r the r e c o m p o s i t i o n of the group 24 hours p r i o r to t e s t i n g . A d d i t i o n a l work r e l a t i n g dominance and a g g r e s s i v e n e s s to mating i s needed. The p r e s e n t r e s u l t s s uggest t h a t the l a r g e d i f f e r e n c e s i n endoc-r i n e weight t h a t accompany p r o l o n g e d i s o l a t i o n and g r o u p i n g (Benton e t al_. , 1978; B r a i n , 1971; B r a i n & N o w e l l , 1971; C h r i s t i a n , 1955, 1959; McKinney & D e s j a r d i n s , 1973a; 1973b) are p r o b a b l y not r e s p o n s i b l e f o r d i f f e r e n t i a l s e x u a l b e h a v i o r , s i n c e the time f a c t o r s i n v o l v e d i n the two e f f e c t s d i f f e r 82 s u b s t a n t i a l l y . However, t h e s e r e s u l t s do not r u l e out involvement o f hormones produced by these g l a n d s and suggest a need f o r e x a m i n a t i o n o f gonadal and a d r e n a l a c t i v i t y a t s h o r t i s o l a t i o n / g r o u p i n g i n t e r v a l s . I n v e s t i g a t i o n s o f e n d o c r i n e a c t i v i t y f o l l o w i n g i s o l a t i o n or g r o u p i n g have tended to employ one week as the minimum i n t e r v a l . F o r example, G o l d s m i t h e_t al_. (1976) measured plasma c o r t i c o s t e r o n e at i n t e r v a l s o f one week and l o n g e r f o l l o w i n g i n t r o d u c t i o n of e x p e r i m e n t a l h o u s i n g c o n d i -t i o n s . A l t h o u g h they f a i l e d to f i n d d i f f e r e n c e s between i s o l a t e d and grouped mice, d i f f e r e n c e s might have o c c u r r e d a t s h o r t e r i n t e r v a l s . S i n c e e n v i r o n m e n t a l m a n i p u l a t i o n s can s i g n i f i c a n t l y a l t e r s t e r o i d l e v e l s i n a m a t t e r o f minutes (e.g., M a c r i d e s , B a r t k e , & D a l t e r i o , 1975), i t would be w o r t h w h i l e t o i n v e s t i g a t e e f f e c t s of s h o r t - i n t e r v a l h o u s i n g on a d r e n a l and gonadal s t e r o i d s . I n t e r m a l e a g g r e s s i o n i n grouped a n i m a l s i s known to produce f a i r l y r a p i d p i t u i t a r y - a d r e n o c o r t i c a l a c t i v a t i o n among more s u b o r d i n a t e group members ( B r a i n & Nowell, 1970; Bronson & E l e f t h e r i o u , 1965), w h i l e d e f e a t i n a g g r e s s i v e e n c o u n t e r s may a l s o produce changes i n h y p o t h a l a m i c l e v e l s o f l u t e i n i z i n g hormone ( E l e f t h e r i o u & Church, 1967, 1968). I t i s p o s s i b l e t h a t the o c c u r r e n c e o f these hormonal e v e n t s , as a r e s u l t o f a g g r e s s i v e e n c o u n t e r s , produces the r e l a t i v e l y low l e v e l s o f s e x u a l b e h a v i o r i n grouped males through some unknown mechanism. I f b i o c h e m i c a l events a r e r e s p o n s i b l e f o r i s o l a t i o n / g r o u p i n g d i f f e r e n c e s i t must be demonstrated t h a t t h e se undergo t r a n s i t i o n s w i t h i n 24 hours o f i s o l a t i o n . At l e a s t i n the case o f c e n t r a l n e u r o t r a n s m i t t e r s , such e v i d e n c e e x i s t s , s i n c e b r a i n c a t e c h o l a m i n e s and s e r o t o n i n undergo r a p i d changes f o l l o w i n g i s o l a t i o n ( G a r a t t i n i e t a l . , 1969; G i a c a l o n e e_t a l . , 1968). I s o l a t e d mice may show g r e a t e r u t i l i z a t i o n o f the n e u r o t r a n s m i t t e r s n o r e -83 p i n e p h r i n e , dopamine, and s e r o t o n i n i n n o v e l s i t u a t i o n s than do grouped mice ( G a r a t t i n i e t a l . , 1969; Welch & Welch, 1969a; 1969b). T h i s e v i d e n c e i s complemented by p h a r m a c o l o g i c a l e v i d e n c e t h a t c a t e c h o l a m i n e a g o n i s t s i n c r e a s e and a n t a g o n i s t s d e c r e a s e s e x u a l b e h a v i o r , w h i l e s e r o t o n i n a g o n i s t s d e c r e a s e and a n t a g o n i s t s i n c r e a s e such b e h a v i o r (Gessa & Ta g l i a m o n t e , 1975). I t i s c o n c e i v a b l e t h a t b i o g e n i c amine u t i l i z a t i o n r a t e s a l s o account f o r the h i g h l e v e l s o f s e x u a l performance observed i n group-housed animals 4 hours a f t e r c a g e - c l e a n i n g . I t i s a common o b s e r v a t i o n t h a t male mice w i l l f i g h t s h o r t l y a f t e r cage c l e a n i n g , even when group i n t e r a c t i o n s have former-l y been s t a b l e . T h i s phenomenon i s q u a n t i f i e d i n Experiment 8, a l b e i t w i t h a r e c o n s t i t u t e d group. A g g r e s s i v e i n t e r a c t i o n s a r e known to be accompanied by h i g h l e v e l s of t u r n o v e r of b i o g e n i c amines ( G a r a t t i n i ejt a l . , 1969; Welch & Welch, 1969a; 1969b). I n c r e a s e d t u r n o v e r o f b i o g e n i c amines, p a r t i -c u l a r l y the c a t e c h o l a m i n e s , n o r e p i n e p h r i n e and dopamine, might c a r r y over i n t o subsequent t e s t s w i t h r e c e p t i v e females. Both i s o l a t i o n - i n d u c e d and c a g e - c l e a n i n g - i n d u c e d f a c i l i t a t i o n o f male s e x u a l b e h a v i o r might thus be accounted f o r by b e h a v i o r a l a c t i v a t i o n due to i n c r e a s e d c a t e c h o l a m i n e u t i l i z a t i o n or perhaps some s e r o t o n e r g i c mechanism. These d a t a may a l s o suggest an involvement o f pheromonal v a r i a b l e s . There i s e v i d e n c e (see Bronson, 1971) t h a t male mice s e c r e t e pheromones i n t h e i r f e c e s and u r i n e . I s o l a t i n g mice might remove them from the immediate v i c i n i t y o f pheromones s e c r e t e d by c o n s p e c i f i c males. Such pheromones c o u l d c o n c e i v a b l y a c t to reduce the s e x u a l performance o f some males, an e f f e c t which may r e l a t e t o the p o p u l a t i o n dynamics o f the s p e c i e s . Such pheromones c o u l d a l s o be i n v o l v e d i n the t r a n s i e n t i n c r e a s e i n performance of grouped a n i m a l s observed i n Experiment 7 f o l l o w i n g c a g e - c l e a n i n g . Cage c l e a n i n g t e m p o r a r i l y removes much of the odor o f c o n s p e c i f i c males, but as f e c e s and u r i n e accumulate t h e s e odors r e t u r n . One problem w i t h t h i s i n t e r p r e t a t i o n i s the r e l a t i v e l y low l e v e l o f performance of i s o l a t e s a f t e r 1 and 4 h r i s o l a t i o n i n Experiment 7. T h i s might be e x p l a i n e d , however, by o t h e r v a r i a b l e s i n v o l v e d i n e a r l y a d a p t a t i o n to i s o l a t i o n . Pheromonal s u p p r e s s i o n of s e x u a l b e h a v i o r i n grouped male mice might p a r a l l e l e f f e c t s found elsewhere (Whitten, 1959) w i t h female mice, where g r o u p i n g may s u p p r e s s e s t r u s and l e n g t h e n d i e s t r u s . 85 SECTION IV: PITUITARY-ADRENAL MEDIATION The experiments o f the p r e s e n t s e c t i o n t e s t the h y p o t h e s i s t h a t p i t u i t a r y - a d r e n a l f a c t o r s a r e i n v o l v e d i n d i f f e r e n c e s i n s e x u a l a c t i v i t y between i s o l a t e d and grouped mice. T h i s r e s e a r c h f o l l o w s from e v i d e n c e t h a t i s o l a t i o n i n mice f r e q u e n t l y lowers p i t u i t a r y - a d r e n o c o r t i c a l a c t i v i t y ( B r a i n , 1975; Burge & Edwards, 1971; Leshner e t a l . , 1973), adrenalectomy o r ACTH d e c r e a s e s w h i l e c o r t i c o s t e r o n e r e s t o r e s i s o l a t i o n - i n d u c e d a g g r e s -s i o n i n a d r e n a l e c t o m i z e d mice (Burge & Edwards, 1971; G o r z a l k a & C a i r a , 1979; Leshner e t a l . . , 1973), and a g g r e s s i o n and s e x u a l a c t i v i t y a r e i n c r e a s e d i n p a r a l l e l by i n d i v i d u a l h o u s i n g i n male mice ( S e c t i o n I ) . The p r e s e n t s e c t i o n i s concerned, i n a d d i t i o n to i s o l a t i o n / g r o u p i n g d i f f e r e n c e s , w i t h the g e n e r a l r o l e o f p i t u i t a r y - a d r e n o c o r t i c a l a c t i v i t y i n the e x p r e s s i o n o f s e x u a l r e s p o n d i n g . A good d e a l o f e v i d e n c e s u g g e s t s t h a t male s e x u a l b e h a v i o r i s p r o b a b l y not dependent on a d r e n a l hormones. Adrenalectomy f a i l s to modify c o p u l a t o r y b e h a v i o r i n g o n a d a l l y i n t a c t r a t s " ( B l o c h & Da v i d s o n , 1968) and c a s t r a t e d r a t s r e c e i v i n g t e s t o -s t e r o n e p r o p i o n a t e ( G o r z a l k a , Rezek, & Whalen, 1975). N e i t h e r a d r e n a l e c -tomy nor treatment w i t h d e s o x y c o r t i c o s t e r o n e a c e t a t e a p p r e c i a b l y i n f l u e n c e s mating a c t i v i t y i n hamsters (Warren & Aronson, 1956). Furthermore, adrena-86 lectomy f a i l s t o reduce the p o s t - c a s t r a t i o n a l c o p u l a t o r y b e h a v i o r t h a t i s e v i d e n t i n male c a t s (Cooper & Aronson, 1958) and dogs (Schwartz & Beach, 1954). S i n c e adrenalectomy l e a d s to a s u s t a i n e d i n c r e a s e i n p i t u i t a r y ACTH l e v e l s (Gemzell, van Dyke, T o b i a s , & Evans, 1951), one might r e a s o n -a b l y p r e d i c t t h a t ACTH a d m i n i s t r a t i o n would a l s o f a i l to a l t e r male s e x u a l b e h a v i o r . The few s t u d i e s o f t h i s i s s u e have y i e l d e d c o n t r a d i c t o r y r e s u l t s . I n t r a v e n o u s l y a d m i n i s t e r e d ACTH i n h i b i t s c o p u l a t o r y a c t i v i t y i n the male r a b b i t ( K o r a n y i , E n d r S c z i , & Tarnok, 1966) w h i l e ACTH a d m i n i s -t e r e d i n t r a v e n t r i c u l a r l y f a c i l i t a t e s s e x u a l a c t i v i t y i n the same s p e c i e s ( B e r t o l i n i e_t aJL., 1975). ACTH i n j e c t i o n s f a c i l i t a t e s e x u a l a c t i v i t y i n 4-10 male r a t s ( B e r t o l i n i e_t al_. , 1975). However, ACTH , a p e p t i d e l a r g e l y d e v o i d o f a d r e n o c o r t i c o t r o p i c a c t i v i t y but p o s s e s s i n g the e f f e c t i v e n e s s of ACTH on av o i d a n c e b e h a v i o r (deWied, 1969), i n c r e a s e s the l a t e n c y o f male r a t s t o e x h i b i t c o p u l a t o r y r e s p o n s e s (Bohus, H e n d r i c k x , van K o l f s c h o t e n , & K r e d i e t , 1975). Thus, w h i l e a d r e n a l e c t o m y - i n d u c e d i n c r e a s e s i n ACTH would appear t o have no e f f e c t on s e x u a l b e h a v i o r , exogenous ACTH seems to i n c r e a s e or d e c r e a s e mating, depending on methodology. Because e x p e r i -m ental paradigms and s p e c i e s have v a r i e d w i d e l y i n the l i t e r a t u r e , i t would seem a p p r o p r i a t e to examine the e f f e c t s o f adrenalectomy and exogenous ACTH w i t h i n a s i n g l e s t u d y . Experiment 9A Adrenalectomy b o t h i n c r e a s e s ACTH l e v e l s and removes the p r i m a r y s o u r c e o f c o r t i c o s t e r o i d s . I f p i t u i t a r y - a d r e n o c o r t i c a l mechanisms a r e i n v o l v e d i n the d i f f e r e n t i a l performance o f grouped and i s o l a t e d mice, i t 87 i s l i k e l y t h a t t h e r e w i l l be an i n t e r a c t i o n between adrenalectomy and s e x u a l b e h a v i o r under d i f f e r e n t h o u s i n g c o n d i t i o n s . The p r e s e n t e x p e r i -ment compared the e f f e c t s o f adrenalectomy and sham adrenalectomy on the mating r e s p o n s e s o f grouped and i s o l a t e d male mice. Method CD-I male mice w e r r o b t a i n e d from Canadian B r e e d i n g Farms a t 55 days o f age. P r e - e x p e r i m e n t a l h o u s i n g and g e n e r a l t e s t i n g c o n d i t i o n s were l i k e those o f Experiment 1A. S t i m u l u s a n i m a l s c o n s i s t e d o f CD-I fem a l e s , o b t a i n e d from the same b r e e d e r and made r e c e p t i v e a c c o r d i n g t o the p r o c e d u r e s o f Experiment 1A. At about 60 days o f age, s u r g e r y was performed on e x p e r i m e n t a l males a d m i n i s t e r e d 2.5 mg. Nembutal (Sodium P e n t o b a r b i t a l , A b bott) anes-t h e s i a . H a l f o f the animals were b i l a t e r a l l y a d r e n a l e c t o m i z e d w h i l e r e -m a i n i n g a n i m a l s were sham-adrenalectomized. A l l animals were r e t u r n e d t o groups of 6. A d r e n a l e c t o m i z e d a n i m a l s were g i v e n a c c e s s to b o t h water and 0.9% s a l i n e s o l u t i o n . One week a f t e r s u r g e r y , b o t h a d r e n a l e c t o m i z e d and sham-adrenalectomized animals were e i t h e r i s o l a t e d or housed i n groups o f 6. " A l l cages were l i k e t h o s e d e s c r i b e d f o r Experiment 1A. A f t e r 2 weeks i n these c o n d i t i o n s , animals were g i v e n t h e i r f i r s t t e s t o f s e x u a l b e h a v i o r i n the p r e s e n c e o f r e c e p t i v e f emales. T e s t s e s s i o n s were conducted f o r 1 h r as i n the p r e v i o u s e x p e r i m e n t s . D u r i n g s e s s i o n s the number, l a t e n c y , and d u r a t i o n o f mounts w i t h o u t i n t r o m i s s i o n (mounts), mounts w i t h i n t r o m i s s i o n and p e l v i c t h r u s t i n g ( 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 were r e c o r d e d v i a an E s t e r l i n e Angus event r e c o r d e r . Each a n i m a l was r e t u r n e d t o i t s i s o l a t i o n or group h o u s i n g c o n d i t i o n and r e t e s t e d one and two weeks f o l l o w i n g t h i s f i r s t t e s t . Of n o n a d r e n a l e c t o m i z e d a n i m a l s , 88 11 i s o l a t e d and 9 grouped animals s u r v i v e d t o f i n i s h a l l t e s t s , w h i l e 9 i s o l a t e d and 9 grouped a d r e n a l e c t o m i z e d animals s u r v i v e d . When grouped animals d i e d they were r e p l a c e d by s u r r o g a t e s tha t ; were t r e a t e d i n the same manner as o t h e r animals i n the group but not i n c l u d e d i n t e s t i n g s e s s i o n s . R e s u l t s and D i s c u s s i o n F i g u r e 7 g i v e s the r e s u l t s f o r a measure of d u r a t i o n o f mounting. T a b l e X g i v e s r e s u l t s f o r the r e m a i n i n g measures. I s o l a t e d sham-adrenal-e c t o m i z e d animals showed s u b s t a n t i a l l y more s e x u a l a c t i v i t y than grouped sham-adrenalectomized a n i m a l s . Grouped a d r e n a l e c t o m i z e d a n i m a l s showed more a c t i v i t y than i s o l a t e d a d r e n a l e c t o m i z e d and grouped sham-adrenalec-tomized a n i m a l s . I n d i v i d u a l . a n a l y s e s o f v a r i a n c e were conducted on each measure, w i t h two b e t w e e n - s u b j e c t s f a c t o r s (adrenalectomized/sham, i s o l a t e d / grouped) and one w i t h i n - s u b j e c t s f a c t o r s (weekly t e s t ) . There was a s i g n i -f i c a n t adrenalectomy-sham by i s o l a t i o n - g r o u p i n g i n t e r a c t i o n i n d u r a t i o n o f mounting (F = 7.66, df_ = 1/33, p_ = .009), mounts (F = 8.71, df = 1/33, p_ = .006), e j a c u l a t i o n s (F = 5.26, df_ = 1/33, _p_ = .028), mount l a t e n c y (F = 6.32, d f = 1/33, _p_ = .016), i n t r o m i s s i o n l a t e n c y (F = 8.13, d f = 1/33, p_ = .007), and e j a c u l a t i o n l a t e n c y (F = 5.11, d_f_ = 1/33, p_ =-.031). Exami-n a t i o n o f s i m p l e main e f f e c t s r e v e a l e d s i g n i f i c a n t sham i s o l a t i o n - g r o u p i n g d i f f e r e n c e s i n d u r a t i o n (F_ = 5.11, d_f = 1/18, _p_ = .036), mounts (F = 4.59, df = 1/18, p = .046), mount l a t e n c y (F = 5.36, d f = 1/18, p = .033), and i n t r o m i s s i o n l a t e n c y (F = 4.59, df_ = 1/18, p_ = .046). There were a d r e n a l e c -tomized i s o l a t i o n - g r o u p i n g d i f f e r e n c e s o n l y i n mounts (F = 4.58, d_f = 1/15, p_ = .049). Comparisons o f sham i s o l a t e and a d r e n a l e c t o m i z e d i s o l a t e c o n d i -t i o n s r e v e a l e d e f f e c t s i n d u r a t i o n (F_ = 5.68, d_f = 1/17, p_ = .029), mounts 89 F i g u r e 7: The mean t o t a l d u r a t i o n o f mounting, w i t h o r w i t h o u t i n t r o m i s s i o n , i n a d r e n a l e c t o m i z e d (Adx) o r sham-adrenalectomized (Sham), i s o l a t e d ( T s o l ) o r grouped (Gp) mice i n Experiment 9A, V e r t i c a l l i n e s i n d i c a t e s t a n d a r d e r r o r s , 90 WEEK 91 T a b l e X Means and Standard E r r o r s o f Measures o f Sexua l Performance i n A d r e n a l e c t o m i z e d o r Sham-Adrenalectomized, I s o l a t e d o r Grouped Male M i c e i n Experiment 9A Measure Week Sham i s o l a t e d grouped A d r e n a l e c t o m i z e d i s o l a t e d grouped Mounts 19.09+4.60 29.18+8.64 21.09+4.52 5.56+4.60 9.00+4.61 12.89+5.63 0.88+0.52 4.63+2.24 8.75+4.07 10.00+3.92 25.67+8.89 13.44+5.03 1 I n t r o m i s s i o n s 2 3 5.00+1.67 8.89+3.77 6.33+1.67 1.82+1.13 5.18+3.01 4.37+1.71 0.50+0.38 4.00+3.34 2.50+1.71 3.11+1.63 6.22+2.72 6.44+2.64 E j a c u l a t i o n s 2 3 0.00+0.00 0.18+0.12 0.36+0.20 0.00+0.00 0.00+0.00 0.11+0.11 0.00+0.00 0.00+0.00 0.12+0.12 0.00+0.00 0.11+0.11 0.44+0.18 Mount L a t e n c y 1 (sec) 2 3 1221+431 696+567 1127+547 2803+431 2047+293 1523+355 2962+375 1900+340, 1013+389 1414+491 1280+580 1005+497 I n t r o m i s s i o n 1 L a t e n c y (sec), 2 3 2202+370 1654+501 1137+344 3123+379 2944+363 2190+564 3186+321 3085+396 2468+480 2759+401 1790+493 1226+465 E j a c u l a t i o n 1 3600+0 3600+0 3600+0 3600+0 L a t e n c y (sec) 2 3349+233 3600+0 3600+0 3494+106 3 2931+349 3550+50 3370+230 2987+310 92 (F = 11.18, df = 1/17, p = .004), mount l a t e n c y (F = 5.42, df = 1/17, £ = .033), and i n t r o m i s s i o n l a t e n c y (F = 6.26, df = 1/17, £ = .023). A l l o t h e r e f f e c t s d i d not r e a c h s i g n i f i c a n c e . I t i s apparent from these r e s u l t s t h a t adrenalectomy a f f e c t s a mechanism t h a t c o n t r i b u t e s to the development o f i s o l a t i o n - g r o u p i n g d i f f e r e n c e s i n s e x u a l performance. S i n c e grouped animals a c t u a l l y showed a f a c i l i t a t i o n o f a c t i v i t y f o l l o w i n g adrenalectomy, i t i s u n l i k e l y t h a t the r e s u l t s of t h i s experiment can be a t t r i b u t e d e n t i r e l y to n o n s p e c i f i c d e b i l i t a t i o n . The mating d e f i c i t s observed i n i s o l a t e s subsequent to adrenalectomy c o u l d be a t t r i b u t e d to e l e v a t e d ACTH l e v e l s , reduced a d r e n a l s t e r o i d l e v e l s , g e n e r a l d e b i l i t a t i o n , or some co m b i n a t i o n of t h ese f a c t o r s . However, none of t h ese p o s s i b i l i t i e s would account f o r the e f f e c t s of adrenalectomy on grouped mice. T h i s would suggest the absence of a s i m p l e monotonic r e l a t i o n s h i p between p i t u i t a r y - a d r e n o c o r t i c a l a c t i v i t y and s e x u a l b e h a v i o r observed under d i f f e r e n t h o u s i n g c o n d i t i o n s . Experiment 9B I t has been shown t h a t c o r t i c o s t e r o n e , a major a d r e n a l s t e r o i d , r e v e r s e s the d e f i c i t s i n i s o l a t i o n - i n d u c e d a g g r e s s i o n f o l l o w i n g a d r e n a l ^ ectomy (Leshner e_t a l . , 1973). I f the a g g r e s s i o n and f a c i l i t a t i o n o f s e x u a l b e h a v i o r - t h a t , f o l l o w i s o l a t i o n a r e under s i m i l a r e n d o c r i n e c o n t r o l , exogenous c o r t i c o s t e r o n e s h o u l d have s i m i l a r e f f e c t s on mating i n a d r e n a l -e c t o m i z e d mice. The p r e s e n t experiment examined whether c o r t i c o s t e r o n e treatment would r e s t o r e normal i s o l a t i o n - g r o u p i n g e f f e c t s i n the a d r e n a l e c t o m i z e d animals examined i n Experiment 9A. 93 Method S u b j e c t s from Experiment 9A were m a i n t a i n e d under the h o u s i n g c o n d i t i o n s d e s c r i b e d f o r t h a t experiment. F o l l o w i n g the l a s t t e s t w i t h r e c e p t i v e females i n Experiment 9A, d a i l y i n j e c t i o n s o f 200 yg c o r t i -c o s t e r o n e sc i n .05 cc peanut o i l were g i v e n to a l l a d r e n a l e c t o m i z e d a n i m a l s . T h i s do'se was d e r i v e d from o t h e r experiments (Leshner e t a l . , 1973; Moyer & L e s h n e r , 1976) d e m o n s t r a t i n g r e s t o r a t i o n o f n o n s e x u a l b e h a v i o r , such as a g g r e s s i o n , i n a d r e n a l e c t o m i z e d mice w i t h c o r t i c o s t e r o n e . Sham-adrenalectomized animals were g i v e n .05 cc o i l d a i l y f o r comparison purposes w i t h Experiment 9A. A f t e r 1, 2, and 3 weeks of t h i s i n j e c t i o n regimen a n i m a l s were t e s t e d a c c o r d i n g to p r o c e d u r e s of Experiment 9A. E i g h t a n i m a l s i n each c o n d i t i o n s u r v i v e d t o complete a l l t e s t s . R e s u l t s and D i s c u s s i o n T a b l e XI g i v e s r e s u l t s f o r a l l measures. The p a t t e r n s e v i d e n t i n Experiment 9A were e s s e n t i a l l y unchanged by treatment w i t h e i t h e r c o r t i -c o s t e r o n e or o i l . A n a l y s e s of v a r i a n c e on i n d i v i d u a l measures r e v e a l e d a s i g n i f i c a n t adrenalectomy-sham by i s o l a t i o n - g r o u p i n g i n t e r a c t i o n i n mounts (F = 5.11, d f = 1/28, p_ = .032) and mount l a t e n c y (F = 7.86, df = 1/28, * £ = .009), w h i l e t h i s i n t e r a c t i o n approached s i g n i f i c a n c e f o r d u r a t i o n of mounting (F_ = 3.48, df_ = 1/28, p_ = .072) and i n t r o m i s s i o n l a t e n c y (F_ = 2.99, df_ = 1/28, £ = .095). A n a l y s e s o f s i m p l e main e f f e c t s r e v e a l e d s i g n i f i c a n t d i f f e r e n c e s between sham i s o l a t e s and a d r e n a l e c t o m i z e d i s o l a t e s i n mounts (F = 11.90, df = 1/14, £ = .004) and mount l a t e n c y (F = 6.58, d f = 1/14, p_ = .022), d i f f e r e n c e s a p p r o a c h i n g s i g n i f i c a n c e between sham i s o l a t e s and sham grouped animals i n mounts (F = 4.15, df_ = 1/14, p_ = .061) and mount l a t e n c y (F_ = 4.39, df_ = 1/14, £ = .055), and d i f f e r e n c e s approach-i n g s i g n i f i c a n c e between a d r e n a l e c t o m i z e d i s o l a t e s and a d r e n a l e c t o m i z e d , 94 T a b l e XI Means and Standard E r r o r s o f Measures o f Sex u a l Performance o f A d r e n a l e c t o m i z e d C o r t i c o s t e r o n e -T r e a t e d and Sham-Adrenalectomized O i l -T r e a t e d M i c e i n Experiment 9B Measur.e Week Sham-Oil A d r e r i a i e c t o m i z e d ^ C o r t i c o s t e r o n e i s o l a t e d -grouped i i s o l a t e d grouped D u r a t i o n o f ':!. 1 Mounting 2 (sec) 3 119.38+31.19 133.25+29.84 101.13+36.29 74.13+29.77 76.25+40.31 48.25+19.12 31.63+23.69 36.37+26.98 36.00+29.26 115.75+41.61 91.88+30.83 48.00+18.02 1 28.38+7.32 10.50+5.26 4.88+2.90 13.13+5.74 Mounts 2 22.50+5.10 10.25+6.45 5.25+2.66 6.50+4.06 3 18.50+5.26 5.63+3.60 2.13+1.49 9.38+5.25 1 5.25+2.18 2.88+1.56 1.50+1.22 5.75+2.97 I n t r o m i s s i o n s 2 6.00+1.44 4.75+2.87 1.25+1.00 5.13+2.95 3 4.00+1.63 1.38+0.73 1.75+1.61 1.75+0.77 1 0.00+0.00 0.25+0.16 0.00+0.00 0.50+0.19 E j a c u l a t i o n s 2 0.00+0.00 0,13j:0.12 0.00+0.00 0.63+0.26 3 0.25+0.16 0.38+0.18 0.25+0.16 0.38+0.18 Mount L a t e n c y 1 706+161 1373+515 2426+507 651+428 (se c ) 2 686+183 2154+481 1538+515 1293+575 3 1297+575 2416+584 2530+541 926+487 I n t r o m i s s i o n 1 L a t e n c y (sec) 2 3 2274+365 1981+423 2000+505 2220+542 2381+478 2454+565 2846+471 3040+385 2731+526 1199+506 1547+516 2362+534 E j a c u l a t i o n 1 L a t e n c y (sec) 2 3 3600+0 3600+0 3321+219 3093+332 3339+261 2801+391 3600+0 3600+0 3060+378 2358+506 2293+549 2578+511 95 grouped a n i m a l s i n mount l a t e n c y (F = 3.64, d_f = 1/14, p_ = .077). I n t e r -a c t i o n f a c t o r s were not s i g n i f i c a n t f o r o t h e r measures but the i s o l a t i o n -g r o u p i n g main e f f e c t was s i g n i f i c a n t f o r e j a c u l a t i o n s (F = 7.00, df = 1/28, £ = .013) and e j a c u l a t i o n l a t e n c y (F = 6.94, df = 1/28, £ = .014). A l l o t h e r e f f e c t s were not s i g n i f i c a n t . Many of the s t a t i s t i c a l d i f f e r e n c e s between t h e s e a n a l y s e s and those of Experiment 9A may be a t t r i b u t a b l e t o l o s s of power due to reduced sample s i z e . The f a i l u r e of c o r t i c o s t e r o n e to r e v e r s e s e x u a l a c t i v i t y i n a d r e n a -l e c t o m i z e d mice a t a dosage s u f f i c i e n t t o r e s t o r e i s o l a t i o n - i n d u c e d a g g r e s -s i o n opens the p o s s i b i l i t y of a d i f f e r e n t i a l hormonal c o n t r o l o f these b e h a v i o r s . S i n c e c o r t i c o s t e r o n e n o r m a l l y reduces ACTH l e v e l s , i t seems l e s s p r o b a b l e t h a t the d e f i c i t s seen i n a d r e n a l e c t o m i z e d i s o l a t e s can be a t t r i -b uted to e l e v a t e d l e v e l s o f ACTH. However, the p o s s i b i l i t y t h a t c o r t i c o s -t e r o n e , under the p r e s e n t regimen, f a i l e d to r e s t o r e endogenous ACTH to p r e -adrenalectomy l e v e l s cannot be e x c l u d e d . R a t h e r , the d e f i c i t s may r e f l e c t an absence of o t h e r a d r e n o c o r t i c a l hormones. R e c e n t l y i t was demonstrated t h a t d e s o x y c o r t i c o s t e r o n e was e f f e c t i v e w h i l e c o r t i c o s t e r o n e was i n e f f e c t i v e i n f a c i l i t a t i n g s e x u a l r e c e p t i v i t y i n o v a r i e c t o m i z e d , e s t r o g e n - t r e a t e d r a t s ( G o r z a l k a & Whalen, 1977). A l t h o u g h the a d r e n a l c o r t e x produces c o n s i d e r a b l y g r e a t e r q u a n t i t i e s of c o r t i c o s t e r o n e than d e s o x y c o r t i c o s t e r o n e , t h e r e i s no r e a s o n to assume t h a t the major s t e r o i d i s n e c e s s a r i l y the most e f f e c t i v e f o r e v e r y b e h a v i o r a l r e s p o n s e . A l t e r n a t i v e l y , the p o s s i b i l i t y t h a t a d i f f e r e n t c o r t i c o s t e r o n e regimen would have r e v e r s e d the s e x u a l performance of a d r e n a l e c t o m i z e d mice cannot be e x c l u d e d . Experiment 10 The r e s u l t s of Experiment 9A s u g g e s t , among o t h e r arguments, t h a t e i t h e r removal of a d r e n a l s t e r o i d s or e l e v a t i o n of ACTH l e v e l s c o u l d mediate the e f f e c t s o f adrenalectomy upon s e x u a l performance. R e s u l t s from Experiment 9B suggest t h a t c o r t i c o s t e r o n e t r e atment, which presumably n o r m a l i z e s ACTH l e v e l s , does not i n f l u e n c e s e x u a l r e s p o n d i n g i n adrena- 1 l e c t o m i z e d a n i m a l s . T h i s l e a d s to a n o t h e r p o s s i b i l i t y , namely, t h a t a p p r o p r i a t e l e v e l s o f b o t h ACTH and s p e c i f i c a d r e n a l c o r t i c o i d s a r e n e c e s s a r y f o r the f a c i l i t a t i o n o f s e x u a l a c t i v i t y i n i s o l a t e s . In o t h e r words, p i t u i t a r y ACTH may p l a y a r e g u l a t o r y r o l e but the b e h a v i o r a l e x p r e s -s i o n o f t h i s mechanism would r e q u i r e a p e r m i s s i v e a c t i o n o f s p e c i f i c a d r e n a l c o r t i c o s t e r o i d s . T h i s h y p o t h e s i s can be t e s t e d by comparing the b e h a v i o r o f a d r e n a l e c t o m i z e d and sham-adrenalectomized mice f o l l o w i n g exogenous ACTH. I f e f f e c t s o f ACTH are dependent on a d r e n a l s t e r o i d s , t hey would o n l y be e v i d e n t i n sham a n i m a l s . I f ACTH i s c a p a b l e of a c t i n g a l o n e t o r e g u l a t e mating then e f f e c t s might be observed i n b o t h a d r e n a l l e c t o m i z e d and sham mice. The p r e s e n t experiment examined the e f f e c t s o f ACTH treatment i n b o t h a d r e n a l e c t o m i z e d and sham-adrenalectomized i s o l a t e d male mice. Method CD-I males were o b t a i n e d a t 55 days of age and housed i n groups of 6. At 60-65 days o f age, about h a l f o f the animals were b i l a t e r a l l y a d r e n a l e c t o m i z e d and the remainder sham-adrenalectomized. Subsequent to s u r g e r y , a l l a n i m a l s were housed i n d i v i d u a l l y i n cages l i k e those d e s c r i b e d f o r Experiment IA. A l l a d r e n a l e c t o m i z e d animals were g i v e n a c c e s s to b o t h water and 0.9% s a l i n e s o l u t i o n . B e g i n n i n g one week f o l l o w i n g s u r g e r y , a p p r o x i m a t e l y h a l f o f the a d r e n a l e c t o m i z e d and sham an i m a l s were g i v e n d a i l y , i n j e c t i o n s o f .5 IU ACTH (Calbiochem.) d i s s o l v e d i n .2 cc p h y s i o l o g i c a l s a l i n e o f pH 7.2. Other work i n our l a b o r a t o r y has shown t h i s to be the 97 m i n i m a l l y e f f e c t i v e ACTH dose f o r i n f l u e n c i n g s e x u a l b e h a v i o r i n the mouse. Remaining animals r e c e i v e d the s a l i n e v e h i c l e a l o n e . A l l i n j e c t i o n s were g i v e n i p . One, two, and t h r e e weeks a f t e r commencement of i n j e c t i o n s , a l l animals were t e s t e d f o r one hour i n the p r e s e n c e o f r e c e p t i v e females. Females were p r e p a r e d and s e s s i o n s conducted a c c o r d i n g to the p r o c e d u r e s o f Experiment 1A. E l e v e n sham s a l i n e , 12 sham ACTH, 9 a d r e n a l e c t o m i z e d s a l i n e , and 6 a d r e n a l e c t o m i z e d ACTH an i m a l s s u r v i v e d to complete a l l t e s t s o f s e x u a l b e h a v i o r . R e s u l t s and D i s c u s s i o n F i g u r e 8 p r e s e n t s r e s u l t s f o r d u r a t i o n o f mounting, w i t h and w i t h -out i n t r o m i s s i o n . T a b l e X I I p r e s e n t s r e s u l t s f o r a l l r e m a i n i n g measures. A d r e n a l e c t o m i z e d animals g i v e n ACTH showed the h i g h e s t s c o r e s on most measures. These s t r o n g l y exceeded s c o r e s of a d r e n a l e c t o m i z e d s a l i n e a n i m a l s . Shanr s a l i n e a nimals showed more b e h a v i o r than a d r e n a l e c t o m i z e d s a l i n e a n i m a l s and m a r g i n a l l y more b e h a v i o r than sham ACTH a n i m a l s . An a n a l y s i s o f v a r i a n c e was conducted on each measure. In the d u r a t i o n measure t h e r e were s i g n i f i c a n t main e f f e c t s of hormone treatment (F_ = 4.93, d_f = 1/34, £ = .033) and weekly t e s t (F = 6.70, df_ = 1/34, £ = .002), and s i g n i f i c a n t weekly t e s t by hormone treatment (F = 4.54, df_ = 2/68, £ = .014) and adr e n a -lectomy-sham by hormone treatment (F_ = 5.07, df_ = 1/34, £ = .031) i n t e r a c -t i o n s . A n a l y s e s o f s i m p l e main e f f e c t s f o r the l a t t e r i n t e r a c t i o n i n d i c a t e d a s i g n i f i c a n t e f f e c t o f hormone treatment i n a d r e n a l e c t o m i z e d a n i m a l s (F = 12.50, d_f = 1/13, £ = .004) and a d i f f e r e n c e between ACTH-treated sham and ACTH-treated a d r e n a l e c t o m i z e d a n i m a l s which approached s i g n i f i c a n c e (F_ = 4.26, df_ = 1/16, £ = .056). A n a l y s e s o f si m p l e main e f f e c t s i n the weeks by hormone i n t e r a c t i o n r e v e a l e d e f f e c t s at week 2 (F = 10.06, d_f = 1/34, £ = .003). In the mounts measure the main e f f e c t s o f hormone treatment 98 F i g u r e 8: The mean t o t a l d u r a t i o n o f mounting, 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 r e n a l e c t o m i z e d (AdxX o r sham-adrenalectomized (Sham) i s o l a t e d mice g i v e n d a i l y s a l i n e ( S a i l o r ACTH i n Experiment 10. V e r t i c a l l i n e s i n d i c a t e - s t a n d a r d e r r o r s . 99 200-o 21 O O100-o cr o Sham-Sal •—• Adx-Sal •--•Sham-ACTH o o Adx -ACTH 1 T" WEEK 3 100 T a b l e X I I Means and Standard E r r o r s of Sexu a l Performance o f A d r e n a l e c t o m i z e d and Sham-A d r e n a l e c t o m i z e d M i c e T r e a t e d w i t h .jACTHrof: .Saline:: i n Experiment 10 Measure Week Sham A d r e n a l e c t o m i z e d S a l i n e ACTH S a l i n e ACTH Mounts 13.81+4.38 12.08+2'-41 9.73+4.18 14.83+3.19 9v27+3.77 10.33+4.28 10.67+3.23 23.00+9.10 9.67+3.00 25.83+5.70 5.67+2.03 13.00+3.78 I n t r o m i s s i o n s 2 3 1.64+0.77 4.91+1.45 4.55+1.69 5.83+1.97 5.36+2.58 2.17+1.34 2.78+1.50 8.67+5.79 2.11+0.98 10.00+2.29 1.67+0.71 3v83+1.01 E j a c u l a t i o n s 2 3 0.00+0.00 0.09+0.91 0.27+0.19 0.17+0.11 0.08+0.08 0.00+0.00 0.00+0.00 0.22+0.15 0.33+0.24 0.17+0.17 0.33+0.21 0.50+0.22 Mount L a t e n c y 1 (sec) 2 3 1781+439 1809+455 1515+393 1139+350 1011+259 2060+398 1582+326 1022+322 1747+442 735+335 505+162 769+222 I n t r o m i s s i o n 1 3140+236 2157+386 2754+376 2169+554 L a t e n c y ( s e c ) 2 2389+376 2116+347 2363+453 1190+511 3 2248+443 2848+339 2620+414 1536+478 E j a c u l a t i o n 1 3600+0 3413+134 3600+0 3423+177 L a t e n c y (sec) 2 3404+195 3525+74 3104+331 3327+175 3 3220+264 3600+0 3388+183 2854+412 101 (F = 4.14, df = 1/34, p_ = .050) and weeks (F = 3.93, cLf = 2/68, £ = .024) were s i g n i f i c a n t . In the i n t r o m i s s i o n s measure t h e r e was a s i g n i f i c a n t i n t e r a c t i o n between t e s t weeks and hormone treatment (F_ = 3.19, d_f = 2/68, p = .047). A n a l y s i s o f s i m p l e main e f f e c t s r e v e a l e d e f f e c t s o f ACTH a t weeks 1 (F = 4.18, d f = 1/34, p_ = .049) and 2 (F = 6.04, df = 1/34, £ = .019). None of the r e m a i n i n g e f f e c t s r e a ched s i g n i f i c a n c e . ACTH appears t o have had a s t r o n g e f f e c t upon performance o f a d r e n a l e c t o m i z e d i s o l a t e s , but r e l a t i v e l y l i t t l e e f f e c t upon sham-adrena-l e c t o m i z e d i s o l a t e s . These r e s u l t s a r e c o n t r a r y to e x p e c t a t i o n s i n c e one would assume an e f f e c t e i t h e r on sham and a d r e n a l e c t o m i z e d mice o r on sham mice o n l y . C l e a r l y one h y p o t h e s i s can.be e l i m i n a t e d , namely, t h a t b e h a v i o r a l e f f e c t i v e n e s s o f ACTH i s dependent on some mi n i m a l l e v e l of a d r e n a l c o r t i -c o i d s . As w i t h the r e s u l t s o f Experiment 9, the d a t a from the p r e s e n t ex-periment i n d i c a t e t h a t the r e l a t i o n s h i p between ACTH and s e x u a l b e h a v i o r i s not a monotonic one. G e n e r a l D i s c u s s i o n T h i s s e r i e s o f experiments a g a i n c o n f i r m s the f i n d i n g t h a t i s o l a -t i o n f a c i l i t a t e s the 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 male mice. Adrenalectomy i n h i b i t e d mating i n i s o l a t e s but produced the o p p o s i t e e f f e c t i n group-housed a n i m a l s (Experiment 9A). T h i s f i n d i n g s u g g e s t s a r a t h e r complex r e l a t i o n s h i p between p i t u i t a r y - a d r e n o c o r t i c a l a c t i v i t y and male s e x u a l b e h a v i o r i n t h i s s p e c i e s . By c o n t r a s t , adrenalectomy n e i t h e r f a c i l i -t a t e d nor i n h i b i t e d mating a c t i v i t y i n g o n a d a l l y i n t a c t hamsters (Warren & Aronson, 1956) and r a t s ( B l o c h & D a v i d s o n , 1968). T h i s f i n d i n g i n the mouse i s , however, c o n s i s t e n t w i t h most r e p o r t s on the e f f e c t o f adrena-lectomy on i s o l a t i o n - i n d u c e d a g g r e s s i o n (e.g. B r a i n , Nowell & Wouters, 1971), 102 a l t h o u g h Burge and Edwards (1971) f i n d no e f f e c t o f adrenalectomy on a g g r e s s i o n . In Experiment 9B, i t was shown t h a t c o r t i c o s t e r o n e f a i l e d to r e s t o r e mating to pr e a d r e n a l e c t o m y l e v e l s i n i s o l a t e s . T h i s c o n t r a s t s w i t h i s o l a t i o n - i n d u c e d a g g r e s s i o n where d e f i c i e n c i e s produced by adrena-lectomy can be r e s t o r e d by c o r t i c o s t e r o n e treatment (Leshner e t a l . , 1973). Experiment 10 demonstrated t h a t exogenous ACTH e l e v a t e d s e x u a l r e s p o n d i n g i n a d r e n a l e c t o m i z e d i s o l a t e s and had l e s s o f an e f f e c t on sham a d r e n a l e c -tomized i s o l a t e s . These r e s u l t s a l s o suggest a d i f f e r e n t i a l c o n t r o l o f s e x u a l and a g g r e s s i v e b e h a v i o r s i n c e a d m i n i s t r a t i o n o f ACTH reduces r a t h e r than e l e v a t e s i s o l a t i o n - i n d u c e d a g g r e s s i o n ( B r a i n e t a l . , 1971). Experiment 9A i n d i c a t e d t h a t adrenalectomy may, under some c i r -cumstances, s i g n i f i c a n t l y reduce s e x u a l b e h a v i o r i n s i n g l y - h o u s e d mice. In Experiment 10, the same t r e n d was e v i d e n t i n the second and t h i r d weeks of t e s t i n g . The absence o f t h i s t r e n d i n the f i r s t week,may r e l a t e to the f a c t t h a t t e s t i n g o c c u r r e d a t a s h o r t e r i n t e r v a l f o l l o w i n g adrenalectomy and the i n c e p t i o n o f i s o l a t i o n . F u rthermore, d a i l y i n t r a p e r i t o n e a l i n j e c -t i o n s i n Experiment 10 may have c o n s t i t u t e d a s t r e s s o r , r e d u c i n g performance of sham i s o l a t e s t hrough p i t u i t a r y - a d r e n a l or o t h e r b i o c h e m i c a l e f f e c t s . Comparable e f f e c t s o f i n j e c t i o n s t r e s s on i n t e r m a l e a g g r e s s i o n have r e c e n t l y been r e p o r t e d ( B r a i n & Bowden, 1978). In t h i s paradigm, h i g h l e v e l s of ACTH may a c t to p r o t e c t a g a i n s t i n j e c t i o n s t r e s s . T h i s c o u l d e x p l a i n the d i f f e -r e n c e i n performance between ACTH- and s a l i n e - i n j e c t e d a d r e n a l e c t o m i z e d mice i n Experiment 10 and the d i f f e r e n c e i n performance between i s o l a t e d , a d r e n a l e c t o m i z e d mice i n Experiments 9A and 10. A c c o r d i n g to t h i s model, one need not assume a d i r e c t r e l a t i o n s h i p between' s e x u a l a c t i v i t y and ACTH t i t e r . E x periments 9A and 10 i n d i c a t e t h a t adrenalectomy has s i g n i f i c a n t 103 e f f e c t s on a t l e a s t some components of s e x u a l r e s p o n d i n g i n mice. There has been a t l e a s t one r e p o r t t h a t adrenalectomy does not reduce the p e r -centage of i s o l a t e d mice t h a t e j a c u l a t e (Thompson, M c G i l l , M a c i n t o s h , & Manning, 1976). There Is a l s o no s i g n i f i c a n t d i f f e r e n c e i n t h i s measure i n the p r e s e n t study. Another group of i n v e s t i g a t o r s f i n d no s i g n i f i c a n t e f f e c t o f adrenalectomy on i n t r o m i s s i o n f r e q u e n c y , mount f r e q u e n c y , and the p e r c e n t a g e o f mice i n t r o m i t t i n g ( W a l l i s & L u t t g e , 1975). However, th e s e i n v e s t i g a t o r s sampled c o n s i d e r a b l y l e s s b e h a v i o r , employing two 20-minute t e s t s as compared to t h r e e 1 hour t e s t s i n the p r e s e n t study. Furthermore, d i f f e r e n c e s i n Experiment 9A were found i n f o u r measures :> d u r a t i o n of mounting, mount f r e q u e n c y , mount l a t e n c y , and i n t r o m i s s i o n l a t e n c y . Three of t h e s e measures were not r e p o r t e d i n e a r l i e r s t u d i e s (Thompson e t a l . , 1976; W a l l i s & L u t t g e , 1975). I t i s c o n c e i v a b l e t h a t adrenalectomy produces n o n s p e c i f i c d e f i c i t s which i n t e r f e r e w i t h s e x u a l performance. For example, the t h e r m o r e g u l a t o r y d y s f u n c t i o n t h a t accompanies adrenalectomy (Tanche, 1976) c o u l d have con-t r i b u t e d t o a d e c l i n e i n the performance o f i s o l a t e s . In grouped a n i m a l s , the symptoms may have been a m e l i o r a t e d by the a n i m a l s ' tendency to huddle t o g e t h e r i n t h e i r home cage. T h i s e x p l a n a t i o n c o u l d p a r t i a l l y account f o r the d i f f e r e n t i a l e f f e c t s o f adrenalectomy on i s o l a t e d and grouped mice i n Experiment 9A. However, the r e s u l t s o f Experiment 9B tend to argue a g a i n s t t h i s i n t e r p r e t a t i o n . C o r t i c o s t e r o n e treatment d i d not f a c i l i t a t e r e c o v e r y i n i s o l a t e s . Moreover, ACTH a l o n e p e r m i t t e d h i g h l e v e l s o f mating i n a d r e n a l e c t o m i z e d i s o l a t e s i n Experiment 10. There i s l i t t l e e v i d e n c e t h a t exogenous ACTH, i n the absence o f the a d r e n a l c o r t e x , has a h e a l t h - p r o m o t i n g p r o p e r t y . 104 D e s p i t e the a l t e r n a t i v e e x p l a n a t i o n o f i n j e c t i o n s t r e s s , b o t h the e f f e c t s o f adrenalectomy on grouped mice i n Experiment 9A and ACTH treatment i n Experiment 10 a r e c o n s i s t e n t w i t h the i d e a t h a t ACTH p o t e n -t i a t e s s e x u a l r e s p o n d i n g . The r e s u l t s o f adrenalectomy on i s o l a t e s i n Experiment 1 sugge s t s an i n h i b i t o r y a c t i o n of ACTH. These p a r a d o x i c a l f i n d i n g s can be r e c o n c i l e d i f one assumes a U-shaped f u n c t i o n w i t h ACTH t i t e r as a b s c i s s a and s e x u a l r e s p o n d i n g as o r d i n a t e . I s o l a t e s , w i t h a s y m p t o t i c c o p u l a t o r y a c t i v i t y and r e l a t i v e l y low p i t u i t a r y ACTH a c t i v i t y , c o u l d be p l o t t e d on a peak o f t h i s graph. Group-housed mice, w i t h d e p r e s s e d s e x u a l a c t i v i t y and e l e v a t e d ACTH l e v e l s , would appear a t a d e s c e n d i n g p o i n t on the c u r v e . Assuming t h a t adrenalectomy p o t e n t i a t e s ACTH l e v e l s e q u a l l y i n i s o l a t e s and group-housed mice, i s o l a t e s c o u l d now be d i s t r i b u t e d on the t r o u g h w h i l e grouped a n i m a l s c o u l d appear on an a s c e n d i n g p o i n t on the cu r v e . A d m i n i s t r a t i o n o f ACTH to a d r e n a l e c t o m i z e d mice would p l a c e t h ese a n i m a l s on the a s c e n d i n g peak o f the graph. A c c o r d i n g to t h i s model, one would expect somewhat lower l e v e l s o f s e x u a l a c t i v i t y i n a d r e n a l l y - i n t a c t mice r e c e i v i n g ACTH s i n c e t o t a l ACTH t i t e r s would be lower than i n adr e n a -l e c t o m i z e d mice. F i g u r e 8 and Ta b l e X I I show a marked t r e n d t h a t i s con-s i s t e n t w i t h t h i s p r e d i c t i o n . A U-shaped f u n c t i o n might a l s o e x p l a i n seem-i n g l y c o n t r a d i c t o r y r e s u l t s i n o t h e r s p e c i e s . F o r example, an i n t r a v e n t r i -c u l a r i n j e c t i o n of ACTH f a c i l i t a t e s s e x u a l a c t i v i t y i n the male r a b b i t ( B e r t o l i n i e_t a l . , 1975) w h i l e an i n t r a v e n o u s i n j e c t i o n i s i n h i b i t o r y ( K o r a n y i e t a l . , 1966). T h i s might s i m p l y r e f l e c t q u a n t i t a t i v e d i f f e r e n c e s i n ACTH l e v e l s a t a p p r o p r i a t e n e u r a l s i t e s . S i n c e the m o d u l a t i n g e f f e c t o f ACTH on murine s e x u a l b e h a v i o r i s not n e c e s s a r i l y mediated by a d r e n o c o r t i c a l a c t i v a t i o n , the p i t u i t a r y hormone may be a c t i n g d i r e c t l y on the b r a i n . I n r e c e n t y e a r s t h e r e has been much 1 0 5 s p e c u l a t i o n as to the mechanism o f a c t i o n o f ACTH on the b r a i n . E v i d e n c e i n d i c a t e s t h a t ACTH has p r o f o u n d e f f e c t s on enzymes a s s o c i a t e d w i t h the metabolism o f c y c l i c AMP, RNA, and p r o t e i n as w e l l as on the n e u r o t r a n s m i t -t e r s dopamine, n o r e p i n e p h r i n e , s e r o t o n i n , and GABA (Dunn & G i s p e n , 1977). F o r example, c a t e c h o l a m i n e t u r n o v e r can be s i g n i f i c a n t l y m o d i f i e d w i t h e i t h e r exogenous ACTH o r tr e a t m e n t s which change endogenous l e v e l s o f ACTH (Dunn & G i s p e n , 1977). Other d a t a i n d i c a t e t h a t n e u r o t r a n s m i s s i o n p r o -c e s s e s a r e i n f l u e n c e d a l s o by i s o l a t i o n . C h r o n i c i s o l a t i o n i n mice has been shown both to reduce t u r n o v e r o f c a t e c h o l a m i n e s and s e r o t o n i n ( V a l z e l l i , 1974; Welch & Welch, 1969a; 1969b) and to produce r e l a t i v e l y g r e a t e r i n c r e a s e s i n t u r n o v e r when an i m a l s a r e exposed t o n o v e l s i t u a t i o n s (Welch & Welch, 1968). S i n c e dopaminergic and s e r o t o n e r g i c systems appear to be i n v o l v e d i n male s e x u a l b e h a v i o r (Gessa & Ta g l i a m o n t e , 1975), they may p r o v i d e a common mechanism f o r the e f f e c t s of i s o l a t i o n and ACTH. 106 SECTION V: PITUITARY-GONADAL MEDIATION  Experiment 11 I t has been e s t a b l i s h e d i n p r e v i o u s s t u d i e s t h a t i s o l a t e d mice show h i g h e r p i t u i t a r y - g o n a d a l a c t i v i t y than do group housed mice (Benton e t a l . , 1978; B r a i n , 1971; B r a i n & N o w e l l , 1971; C h r i s t i a n , 1955, Vandenbergh, 1960). T h i s i s r e f l e c t e d e s p e c i a l l y i n h i g h e r w e i g h t s of t e s t e s , p r e p u t i a l s , p r o s t a t e s , and s e m i n a l v e s i c l e s . I n c r e a s e s i n p i t u i -t a r y - g o n a d a l a c t i v i t y i n i s o l a t e s may o c c u r consequent to d e c r e a s e s i n p i t u i t a r y - a d r e n a l a c t i v i t y i n t h e s e a n i m a l s (Benton e_t al_. , 1978; B u l l o c k & New, 1971; D e s j a r d i n s & Ewing, 1971). Because p i t u i t a r y - g o n a d a l a c t i v i t y i s s t r o n g l y i n v o l v e d i n the c o n t r o l o f male s e x u a l b e h a v i o r ( G o r z a l k a & Mogenson, 1977; Quadagno e_t a l . , 1977), i t i s c o n c e i v a b l e t h a t d i f f e r e n c e s i n a c t i v i t y o f t h i s system -A mediate i s o l a t i o n / g r o u p i n g d i f f e r e n c e s i n s e x u a l performance. The p r e s e n t experiment was d e s i g n e d to t e s t whether l e v e l s of the major male gonadal s t e r o i d , t e s t o s t e r o n e , might i n f l u e n c e i s o l a t i o n / g r o u p i n g e f f e c t s . The d e s i g n i n v o l v e d comparison o f i s o l a t e d and grouped mice t h a t were i n t a c t and g i v e n o i l p l a c e b o i n j e c t i o n s w i t h o t h e r s c a s t r a t e d and g i v e n e i t h e r o f two doses of t e s t o s t e r o n e . I f i s o l a t e d and grouped mice d i f f e r when i n t a c t but do not when t h e i r t e s t o s t e r o n e l e v e l i s c o n t r o l l e d , gonadal a c t i v i t y 107 may be i n v o l v e d i n i s o l a t i o n / g r o u p i n g e f f e c t s . Method E x p e r i m e n t a l animals c o n s i s t e d o f 120 male CD-I mice, r e c e i v e d from Canadian B r e e d i n g Farms at 50-55 days of age. Animals were housed, m a i n t a i n e d , and t e s t e d under the c o n d i t i o n s d e s c r i b e d f o r Experiment IA. S t i m u l u s females were p r e p a r e d as d e s c r i b e d f o r Experiment IA. At 55-60 days o f age, 72 o f t h e mice were o r c h i d e c t o m i z e d under 2.5 mg. Nembutal (Sodium P e n t o b a r b i t a l , Abbott) a n a e s t h e s i a . These were r e t u r n e d to groups of 6. One week f o l l o w i n g t h i s s u r g e r y , b o t h i n t a c t and o p e r a t e d mice were housed 1, 6, or 12 per cage. Cages were i d e n t i c a l t o those d e s c r i b e d f o r Experiment IA. Commencing on the same day as d i f f e r e n t i a l h o u s i n g and d a i l y throughout the remainder of the experiment, s u b j e c t s were g i v e n sc i n j e c t i o n s . H a l f o f the o p e r a t e d a n i m a l s r e c e i v e d 25 yg t e s t o s t e r o n e p r o p i o n a t e i n .05 cc o i l , w h i l e the o t h e r h a l f r e c e i v e d 500 yg t e s t o s t e r o n e p r o p i o n a t e i n .05 cc o i l . A l l i n t a c t a n i m a l s r e c e i v e d the o i l v e h i c l e o n l y . The low dose of t e s t o s t e r o n e was chosen as a dose j u s t below the t h r e s h o l d l e v e l r e q u i r e d to m a i n t a i n f u l l s e x u a l b e h a v i o r , w h i l e the h i g h dose was w e l l above t h i s t h r e s h o l d (Champlin, B l i g h t , & M c G i l l , 1963). Two weeks a f t e r the i n t r o d u c t i o n of d i f f e r e n t i a l h o u s i n g and commencement o f i n j e c t i o n s , males were t e s t e d f o r 1 h r i n the p r e s e n c e of r e c e p t i v e females a c c o r d i n g to the p r o c e d u r e s of the p r e v i o u s e x p e r i -ments. T h i s t e s t i n g was r e p e a t e d one and two weeks f o l l o w i n g the f i r s t t e s t . An a n i m a l ' s i n j e c t i o n s were o m i t t e d on each day t h a t i t was t e s t e d to a v o i d p o s s i b l e e f f e c t s of r e c e n t i n j e c t i o n s t r e s s on performance. R e s u l t s F i g u r e 9 g i v e s the r e s u l t s f o r the measure of d u r a t i o n of mount-i n g . T a b l e X I I I g i v e s a l l r e m a i n i n g measures. I n t a c t , o i l - t r e a t e d i s o -108 F i g u r e 9: The mean t o t a l d u r a t i o n o f mounting, w i t h o r w i t h o u t i n t r o m i s s i o n , i n i n t a c t o i l - t r e a t e d and c a s t r a t e d t e s t o s t e r o n e - t r e a t e d m i c e i n Experiment 11. The open squares r e p r e s e n t i s o l a t e d mice, the open c i r c l e s - m i c e grouped i n 6, and t h e c l o s e d c i r c l e s mice grouped i n 12, • ' V e r t i c a l l i n e s i n d i c a t e s t a n d a r d e r r o r s , Table XIII Means and Standard Errors of Sexual Performance of Intact or Castrated Male Mice Treated With Oil or Testosterone Propionate in Experiment 11 Intact-Oil Castrate-25mg Testosterone Castrate-500mg Testosterone M p a Q I I T " n per Week cage: 1 6 12 1 6 12 1 6 L l C a o U L C Mounts 1 2 3 25.36±5.05 16.2413.61 24.8014.30 7.4213.65 13.6717.05 6.5013.25 9.6714.55 8.0013.83 8.00+3.34 5.2714.33 9.8213.56 14.2718.58 2.6711.99 9.00+3.60 15.1713.11 4.75+2.24 7.5812.49 9.3314.12 14.171 5.27 38.67110.42 46.58+10.32 16.081 6.42 38.42114.90 35.501 9.06 11.7013.53 11.7012.62 19.7014.67 Intromissions 1 2 3 8.96+2.09 9.36±2.54 9.16±1.72 2.0811.14 5.6714.22 2.33+0.92 4.17+1.85 7.00+2.98 6.0012.64 1.7311.73 1.27+1.01 3.7312.39 1.2511.01 4.5812.69 2.33+1.14 3.08+1.26 6.1711.97 2.6710.98 8.501 2.37 12.001 3.35 13.171 3.35 10.7514.67 13.3315.14 18.50+5.06 7.5011.72 13.9013.12 20.7015.28 Ejaculations 1 2 3 0.08+0.06 0.32±0.10 0.1610.07 0.08+0.08 0.0810.08 0.3310.14 0.1710.11 0.2510.13 0.1710.11 0.0010.00 0.0010.00 0.0910.09 0.0810.08 0.1710.11 0.0810.08 0.0010.00 0.1710.11 0.08+0.11 0.001 0.00 0.001 0.00 0.001 0.00 0.1710.11 0.0010.00 0.2510.18 0.2010.13 0.1010.10 0.4010.22 Mount Latency (sec) 1 2 3 11491198 15471265 12321242 26901315 2308+407 23871423 21391442 23831451 17711473 27731431 19091396 27261522 30981339 23731379 13761325 23241394 18181309 1663+361 1932+385 1711+400 10311361 19011448 14691400 9961362 13711268 12281378 4521200 Intromission Latency (sec) 1 2 3 2045+261 21591283 17791278 30491268 30251304 29601258 25011428 24051441 24721436 33111289 34061130 2949+275 31421310 27661374 28991343 26581358 24841336 26801368 23751344 2043+399 18251402 24701417 24391429 17421427 18971336 17621396 5501201 Ejaculation Latency (sec) 1 2 3 35171 66 32511142 34251 83 35181 82 3496+104 3177+229 35651 26 3465+ 89 34481152 36001 0 36001 0 35551 45 . 35091 91 35241 74 35481 52 3600+ 0 35001100 32921210 36001 0 36001 0 3600+ 0 3399H65 36001 0 33351187 35201 59 34091200 28981413 i i i l a t e s showed about t w i c e as much s e x u a l a c t i v i t y as d i d i n t a c t , o i l - t r e a t e d males grouped i n 6 o r 12. There were no e v i d e n t d i f f e r e n c e s between gonadectomized i s o l a t e d and grouped males t r e a t e d w i t h e i t h e r dose o f t e s t o s t e r o n e . Animals from a l l h o u s i n g c o n d i t i o n s showed low l e v e l s o f a c t i v i t y i n the 25 yg t e s t o s t e r o n e p r o p i o n a t e c o n d i t i o n . Animals from a l l h o u s i n g c o n d i t i o n s showed h i g h l e v e l s o f a c t i v i t y i n the 500 yg t e s t o s t e -rone p r o p i o n a t e c o n d i t i o n ; t h i s performance was comparable to t h a t o f the i s o l a t e d , i n t a c t , o i l t r e a t e d mice. A 3 (no. of a n i m a l s per cage) x 3 ( s u r g e r y and dose) x 3 (weekly t e s t ) a n a l y s i s o f v a r i a n c e was conducted f o r each measure, t r e a t i n g the l a s t f a c t o r as w i t h i n s u b j e c t s . D e s p i t e an apparent i n t e r a c t i o n between the number of animals p e r cage and s u r g e r y dose t r e a t m e n t s i n many of the measures, t h i s f a c t o r reached s i g n i f i c a n c e o n l y f o r the measure of mount l a t e n c y (F = 2.66, df_ = 4/108, p_ = .037). In the o t h e r measures the v a l u e s f o r t h i s i n t e r a c t i o n were as f o l l o w s : d u r a t i o n o f mounting (F = 1.02, df = 4/109, £ = .400), mounts (F = 1.18, df. = 4/109, p_ = .325), i n t r o m i s s i o n s (F = 1.09, d f = 4/109, p_ = .367), e j a c u l a t i o n s (F = .75, d f = 4/109, p_ = . 563), i n t r o m i s s i o n l a t e n c y (F_ = 1.89, df = 4/109, £ = .117), and e j a -c u l a t i o n l a t e n c y (F_ = 1.43, d_f = 4/109, p_ = .228). The s u r g e r y and dose f a c t o r was s i g n i f i c a n t f o r d u r a t i o n o f mounting (F = 8.69, df. = 2/109, £ <.001), mounts (F = 9.01, df = 2/109, £ <.001), i n t r o m i s s i o n s (F = 12.12, df = 2/109, £ <.001), mount l a t e n c y (F = 6.43, d_f = 2/109, £ = .002), and i n t r o m i s s i o n l a t e n c y (F = 7.61, d_f = 2/109, £ <.001). In a l l cases Newman Keu l s t e s t s (p <.05) i n d i c a t e d a s i g n i f i c a n t d i f f e r e n c e between the h i g h and low dose o f t e s t o s t e r o n e c o n d i t i o n s . There was a s i g n i f i c a n t main e f f e c t o f number of a n i m a l s per cage i n mounts (F_ = 4.19, df_ = 2/109, £ = .018); 112 Newman Ke u l s t e s t s (p <.05) i d e n t i f i e d a d i f f e r e n c e here between i s o l a t e d males and those grouped i n 12. There was a l s o a s i g n i f i c a n t e f f e c t o f weekly r e p e a t e d t e s t f o r most measures: d u r a t i o n o f mounting (F = 6.70, df = 2/218, £ = .002), mounts (F = 10.38, df = 2/218, £ <.001), i n t r o -m i s s i o n s (F = 9.13, df_ = 2/218, £ <.001) ^ mount l a t e n c y . (F_ = 12.74, df = 2/218, £ <.001), i n t r o m i s s i o n l a t e n c y (F = 8.18, c[f = 2/218, £ <.001), and e j a c u l a t i o n l a t e n c y (F = 5.58, df = 2/218, £ = .004). The s i m p l e main e f f e c t s o f number o f animals per cage were a l s o examined i n s e p a r a t e a n a l y s e s o f v a r i a n c e f o r each s u r g e r y and dose l e v e l . In the o i l - t r e a t e d i n t a c t males t h e r e was a s i g n i f i c a n t e f f e c t of number of a n i m a l s per cage i n mounts (F = 4.32, d_f = 2/46, £ = .019) and mount l a t e n c y (F = 4.67, d_f = 2/46, £ = .014); Newman K e u l s t e s t s (£ <.05) i n d i -c a t e d t h a t t h e se d i f f e r e n c e s were between the i s o l a t e d a n i m a l s on the one hand and the ani m a l s grouped i n 6 and 12 on the o t h e r . These same e f f e c t s approached s i g n i f i c a n c e i n t h e d u r a t i o n o f mounting (F = 2.38, d_f_ = 2/46, £ = .104) and i n t r o m i s s i o n l a t e n c y (F_ = 3.03, df_ = 2/46, £ = .058) measures. D i s c u s s i o n There i s an apparent t r e n d i n t h e s e d a t a i n d i c a t i n g t h a t c o n t r o l l -i n g the l e v e l o f t e s t o s t e r o n e e l i m i n a t e s i s o l a t i o n / g r o u p i n g d i f f e r e n c e s . T h i s i s suggested p a r t i c u l a r l y by the h i g h l e v e l o f performance o f group-housed c a s t r a t e d males g i v e n the h i g h dose o f t e s t o s t e r o n e . I t i s f u r t h e r -more suggested by the p r e s e n c e o f major i s o l a t i o n / g r o u p i n g d i f f e r e n c e s o n l y i n i n t a c t , o i l t r e a t e d a n i m a l s . However, t h i s t r e n d r e c e i v e s s t r o n g s t a t i s t i c a l s upport o n l y i n the mount l a t e n c y measure, where a_l s i g n i f i c a n t i n t e r a c t i o n o b t a i n e d between the number o f ani m a l s per cage and the s u r g e r y / d o s e f a c t o r s . The e x i s t e n c e of t h e apparent .trend i s n o t - s t r o n g l y s u p p o r t e d i n . * 113 the s t a t i s t i c a l a n a l y s e s of a l l of the o t h e r measures. The absence of a s i g n i f i c a n t i n t e r a c t i o n i n these measures does not n e c e s s a r i l y demonstrate a l a c k of involvement o f t e s t o s t e r o n e i n the i s o l a t i o n / g r o u p i n g e f f e c t s u s u a l l y found w i t h these measures. R a t h e r , t h e r e may have been i n s u f f i -c i e n t s t a t i s t i c a l power to make the apparent t r e n d r e a c h s i g n i f i c a n c e i n a l l measures. There i s a l a r g e amount o f v a r i a n c e i n the s c o r e s w i t h i n each treatment c o m b i n a t i o n , which weakens s t a t i s t i c a l power d e s p i t e f a i r l y l a r g e d i f f e r e n c e s among the means. Thus, f u r t h e r r e s e a r c h i s r e q u i r e d to e s t a b l i s h f i r m l y whether t e s t o s t e r o n e l e v e l d i f f e r e n c e s r e l a t e to i s o l a -t i o n / g r o u p i n g d i f f e r e n c e s , but these d a t a suggest such a r e l a t i o n s h i p . The f i n d i n g t h a t exogenous t e s t o s t e r o n e m a i n t a i n s h i g h l e v e l s of 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 males i s c o n s i s t e n t w i t h the f i n d i n g s of numerous o t h e r s t u d i e s (see G o r z a l k a & Mogenson, 1977). However, the i n d i -c a t i o n s t h a t t e s t o s t e r o n e might i n c r e a s e the performance o f animals t h a t a r e s e x u a l l y s l u g g i s h , i n t h i s case the grouped males, are n o v e l . In o t h e r s t u d i e s , t e s t o s t e r o n e t r e a t m e n t has not a p p r e c i a b l y r a i s e d the p e r -formance of i n t a c t males. In one experiment, Grunt and Young (1953) d i v i d e d male g u i n e a p i g s i n t o " h i g h " , "medium", and "low" s e x u a l b e h a v i o r groups on the b a s i s of i n i t i a l t e s t s . Animals from a l l o f the groups were then c a s t r a t e d , e l i m i n a t i n g the group d i f f e r e n c e s and g r e a t l y r e d u c i n g . s e x u a l b e h a v i o r . However, when a n i m a l s were a l l a d m i n i s t e r e d e q u a l amounts of t e s t o s t e r o n e , the group d i f f e r e n c e s r e t u r n e d . S t u d i e s of male s e x u a l b e h a v i o r i n r a t s ( L a r s s o n , 1966; Whalen, Beach, & Kuehn, 1961) have s i m i -l a r l y found t h a t p r e o p e r a t i v e d i f f e r e n c e s between " c o p u l a t o r s " and "non-c o p u l a t o r s a r e m a i n t a i n e d a f t e r c a s t r a t i o n and a d m i n i s t r a t i o n of exogenous t e s t o s t e r o n e . These o t h e r s t u d i e s suggest t h a t d i f f e r e n c e s i n plasma t e s t o -s t e r o n e l e v e l s do not c o n t r i b u t e to i n t e r ^ i n d i v i d u a l v a r i a n c e i n s e x u a l 114 a c t i v i t y i n these s p e c i e s . B a t t y (1978a; 1978b) has r e c e n t l y examined endogenous plasma t e s t o s t e r o n e l e v e l s i n house mice d i s p l a y i n g d i f f e r e n t amounts of s e x u a l b e h a v i o r . She a c t u a l l y o b t a i n e d a n e g a t i v e c o r r e l a t i o n between measures of s e x u a l a c t i v i t y and plasma t e s t o s t e r o n e i n a comparison of d i f f e r e n t g e n e t i c s t r a i n s o f the s p e c i e s . W i t h i n each of the s t r a i n s t h e r e was a wide v a r i a t i o n i n plasma t e s t o s t e r o n e among i n d i v i d u a l s , and t h e s e l e v e l s were not r e l a t e d t o any measures o f s e x u a l b e h a v i o r . However, when she examined acu t e changes i n plasma t e s t o s t e r o n e i n a s e x u a l c o n t e x t , t h e r e was a p o s i t i v e r e l a t i o n s h i p t o b e h a v i o r . Plasma t e s t o s t e r o n e l e v e l s were h i g h e r i n c o p u l a t o r s than n o n - c o p u l a t o r s when b l o o d samples were removed imme d i a t e l y a f t e r a t e s t . B l o o d samples removed at p a r t i c u l a r s t a g e s of s e x u a l b e h a v i o r suggested t h a t t e s t o s t e r o n e l e v e l s were g r e a t e s t a t the i n i t i a t i o n o f mounting r e s p o n s e s and d e c l i n e d d u r i n g c o p u l a t i o n . These f i n d i n g s a r e c o n s i s t e n t w i t h o t h e r f i n d i n g s i n the l i t e r a t u r e (e.g. M a c r i d e s , B a r t k e , & D a l t e r i o , 1975; P u r v i s & Haynes, 1974) t h a t exposure to s e x u a l s t i m u l i produces an a c u t e i n c r e a s e i n t e s t o s t e r o n e . T h i s a c u t e i n c r e a s e i s c o r r e l a t e d w i t h the o n s e t of s e x u a l a c t i v i t y , but does not prove a c a u s a l r e l a t i o n s h i p between t e s t o s t e r o n e i n c r e a s e s and commence-ment of s e x u a l b e h a v i o r . I t i s a l s o i m p o r t a n t to note t h a t changes i n t e s t o s t e r o n e a r e the p r o d u c t of a sequence of n e u r o e n d o c r i n e e v e n t s , and t h a t any of the p r e c e d i n g l i n k s may be i n v o l v e d i n the c o n t r o l of s e x u a l b e h a v i o r . Thus a c o r r e l a t i o n o f s e x u a l a c t i v i t y w i t h t e s t o s t e r o n e i m p l i e s a c o r r e l a t i o n w i t h p i t u i t a r y g o n a d o t r o p i n s , such as l u t e i n i z i n g hormone, and h y p o t h a l a m i c r e l e a s i n g f a c t o r s , such as l u t e i n i z i n g hormone r e l e a s i n g hormone. 115 The e v i d e n c e from o t h e r s t u d i e s , then, s u g g e s t s t h a t s u s t a i n e d d i f f e r e n c e s i n t e s t o s t e r o n e t i t e r do not produce d i f f e r e n c e s i n s e x u a l performance. However, a major r e d u c t i o n i n t e s t o s t e r o n e l e v e l and o t h e r p i t u i t a r y - g o n a d a l a c t i v i t y i n a d u l t h o o d , f o r example through c a s t r a t i o n or treatment w i t h a n t i a n d r o g e n s , does reduce or e l i m i n a t e male s e x u a l a c t i v i t y ( G o r z a l k a & Mogenson, 1977). I t might be c o n c l u d e d , then, t h a t v a r i a t i o n i n t e s t o s t e r o n e above a c e r t a i n m inimal t h r e s h o l d l e v e l does not a f f e c t male s e x u a l performance. N e v e r t h e l e s s , t e s t o s t e r o n e l e v e l s may be i n v o l v e d i n i s o l a t i o n / g r o u p i n g d i f f e r e n c e s i n s e x u a l a c t i v i t y . A l a c k o f c o r r e l a t i o n between t e s t o s t e r o n e l e v e l s and n a t u r a l v a r i a t i o n i n s e x u a l a c t i v i t y among an i m a l s housed i n u n i f o r m environments would not n e c e s s a r i l y e x c l u d e an i n v o l v e -ment o f t e s t o s t e r o n e i n e n v i r o n m e n t a l l y - i n d u c e d s e x u a l d e f i c i t s . V a r i -a b i l i t y among an i m a l s housed i n u n i f o r m environments (as i n B a t t y , 1978a; 1978b; Grunt & Young, 1953; L a r s s o n , 1966; Whalen e £ a l . , 1961) may r e l a t e to such f a c t o r s as g e n e t i c d i f f e r e n c e s and be independent of p i t u i t a r y -gonadal a c t i v i t y . E n v i r o n m e n t a l v a r i a b i l i t y , however, might i n d u c e v a r i a b i l i t y i n gonadal a c t i v i t y and c o n s e q u e n t l y i n s e x u a l a c t i v i t y . S t r e s s f u l environments may s u p p r e s s gonadal a c t i v i t y (Rose, 1969; Rose, Bourne, Poe, Mougey, C o l l i n s , & Mason, 1969) as may group h o u s i n g i n mice (Benton e t a l . , 1978; B r a i n , 1971; B r a i n & N o w e l l , 1971; C h r i s t i a n , 1955; Vandenbergh, 1960). I f gonadal a c t i v i t y i s s u p p r e s s e d to below the t h r e s -h o l d l e v e l n e c e s s a r y to m a i n t a i n normal s e x u a l a c t i v i t y , g r o u p i n g may reduce s e x u a l performance v i a e f f e c t s on the p i t u i t a r y - g o n a d a l system. I f treatment w i t h exogenous t e s t o s t e r o n e e n t i r e l y e l i m i n a t e s d e f i c i t s i n s e x u a l a c t i v i t y i n d u c e d by group-housing, t h i s does not n e c e s -s a r i l y i m p l i c a t e t e s t o s t e r o n e l e v e l d i f f e r e n c e s as the e x c l u s i v e m e d i a t o r s 116 of i s o l a t i o n / g r o u p i n g s e x u a l a c t i v i t y d i f f e r e n c e s . I t remains p o s s i b l e t h a t h i g h doses of exogenous t e s t o s t e r o n e a l t e r the a c t i v i t y o f o t h e r hormonal and n e u r o c h e m i c a l systems t h a t more d i r e c t l y mediate t h e s e e f f e c t s , F o r example, K i t a y (1968) has found t h a t exogenous t e s t o s t e r o n e may a l t e r p i t u i t a r y - a d r e n a l a c t i v i t y . T h i s c o n s i d e r a t i o n n o t w i t h s t a n d i n g , such r e s u l t s would suggest t h a t t e s t o s t e r o n e l e v e l i s a t l e a s t one of s e v e r a l v a r i a b l e s i n f l u e n c i n g i s o l a t i o n / g r o u p i n g e f f e c t s . 117 OVERALL DISCUSSION AND CONCLUSIONS The Nature of I s o l a t i o n E f f e c t s on Sexual B e h a v i o r The p r e s e n t r e s e a r c h has demonstrated t h a t p o s t p u b e r t a l l y i s o l a t e d male mice show h i g h e r l e v e l s o f s e x u a l a c t i v i t y than do c o n s p e c i f i c males housed i n groups. T h i s f a c i l i t a t i o n o f s e x u a l a c t i v i t y by i s o l a t i o n o c c u r s when a n i m a l s a r e s e x u a l l y n a i v e or e x p e r i e n c e d and i s not s u b s t a n t i a l l y d i m i n i s h e d by r e p e a t e d weekly measurement of a n i m a l s . I t o c c u r s e q u a l l y a f t e r b r i e f (24 h r ) and l o n g (4 week) p e r i o d s of s o c i a l i s o l a t i o n . P e r f o r -mance o f grouped and i s o l a t e d mice r e v e r s e s when t h e i r h o u s i n g c o n d i t i o n s a r e r e v e r s e d . The phenomenon r e l a t e s s p e c i f i c a l l y t o i s o l a t i o n v e r s u s group-housing r a t h e r than to d i f f e r e n c e s i n volume o f space per a n i m a l . There i s some i n d i c a t i o n t h a t performance of males housed i n l a r g e r groups i s p o o r e r than t h a t o f males i n s m a l l e r groups (Experiments 2, 3, & 6 ) , but t h i s e f f e c t d i d not always o c c u r (see Experiment 1A) and i n no case reached s t a t i s t i c a l s i g n i f i c a n c e . The e f f e c t was demonstrated i n a l l i n b r e d g e n e t i c s t r a i n s o f mice t h a t were measured, i n c l u d i n g CD-I (Experiments 1 , 2 , 3, 6, 7, 8, 9, 10, & 11) and C57/B1, DBA2, and Swiss-Webster (Experiment 4) mice. By c o n t r a s t , the e f f e c t was absent i n male r a t s , hamsters, and g e r b i l s . Indeed, i n r a t s and g e r b i l s an o p p o s i t e e f f e c t o c c u r r e d ; males of t h e s e s p e c i e s showed more 118 s e x u a l a c t i v i t y when group-housed. T h i s s p e c i e s d i f f e r e n c e may r e l a t e to d i f f e r e n c e s i n s o c i a l dynamics and p h y s i o l o g i c a l r e s p o n s e to s o c i a l i s o l a t i o n (see S e c t i o n I I , G e n e r a l D i s c u s s i o n ) . Decrements i n s e x u a l a c t i v i t y i n r a t s i n d u c e d by p o s t p u b e r t a l s o c i a l i s o l a t i o n may p a r a l l e l decrements i n t h i s s p e c i e s i n d u c e d by p r e p u b e r t a l i s o l a t i o n ( c f . Folman & D r o r i , 1965; G e r a l l e t a l . , 1967; G r u endel & A r n o l d , 1974). F a c i l i t a t i o n of s e x u a l a c t i v i t y by s o c i a l i s o l a t i o n i n mice was u s u a l l y r e f l e c t e d i n s e v e r a l measures, i n c l u d i n g the d u r a t i o n o f mounting, number o f mounts, number of i n t r o m i s s i o n s , l a t e n c y to mount, and l a t e n c y to i n t r o m i t . The r e s u l t s f o r number of e j a c u l a t i o n s and l a t e n c y to e j a -c u l a t e a r e not c l e a r . In s e v e r a l cases where i n t a c t i s o l a t e d and grouped mice were compared f o r number of e j a c u l a t i o n s , t h e r e was a t r e n d toward more such r e s p o n s e s i n the i s o l a t e s ( E x p e r i m e n t s a t 2 and 4 weeks, E x p e r i -ments 4, 6, & 9A). However, i n none of these cases d i d such a t r e n d 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 . In some of the o t h e r experiments (3, 7, & 11) t h e r e was no apparent t r e n d , w h i l e i n Experiment 9B t h e r e was a t r e n d t o -ward more e j a c u l a t i o n s i n the grouped males. Comparisons on measures o f e j a c u l a t i o n g e n e r a l l y d i d not 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 because of the i n f r e q u e n c y o f such r e s p o n s e s and the l a r g e number of a n i m a l s i n a l l t reatment c o n d i t i o n s t h a t f a i l e d t o e j a c u l a t e . T h i s o c c u r r e d d e s p i t e s e v e r a l r e p e a t e d measures of performance taken i n some of the experiments (9 & 11) and l a r g e numbers o f grouped and i s o l a t e d a nimals compared i n o t h e r s (2, 3, 4, 6, & 7). In o t h e r e x p e r i m e n t a t i o n i n our l a b o r a t o r y , i t has been found t h a t even when 3-hour t e s t s of b e h a v i o r a r e employed, the number of e j a c u l a t i o n s remains s m a l l . Thus, e j a c u l a t i o n measures may not have shown s i g n i f i c a n t t r e n d s i n the same d i r e c t i o n as o t h e r measures because of a l a c k of s t a t i s t i c a l power. 119 The s i t u a t i o n w i t h e j a c u l a t i o n s may be c o m p l i c a t e d f u r t h e r by o t h e r f a c t o r s . F o r example, Experiment 8 i n d i c a t e s t h a t i n t e r m a l e mounting may c o r r e l a t e w i t h subsequent e j a c u l a t i o n f r e q u e n c y w i t h s t i m u l u s f emales. I t i s c o n c e i v a b l e t h a t I n t e r m a l e mounting may'reduce the l a t e n c y to e j a c u -l a t e f o r some grouped a n i m a l s but not a f f e c t o t h e r measures. The t h r e s -h o l d to e j a c u l a t e c o u l d be lowered i n t h e se few a n i m a l s , w i t h mounting of males a c t i n g i n the same manner as mounting of females as a p r e c u r s o r o f an e j a c u l a t i o n i n the c o p u l a t o r y sequence. Furthermore, G o r z a l k a e t a l . , (1975) have noted t h a t t r e a t m e n t s a f f e c t i n g e j a c u l a t i o n s do not n e c e s s a r i l y i n f l u e n c e mounts and i n t r o m i s s i o n s , s u g g e s t i n g d i f f e r e n t i a l p h y s i o l o g i c a l c o n t r o l o f t h e s e response c l a s s e s . I t remains p o s s i b l e t h a t e j a c u l a t i o n s do not d i f f e r i n the comparisons of the p r e s e n t study because the v a r i a b l e s m e d i a t i n g d i f f e r e n t r e sponse c l a s s e s a r e d i f f e r e n t i a l l y a f f e c t e d by i s o l a -t i o n and g r o u p i n g . In most of the e x p e r i m e n t s , s o c i a l l y i s o l a t e d mice showed an a v e r -age o f two o r t h r e e times as many mounts and i n t r o m i s s i o n s as d i d group-housed mice. N e v e r t h e l e s s , t h e r e was a l a r g e amount o f v a r i a n c e i n p e r f o r -mance w i t h i n each c o n d i t i o n . A few i s o l a t e s showed l i t t l e or no s e x u a l a c t i v i t y , w h i l e some grouped males showed v e r y h i g h l e v e l s of such a c t i v i t y . D e s p i t e the r e l i a b i l i t y and magnitude of the i s o l a t i o n / g r o u p i n g d i f f e r e n c e s , t h i s v a r i a n c e reduced s t a t i s t i c a l power. Thus i t i s i n the experiments where f a c t o r i a l d e s i g n s p o o l i n g l a r g e numbers of s u b j e c t s (e.g. Experiments 2, 3, 4, & 6) and experiments employing r e p e a t e d measures (e.g. Experiments 1 & 9) t h a t s t a t i s t i c a l s i g n i f i c a n c e was g r e a t e s t . T h i s v a r i a n c e a l s o sub-s t a n t i a l l y reduced the a b i l i t y o f f a c t o r i a l d e s i g n s to demonstrate s i g n i -f i c a n t i n t e r a c t i o n s . F o r example, the means i n many measures of Experiments 3 and 11 would appear to i n d i c a t e the p r e s e n c e of i n t e r a c t i o n s , y e t t h e se d i d 120 not 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 . U n f o r t u n a t e l y , t h i s v a r i a n c e imposes l i m i t a t i o n s on the types o f e x p e r i m e n t a l q u e s t i o n s t h a t can be asked about t h i s phenomenon, i n t h a t s t a t i s t i c a l power f o r some d e s i g n s may not be adequate w i t h o u t the use of v e r y l a r g e numbers of s u b j e c t s . The measuring system f o r the s e x u a l b e h a v i o r o f mice employed here d i f f e r s somewhat from t h a t employed elsewhere. In some o t h e r s t u d i e s (e.g. M c G i l l , 1965; M o s i g & Dewsbury, 1976) m u l t i p l e c r i t e r i a f o r commence-ment and t e r m i n a t i o n of b e h a v i o r a l o b s e r v a t i o n have been employed. F o r example, an a n i m a l may be e x c l u d e d from study i f i t has not mounted w i t h -i n 20 minutes o f commencement of o b s e r v a t i o n . A l s o , measurement of a n i m a l s i s o f t e n t e r m i n a t e d i n these o t h e r s t u d i e s d i f f e r e n t l y dependent on the p a r t i c u l a r a n i m a l ' s performance; f o r example, when an a n i m a l e j a c u l a t e s he may no l o n g e r be t e s t e d , w h i l e n o n - e j a c u l a t i n g a n i m a l s may be measured f o r a f i x e d p e r i o d o f time. In the p r e s e n t s t u d y , a l l animals were t e s t e d , r e g a r d l e s s o f t h e i r performance, i n f i x e d 1-hr s e s s i o n s . The p r e s e n t p r o -cedure has the advantages of t r e a t i n g a l l animals i n an e q u i v a l e n t manner and a l l o w i n g the g e n e r a l i z a t i o n o f f i n d i n g s . t o the e n t i r e p o p u l a t i o n from which a n i m a l s a r e sampled. Moreover, the p r e s e n t r e s u l t s might not be o b t a i n a b l e u s i n g a p r o c e d u r e t h a t e l i m i n a t e s low s c o r i n g a n i m a l s from t e s t i n g . Indeed, such a p r o c e d u r e would p r o b a b l y e l i m i n a t e more grouped than i s o l a t e d a n i m a l s from t e s t i n g and thus tend to equate the two c o n d i -t i o n s . P a r t of the purpose of the p r e s e n t study was to i d e n t i f y causes of v a r i a b i l i t y i n s e x u a l performance; the e l i m i n a t i o n o f p o o r l y p e r f o r m i n g a n i m a l s would d e f e a t t h i s purpose. The M e d i a t i o n of I s o l a t i o n E f f e c t s There a r e some i n d i c a t i o n s i n the p r e s e n t d a t a of p o s s i b l e media-t o r s o f i s o l a t i o n / g r o u p i n g d i f f e r e n c e s i n s e x u a l performance. These i n d i -121 c a t i o n s , t aken w i t h d a t a from e x p e r i m e n t a t i o n performed i n o t h e r l a b o r a -t o r i e s , p r e s e n t a f a i r l y c o n s i s t e n t p i c t u r e but c l e a r l y suggest a need f o r f u t u r e r e s e a r c h . The m e d i a t i o n of t h i s phenomenon appears to occur on two l e v e l s . F i r s t , d i f f e r e n c e s i n b e h a v i o r a l e x p e r i e n c e between grouped and i s o l a t e d mice may produce d i f f e r e n c e s i n p h y s i o l o g y and r e -a c t i v i t y t o n o v e l s t i m u l i . Second, p h y s i o l o g i c a l d i f f e r e n c e s and d i f f e -r e n c e s i n r e a c t i v i t y may produce d i f f e r e n t l e v e l s o f s e x u a l a c t i v i t y . Grouped male mice a r e exposed to a v a r i e t y o f s t i m u l i t h a t a r e absent from the environments of s o c i a l l y i s o l a t e d mice. Grouped mice must compete f o r space and o t h e r r e s o u r c e s ; t h i s c o m p e t i t i o n i s o f t e n e v i d e n t i n h i g h l e v e l s o f i n t e r m a l e a g g r e s s i o n . Grouped mice w i l l a l s o o c c a s i o n a l l y engage i n i n t e r m a l e mounting and thus may have d i f f e r e n t s e x u a l e x p e r i e n c e than i s o l a t e s . Furthermore, grouped mice a r e c o n s t a n t l y exposed to a v a r i e t y o f t a c t i l e , v i s u a l , a u d i t o r y , and o l f a c t o r y s t i m u l i r e l a t e d t o the p r e s e n c e o f male c o n s p e c i f i c s . I s o l a t e d mice, by c o n t r a s t , l e a d r a t h e r s e d a t e l i v e s . Experiment 8 i n d i c a t e s t h a t one form of s o c i a l i n t e r a c t i o n among male mice, i n t e r m a l e mounting, i s p r o b a b l y not i n v o l v e d i n i s o l a t i o n / g r o u p -i n g d i f f e r e n c e s i n mount and i n t r o m i s s i o n f r e q u e n c y and l a t e n c y . I n t e r -male mounting d i d not o c c u r w i t h s u f f i c i e n t f r e q u e n c y to account f o r the r e l a t i v e d e f i c i t s i n s e x u a l a c t i v i t y i n grouped males t h a t can develop w i t h i n 24 hours o f d i f f e r e n t i a l h o u s i n g . However, as mentioned above, i n t e r m a l e mounting may a f f e c t e j a c u l a t i o n l a t e n c y and f r e q u e n c y . The s t u d i e s of S e c t i o n I I I a l s o suggest t h a t odors of males may a c t as pheromones, a f f e c t i n g the b e h a v i o r of o t h e r males. I t i s c o n c e i v -a b l e t h a t such odors a c t to suppress male s e x u a l a c t i v i t y i n grouped males. A c c o r d i n g l y , i s o l a t e s may show h i g h e r performance l e v e l s because they a r e 122 not exposed to such odors. S i m i l a r l y , the c a g e - c l e a n i n g m a n i p u l a t i o n of Experiment 7 may have i n c r e a s e d the s e x u a l a c t i v i t y o f grouped males because i t removed these o d o r s . One f i n d i n g t h a t i s i n c o n s i s t e n t w i t h t h i s n o t i o n i s t h a t i s o l a t e s d i d not show f a c i l i t a t e d performance a f t e r i n t e r v a l s as s h o r t as those n e c e s s a r y f o r the c a g e - c l e a n i n g phenomenon i n grouped males. Perhaps the s t r o n g e s t argument can be made f o r an involvement of i n t e r m a l e a g g r e s s i o n . In Experiment 8, a g g r e s s i o n i n grouped males o c c u r r e d w i t h a s u f f i c i e n t l y h i g h f r e q u e n c y to account f o r r e l a t i v e s e x u a l d e f i c i t s d e v e l o p i n g i n t h e s e a n i m a l s w i t h i n 24 hours o f d i f f e r e n t i a l hous-i n g . F u r t h e r s u p p o r t comes from the study by Kahn (1961), w h e r e i n mice s u b j e c t e d t o d e f e a t i n a g g r e s s i v e e n c o u n t e r s showed poor s e x u a l p e r f o r -mance. T h i s r e i n f o r c e s the n o t i o n t h a t i n t e r m a l e a g g r e s s i o n mediates i s o l a t i o n / g r o u p i n g d i f f e r e n c e s i n s e x u a l performance because many grouped males must be r e g u l a r l y s u b j e c t e d to d e f e a t . Data from s e v e r a l o t h e r s t u d i e s suggest how i n t e r m a l e f i g h t i n g among grouped males c o u l d produce p h y s i o l o g i c a l c o n d i t i o n s c o n d u c i v e to poor s e x u a l performance. I n t e r m a l e a g g r e s s i v e e n c o u n t e r s can produce f a i r l y r a p i d p i t u i t a r y - a d r e n o c o r t i c a l a c t i v a t i o n ( B r a i n & Nowell, 1970; Bronson & E l e f t h e r i o u , 1965), changes i n h y p o t h a l a m i c l e v e l s o f l u t e i n i z i n g hormone ( E l e f t h e r i o u & Church, 1967; 1968), and changes i n u t i l i z a t i o n r a t e s o f n o r e p i n e p h r i n e , dopamine, and s e r o t o n i n ( G a r a t t i n i e t a l . , 1969; Welch & Welch, 1969a; 1969b). These p h y s i o l o g i c a l changes o c c u r s u f f i c i e n t l y soon a f t e r a g g r e s s i o n , and may be r e v e r s e d s u f f i c i e n t l y r a p i d l y a f t e r s o c i a l i s o l a t i o n , to account f o r the development of i s o l a t i o n / g r o u p i n g d i f f e r e n c e s w i t h i n 24 hours of d i f f e r e n -t i a l h o u s i n g . The p o s s i b l e i n volvement of t h e s e p h y s i o l o g i c a l f a c t o r s i n the c o n t r o l o f s e x u a l performance w i l l be d i s c u s s e d below. 123 Experiments 9A and 11 i n d i c a t e t h a t b o t h a d r e n a l and t e s t i c u l a r hormones may be i n v o l v e d i n i s o l a t i o n / g r o u p i n g d i f f e r e n c e s i n s e x u a l a c t i v i t y . U n f o r t u n a t e l y , t h e se experiments do not s p e c i f y the n a t u r e o f such i n v o l v e m e n t . S e v e r a l p o s s i b i l i t i e s remain open, p a r t i c u l a r l y i n view o f the f a c t t h a t v a r i o u s hormonal and n e u r o c h e m i c a l systems i n t e r -a c t i n complex manners. A l s o , e f f e c t s o f the m a n i p u l a t i o n s o f t h e s e e x p e r i -ments, g l a n d u l a r e x t r a c t i o n s and a d m i n i s t r a t i o n o f exogenous hormones, may be d i f f u s e and i n d i r e c t . A c c o r d i n g l y , e f f e c t s o f the t e c h n i q u e s may not always i m p l i c a t e the a f f e c t e d hormonal system i n the n a t u r a l phenomena under i n v e s t i g a t i o n . F o r example, i t i s d i f f i c u l t to r u l e out e n t i r e l y the p o s s i b i l i t y t h a t observed e f f e c t s o f adrenalectomy (see Experiment 9) a r e due to some n o n - s p e c i f i c e f f e c t o f t h i s m a n i p u l a t i o n . However, the r e s u l t s o f Experiment 9A, i n d i c a t i n g t h a t a d r e n a l e c -tomy r e v e r s e s i s o l a t i o n / g r o u p i n g d i f f e r e n c e s , do suggest an involvement o f the p i t u i t a ' r y - a d r e n a l system. M e d i a t i o n o f i s o l a t i o n / g r o u p i n g s e x u a l a c t i -v i t y d i f f e r e n c e s by t h i s system i s a l s o p l a u s i b l e because p r o l o n g e d i s o l a -t i o n a l t e r s a d r e n a l weight (Benton e_t al_. , 1978; B r a i n & N o w e l l , 1971; Bronson, 1967), i n t e r m a l e a g g r e s s i o n a l t e r s p i t u i t a r y - a d r e n a l a c t i v i t y ( B r a i n & N o w e l l , 1970; Bronson & E l e f t h e r i o u , 1965), and t h i s system i s i n v o l v e d i n i s o l a t i o n - i n d u c e d a g g r e s s i o n (Leshner e_t a l . , 1973). E x p e r i -ment 9B s u g g e s t s t h a t d i f f e r e n c e s i n s u s t a i n e d l e v e l s o f c o r t i c o s t e r o n e , the p r i n c i p a l a d r e n a l s t e r o i d i n t h i s s p e c i e s , a r e not r e s p o n s i b l e f o r the e f f e c t s o f adrenalectomy. T h i s does not e l i m i n a t e the p o s s i b i l i t y t h a t a c u t e changes i n c o r t i c o s t e r o n e l e v e l s d u r i n g s e x u a l a c t i v i t y might be i n v o l v e d , s i n c e t h e se would remain absent i n a d r e n a l e c t o m i z e d a n i m a l s g i v e n c h r o n i c c o r t i c o s t e r o n e . Other a d r e n a l s t e r o i d s might a l s o be i n v o l v e d . 124 Experiment 10 sugges t s t h a t ACTH does not mediate i s o l a t i o n / g r o u p i n g d i f f e r e n c e s i n s e x u a l a c t i v i t y , a l t h o u g h such an i n t e r p r e t a t i o n o f t h i s experiment must be q u a l i f i e d . ACTH p r e p a r a t i o n s tend t o v a r y i n b i o l o g i c a l e f f e c t i v e n e s s ( B r a i n & P o o l e , 1974), and the p a r t i c u l a r p r e p a r a t i o n employed i n Experiment 10 may not have been adequate to t e s t the h y p o t h e s i s under stu d y . Moreover, t h e r e i s some q u e s t i o n as to whether p e r i p h e r a l l y - i n t r o -duced ACTH re a c h e s a l l o f the t a r g e t t i s s u e s o f t h i s hormone (see Dunn & Gi s p e n , 1977); thus the ACTH a d m i n i s t e r e d i n Experiment 10 may not have mimicked a l l of the e f f e c t s o f endogenous ACTH. There i s not much o t h e r e v i d e n c e i n the l i t e r a t u r e of d i r e c t e f f e c t s o f p i t u i t a r y - a d r e n a l m a n i p u l a t i o n s on s e x u a l a c t i v i t y (see S e c t i o n IV, G e n e r a l D i s c u s s i o n ) , F o r example, o t h e r s t u d i e s ( B i o c h & Davidson, 1968; G o r z a l k a et^ al_. , 1975) r e p o r t no e f f e c t o f adrenalectomy on male s e x u a l b e h a v i o r . Such e f f e c t s may o n l y be p r e s e n t when an i m a l s a r e housed i n c e r t a i n l i m i t e d e n v i r o n m e n t a l c o n d i t i o n s and show p a r t i c u l a r l e v e l s o f p i t u i t a r y - a d r e n a l a c t i v a t i o n . I t may thus be n e c e s s a r y to measure an i m a l s housed i n a v a r i e t y o f environments, as i n Experiment 9, to observe e f f e c t s of a d r e n a l m a n i p u l a t i o n s on s e x u a l b e h a v i o r . One p i t u i t a r y - a d r e n a l e f f e c t t h a t i s r e l a t i v e l y w e l l documented i s t h a t ACTH c a n n u l a t e d i n t o the v e n t r i c u l a r system of the b r a i n may s t i -mulate male s e x u a l a c t i v i t y ( B e r t o l i n i e t a l . , 1975). I t i s c o n c e i v a b l e t h a t t h i s e f f e c t c o u l d h e l p to e x p l a i n i s o l a t i o n / g r o u p i n g d i f f e r e n c e s i n s e x u a l a c t i v i t y . A l t h o u g h t h e r e a r e i n d i c a t i o n s t h a t i s o l a t e s show lower b a s e l i n e p i t u i t a r y - a d r e n a l a c t i v i t y than do grouped males, as e v i d e n c e d e s p e c i a l l y by t h e i r lower a d r e n a l w e i g h t s (Benton e t a l . , 1978; B r a i n & Now e l l , 1971), they may show a g r e a t e r p i t u i t a r y - a d r e n a l r e sponse to n o v e l and s t r e s s f u l s t i m u l a t i o n (see B r a i n , 1975; G o l d s m i t h e t a l . , 1976). 125 P r e s e n t a t i o n of s t i m u l u s females would p r o b a b l y c o n s t i t u t e a n o v e l s i t u a -t i o n and may a c c o r d i n g l y s t i m u l a t e g r e a t e r r e l e a s e of endogenous ACTH i n i s o l a t e s , p r o d u c i n g h i g h e r l e v e l o f s e x u a l a c t i v i t y i n t h e s e a n i m a l s . One o t h e r s t r o n g p o s s i b i l i t y i s t h a t the e f f e c t s o f a d r e n a l e c -tomy on d i f f e r e n t i a l s e x u a l performance are i n d i r e c t . L e v e l s of p i t u i t a r y -a d r e n a l a c t i v i t y a f f e c t b o t h the p i t u i t a r y - g o n a d a l ( B u l l o c k & New* 1971; D e s j a r d i n s & Ewing, 1971) and c e n t r a l c a t e c h o l a m i n e r g i c (Dunn & G i s p e n , 1977) systems; t h e s e systems a r e known t o have f a i r l y d i r e c t i n f l u e n c e s on male s e x u a l a c t i v i t y (Gessa & T a g l i a m o n t e , 1975; G o r z a l k a & Mogenson, 1977). The r e s u l t s o f Experiment 11 suggest, but do not demonstrate, an i n v o l v e m e n t of t e s t o s t e r o n e l e v e l s i n i s o l a t i o n / g r o u p i n g s e x u a l a c t i v i t y d i f f e r e n c e s . Other s u p p o r t f o r the n o t i o n t h a t t e s t o s t e r o n e may mediate these d i f f e r e n c e s comes from experiments i n d i c a t i n g t h a t t e s t i c u l a r a c t i v i t y i s g r e a t e r i n i s o l a t e d than i n grouped mice (Benton e t a l . , 1978; B r a i n , 1971; C h r i s t i a n , 1955; Vandenbergh, 1960). However, the mechanism of such p o s s i b l e m e d i a t i o n i s u n c l e a r . There i s l i t t l e e v i d e n c e t h a t t e s t o s t e r o n e l e v e l s , above a c e r t a i n t h r e s h o l d l e v e l , a r e c o r r e l a t e d w i t h d i f f e r e n c e s i n s e x u a l a c t i v i t y ( c f . B a t t y , 1978a; 1978b; G o r z a l k a & Mogenson, 1977; Grunt & Young, 1953; L a r s s o n , 1966; Whalen e t a l . , 1961). L e v e l s of t e s t o s t e r o n e would p r o b a b l y need to be e x c e e d i n g l y low i n some group members to account f o r the s e x u a l a c t i v i t y d e f i c i t s accompanying group-housing. F u r t h e r p h y s i o l o g i c a l f a c t o r s t h a t were not d i r e c t l y e x p l o r e d h e r e and might mediate i s o l a t i o n / g r o u p i n g d i f f e r e n c e s i n v o l v e c e n t r a l n e u r o c h e m i c a l s . The a c t i v i t y o f the c a t e c h o l a m i n e s , n o r e p i n e p h r i n e and do-pamine, and the i n d o l e a m i n e , s e r o t o n i n , i s m o d i f i e d by s o c i a l i s o l a t i o n ( G a r a t t i n i e t a l . , 1969; Welch & Welch, 1969a; 1969b). The c a t e c h o l a m i n e s , p a r t i c u l a r l y , show h i g h e r u t i l i z a t i o n r a t e s i n i s o l a t e s than grouped animals 126 i n n o v e l and demanding c o n t e x t s . I n c r e a s e d u t i l i z a t i o n o f dopamine may i n c r e a s e s e x u a l b e h a v i o r i n males (Gessa & T a g l i a m o n t e , 1975; Malmnas, 1976). Furthermore, the time frame f o r changes i n n e u r o c h e m i c a l u t i l i z a -t i o n ( G a r a t t i n i e t a l . , 1969; G i a c a l o n e e t a l . , 1968) may be adequate to account f o r the time frame of i s o l a t i o n e f f e c t s on male s e x u a l performance (Experiments 6 & 7 ) . In a d d i t i o n , i s o l a t i o n / g r o u p i n g n e u r o c h e m i c a l u t i l i z a -t i o n d i f f e r e n c e s may r e s u l t from i n t e r m a l e a g g r e s s i o n ( G a r a t t i n i ej: a l _ . , 1969; Welch & Welch, 1969a; 1969b) and may i n t e r r e l a t e w i t h p i t u i t a r y - a d r e n o -c o r t i c a l e v e n t s , p a r t i c u l a r l y ACTH l e v e l s (Dunn & G i s p e n , 1977). In any event, i t seems l i k e l y t h a t i s o l a t i o n / g r o u p i n g d i f f e r e n c e s i n s e x u a l a c t i v i t y r e s u l t from an i n t e r a c t i o n o f s e v e r a l f a c t o r s r a t h e r than any one p a r t i c u l a r f a c t o r . A number o f i n t e r r e l a t i n g p h y s i o l o g i c a l and b e h a v i o r a l v a r i a b l e s a r e a f f e c t e d by s o c i a l i s o l a t i o n and g r o u p i n g . Many of t h e s e v a r i a b l e s may i n d e p e n d e n t l y modulate s e x u a l a c t i v i t y , w h i l e the t o t a l i s o l a t i o n / g r o u p i n g e f f e c t may r e s u l t from t h e i r a d d i t i v e o r s y n e r -g i s t i c e f f e c t s . G e n e r a l I m p l i c a t i o n s I s o l a t i o n - i n d u c e d f a c i l i t a t i o n o f male s e x u a l b e h a v i o r i n mice i s an i n t r i n s i c a l l y i n t e r e s t i n g phenomenon f o r s e v e r a l r e a s o n s . I s o l a t e d and group-housed male mice p r o v i d e two d i f f e r e n t p r e p a r a t i o n s f o r the study of the e f f e c t s o f a v a r i e t y o f m a n i p u l a t i o n s of b e h a v i o r and p h y s i o l o g y . These d i f f e r e n t p r e p a r a t i o n s may f a c i l i t a t e e x a m i n a t i o n of i n t e r a c t i o n s be-tween s u s t a i n e d e n v i r o n m e n t a l c o n d i t i o n s and e f f e c t s o f o t h e r m a n i p u l a t i o n s . T h i s i s e v i d e n t , f o r example, i n Experiment 9A, where the e f f e c t o f a d r e n a -lectomy on s e x u a l a c t i v i t y was dependent on the a n i m a l s ' environment. The phenomenon i s a l s o i m p o r t a n t i n t h a t i t i n d i c a t e s the need f o r c a r e f u l con-127 t r o l o f e n v i r o n m e n t a l and s o c i a l v a r i a b l e s i n f u t u r e s t u d y o f murine s e x u a l b e h a v i o r . I t f u r t h e r m o r e p r o v i d e s s e v e r a l i n d i c a t i o n s about the s o c i a l and p h y s i o l o g i c a l d e t e r m i n a n t s of s e x u a l a c t i v i t y and the way i n which s e x u a l m o t i v a t i o n i n t e r r e l a t e s w i t h o t h e r m o t i v a t i o n a l v a r i a b l e s . The i s o l a t i o n / g r o u p i n g m a n i p u l a t i o n i s a c o n v e n i e n t and e a s i l y e f f e c t e d m a n i p u l a t i o n t h a t may thus f a c i l i t a t e the s t u d y o f s e x u a l b e h a v i o r . There a r e a t l e a s t two l a r g e r c o n t e x t s t h a t may h e l p to e x p l a i n the a pparent r e l a t i o n s h i p s among e n v i r o n m e n t a l e v e n t s , p h y s i o l o g y , and subsequent s e x u a l a c t i v i t y l e v e l s . These i n v o l v e the concept of " s t r e s s " and the r e l a t e d concept o f " a r o u s a l " . The study o f i s o l a t i o n / g r o u p i n g d i f f e r e n c e s i n s e x u a l a c t i v i t y may i n t u r n e l u c i d a t e t h e se l a r g e r i s s u e s . There have been a number of s u g g e s t i o n s t h a t s t r e s s a n t a g o n i z e s s e x u a l performance. S t r e s s i s g e n e r a l l y d e f i n e d as i n v o l v i n g a c t i v a t i o n o f the p i t u i t a r y - a d r e n a l system i n r e sponse to e n v i r o n m e n t a l demands ( L e v i n e , 1975; S e l y e 1956). S e l y e (1961) b r i e f l y d i s c u s s e d some human c l i n i c a l i n d i c a t i o n s t h a t impotence and s e x u a l d i s i n t e r e s t i n males might r e l a t e to s t r e s s . C h r i s t i a n (1971) reviewed a l a r g e amount of mammalian l i t e r a t u r e i n d i c a t i n g t h a t r e p r o d u c t i v e f u n c t i o n i n g i n g e n e r a l d e c l i n e s under s t r e s s ; i t might be i n f e r r e d t h a t one component of t h i s d e c l i n i n g r e p r o d u c t i v e f u n c t i o n i n g i n v o l v e s s e x u a l b e h a v i o r . Gray (1971) e x p l i c i t l y h y p o t h e s i z e d an antagonism between s t r e s s and mammalian s e x u a l b e h a v i o r . There have, however, been few p r e v i o u s e x p e r i m e n t a l d e m o n s t r a t i o n s of a s t r e s s - s e x antagonism (but see a l s o Anderson, 1938a; 1938b; He d i g e r , 1965; Ward, 1972); the p r e s e n t s t u d y may c o n s t i t u t e such a d e m o n s t r a t i o n . S i n c e grouped males show p h y s i o l o g i c a l p a t t e r n s c h a r a c t e r i s t i c of s t r e s s (see B r a i n , 1975), i n c l u d i n g the p i t u i t a r y - a d r e n a l , p i t u i t a r y - g o n a d a l , and 128 n e u r o c h e m i c a l c o n d i t i o n s d i s c u s s e d above, t h e i r s e x u a l performance d e f i c i t s might be c o n s t r u e d as b e i n g s t r e s s - i n d u c e d . The concept of a r o u s a l may a l s o h e l p to e x p l a i n these d a t a . I s o -l a t e d mice p r e s e n t e d w i t h r e c e p t i v e females may be viewed as b e i n g s i m p l y more aroused i n t h i s s i t u a t i o n because of i t s r e l a t i v e n o v e l t y . A grouped mouse i s c o n s t a n t l y i n the p r e s e n c e o f a c t i v e c o n s p e c i f i c s ; t o an i s o l a t e d mouse a p r e s e n t e d female may be a r e l a t i v e l y s a l i e n t n o v e l f e a t u r e of the environment. I n c r e a s e d a r o u s a l might be mediated by b o t h the p i t u i t a r y -a d r e n a l and n e u r o c h e m i c a l a c t i v a t i o n d i s c u s s e d above. Indeed, t h e r e i s e v i d e n c e t h a t s i m p l e a r o u s a l i n c r e a s e s male c o p u l a t i o n ; s e v e r a l r e p o r t s (e.g. B a r f i e l d & Sachs, 1968; C a g g i u l a & E i b e r g e n , 1969; Sachs & B a r f i e l d , 1974) i n d i c a t e t h a t m i l d e l e c t r i c shocks d e l i v e r e d to the s k i n w i l l evoke s e x u a l a c t i v i t y i n male r a t s . I n c r e a s e d g e n e r a l a r o u s a l i n i s o l a t e s i n n o v e l s i t u a t i o n s might h e l p to e x p l a i n not o n l y the p r e s e n t phenomenon but a l s o i s o l a t i o n - i n d u c e d a g g r e s s i o n (see S c o t t , 1966; V a l z e l l i , 1969) and i s o l a t i o n - i n d u c e d locomotor a c t i v i t y (see B r a i n e t a l . , 1971; Essman, 1968). The p r e s e n t r e s u l t s may a l s o shed l i g h t on p o s s i b l e s e x - a g g r e s -s i o n i n t e r a c t i o n s . Many o f the m a n i p u l a t i o n s of the p r e s e n t study p a r a l l e l those t h a t have been c a r r i e d out i n i n v e s t i g a t i n g i s o l a t i o n - i n d u c e d a g g r e s -s i o n . As e v i d e n t i n S e c t i o n I and numerous o t h e r s t u d i e s (see B r a i n , 1975; S c o t t , 1966; V a l z e l l i , 1969), i s o l a t i o n i n c r e a s e s a g g r e s s i o n i n subsequent i n t e r m a l e i n t e r a c t i o n s as i t does s e x u a l b e h a v i o r i n subsequent male-female i n t e r a c t i o n s . As i n d i c a t e d i n Experiments 1 and 3, a g g r e s s i o n and s e x u a l a c t i v i t y respond s i m i l a r l y to i s o l a t i o n , b o t h r e v e r s e when h o u s i n g c o n d i t i o n s a r e r e v e r s e d , and a r e perhaps o n l y m o d e r a t e l y a f f e c t e d by a r e a of space per a n i m a l . However, i s o l a t i o n - i n d u c e d f a c i l i t a t i o n of male s e x u a l b e h a v i o r may 129 r e q u i r e b r i e f e r p e r i o d s o f i s o l a t i o n than does i s o l a t i o n - i n d u c e d a g g r e s s i o n (see S e c t i o n I I I ) . P i t u i t a r y - a d r e n a l a c t i v i t y i s i n v o l v e d i n b o t h pheno-mena, but p e r i p h e r a l ACTH s u p p r e s s e s i s o l a t i o n - i n d u c e d a g g r e s s i o n but not i s o l a t i o n - i n d u c e d s e x u a l b e h a v i o r ( c f . B r a i n & P o o l e , 1974; Leshner e t al_. , 1973; S e c t i o n I V ) . The r e s u l t s o f Experiment 11 suggest a p o s s i b l e r o l e of t e s t o s t e r o n e l e v e l s i n i s o l a t i o n i n d u c e d s e x u a l b e h a v i o r ; adequate t e s t o s t e r o n e l e v e l s a r e n e c e s s a r y f o r a g g r e s s i o n i n mice but may not mediate i s o l a t i o n / g r o u p i n g d i f f e r e n c e s i n t h i s b e h a v i o r (see B r a i n , 1975; B r a i n & P o o l e , 1976; Leshner e t a l . , 1973). Another i s s u e r a i s e d by f i n d i n g s h e r e i s t h a t o f the r e l a t i o n s h i p o f s o c i a l dominance t o i n t r a g r o u p v a r i a n c e i n s e x u a l performance. In the p r e s e n t s t u d y i t was noted t h a t t h e r e was f r e q u e n t l y a l a r g e amount of i n t e r - i n d i v i d u a l v a r i a b i l i t y i n the performance o f grouped males. T h i s v a r i a b i l i t y i s s i m i l a r to t h a t found among grouped males i n s e v e r a l o t h e r b e h a v i o r a l and p h y s i o l o g i c a l v a r i a b l e s , i n c l u d i n g a g g r e s s i v e n e s s , a c t i v i t y l e v e l s , a d r e n a l f u n c t i o n i n g , and gonadal f u n c t i o n i n g (see Benton e t a l . , 1978; B r a i n , 1975; M e s s e r i e_t a l . , 1975). B r a i n (1975) has c o n c l u d e d t h a t i s o l a t e d males resemble more dominant grouped males a c c o r d i n g t o s e v e r a l b e h a v i o r a l and p h y s i o l o g i c a l i n d i c e s . T h i s s u g g e s t s t h a t the more dominant males i n a group might show h i g h e r l e v e l s o f s e x u a l a c t i v i t y than more sub-o r d i n a t e males. Indeed, D e F r i e s and M c C l e a r n (1970; 1972) found t h a t dominant males s i r e d the v a s t m a j o r i t y of o f f s p r i n g when females were housed w i t h s e v e r a l males. Dominance l e v e l i n these experiments was i n d i c a t e d by the pres e n c e or absence o f s c a r r i n g on the h i n d q u a r t e r s and f l a n k s ; a n i m a l s w i t h more s c a r s were assumed to be s u b j e c t to more a t t a c k s and c l a s s i f i e d as b e i n g more s u b o r d i n a t e . These r e s u l t s may suggest t h a t dominant males 130 ar e more s e x u a l l y a c t i v e , but a r e s u b j e c t to o t h e r i n t e r p r e t a t i o n s . I t remains p o s s i b l e t h a t they i n d i c a t e an a c t i v e p r e v e n t i o n o f mating o f sub-o r d i n a t e s by dominants r a t h e r than i n t r i n s i c d i f f e r e n c e s i n a c t i v i t y among group members. The semen of dominants may a l s o be more f e r t i l e than t h a t of s u b o r d i n a t e s . F urthermore, d i f f e r e n c e s i n s o c i a l p o s i t i o n were con-founded w i t h d i f f e r e n c e s i n g e n e t i c s t r a i n i n the s t u d i e s o f D e F r i e s and McCle a r n . The q u e s t i o n o f the r e l a t i o n s h i p o f dominance l e v e l to s e x u a l a c t i v i t y i n t h i s s p e c i e s thus remains open. I f d i f f e r e n c e s i n s e x u a l performance among mice at d i f f e r e n t l e v e l s o f s o c i a l h i e r a r c h i e s do o b t a i n , they might be o f c o n s i d e r a b l e importance i n e l u c i d a t i n g the n a t u r a l s o c i o b i o l o g y o f t h i s s p e c i e s . Know-ledg e o f which s o c i a l members a r e s u c c e s s f u l i n p a s s i n g t h e i r genes i n t o f u t u r e g e n e r a t i o n s might improve u n d e r s t a n d i n g o f the e v o l u t i o n a r y s e l e c -t i v e p r e s s u r e s a f f e c t i n g the s p e c i e s . T h i s may be p a r t i c u l a r l y t r u e i f i n t r i n s i c changes i n s u b o r d i n a t e mice produce s u p p r e s s i o n o f t h e i r s e x u a l a c t i v i t y . C h r i s t i a n (1971) and Gray (1971) have suggested t h a t the sup-p r e s s i o n of r e p r o d u c t i o n among s o c i a l l y s t r e s s e d and s u b o r d i n a t e a n i m a l s might r e q u i r e group s e l e c t i o n p r o c e s s e s l i k e t h o s e o u t l i n e d by Wynne-Edwards (1962). T h i s i s s u e i s c o n t r o v e r s i a l ( c f . Wiens, 1971; W i l s o n , 1975; Wynne-Edwards, 1971); phenomena l i k e those o f the p r e s e n t s t u d y might be of v a l u e i n a d d r e s s i n g such c o n t r o v e r s y . I t would seem im p o r t a n t t h a t f u t u r e work r e l a t e the f i n d i n g s o f the p r e s e n t s t u d y t o an i m a l s l i v i n g i n more n a t u r a l c o n d i t i o n s . Animals here were housed i n c o n t r i v e d , a l b e i t w e l l - c o n t r o l l e d , environments. These environments may not resemble the l i v i n g c o n d i t i o n s o f n a t u r a l p o p u l a t i o n s of the s p e c i e s ( c f . C r o w c r o f t & Rowe, 1963; M a c i n t o s h , 1970; Reimer & 131 P e t r a s , 1967; Rowe & R e d f e r n , 1969), a l t h o u g h i t c o u l d be argued t h a t the s t r a i n s employed here a r e adapted s p e c i f i c a l l y t o t h e l a b o r a t o r y e n v i r o n -ment. S t u d i e s i n l a b o r a t o r y environments a l l o w s y s t e m a t i c and r i g o r o u s a n a l y s i s o f the e f f e c t s o f v a r i o u s parameters, but s h o u l d be complemented by s t u d i e s i n more n a t u r a l i s t i c environments. 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