UBC Theses and Dissertations

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UBC Theses and Dissertations

Dopaminergic mechanisms in conditioned circling Szostak, Carolyn Margaret 1988

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DOPAMINERGIC MECHANISMS IN CONDITIONED CIRCLING By CAROLYN MARGARET SZOSTAK B.A. ( H o n o u r s ) , C a r l e t o n U n i v e r s i t y , 1981 M.A., C a r l e t o n U n i v e r s i t y , 1983 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n THE FACULTY OF GRADUATE STUDIES (G r a d u a t e Program i n N e u r o s c i e n c e ) We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA J a n u a r y 1988 (§) C a r o l y n M a r g a r e t S z o s t a k In p r e s e n t i n g this thesis in part ial fu l f i lment of the r e q u i r e m e n t s for an a d v a n c e d d e g r e e at the Univers i ty o f Br i t ish C o l u m b i a , I agree that the Library shal l m a k e it freely avai lable for re ference a n d s t u d y . I further agree that p e r m i s s i o n for e x t e n s i v e c o p y i n g o f this thesis for s c h o l a r l y p u r p o s e s may b e g r a n t e d b y the h e a d of m y d e p a r t m e n t o r b y his o r her representa t ives . It is u n d e r s t o o d that c o p y i n g o r p u b l i c a t i o n o f this thesis for f inanc ia l g a i n shal l no t b e a l l o w e d w i t h o u t m y w r i t t e n p e r m i s s i o n . D e p a r t m e n t o f N e u r o l o g i c a l S c i e n c e s T h e U n i v e r s i t y o f Brit ish C o l u m b i a 1956 M a i n M a l l V a n c o u v e r , C a n a d a ' V 6 T 1Y3 D a t e A p r i l 1 1 . 1 9 8 8 - i i -ABSTRACT A f t e r u n i l a t e r a l l e s i o n s o f t h e m e s o t e l e n c e p h a l i c dopamine (DA) syst e m , t h e a d m i n i s t r a t i o n o f DA r e c e p t o r a g o n i s t s r e s u l t s i n c i r c l i n g . T h i s r e s p o n s e i s b e l i e v e d t o r e f l e c t an asymmetry i n m e s o t e l e n c e p h a l i c DA a c t i v i t y . M o r e o v e r , d r u g - i n d u c e d c i r c l i n g i s t h o u g h t t o be d i r e c t e d away from t h e p r o j e c t i o n o f h i g h e r d o p a m i n e r g i c a c t i v i t y . R e c e n t l y , i t has been r e p o r t e d t h a t c i r c l i n g c a n be e s t a b l i s h e d and m a i n t a i n e d u s i n g o p e r a n t p r o c e d u r e s i n s u r g i c a l l y i n t a c t and d r u g n a i v e r a t s . The phenomenon o f c o n d i t i o n e d c i r c l i n g has been a s s o c i a t e d w i t h an a s y m m e t r i c a l change i n DA m e t a b o l i s m w i t h i n t h e s t r i a t u m and n u c l e u s accumbens. The p r e s e n t s e r i e s o f e x p e r i m e n t s was d e s i g n e d t o c h a r a c t e r i z e f u r t h e r t h e i n v o l v e m e n t o f m e s o t e l e n c e p h a l i c DA i n c o n d i t i o n e d c i r c l i n g . R a t s t r a i n e d t o c i r c l e f o r w a t e r a c c o r d i n g t o a c o n t i n u o u s s c h e d u l e o f r e i n f o r c e m e n t d i d n o t e x h i b i t i n c r e a s e d DA m e t a b o l i s m w i t h i n e i t h e r t h e s t r i a t u m o r t h e n u c l e u s accumbens ( E x p e r i m e n t I ) . However, a b i l a t e r a l a u g m e n t a t i o n was o b s e r v e d when r a t e s o f r e s p o n d i n g were i n c r e a s e d by i m p l e m e n t i n g an i n t e r m i t t e n t s c h e d u l e o f r e i n f o r c e m e n t ( E x p e r i m e n t I I ) . C o n c u r r e n t i n c r e a s e s i n t h e b i o s y n t h e s i s o f DA, as e s t i m a t e d by a c c u m u l a t i o n o f DOPA f o l l o w i n g t h e a d m i n i s t r a t i o n o f a DOPA d e c a r b o x y l a s e i n h i b i t o r , were n o t o b s e r v e d ( E x p e r i m e n t I I I ) . E x p e r i m e n t s I V a and IVb examined t h e e x t e n t t o w h i c h i n h e r e n t d i r e c t i o n a l b i a s e s , w h i c h p l a y a r o l e i n d e t e r m i n i n g t h e magnitude and d i r e c t i o n o f d r u g - i n d u c e d c i r c l i n g , i n f l u e n c e d t h e a c q u i s i t i o n and p e r f o r m a n c e o f t h e c o n d i t i o n e d c i r c l i n g r e s p o n s e . No e f f e c t s were e v i d e n t . M o r e o v e r , a s y m m e t r i c a l , b i l a t e r a l enhancement i n DA m e t a b o l i s m was o b s e r v e d i n t h e s t r i a t u m , i r r e s p e c t i v e o f d i r e c t i o n a l p r e f e r e n c e s . W h i l e c o n d i t i o n e d c i r c l i n g c an be e s t a b l i s h e d and m a i n t a i n e d by r e i n f o r c i n g t h e r e s p o n s e w i t h f o o d , f o o d i t s e l f i n f l u e n c e d DA m e t a b o l i s m and t h e r e f o r e p r e c l u d e d t h e d e t e c t i o n o f changes i n DA m e t a b o l i s m s p e c i f i c t o t h e c i r c l i n g r e s p o n s e . S p e c i f i c a l l y , s t r i a t a l and accumbens DA m e t a b o l i s m was augmented t o a s i m i l a r e x t e n t i n a n i m a l s g i v e n matched amounts o f n o n - c o n t i n g e n t l y p r e s e n t e d f o o d ( E x p e r i m e n t V ) . C o n c e n t r a t i o n s o f DA, DOPAC and h o m o v a n i l l i c a c i d (HVA) were f o u n d t o be d i f f e r e n t i a l l y d i s t r i b u t e d t h r o u g h o u t t h e s t r i a t u m ( E x p e r i m e n t V i a ) , s u g g e s t i n g a p o s s i b l e c h e m i c a l b a s i s f o r t h e h e t e r o g e n e i t y o f s t r i a t a l D A e r g i c f u n c t i o n s . Changes i n s t r i a t a l DA m e t a b o l i s m a s s o c i a t e d w i t h c o n d i t i o n e d c i r c l i n g were o b s e r v e d o n l y w i t h i n l o c a l i z e d r e g i o n s o f t h e a n t e r i o r s t r i a t u m ( E x p e r i m e n t V I b ) . A l l changes n o t e d were, however, b i l a t e r a l i n n a t u r e . F i n a l l y , u n i l a t e r a l l e s i o n s o f t h e m e s o t e l e n c e p h a l i c DA p r o j e c t i o n , f o l l o w i n g t h e e s t a b l i s h m e n t o f t h e c o n d i t i o n e d c i r c l i n g r e s p o n s e , d i s r u p t e d r e s p o n d i n g , i r r e s p e c t i v e o f t h e r e l a t i v e l o c u s o f t h e l e s i o n ( i . e . i p s i l a t e r a l o r c o n t r a l a t e r a l t o t h e d i r e c t i o n o f t u r n i n g ) ( E x p e r i m e n t V I I ) . However, t h e e x t e n t o f t h e b e h a v i o r a l d e f i c i t was more s e v e r e f o l l o w i n g c o n t r a l a t e r a l l y p l a c e d l e s i o n s . I t i s c o n c l u d e d t h a t c i r c l i n g , e s t a b l i s h e d and m a i n t a i n e d by p o s i t i v e r e i n f o r c e m e n t , i s s u b s e r v e d by a b i l a t e r a l a u g m e n t a t i o n i n DA m e t a b o l i s m w i t h i n t h e n u c l e u s accumbens and d i s c r e t e r e g i o n s o f t h e s t r i a t u m . However, l e s i o n s t u d i e s i n d i c a t e an a s y m m e t r i c a l i n v o l v e m e n t o f t h e i p s i l a t e r a l and c o n t r a l a t e r a l p r o j e c t i o n s i n t h i s r e s p o n s e . - i v -TABLE OF CONTENTS A b s t r a c t i i T a b l e o f C o n t e n t s i 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 INTRODUCTION 1 L e s i o n - i n d u c e d C i r c l i n g : A Model f o r M e s o t e l e n c e p h a l i c DA F u n c t i o n 4 R o l e o f Non-DAergic N e u r o c h e m i c a l Systems i n L e s i o n - i n d u c e d C i r c l i n g 7 R o l e o f M e s o t e l e n c e p h a l i c DA i n C i r c l i n g E x h i b i t e d by I n t a c t R a t s S F u n c t i o n o f t h e M e s o t e l e n c e p h a l i c DA P r o j e c t i o n i n I n t a c t R a t s 11 R o l e o f M e s o t e l e n c e p h a l i c DA i n C o n d i t i o n e d C i r c l i n g 14 EXPERIMENT I E f f e c t o f C o n d i t i o n e d C i r c l i n g M a i n t a i n e d by a C o n t i n u o u s S c h e d u l e o f R e i n f o r c e m e n t on M e s o t e l e n c e p h a l i c DA M e t a b o l i s m 15 M a t e r i a l s and Methods 15 R e s u l t s and D i s c u s s i o n 18 EXPERIMENT I I E f f e c t o f C o n d i t i o n e d C i r c l i n g M a i n t a i n e d by an I n t e r m i t t e n t S c h e d u l e o f R e i n f o r c e m e n t on M e s o t e l e n c e p h a l i c DA M e t a b o l i s m 23 M a t e r i a l s and Methods 23 R e s u l t s 25 -y-D i s c u s s i o n 23 EXPERIMENT I I I E f f e c t s o f C o n d i t i o n e d C i r c l i n g on S y n t h e s i s o f M e s o t e l e n c e p h a l i c DA 34 M a t e r i a l s and Methods '. 35 R e s u l t s 38 D i s c u s s i o n 39 EXPERIMENT IV I n f l u e n c e o f I n h e r e n t D i r e c t i o n a l B i a s e s on N e u r o c h e m i c a l Consequences o f C o n d i t i o n e d C i r c l i n g 41 E x p e r i m e n t I V a - Assessment o f R a t ' s I n h e r e n t D i r e c t i o n a l B i a s e s 42 M a t e r i a l s and Methods 44 R e s u l t s and D i s c u s s i o n 45 E x p e r i m e n t IVb - E f f e c t s o f D i r e c t i o n a l B i a s e s on N e u r o c h e m i c a l Consequences o f C o n d i t i o n e d C i r c l i n g 48 M a t e r i a l s and Methods 49 R e s u l t s 50 D i s c u s s i o n 61 EXPERIMENT V N e u r o c h e m i c a l Consequences o f C o n d i t i o n e d C i r c l i n g M a i n t a i n e d by Food R e i n f o r c e m e n t 62 M a t e r i a l s and Methods 63 R e s u l t s 64 D i s c u s s i o n 72 EXPERIMENT V I N e u r o c h e m i c a l C o r r e l a t e s o f C o n d i t i o n e d C i r c l i n g W i t h i n L o c a l i z e d R e g i o n s o f t h e S t r i a t u m 76 - v i -E x p e r i m e n t V i a - R e g i o n a l D i s t r i b u t i o n o f DA and I t s Two P r i m a r y M e t a b o l i t e s 77 M a t e r i a l s and Methods 78 R e s u l t s 80 D i s c u s s i o n 91 E x p e r i m e n t V I b - E f f e c t s o f C o n d i t i o n e d C i r c l i n g on DA M e t a b o l i s m w i t h i n S u b - r e g i o n s o f t h e S t r i a t u m 93 M a t e r i a l s and Methods 94 R e s u l t s 96 D i s c u s s i o n 104 EXPERIMENT V I I E f f e c t s o f U n i l a t e r a l L e s i o n s o f The M e s o t e l e n c e p h a l i c DA P r o j e c t i o n on C o n d i t i o n e d C i r c l i n g 106 M a t e r i a l s and Methods 108 R e s u l t s 112 D i s c u s s i o n 121 GENERAL DISCUSSION 127 I n v o l v e m e n t o f t h e M e s o t e l e n c e p h a l i c DA P r o j e c t i o n i n C o n d i t i o n e d C i r c l i n g 129 F u n c t i o n a l S i g n i f i c a n c e o f t h e B i l a t e r a l I n c r e a s e s i n DA M e t a b o l i s m : I s C o n d i t i o n e d C i r c l i n g a L a t e r a l i z e d B e h a v i o r ? 132 I d e n t i f i c a t i o n o f O t h e r N e u r a l P r o c e s s e s I n v o l v e d i n C o n d i t i o n e d C i r c l i n g 134 C i r c l i n g : I s I t a U n i t a r y Phenomenon? 137 - v i i -F u n c t i o n s S u b s e r v e d by t h e M e s o t e l e n c e p h a l i c DA P r o j e c t i o n : Beyond C i r c l i n g 139 Summary 140 BIBLIOGRAPHY 142 - v i i i -LIST OF TABLES T a b l e 1. Mean (± 3EM) c o n c e n t r a t i o n s o f DA, DOPAC and HVA (nmol/g p r o t e i n ) i n t h e s t r i a t u m and n u c l e u s accumbens i p s i l a t e r a l and c o n t r a l a t e r a l t o t h e d i r e c t i o n o f t u r n i n g i n r a t s t r a i n e d t o c i r c l e u s i n g a CRF s c h e d u l e and i n n o n - c i r c l i n g c o n t r o l s 22 T a b l e 2. Mean (± SEM) c o n c e n t r a t i o n s o f DA, DOPAC and HVA (nmol/g p r o t e i n ) i n t h e 8TR, NA3 and OT i p s i l a t e r a l and c o n t r a l a t e r a l t o d i r e c t i o n o f t u r n i n g i n r a t s t r a i n e d t o c i r c l e u s i n g a FR-2 s c h e d u l e and i n n o n - c i r c l i n g c o n t r o l s 26 T a b l e 3. Mean (± 3.E.M.) c o n c e n t r a t i o n s o f DOPA (nmol/g p r o t e i n ) i n t h e s t r i a t u m , n u c l e u s accumbens and o l f a c t o r y t u b e r c l e i p s i l a t e r a l and c o n t r a l a t e r a l t o t h e d i r e c t i o n o f t u r n i n g i n r a t s t r a i n e d t o c i r c l e u s i n g a FR-2 s c h e d u l e o f r e i n f o r c e m e n t and i n n o n - c i r c l i n g c o n t r o l s 40 T a b l e 4. D i r e c t i o n a l b i a s e s measured u s i n g amphetamine and non-d i f f e r e n t i a l r e i n f o r c e m e n t s c r e e n i n g p aradigms 46 T a b l e 5. Mean (± 3.E.M.) c o n c e n t r a t i o n s (nmol/g p r o t e i n ) o f DA, DOPAC and HVA w i t h i n d i s c r e t e s u b - r e g i o n s o f t h e s t r i a t u m 81 T a b l e &. Mean (± 3.E.M.) c o n c e n t r a t i o n s (nmol/g p r o t e i n ) o f DA, DOPAC and HVA w i t h i n d i s c r e t e s u b - r e g i o n s o f t h e a n t e r i o r s t r i a t u m o f w a t e r - d e p r i v e d r a t s and r a t s t r a i n e d t o c i r c l e f o r w a t e r r e i n f o r c e m e n t 101 - i x -T a b l e 7. Mean (± 3.E.M.) c o n c e n t r a t i o n s (nmol/g p r o t e i n ) o f DA, DOPAC and HVA w i t h i n d i s c r e t e s u b - r e g i o n s o f t h e p o s t e r i o r s t r i a t u m o f w a t e r - d e p r i v e d r a t s and r a t s t r a i n e d t o c i r c l e , f o r w a t e r r e i n f o r c e m e n t 102 T a b l e 8. Mean (± S.E.M.) c o n c e n t r a t i o n s (nmol/g p r o t e i n ) o f DA, DOPAC and HVA w i t h i n d i s c r e t e s u b - r e g i o n s o f t h e t a i l o f t h e s t r i a t u m o f w a t e r - d e p r i v e d r a t s and r a t s t r a i n e d t o c i r c l e f o r w a t e r r e i n f o r c e m e n t 103 T a b l e 9. Mean (± S.E.M.) c o n c e n t r a t i o n s (nmol/g p r o t e i n ) o f DA w i t h i n t h e STR, NA3 and OT o f r a t s f o l l o w i n g u n i l a t e r a l 6-OHDA-induced l e s i o n s o f t h e MFB 113 - X -LIST OF FIGURES F i g u r e 1. E f f e c t s o f s c h e d u l e o f r e i n f o r c e m e n t on r a t e o f c o n d i t i o n e d c i r c l i n g 20 F i g u r e 2. E f f e c t s o f c o n d i t i o n e d c i r c l i n g m a i n t a i n e d by i n t e r m i t t e n t r e i n f o r c e m e n t on DOPAC:DA and HVA:DA r a t i o s w i t h i n t h e i p s i l a t e r a l and c o n t r a l a t e r a l s t r i a t a 28 F i g u r e 3. R a t i o s o f DOPAC and HVA t o DA w i t h i n t h e NA3 i p s i l a t e r a l and c o n t r a l a t e r a l t o d i r e c t i o n o f c i r c l i n g 31 F i g u r e 4. E f f e c t s o f NSD-1015, a dopa d e c a r b o x y l a s e i n h i b i t o r , on r a t e o f c o n d i t i o n e d c i r c l i n g 33 F i g u r e 5. I n f l u e n c e o f i n h e r e n t d i r e c t i o n a l b i a s e s on r a t e o f c o n d i t i o n e d c i r c l i n g 52 F i g u r e &. E f f e c t s o f i n h e r e n t d i r e c t i o n a l b i a s e s and w a t e r -c o n s u m p t i o n on i n c r e a s e s i n s t r i a t a l DA m e t a b o l i s m a s s o c i a t e d w i t h c o n d i t i o n e d c i r c l i n g 55 F i g u r e 7. E f f e c t s o f i n h e r e n t d i r e c t i o n a l b i a s e s and w a t e r -c o n s u m p t i o n on i n c r e a s e s i n accumbens DA m e t a b o l i s m i n d u c e d by c o n d i t i o n e d c i r c l i n g 58 F i g u r e 8. E f f e c t s o f d i r e c t i o n a l b i a s e s on DA m e t a b o l i s m w i t h i n t h e o l f a c t o r y t u b e r c l e o f r a t s e x h i b i t i n g h i g h r a t e s o f c o n d i t i o n e d c i r c l i n g &0 F i g u r e 9. E f f e c t s o f i n h e r e n t d i r e c t i o n a l b i a s e s on r a t e o f r e s p o n d i n g m a i n t a i n e d by f o o d r e i n f o r c e m e n t 66 F i g u r e 10. I n c r e a s e s i n s t r i a t a l DA m e t a b o l i s m a s s o c i a t e d w i t h c o n d i t i o n e d c i r c l i n g masked by i n c r e a s e s due t o t h e co n s u m p t i o n o f f o o d 69 - x i - -F i g u r e 11. I n c r e a s e s i n DA m e t a b o l i s m w i t h i n t h e n u c l e u s acccumbens i n d u c e d by con s u m p t i o n o f f o o d 71 F i g u r e 12. E f f e c t s o f f o o d c o n s u m p t i o n on DA m e t a b o l i s m w i t h i n t h e o l f a c t o r y t u b e r c l e 74 F i g u r e 13. S c h e m a t i c r e p r e s e n t a t i o n o f t h e d i s t r i b u t i o n s o f DA, DOPAC and HVA w i t h i n t e n s u b - r e g i o n s o f t h e s t r i a t u m 35 F i g u r e 14. R a t i o s o f DOPAC and HVA t o DA i n 3 s u b - r e g i o n s o f t h e s t r i a t u m 89 F i g u r e 15. R a t i o s o f DOPAC and HVA t o DA i n t h e d o r s o m e d i a l , d o r s o l a t e r a l , v e n t r o m e d i a l and v e n t r o l a t e r a l q u a d r a n t s o f t h e a n t e r i o r s t r i a t u m o f r a t s t r a i n e d t o c i r c l e f o r r e i n f o r c e m e n t and w a t e r - d e p r i v e d c o n t r o l s 98 F i g u r e 16. R a t i o s o f DOPAC and HVA t o DA i n t h e d o r s o m e d i a l , d o r s o l a t e r a l , v e n t r o m e d i a l and v e n t r o l a t e r a l q u a d r a n t s o f t h e p o s t e r i o r s t r i a t u m o f r a t s t r a i n e d t o c i r c l e f o r r e i n f o r c e m e n t and w a t e r - d e p r i v e d c o n t r o l s 100 F i g u r e 17. S c h e m a t i c r e p r e s e n t a t i o n o f t h e p o s t - o p e r a t i v e b e h a v i o r a l t e s t i n g regime employed i n E x p e r i m e n t V I I . ... I l l F i g u r e 18. Number o f r e i n f o r c e d r o t a t i o n s e m i t t e d d u r i n g R e v e r s a l and N o n - R e v e r s a l t e s t s e s s i o n s as a f u n c t i o n o f l o c u s o f l e s i o n 116 F i g u r e 19. Number o f n o n - r e i n f o r c e d r o t a t i o n s e m i t t e d d u r i n g R e v e r s a l and N o n - R e v e r s a l t e s t s e s s i o n s as a f u n c t i o n o f l o c u s o f l e s i o n 120 - x i i -ACKNOWLEDGEMENTS I would l i k e t o t h a n k my a d v i s o r , Dr. C h r i s F i b i g e r , f o r h i s s u p p o r t , encouragement and t h e words o f wisdom o f f e r e d t o me w h i l e w o r k i n g on t h i s d i s s e r t a t i o n . A p p r e c i a t i o n i s e x t e n d e d t o A l e x J a k u b o v i c , D a v i n a F u , and S t e l l a A t m a d j a f o r t h e i r t e c h n i c a l a s s i s t a n c e , and t o Maureen Cromie f o r a l l o f h e r h e l p i n d e a l i n g w i t h t h e a d m i n i s t r a t i v e end o f t h i n g s . S p e c i a l t h a n k s go t o J a n e t F i n l a y , who has h e l p e d a t a l l s t a g e s o f t h e r e s e a r c h and w r i t i n g , and t o J i m Radke f o r h i s " k i l l e r " i n s t i n c t . I would a l s o l i k e t o acknowledge t h e s u p p o r t and encouragement t h a t I r e c e i v e d from L o i s Reimer and C h e r y l B r a d l e y , f r i e n d s who may n o t have u n d e r s t o o d what I was d o i n g b u t e n c o u r a g e d me anyway. I am a l s o v e r y g r a t e f u l t o my f a m i l y f o r t h e i r l o v e , s u p p o r t and r e a s s u r a n c e s . F i n a l l y , I would l i k e t o t h a n k Dr. Tony P h i l l i p s and t h e o t h e r members o f my S u p e r v i s o r y Committee f o r t h e comments and s u g g e s t i o n s o f f e r e d . 1 -±-E v i d e n c e f o r t h e c r i t i c a l i n v o l v e m e n t o f t h e n i g r o s t r i a t a l dopamine (DA) system i n movement was o r i g i n a l l y p r o v i d e d by r e s e a r c h on t h e p a t h o l o g y a s s o c i a t e d w i t h P a r k i n s o n ' s d i s e a s e , a syndrome c h a r a c t e r i z e d by t h e o c c u r r e n c e o f a k i n e s i a , r i g i d i t y and t r e m o r ( s e e , f o r example, B y e r & D e x t e r , 1983; Marsden, 1982). The i n v o l v e m e n t o f t h e s u b s t a n t i a n i g r a i n P a r k i n s o n ' s d i s e a s e had been w e l l e s t a b l i s h e d when i t was d i s c o v e r e d t h a t c o n c e n t r a t i o n s o f DA were s u b s t a n t i a l l y r e d u c e d w i t h i n t h e s t r i a t u m o f p a t i e n t s w i t h P a r k i n s o n ' s (see H o r n y k i e w i c z , 1973). The r e l a t i o n s h i p between t h e s e two o b s e r v a t i o n s became e v i d e n t when i t was d e m o n s t r a t e d t h a t c e l l s w i t h i n t h e s u b s t a n t i a n i g r a p r o j e c t e d t o t h e s t r i a t u m and t h a t t h e s e c e l l s u t i l i z e d DA as t h e i r n e u r o t r a n s m i t t e r ( U n g e r s t e d t , 1971a). F u r t h e r u n d e r s t a n d i n g o f t h e f u n c t i o n a l r o l e s o f t h e n i g r o s t r i a t a l DA p r o j e c t i o n has been g a i n e d by t h e assessment o f b e h a v i o r a l d e f i c i t s , o b s e r v e d f o l l o w i n g e x p e r i m e n t a l l y - i n d u c e d l e s i o n s o f t h i s s y s t e m , i n b o t h monkeys and r a t s . The b e h a v i o r a l symptomatology o b s e r v e d i n monkeys f o l l o w i n g d i s c r e t e l e s i o n s o f n i g r a l D A e r g i c neurones i s s i m i l a r t o t h a t a s s o c i a t e d w i t h P a r k i n s o n ' s d i s e a s e ( s e e S c h u l t z , 1982 f o r r e v i e w ) . F o r example, monkeys a r e r e n d e r e d h y p o k i n e t i c by b i l a t e r a l l e s i o n s o f t h e s u b s t a n t i a n i g r a o r o f t h e a s c e n d i n g n i g r o s t r i a t a l f i b e r s . L e s i o n - i n d u c e d t r e m o r and r i g i d i t y , t h e o t h e r major symptoms o f P a r k i n s o n ' s d i s e a s e , have a l s o been p r o d u c e d e x p e r i m e n t a l l y . However, t h e s e r e s p o n s e s a r e o n l y o b s e r v e d when e x t r a n i g r a l r e g i o n s , and, i n p a r t i c u l a r t h e p a r v o c e l l u l a r p a r t o f t h e r e d n u c l e u s , a r e damaged i n c o n j u n c t i o n w i t h e x t e n s i v e n i g r a l c e l l l o s s ( s e e S c h u l t z , 1982 f o r r e v i e w ) . W h i l e t h e d e f i c i t s o b s e r v e d i n monkeys p a r a l l e l t h e c l i n i c a l o b s e r v a t i o n s , i t can be d i f f i c u l t t o i n d u c e s e l e c t i v e and d i s c r e t e l e s i o n s o f t h e DA m e s o t e l e n c e p h a l i c p r o j e c t i o n i n monkeys because t h e D A e r g i c -2-n i g r o s t r i a t a l neurones a r e i n t e r s p e r s e d w i t h t h e non-DAergic c e l l s t h a t f o r m t h e s u b s t a n t i a n i g r a p a r s r e t i c u l a t a ( S c h u l t z , 1982). I n c o n t r a s t , w i t h i n t h e r a t b r a i n , DA c e l l b o d i e s a r e l o c a l i z e d i n f a i r l y d i s c r e t e r e g i o n s o f t h e mesencephalon ( s u b s t a n t i a n i g r a , p a r s compacta ( A 9 ) ; and n e i g h b o r i n g r e g i o n s o f t h e v e n t r a l t e g m e n t a l a r e a (A10 and A8) ( U n g e r s t e d t , 1 9 7 1 a ) ) . Due t o t h e r e l a t i v e ease i n p r o d u c i n g d i s c r e t e l e s i o n s o f t h e m e s o t e l e n c e p h a l i c D A e r g i c systems i n r a t s , c l a r i f i c a t i o n o f t h e f u n c t i o n s s u b s e r v e d by t h i s p r o j e c t i o n has been l a r g e l y a t t a i n e d t h r o u g h work w i t h r a t s . F o l l o w i n g b i l a t e r a l l e s i o n s , r a t s a r e r e n d e r e d h y p o p h a g i c , h y p o d i p s i c , and h y p o k i n e t i c ( e . g . F i b i g e r , Z i s & McGeer, 1973; M a r s h a l l & T e i t e l b a u m , 1974; see I v e r s e n , 1977 f o r r e v i e w ) . D e t a i l e d a n a l y s i s o f t h e s e symptoms has r e v e a l e d t h a t t h e d e f i c i t s a r e n e i t h e r p u r e l y s e n s o r y n o r p u r e l y m o t o r i c ( L j u n g b e r g & U n g e r s t e d t , 1976). I n s t e a d , t h e b e h a v i o r s e x h i b i t e d f o l l o w i n g b i l a t e r a l l e s i o n s a r e c h a r a c t e r i s t i c o f a d i s r u p t i o n i n t h e i n t e g r a t i o n o f s e n s o r i m o t o r f u n c t i o n s . F o r example, t h e p r e s e n t a t i o n o f p a l a t a b l e f o o d s w i l l i n d u c e r a t s t o e a t ( see W h i t e , 1986 f o r r e v i e w ) , d e m o n s t r a t i n g t h a t t h e y a r e m o t o r i c a l l y c a p a b l e o f e a t i n g . A p p r o p r i a t e m o t o r i c r e s p o n s e s a r e a l s o o b s e r v e d when t h e i n t e n s i t y o f t h e s e n s o r y s t i m u l u s i s i n c r e a s e d ( e . g . M a r s h a l l , L e v i t a n & S t r i e k e r , 1976; R a n j e & U n g e r s t e d t , 1977). A l t h o u g h l e s i o n e d r a t s do n o t e x h i b i t o r i e n t i n g r e s p o n s e s ( e . g . movement d i r e c t e d t o t h e l o c u s o f t h e s t i m u l a t i o n ) , t h e y do r e s p o n d t o t h e s t i m u l u s ( e . g . w i t h f l i n c h , eye b l i n k , v o c a l i z a t i o n , e t c . ) s u g g e s t i n g t h a t t h e l e s i o n s have n o t d i s r u p t e d t h e s e n s o r y i n p u t , p e r se ( T u r n e r , 1973; M a r s h a l l & T e i t e l b a u m , 1974). I t s h o u l d be n o t e d t h a t some of t h e symptoms o f P a r k i n s o n ' s d i s e a s e a l s o appear t o r e f l e c t s e n s o r i m o t o r d e f i c i t s . F o r example, p a t i e n t s w i t h P a r k i n s o n ' s d i s e a s e can r e s p o n d more r e a d i l y under c o n d i t i o n s o f s t r o n g s t i m u l u s c o n t r o l ( s e e I v e r s e n , 1977). I t s h o u l d be n o t e d t h a t t h e b e h a v i o r a l syndrome i s a p p a r e n t o n l y f o l l o w i n g v e r y e x t e n s i v e ( i . e . > 90%) d e p l e t i o n s o f DA (see S t r i e k e r & Zigmond, 1986, f o r r e v i e w ) . F o l l o w i n g i n c o m p l e t e l e s i o n s , a n i m a l s e x h i b i t b e h a v i o r a l r e c o v e r y . However, i t has been r e p o r t e d t h a t s u b t l e b e h a v i o r a l d e f i c i t s p e r s i s t ( e . g . c o n t i n u i n g d i s r e g u l a t i o n o f f o o d i n t a k e ) ( F i b i g e r , e t a l . , 1973b). The need f o r e x t e n s i v e d e p l e t i o n s o f DA i s a l s o e v i d e n t c l i n i c a l l y . F o r example, p a t i e n t s w i t h l e s s t h a n a 75% d e p l e t i o n o f s t r i a t a l DA a r e t y p i c a l l y asymptomatic ( H o r n y k i e w i c z , 1973; see a l s o S c h u l t z , 1982). F u r t h e r e v i d e n c e t h a t t h e d e f i c i t s o b s e r v e d i n r a t s , monkeys and humans a r e r e l a t e d t o a l e s i o n - i n d u c e d d e p l e t i o n o f DA has been p r o v i d e d by t h e use o f n e u r o t o x i c s u b s t a n c e s such as 6-hydroxydopamine (6-OHDA) ( e . g . U n g e r s t e d t , 1971b,c) and, more r e c e n t l y , 1 - m e t h y l - l , 2 , 3 , 6 -t e t r a h y d r o p y r i d i n e (MPTP) ( e . g . H e i k k i l a , M a n z i n o , Cabbat & D u v o i s i n , 1984) t o p r o d u c e s e l e c t i v e l e s i o n s o f DA ne u r o n e s . M o reover, r e v e r s a l o f some o f t h e l e s i o n - i n d u c e d symptoms i s o b s e r v e d f o l l o w i n g t h e a d m i n i s t r a t i o n o f DA a g o n i s t s ( s e e I v e r s e n , 1977; S c h u l t z , 1982, f o r r e v i e w s ) . C o n v e r s e l y , t h e s e v e r i t y o f t h e d e f i c i t s i n e x p e r i m e n t a l s u b j e c t s can be augmented by t h e a d m i n i s t r a t i o n o f DA a n t a g o n i s t s , such as h a l o p e r i d o l , a DA r e c e p t o r b l o c k e r o r a l p h a m e t h y l - p a r a - t y r o s i n e (AMPT) a DA s y n t h e s i s i n h i b i t o r (Zigmond & S t r i e k e r , 1973). Due t o t h e s e v e r i t y o f t h e b e h a v i o r a l d e f i c i t s o b s e r v e d f o l l o w i n g e x t e n s i v e l e s i o n s and t h e need f o r such e x t e n s i v e l e s i o n s i n o r d e r t o d e t e c t r e l i a b l e b e h a v i o r a l d e f i c i t s , i t has been d i f f i c u l t t o g a i n a c l e a r u n d e r s t a n d i n g o f t h e d i s c r e t e f u n c t i o n s s u b s e r v e d by t h e m e s o t e l e n c e p h a l i c -4-DA p r o j e c t i o n u s i n g t h e b i l a t e r a l l e s i o n p r e p a r a t i o n . The b e h a v i o r a l e f f e c t s o f u n i l a t e r a l l e s i o n s o f t h e m e s o t e l e n c e p h a l i c DA s y s t e m have, however, been s t u d i e d e x t e n s i v e l y and have been w e l l c h a r a c t e r i z e d . The r e s u l t s o f t h e s e e x p e r i m e n t s a r e d i s c u s s e d i n d e t a i l i n t h e f o l l o w i n g s e c t i o n . L e s i o n - i n d u c e d C i r c l i n g : A Model f o r M e s o t e l e n c e p h a l i c DA F u n c t i o n u n i l a t e r a l l e s i o n s o f t h e m e s o t e l e n c e p h a l i c DA p r o j e c t i o n , c e l l b o d i e s o r t e r m i n a l r e g i o n s i n d u c e l a t e r a l i z e d d e f i c i t s i n s e n s o r i m o t o r f u n c t i o n i n g ( M a r s h a l l & T e i t e l b a u m , 1974). W h i l e t r a n s i e n t h y p o p h a g i a and h y p o d i p s i a a r e o b s e r v e d f o l l o w i n g u n i l a t e r a l l e s i o n s , t h e s e v e r i t y o f t h e s e symptoms i s g r e a t l y r e d u c e d , r e l a t i v e t o what i s o b s e r v e d f o l l o w i n g b i l a t e r a l l e s i o n s ( F i b i g e r , P h i l l i p s & C l o u s t o n , 1973; U n g e r s t e d t , 1971b). However, r a t s f a i l t o o r i e n t t o s e n s o r y s t i m u l a t i o n o f body r e g i o n s c o n t r a l a t e r a l t o t h e l e s i o n s i t e ( T u r n e r , 1973; M a r s h a l l & T e i t e l b a u m , 1974). The s e n s o r i m o t o r d e f i c i t s f o l l o w i n g u n i l a t e r a l l e s i o n s have a l s o been c h a r a c t e r i z e d by t h e o c c u r r e n c e o f r o t a t i o n a l b e h a v i o r . S p e c i f i c a l l y , u n i l a t e r a l l e s i o n s o f t h e m e s o t e l e n c e p h a l i c DA p r o j e c t i o n i n d u c e c i r c l i n g t o wards t h e l e s i o n e d s i d e ( i . e . i p s i v e r s i v e c i r c l i n g ) ( u n g e r s t e d t , 1971b). W h i l e t h i s spontaneous b e h a v i o r i s a p p a r e n t f o r o n l y a few days f o l l o w i n g s u r g e r y , i t can be r e i n s t a t e d by p l a c i n g t h e r a t i n a n o v e l e n v i r o n m e n t o r when t h e a n i m a l i s d i s t u r b e d ( e . g . h a n d l i n g t h e r a t , C o s t a l l , K e l l y & N a y l o r , 1983). I t i s g e n e r a l l y t h o u g h t t h a t t h e a s y m m e t r i c a l p o s t u r i n g i n d u c e d by u n i l a t e r a l l e s i o n s o f t h e m e s o t e l e n c e p h a l i c DA system r e f l e c t s m o t o r i c d e f i c i t s i n c o m b i n a t i o n w i t h s e n s o r y n e g l e c t o f t h e c o n t r a l a t e r a l s i d e o f t h e body ( I v e r s e n , 1977). F o l l o w i n g t h e r e m i s s i o n o f spontaneous c i r c l i n g , t h i s r e s p o n s e can a l s o be i n d u c e d by t h e s y s t e m i c a d m i n i s t r a t i o n o f DA a g o n i s t s , s u c h as amphetamine and apomorphine ( U n g e r s t e d t , 1971b,c). -b-However, t h e d i r e c t i o n o f d r u g - i n d u c e d c i r c l i n g i s dependent upon 1/ t h e t y p e o f a g o n i s t employed, 2/ t h e method u s e d t o l e s i o n t h e p r o j e c t i o n o r s t r u c t u r e ( e . g . e l e c t r o l y t i c v s s e l e c t i v e n e u r o t o x i c l e s i o n s ) and, 3/ t h e t e m p o r a l i n t e r v a l between s u r g e r y and d r u g a d m i n i s t r a t i o n . I n d i r e c t a g o n i s t s , s u c h as amphetamine, t h a t i n f l u e n c e t h e r e l e a s e and r e u p t a k e o f DA ( e . g . S e i d e n & D y k s t r a , 1977), p r o d u c e i p s i v e r s i v e c i r c l i n g f o l l o w i n g b o t h e l e c t r o l y t i c and &-hydroxydopamine (6-OHDA) - i n d u c e d l e s i o n s ( C o s t a l l , e t a l . , 1983; U n g e r s t e d t , 1971b). W h i l e i t has g e n e r a l l y been assumed t h a t t h i s r e s p o n s e r e f l e c t s t h e enhanced r e l e a s e o f DA from neurons i n t h e i n t a c t s t r i a t u m , d i r e c t e v i d e n c e f o r t h i s h y p o t h e s i s has o n l y r e c e n t l y been o b t a i n e d . U s i n g i n v i v o m i c r o d i a l y s i s t e c h n i q u e s , Z e t t e r s t r o m , H e r r e r a -M a r s c h i t z and U n g e r s t e d t (1987) have d e m o n s t r a t e d t h a t t h e p r o f i l e o f amphetamine-induced c i r c l i n g i s h i g h l y c o r r e l a t e d w i t h t h e magnitude and t i m e - c o u r s e o f amphetamine-induced r e l e a s e o f DA w i t h i n t h e i n t a c t s t r i a t u m and n o t t h e l e s i o n e d s t r i a t u m . I p s i v e r s i v e c i r c l i n g i s a l s o o b s e r v e d f o l l o w i n g t h e a d m i n i s t r a t i o n o f d i r e c t - a c t i n g DA a g o n i s t s , s u c h as apomorphine and L-DOPA, t o r a t s w i t h e l e c t r o l y t i c a l l y - i n d u c e d l e s i o n s o f t h e s t r i a t u m ( C o s t a l l , e t a l . , 1983). I t i s g e n e r a l l y assumed t h a t t h e i p s i v e r s i v e c i r c l i n g o b s e r v e d under t h e s e e x p e r i m e n t a l c o n d i t i o n s i s due t o d i r e c t s t i m u l a t i o n o f t h e DA p o s t - s y n a p t i c r e c e p t o r s i n t h e i n t a c t s t r i a t u m . I n c o n t r a s t , c o n t r a v e r s i v e c i r c l i n g i s o b s e r v e d upon a d m i n i s t r a t i o n o f DA a g o n i s t s f o l l o w i n g &-OHDA-induced l e s i o n s ( C o s t a l l , e t a l . , 1983; U n g e r s t e d t , 1 9 7 1 c ) . T h i s l a t t e r r e s p o n s e i s t h o u g h t t o r e f l e c t t h e development o f p o s t - s y n a p t i c r e c e p t o r s u p e r s e n s i t i v i t y w i t h i n t h e l e s i o n e d s t r i a t u m ( u n g e r s t e d t , 1 9 7 1 c ) . I n t h e c a s e o f L-DOPA-induced c i r c l i n g , L-DOPA may be d e c a r b o x y l a t e d t o fo r m DA w i t h i n t h e r e m a i n i n g DA f i b e r s and s t r i a t a l s e r o t o n e r g i c neurons (Ng, Chase, C o l b u r n & K o p i n , - o -1970). M o r e o v e r , u n g e r s t e d t (1971c) o b s e r v e d t h a t i n h i b i t i o n o f DOPA d e c a r b o x y l a s e b l o c k s L-DOPA-induced c i r c l i n g , s u g g e s t i n g t h a t L-DOPA must be d e c a r b o x y l a t e d i n t o DA i n o r d e r t o s t i m u l a t e t h e s u p e r s e n s i t i v e p o s t -s y n a p t i c r e c e p t o r s . On t h e b a s i s o f t h e s e r e s u l t s , i t has been h y p o t h e s i z e d t h a t t h e d i r e c t i o n o f c i r c l i n g i s dependent upon w h i c h s t r i a t u m i s dominant w i t h r e s p e c t t o DA a c t i v i t y , and t h a t t h e c i r c l i n g i s d i r e c t e d away f r o m t h e dominant s t r i a t u m ( s e e P y c o c k , 1980, f o r r e v i e w ) . A d m i n i s t r a t i o n o f FLA-63, a d o p a m i n e - b e t a - h y d r o x y l a s e i n h i b i t o r w h i c h b l o c k s t h e s y n t h e s i s o f n o r e p i n e p h r i n e f r o m DA, d i d n o t a t t e n u a t e amphetamine-induced c i r c l i n g when a dose t h a t s e l e c t i v e l y i n f l u e n c e d c o n c e n t r a t i o n s o f n o r e p i n e p h r i n e was u s e d (Marsden & G u l d b e r g , 1973). A c c o r d i n g l y , i t does n o t appear t h a t n o r e p i n e p h r i n e i s i n v o l v e d i n t h e m e d i a t i o n o f t h i s r e s p o n s e . However, amphetamine-induced c i r c l i n g i s a t t e n u a t e d f o l l o w i n g t h e i n h i b i t i o n o f DA s y n t h e s i s ( U n g e r s t e d t , 1971b) o r b l o c k a d e o f DA r e c e p t o r s ( U n g e r s t e d t , 1971b; K e l l y £ Moore, 1977). I n c o n t r a s t , i n h i b i t i o n o f DA s y n t h e s i s does n o t i n f l u e n c e c i r c l i n g i n d u c e d by t h e a d m i n i s t r a t i o n o f d i r e c t - a c t i n g DA a g o n i s t s ( G e r s h a n i k , H e i k k i l a & D u v o i s i n , 1983). However, t h e a d m i n i s t r a t i o n o f DA r e c e p t o r a n t a g o n i s t s ( e . g . h a l o p e r i d o l , p i m o z i d e ) does b l o c k a p o m o r p h i n e - i n d u c e d c i r c l i n g ( C o s t a l l , e t a l . , 1983; K e l l y & M i l l e r , 1975; Tye, Horsman, W r i g h t , L a r g e & P u l l a r , 1977). These o b s e r v a t i o n s a r e c o n s i s t e n t w i t h t h e h y p o t h e s i s t h a t t h e two c l a s s e s o f d r u g s i n d u c e c i r c l i n g by d i f f e r e n t mechanisms ( i . e . p r e s y n a p t i c v s p o s t s y n a p t i c i n t e r a c t i o n s ) . F u r t h e r e v i d e n c e o f t h e d o p a m i n e r g i c i n v o l v e m e n t i n c i r c l i n g has a l s o been d e r i v e d f r o m r e p o r t s t h a t u n i l a t e r a l m i c r o i n j e c t i o n s o f DA i n t o t h e d o r s a l s t r i a t u m p r o d u c e c o n t r a l a t e r a l t u r n i n g ( J o y c e & van H a r t e s v e l d t , -7-1984; J o y c e , D a v i s & van H a r t e s v e l d t , 1981). S i m i l a r l y , W o l f s o n & Brown (1983) have o b s e r v e d t h a t c i r c l i n g i n d u c e d by i n t r a s t r i a t a l i n f u s i o n s o f DA i s dependent upon t h e c o n c e n t r a t i o n o f DA a t t a i n e d w i t h i n t h e d o r s a l r e g i o n o f t h e s t r i a t u m . W h i l e a t t e n t i o n has been f o c u s s e d upon t h e c r i t i c a l r o l e o f t h e s t r i a t a l D A e r g i c i n n e r v a t i o n i n c i r c l i n g , i t has become e v i d e n t t h a t t h e m e s o l i m b i c DA p r o j e c t i o n i s a l s o i n v o l v e d . However, t h e two systems appear t o s u b s e r v e d i s c r e t e components o f t h i s r e s p o n s e . S p e c i f i c a l l y , t h e n i g r o s t r i a t a l s y s t e m a p p e a r s t o s u b s e r v e t h e p o s t u r a l asymmetry i n v o l v e d i n c i r c l i n g whereas t h e r a t e o f c i r c l i n g i s m e d i a t e d by DA a c t i v i t y w i t h i n t h e n u c l e u s accumbens ( K e l l y , 1977; K e l l y & Moore, 1976, 1977; P y c o c k & Marsden, 1973). I t has been s u g g e s t e d t h a t t h e r a t e o f d r u g - i n d u c e d c i r c l i n g i s d e t e r m i n e d by t h e a c t i v i t y o f m e s o l i m b i c DA r e c e p t o r s w h i c h s e r v e s t o a m p l i f y t h e asymmetry i n s t r i a t a l DA a c t i v i t y ( K e l l y , 1977). F o r example, as p r e v i o u s l y i n d i c a t e d , t h e a d m i n i s t r a t i o n o f amphetamine f o l l o w i n g u n i l a t e r a l l e s i o n s o f t h e s u b s t a n t i a n i g r a o r o f t h e m e s o t e l e n c e p h a l i c DA p r o j e c t i o n , r e s u l t s i n i p s i v e r s i v e c i r c l i n g . The i n t e n s i t y o f d r u g - i n d u c e d c i r c l i n g i s a t t e n u a t e d , however, f o l l o w i n g b i l a t e r a l l e s i o n s o f t h e n u c l e u s accumbens, d e s p i t e t h e f a c t t h a t t h e s e a n i m a l s e x h i b i t n o r m a l l e v e l s o f spontaneous l o c o m o t o r a c t i v i t y ( K e l l y and Moore, 1976; P y c o c k & Marsden, 1978). R o l e o f Non-DAergic N e u r o c h e m i c a l Systems i n L e s i o n - I n d u c e d C i r c l i n g W h i l e a s t r o n g c a s e has been made f o r t h e i n v o l v e m e n t o f DA i n c i r c l i n g , o t h e r systems have a l s o been i m p l i c a t e d . F o r example, m a n i p u l a t i o n s o f s e r o t o n e r g i c , c h o l i n e r g i c , n o r a d r e n e r g i c and GABAergic systems have been f o u n d e i t h e r t o evoke o r t o modulate d r u g - i n d u c e d r o t a t i o n , i n d i c a t i n g t h a t DA i s n o t u n i q u e l y i n v o l v e d ( s ee K e l l y , 1977; -8-P y c o c k , 1980 f o r r e v i e w s ) . A l t h o u g h t h e m e s o t e l e n c e p h a l i c DA system i s o f t e n i d e n t i f i e d as b e i n g t h e n e u r a l s u b s t r a t e o f c i r c l i n g , o b v i o u s l y t h i s s y stem does n o t o p e r a t e i n i s o l a t i o n o f o t h e r b r a i n r e g i o n s o r c h e m i c a l s y s t e m s . A c c o r d i n g l y , i t i s p o s s i b l e t h a t c i r c l i n g o b s e r v e d f o l l o w i n g t h e m a n i p u l a t i o n o f o t h e r n e u r o c h e m i c a l systems r e f l e c t s changes o c c u r r i n g e i t h e r u p s t r e a m o r downstream from t h e D A e r g i c " l i n k " i n t h e n e u r a l s u b s t r a t e o f c i r c l i n g . F o r example, s t r i a t a l DA neurons appear t o i n t e r a c t w i t h s t r i a t a l c h o l i n e r g i c neurons i n an a n t a g o n i s t i c manner ( C o r r o d i , Fuxe & L i d b r i n k , 1972). C o n s i s t e n t w i t h t h i s n e u r o n a l r e l a t i o n s h i p a r e r e p o r t s t h a t s c o p o l a m i n e , an a n t i m u s c a r i n i c a g e n t , i n d u c e s weak i p s i v e r s i v e c i r c l i n g f o l l o w i n g u n i l a t e r a l l e s i o n s o f t h e s u b s t a n t i a n i g r a ( K e l l y & M i l l e r , 1975). M o r e o v e r , amphetamine- and a p o m o r p h i n e - i n d u c e d c i r c l i n g i s p o t e n t i a t e d by t h e a d m i n i s t r a t i o n o f a n t i c h o l i n e r g i c d rugs ( K u r u v i l l a & U r e t s k y , 1984; Marsden & G u l d b e r g , 1973) and a t t e n u a t e d by a d m i n i s t r a t i o n o f c h o l i n o m i m e t i c s ( K e l l y & M i l l e r , 1975; K u r u v i l l a & U r e t s k y , 1984; Marsden & G u l d b e r g , 1973). Thus, i t would appear t h a t t h e s t r i a t a l c h o l i n e r g i c neurons a r e i n v o l v e d i n t h e m e d i a t i o n o f c i r c l i n g . S i m i l a r l y , i t has been o b s e r v e d t h a t l e s i o n s o f s t r i a t a l e f f e r e n t p r o j e c t i o n s , and i n p a r t i c u l a r t h e s t r i o n i g r a l p r o j e c t i o n , a t t e n u a t e a p o m o r p h i n e - i n d u c e d c i r c l i n g ( M a r s h a l l & U n g e r s t e d t , 1977; see a l s o D i C h i a r a , P o r c e d d u , M o r e l l i , Mulas & G e s s a , 1979; G a r c i a - M u n o z , N i c o l a u , T u l l o c h , W r i g h t & A r b u t h n o t t , 1977). F u r t h e r e x p e r i m e n t s a r e c l e a r l y r e q u i r e d t o i d e n t i f y more c o m p l e t e l y t h e n e u r a l mechanisms t h a t u n d e r l y c i r c l i n g . R o l e o f M e s o t e l e n c e p h a l i c DA i n C i r c l i n g E x h i b i t e d by I n t a c t R a t s W h i l e a s s e s s i n g t h e b e h a v i o r a l e f f e c t s o f d r u g - l e s i o n i n t e r a c t i o n s , i t was s e r e n d i p i t o u s l y o b s e r v e d t h a t n e u r o l o g i c a l l y i n t a c t r a t s , s e r v i n g as c o n t r o l s u b j e c t s , c i r c l e d p r e f e r e n t i a l l y i n one d i r e c t i o n f o l l o w i n g t h e -9-s y s t e m i c a d m i n i s t r a t i o n o f d-amphetamine ( J e r u s s i & C l i c k , 1974; see a l s o C l i c k & S h a p i r o , 1985 f o r r e v i e w ) . W h i l e t h e r a t e o f r o t a t i o n e x h i b i t e d by i n t a c t r a t s i s s u b s t a n t i a l l y l o w e r t h a n t h a t o b s e r v e d i n u n i l a t e r a l l y l e s i o n e d r a t s , r a t s c i r c l e c o n s i s t e n t l y i n one d i r e c t i o n ( t h e d i r e c t i o n b e i n g random a c r o s s s u b j e c t s ) . I n a d d i t i o n , r a t s c i r c l e s p o n t a n e o u s l y d u r i n g t h e n o c t u r n a l phase o f t h e i r d i u r n a l c y c l e ( C l i c k and Cox, 1978). The p r e f e r r e d d i r e c t i o n o f n o c t u r n a l c i r c l i n g c o r r e l a t e s w i t h t h e d i r e c t i o n o f amphetamine-induced c i r c l i n g i n i n t a c t a n i m a l s . P h a r m a c o l o g i c a l c h a l l e n g e s have s u g g e s t e d t h a t t h e c i r c l i n g o b s e r v e d i n i n t a c t r a t s i s a l s o m e d i a t e d by DA. F o r example, amphetamine-induced c i r c l i n g i s a t t e n u a t e d f o l l o w i n g t h e a d m i n i s t r a t i o n o f DA r e c e p t o r a n t a g o n i s t s and DA s y n t h e s i s i n h i b i t o r s w h i l e NE s y n t h e s i s i n h i b i t o r s a r e w i t h o u t e f f e c t ( J e r u s s i & G l i c k , 1976). However, a p o m o r p h i n e - i n d u c e d c i r c l i n g i s n o t a n t a g o n i z e d f o l l o w i n g i n h i b i t i o n o f DA s y n t h e s i s ( J e r u s s i & G l i c k , 1975), s u g g e s t i n g an asymmetry i n p o s t - s y n a p t i c DA r e c e p t o r s . I n l i g h t o f t h e s e o b s e r v a t i o n s , i t has been h y p o t h e s i z e d t h a t t h e r e i s an i n h e r e n t asymmetry i n s t r i a t a l DA a c t i v i t y and t h a t r a t s c i r c l e away fr o m t h e s t r i a t u m p o s s e s s i n g t h e g r e a t e s t DA a c t i v i t y . S u p p o r t f o r t h i s h y p o t h e s i s has been o b t a i n e d i n e x p e r i m e n t s u s i n g f e m a l e r a t s . Thus, f o l l o w i n g t h e a d m i n i s t r a t i o n o f amphetamine, c o n c e n t r a t i o n s o f DA have been r e p o r t e d t o be h i g h e r i n t h e s t r i a t u m c o n t r a l a t e r a l t o t h e p r e f e r r e d d i r e c t i o n o f c i r c l i n g t h a n i n t h e i p s i l a t e r a l s t r i a t u m ( J e r u s s i & G l i c k , 1976). A s i m i l a r asymmetry has n o t , however, been c o n s i s t e n t l y o b s e r v e d i n male r a t s ( s e e R o b i n s o n , B e c k e r , Camp & Mansour, 1985 f o r r e v i e w ) . W h i l e t h e e x i s t e n c e o f an i n h e r e n t asymmetry i n s t r i a t a l DA a c t i v i t y i n male r a t s i s n o t c l e a r , i t has been d e m o n s t r a t e d t h a t t h e d i r e c t i o n a l b i a s e s o f male and f e m a l e r a t s can i n f l u e n c e t h e e f f e c t s o f amphetamine -10-( R o b i n s o n & B e c k e r , 1983) and apomorphine ( J e r u s s i & G l i c k , 1975) f o l l o w i n g u n i l a t e r a l l e s i o n s o f t h e m e s o t e l e n c e p h a l i c DA system. F o r example, t h e d i r e c t i o n and i n t e n s i t y o f d r u g - i n d u c e d c i r c l i n g i s dependent upon whether t h e dominant o r non-dominant system i s l e s i o n e d . E x t e n s i v e l e s i o n s o f t h e non-dominant p r o j e c t i o n r e s u l t i n h i g h r a t e s o f i p s i v e r s i v e c i r c l i n g f o l l o w i n g t h e a d m i n i s t r a t i o n o f amphetamine. I n c o n t r a s t , t h e d i r e c t i o n o f d r u g - i n d u c e d c i r c l i n g f o l l o w i n g l e s i o n s o f t h e dominant p r o j e c t i o n depends upon t h e e x t e n t o f t h e l e s i o n . That i s , i n c o m p l e t e l e s i o n s ( i . e . l e s s t h a n 90% d e p l e t i o n ) r e s u l t i n c o n t r a v e r s i v e c i r c l i n g , a l t h o u g h t h e r a t e o f c i r c l i n g i s r e d u c e d i n r e l a t i o n t o t h a t o b s e r v e d i n r a t s w i t h non-dominant l e s i o n s . I f , however, t h e l e s i o n i s n e a r l y c o m p l e t e ( i . e . g r e a t e r t h a n 90%) i p s i v e r s i v e c i r c l i n g i s e x h i b i t e d ( R o b i n s o n & B e c k e r , 1983). As s u c h , i t i s c l e a r t h a t t h e i n h e r e n t d i r e c t i o n a l b i a s e s c a n i n t e r a c t w i t h m a n i p u l a t i o n s o f t h e m e s o t e l e n c e p h a l i c DA system. However, t h e mechanism u n d e r l y i n g t h i s i n t e r a c t i o n r e m a i n s t o be i d e n t i f i e d . I t has r e c e n t l y been s u g g e s t e d t h a t t h e r e l a t i o n s h i p between d i r e c t i o n a l b i a s e s and asymmetry i n s t r i a t a l DA f u n c t i o n i s n o t as s i m p l e as o r i g i n a l l y h y p o t h e s i z e d . S h a p i r o , G l i c k & Hough (1986) r e p o r t e d t h a t t h e degree o f asymmetry i n DA a c t i v i t y , as d e t e r m i n e d by t h e Vmax f o r DA u p t a k e s i t e s , c o r r e l a t e s w i t h t h e magnitude b u t n o t n e c e s s a r i l y t h e d i r e c t i o n o f t h e r o t a t i o n a l b i a s . That i s , t h e i p s i l a t e r a l s t r i a t u m o f some r a t s (male and f e m a l e ) p o s s e s s g r e a t e r DA a c t i v i t y t h a n t h e c o n t r a l a t e r a l s t r i a t u m , w h i l e t h e o p p o s i t e r e l a t i o n i s n o t e d i n o t h e r r a t s . On t h e b a s i s o f t h e s e r e s u l t s , G l i c k and a s s o c i a t e s h y p o t h e s i z e d t h a t t h e r e a r e two p o p u l a t i o n s o f r a t s -- t h o s e t h a t c i r c l e away f r o m t h e dominant s t r i a t u m (C>I) and t h o s e t h a t c i r c l e t o w a r d s t h e dominant s t r i a t u m (I>C) ( G l i c k & S h a p i r o , 1985; S h a p i r o , e t a l . , 1986). S u p p o r t f o r t h i s s u g g e s t i o n was d e r i v e d f r o m t h e o b s e r v a t i o n t h a t t h e two groups c o u l d be d i s t i n g u i s h e d f r o m one a n o t h e r n e u r o c h e m i c a l l y . S p e c i f i c a l l y , t h e Vmax w i t h i n t h e c o n t r a l a t e r a l s t r i a t u m o f t h e O I group was s i g n i f i c a n t l y h i g h e r t h a n t h a t o f t h e I>C group w h i l e i p s i l a t e r a l v a l u e s were n o t d i f f e r e n t a c r o s s t h e two g r o u p s ( S h a p i r o , e t a l . , 1986). The s i g n i f i c a n c e o f t h i s o b s e r v a t i o n i s u n c l e a r a t t h e p r e s e n t t i m e , p a r t i c u l a r l y s i n c e t h e p r o p o n e n t s o f t h i s h y p o t h e s i s r e c e n t l y f a i l e d t o o b s e r v e a c o r r e l a t i o n between asymmetries i n s t r i a t a l DA c o n c e n t r a t i o n s and t h e magnitude o f d i r e c t i o n a l b i a s e s ( S h a p i r o , Camarota & G l i c k , 1987). F u r t h e r e x p e r i m e n t a t i o n i s c l e a r l y r e q u i r e d i n o r d e r t o s u b s t a n t i a t e t h e v a l i d i t y o f t h e r e v i s e d h y p o t h e s i s and, t o c l a r i f y t h e r o l e o f s t r i a t a l DA i n t h i s b e h a v i o r . F u n c t i o n o f t h e M e s o t e l e n c e p h a l i c DA P r o j e c t i o n i n I n t a c t R a t s As i l l u s t r a t e d above, t h e i d e n t i f i c a t i o n o f t h e n e u r a l s u b s t r a t e s o f a s p e c i f i c b e h a v i o r ( a n d , c o n v e r s e l y , t h e f u n c t i o n s o f n e u r a l systems) has been sought p r e d o m i n a n t l y t h r o u g h t h e use o f p h a r m a c o l o g i c a l m a n i p u l a t i o n s and s e l e c t i v e l e s i o n i n g t e c h n i q u e s . W h i l e t h e s e e x p e r i m e n t a l p r o c e d u r e s have formed t h e c o r n e r s t o n e i n t h e a t t e m p t s t o i d e n t i f y and u n d e r s t a n d b r a i n - b e h a v i o r i n t e r a c t i o n s , t h e s e methods a l s o have l i m i t i n g f a c t o r s . F o r example, p r e s e n t u n d e r s t a n d i n g o f t h e f u n c t i o n o f t h e m e s o t e l e n c e p h a l i c DA s y s t e m i s l a r g e l y b a s e d upon assessment o f l e s i o n - d r u g ( e . g . u n g e r s t e d t , 1971b,c) and l e s i o n - l e s i o n i n t e r a c t i o n s ( K e l l y & Moore, 1977; P y c o c k & Marsden, 1978). I n some c a s e s , even h i g h e r - o r d e r i n t e r a c t i o n s have been a n a l y z e d ( e . g . l e s i o n - d r u g - d r u g i n t e r a c t i o n s ) ( e . g . C o s t a l l , e t a l . , 1983; K e l l y & M i l l e r , 1975). D i f f i c u l t y i n i n t e r p r e t i n g t h e s e d a t a a r i s e b ecause t h e d r u g s u s e d g e n e r a l l y have m u l t i p l e s i t e s and mechanisms o f a c t i o n . Thus, i t i s t y p i c a l l y n o t c l e a r how t h e v a r i o u s a g o n i s t s and/or a n t a g o n i s t s -12-i n t e r a c t w i t h one a n o t h e r n e u r o c h e m i c a l l y . That i s , do DA r e c e p t o r a n t a g o n i s t s f u n c t i o n a l l y r e v e r s e t h e n e u r o c h e m i c a l e f f e c t s o f DA a g o n i s t s , and, i f s o , how? H a l o p e r i d o l b l o c k s DA r e c e p t o r s , i n d u c e s an i n c r e a s e i n DA m e t a b o l i s m and i n h i b i t s t h e t r a n s p o r t o f DA m e t a b o l i t e s away f r o m t h e i r s i t e o f p r o d u c t i o n ( s e e Commissiong, 1985). Amphetamine, an i n d i r e c t DA a g o n i s t , i s known t o b l o c k t h e r e u p t a k e o f DA and t o s t i m u l a t e t h e r e l e a s e o f DA. W h i l e t h e b e h a v i o r a l e f f e c t s o f amphetamine a d m i n i s t e r e d t o i n t a c t a n i m a l s can be a t t e n u a t e d by h a l o p e r i d o l i n a dose-dependent f a s h i o n ( e . g . J e r u s s i & G l i c k , 1 9 7 6 ) , t h e p r e c i s e n e u r o c h e m i c a l b a s i s f o r t h e b e h a v i o r a l r e v e r s a l i s n o t known. Moreover, a l t h o u g h t h e b e h a v i o r a l e f f e c t s o f amphetamine can be a t t e n u a t e d , t h i s i s n o t t o s a y t h a t t h e a n i m a l i s r e n d e r e d " n o r m a l " . R a t h e r , a new s e t o f "symptoms" may emerge ( e . g . S c h a e f e r & M i c h a e l , 1984). To add t o t h e c o n f u s i o n , i n t e r a c t i o n s between DA a n t a g o n i s t s and amphetamine a r e o f t e n a n a l y z e d i n r a t s f o l l o w i n g u n i l a t e r a l l e s i o n s o f t h e m e s o t e l e n c e p h a l i c DA p r o j e c t i o n ( e . g . C o s t a l l , e t a l . , 1983). However, t h e n e u r o c h e m i c a l consequences o f t h e l e s i o n s depend upon a/ t h e e x t e n t o f t h e l e s i o n , b/ t h e n a t u r e o f t h e l e s i o n ( e . g . e l e c t r o l y t i c v s n e u r o t o x i c ) c/ t h e l o c u s o f l e s i o n ( i . e . c e l l b o d i e s v s t e r m i n a l r e g i o n s v s a s c e n d i n g f i b e r s ) , d/ t h e s p e c i f i c i t y o f t h e l e s i o n ( e . g . were n o r a d r e n e r g i c neurons p r o t e c t e d ) , and e/ t h e r e c o v e r y p e r i o d f o l l o w i n g t h e l e s i o n . A n o t h e r p r o b l e m a s s o c i a t e d w i t h a s s e s s i n g l e s i o n - d r u g i n t e r a c t i o n s , e s p e c i a l l y i n t h o s e c a s e s where t h e d r u g i s a d m i n i s t e r e d s y s t e m i c a l l y , i s t h a t t h e e f f e c t s o f t h e d r u g a r e n o t l o c u s - s p e c i f i c . A c c o r d i n g l y , a t t e n u a t i o n o r p r e c i p i t a t i o n o f symptoms may r e f l e c t t h e i n v o l v e m e n t o f o t h e r r e g i o n s . W h i l e , as p r e v i o u s l y i n d i c a t e d , t h i s l i n e o f r e s e a r c h has been c r u c i a l i n a c q u i r i n g an i n i t i a l u n d e r s t a n d i n g o f t h e n e u r a l s u b s t r a t e s o f -13-b e h a v i o r a l f u n c t i o n s , i t i s d e s i r a b l e t o d e t e r m i n e t h e r o l e o f v a r i o u s n e u r a l systems i n b e h a v i o r e x h i b i t e d by i n t a c t , d r u g - n a i v e a n i m a l s . R e c e n t l y , a t t e n t i o n has been f o c u s s e d upon t h e e s t a b l i s h m e n t o f b e h a v i o r a l p a radigms t h a t p e r m i t t h e i d e n t i f i c a t i o n and assessment o f n e u r a l s u b s t r a t e ( s ) u n d e r l y i n g d i s c r e t e b e h a v i o r a l f u n c t i o n s . F o r example, Yamamoto & F r e e d (1982; 1984a) have r e p o r t e d t h a t r a t s can be t r a i n e d t o c i r c l e f o r r e i n f o r c e m e n t and t h a t , upon e s t a b l i s h m e n t o f t h i s r e s p o n s e , s e l e c t i v e changes i n m e s o t e l e n c e p h a l i c DA a c t i v i t y a r e o b s e r v e d . S p e c i f i c a l l y , Yamamoto & F r e e d (1982) r e p o r t e d t h a t c o n c e n t r a t i o n s o f DA and i t s m e t a b o l i t e 3 , 4 - d i h y d r o x y p h e n y l a c e t i c a c i d (DOPAC) were u n i l a t e r a l l y i n c r e a s e d w i t h i n t h e s t r i a t u m and n u c l e u s accumbens c o n t r a l a t e r a l t o t h e d i r e c t i o n o f r e i n f o r c e d c i r c l i n g . T h i s o b s e r v a t i o n i s c o n s i s t e n t w i t h t h e h y p o t h e s e s o u t l i n e d above, t h a t c i r c l i n g i s s u b s e r v e d by an asymmetry i n s t r i a t a l DA a c t i v i t y and, t h a t c i r c l i n g i s d i r e c t e d away f r o m t h e dominant h e m i s p h e r e . A c c o r d i n g l y , t h e c o n d i t i o n e d c i r c l i n g p a r a d i g m p r o v i d e s a means f o r i n v e s t i g a t i n g t h e n e u r a l s u b s t r a t e s o f c i r c l i n g and, c o n v e r s e l y , f o r a s s e s s i n g t h e n a t u r e o f t h i s r e s p o n s e . The f i n d i n g s o f Yamamoto & F r e e d (1982, 1984a) a r e a l s o i m p o r t a n t as t h e y s u g g e s t t h a t l o c a l i z e d and s p e c i f i c n e u r o c h e m i c a l a l t e r a t i o n s may be a s s o c i a t e d w i t h t h e p e r f o r m a n c e o f a s p e c i f i c b e h a v i o r a l r e s p o n s e . W h i l e enhanced s y n t h e s i s and t u r n o v e r o f DA has been a s s o c i a t e d w i t h l e v e r -p r e s s i n g ( H e f f n e r & S e i d e n , 1980; H e f f n e r , L u t t i n g e r , Hartman & S e i d e n , 1981), changes i n t h e c o n c e n t r a t i o n s o f DA and i t s m e t a b o l i t e s s p e c i f i c t o t h e p e r f o r m a n c e o f t h e l e v e r - p r e s s i n g r e s p o n s e a r e n o t a p p a r e n t when a n i m a l s a r e t e s t e d i n a d r u g - f r e e s t a t e ( H e f f n e r , Vosmer & S e i d e n , 1984). -14-R o l e o f M e s o t e l e n c e p h a l i c DA i n C o n d i t i o n e d C i r c l i n g The p r e s e n t s e r i e s o f e x p e r i m e n t s was d e s i g n e d t o c h a r a c t e r i z e f u r t h e r t h e i n v o l v e m e n t o f t h e m e s o t e l e n c e p h a l i c DA system i n c i r c l i n g u s i n g t h e c o n d i t i o n e d t u r n i n g p a r a d i g m , as d e s c r i b e d by Yamamoto & F r e e d ( 1 9 8 2 ) . I n th e f i r s t e x p e r i m e n t , r a t s were t r a i n e d t o c i r c l e u s i n g a c o n t i n u o u s s c h e d u l e o f r e i n f o r c e m e n t i n an a t t e m p t t o r e p l i c a t e t h e b a s i c f i n d i n g s o f Yamamoto & F r e e d ( 1 9 8 2 ) . That i s , does c o n d i t i o n e d c i r c l i n g i n d u c e an i n c r e a s e i n c o n c e n t r a t i o n s o f b o t h DA and DOPAC s e l e c t i v e l y w i t h i n t h e s t r i a t u m and n u c l e u s accumbens c o n t r a l a t e r a l t o t h e d i r e c t i o n o f t u r n i n g ? A second e x p e r i m e n t was c o n d u c t e d t o a s s e s s t h e e x t e n t t o w h i c h t h e r a t e o f c i r c l i n g w o u l d i n f l u e n c e t h e n e u r o c h e m i c a l consequences o f c i r c l i n g . The e f f e c t s o f c o n d i t i o n e d c i r c l i n g on t h e b i o s y n t h e s i s o f DA, as e s t i m a t e d by th e a c c u m u l a t i o n o f L - 3 , 4 - d i h y d r o x y p h e n y l a l a n i n e (DOPA) f o l l o w i n g i n h i b i t i o n o f DOPA d e c a r b o x y l a s e , was a s s e s s e d i n t h e t h i r d e x p e r i m e n t . As p r e v i o u s l y m e n t i o n e d , r a t s ' i n h e r e n t d i r e c t i o n a l b i a s e s a r e an i m p o r t a n t f a c t o r when a s s e s s i n g amphetamine-induced c i r c l i n g f o l l o w i n g u n i l a t e r a l l e s i o n s ( R o b i n s o n & B e c k e r , 1983). A c c o r d i n g l y , t h e e x t e n t t o w h i c h i n h e r e n t d i r e c t i o n a l p r e f e r e n c e s i n f l u e n c e t h e n e u r o c h e m i c a l changes a s s o c i a t e d w i t h c o n d i t i o n e d c i r c l i n g was d e t e r m i n e d i n E x p e r i m e n t s I V a and IVb. I n t h e f i f t h e x p e r i m e n t , t h e n e u r o c h e m i c a l changes a s s o c i a t e d w i t h c i r c l i n g e s t a b l i s h e d and m a i n t a i n e d by f o o d r e i n f o r c e m e n t was d e t e r m i n e d . E x p e r i m e n t s V i a and V I b examined t h e e x t e n t t o w h i c h changes i n s t r i a t a l DA m e t a b o l i s m a s s o c i a t e d w i t h c o n d i t i o n e d c i r c l i n g a r e p r e s e n t t h r o u g h o u t t h e s t r i a t u m . F i n a l l y , t h e e f f e c t s o f u n i l a t e r a l 6-OHDA l e s i o n s o f t h e m e s o t e l e n c e p h a l i c p r o j e c t i o n on i p s i - and c o n t r a v e r s i v e l y d i r e c t e d c o n d i t i o n e d c i r c l i n g were examined i n E x p e r i m e n t V I I . -15-EXPERIMENT I Effects of Conditioned Circling Maintained by a Continuous Schedule of Reinforcement on Mesotelencephalic DA Metabolism I t has been r e p o r t e d t h a t r a t s t r a i n e d t o c i r c l e a c c o r d i n g t o a c o n t i n u o u s s c h e d u l e o f r e i n f o r c e m e n t (CRF) e x h i b i t i n c r e a s e d c o n c e n t r a t i o n s o f DA and DOPAC i n t h e s t r i a t u m and n u c l e u s accumbens c o n t r a l a t e r a l t o t h e d i r e c t i o n i n w h i c h t h e y t u r n (Yamamoto & F r e e d , 1982). The f i r s t e x p e r i m e n t was c o n d u c t e d t o d e t e r m i n e t h e r e l i a b i l i t y o f t h i s phenomenon. A c c o r d i n g l y , r a t s were t r a i n e d t o c i r c l e u s i n g a c o n t i n u o u s s c h e d u l e o f r e i n f o r c e m e n t . Upon a t t a i n m e n t o f a s y m p t o t i c r a t e s o f r e s p o n d i n g , t h e e f f e c t s o f c o n d i t i o n e d c i r c l i n g on DA, DOPAC and HVA c o n c e n t r a t i o n s w i t h i n t h e s t r i a t u m and n u c l e u s accumbens were d e t e r m i n e d . Materials and Methods S u b j e c t s and A p p a r a t u s N a i v e , male Sprague-Dawley r a t s ( C h a r l e s R i v e r L a b o r a t o r i e s ) , w e i g h i n g between 250-350 g, s e r v e d as s u b j e c t s . R a t s were i n d i v i d u a l l y housed i n a t e m p e r a t u r e c o n t r o l l e d room w i t h an a u t o m a t i c 12 h l i g h t / d a r k c y c l e ( l i g h t s on: 8:00 - 2 0 : 0 0 ) . Food and w a t e r were a v a i l a b l e ad l i b i t u m i n t h e home cage. A n i m a l s were a c c l i m a t i z e d t o t h e l a b o r a t o r y f o r 1 week p r i o r t o commencement o f t h e e x p e r i m e n t . A l l b e h a v i o r a l t e s t i n g was c o n d u c t e d i n a p l a s t i c c y l i n d r i c a l c o n t a i n e r ( d i a m e t e r - 26 cm; h e i g h t - 30 cm). The c o n t a i n e r was e q u i p p e d w i t h a m a n u a l l y o p e r a t e d , m o t o r - d r i v e n l i q u i d d i s p e n s e r ( S k i n n e r E l e c t r i c V a l v e D i v i s i o n ) c a l i b r a t e d t o d e l i v e r .07 - .09 ml o f w a t e r p e r r e i n f o r c e m e n t . The w a t e r was d e l i v e r e d i n t o a t r o u g h l o c a t e d a t t h e p e r i m e t e r o f t h e a p p a r a t u s 4 cm from t h e f l o o r . -16-P r o c e d u r e B e h a v i o r a l P r o t o c o l . E i g h t r a t s were w a t e r - d e p r i v e d f o r 23 h p r i o r t o commencement o f t r a i n i n g . S u b j e c t s were t r a i n e d t o t u r n 360° f o r w a t e r u s i n g t h e method o f s u c c e s s i v e a p p r o x i m a t i o n s . The d i r e c t i o n o f t u r n i n g was a s s i g n e d r a n d o m l y , such t h a t h a l f o f t h e r a t s were r e q u i r e d t o c i r c l e t o t h e l e f t and t h e r e m a i n i n g s u b j e c t s t o t h e r i g h t . Upon a c q u i s i t i o n o f t h e r e s p o n s e each c o m p l e t e c i r c l e e m i t t e d i n t h e a p p r o p r i a t e d i r e c t i o n was r e i n f o r c e d . A n i m a l s r e c e i v e d 8-9 d a i l y t r a i n i n g s e s s i o n s o f 20 min d u r a t i o n . D u r i n g t h e e x p e r i m e n t a l r e g i m e n , f o o d c o n t i n u e d t o be a v a i l a b l e ad l i b i t u m i n t h e home cage. However, a c c e s s t o w a t e r was l i m i t e d t o t h a t r e c e i v e d i n t h e t e s t a p p a r a t u s (3-12 m i s / d a y ) . The imposed s c h e d u l e o f wa t e r d e p r i v a t i o n r e s u l t e d i n a n i m a l s m a i n t a i n i n g w e i g h t s 30-85% o f t h e i r ad l i b i t u m body w e i g h t s . On t h e day f o l l o w i n g t h e l a s t t r a i n i n g s e s s i o n (Day 9-10) a n i m a l s were t e s t e d f o r c i r c l i n g b e h a v i o r f o r 20 min. The e x p e r i m e n t a l c o n t i n g e n c i e s u s e d d u r i n g t r a i n i n g r e m a i n e d i n e f f e c t . I m m e d i a t e l y f o l l o w i n g t h e s e s s i o n , r a t s were d e c a p i t a t e d . E i g h t a d d i t i o n a l r a t s s e r v e d as c o n t r o l s u b j e c t s . These r a t s were p l a c e d on a 23.5 h w a t e r - d e p r i v a t i o n s c h e d u l e and h a n d l e d d a i l y f o r t h e d u r a t i o n o f t h e e x p e r i m e n t . C o n t r o l s u b j e c t s d i d n o t r e c e i v e any b e h a v i o r a l t r a i n i n g o r e x p e r i e n c e i n t h e t e s t a p p a r a t u s . On t h e t e s t day c o n t r o l s u b j e c t s were d e c a p i t a t e d a f t e r h a v i n g a c c e s s t o w a t e r i n t h e i r home cage f o r 20 min. D i s s e c t i o n and A s s a y P r o t o c o l s . I m m e d i a t e l y f o l l o w i n g d e c a p i t a t i o n , b r a i n s were r a p i d l y removed, a c o r o n a l c u t was made s l i g h t l y c a u d a l t o t h e o p t i c c h i a s m and t h e a n t e r i o r s e c t i o n f r o z e n on a microtome. Two c o n s e c u t i v e 1-mm c o r o n a l s l i c e s were t a k e n and p l a c e d on i c e so t h a t t h e r o s t r a l s u r f a c e was f a c e up. A c c o r d i n g t o K o n i g & K l i p p e l ( 1 9 6 3 ) , t h e r o s t r a l e x t e n t o f t h e a n t e r i o r s l i c e was a p p r o x i m a t e l y a t t h e l e v e l o f A9820 u w h i l e t h e r o s t r a l l i m i t o f t h e second s l i c e was a p p r o x i m a t e l y a t A8620 u. The n u c l e u s accumbens was d i s s e c t e d from t h e r o s t r a l s l i c e ; i t was d e f i n e d as b e i n g v e n t r a l t o t h e genu o f t h e c o r p u s c a l l o s u m and d o r s a l t o t h e o l f a c t o r y t u b e r c l e (demarcated by s m a l l f i b e r b u n d l e s f o r m i n g t h e o l f a c t o r y r a d i a t i o n s ) . The a n t e r i o r commissure was i n c l u d e d i n t h e sample. The s t r i a t a l sample was d i s s e c t e d f r o m t h e c a u d a l s l i c e and was d e f i n e d d o r s a l l y and l a t e r a l l y by t h e c o r p u s c a l l o s u m . The m e d i a l b o r d e r was formed by t h e l a t e r a l v e n t r i c l e s . The v e n t r a l l i m i t was imposed by making a h o r i z o n t a l c u t a t t h e l e v e l o f t h e a n t e r i o r commissure. I n subsequent e x p e r i m e n t s , t h e e f f e c t s o f c o n d i t i o n e d c i r c l i n g on DA m e t a b o l i s m w i t h i n t h e o l f a c t o r y t u b e r c l e was a l s o examined. Thus, i n subsequent e x p e r i m e n t s t h e o l f a c t o r y t u b e r c l e was d i s s e c t e d f r o m b o t h c o r o n o l s l i c e s . The o l f a c t o r y t r a c t s e r v e d as t h e l a t e r a l l i m i t o f t h e o l f a c t o r y t u b e r c l e ( b o t h s l i c e s ) w h i l e t h e s e p t a l r e g i o n marked t h e m e d i a l b o r d e r . The d o r s a l b o r d e r was t h e v e n t r a l l i m i t o f t h e n u c l e u s accumbens. The t i s s u e samples o f t h e d i f f e r e n t b r a i n a r e a s were i m m e d i a t e l y weighed and t h e n homogenized by an u l t r a s o n i c c e l l d i s r u p t e r i n 0.2 M HCIO4 c o n t a i n i n g 0.15% Na 2S205 and 0.5% Na 2EDTA c o n t a i n e d i n 1.5 ml p o l y p r o p y l e n e c e n t r i f u g e t u b e s . F o l l o w i n g c e n t r i f u g a t i o n (30,000 g f o r 15 min) t h e s u p e r n a t a n t was removed and s t o r e d a t -30°C u n t i l a s s a y e d . The p r e c i p i t a t e o b t a i n e d a f t e r c e n t r i f u g a t i o n was u s e d f o r p r o t e i n d e t e r m i n a t i o n (Lowry, Rosebrough, F a r r & R a n d a l l , 1951). B e f o r e a n a l y s i s , t h e samples o f s u p e r n a t a n t were f i l t e r e d t h r o u g h a membrane (0.2 [i p o r e s i z e , S c h l e i c h e r and S c h u e l l ) and a 20 \il a l i q u o t u s e d f o r d i r e c t s i m u l t a n e o u s d e t e r m i n a t i o n o f DA, DOPAC and HVA. N e u r o c h e m i c a l a s s a y s were c o n d u c t e d u s i n g h i g h p r e s s u r e l i q u i d c hromotography w i t h e l e c t r o c h e m i c a l d e t e c t i o n (HPLC-ED). The system c o n s i s t e d o f a Beckman model 100A pump, LC-4B amperometric d e t e c t o r w i t h a g l a s s y c a r b o n TL-5 w o r k i n g e l e c t r o d e ( BAS), a 3390A r e c o r d e r i n t e g r a t o r ( H e w l e t t - P a c k a r d ) and a ^Bondapak CIS ( l O u , 150 x 3.9 mm) column ( W a t e r s ) . The p o t e n t i a l was s e t a t +.75 V v e r s u s an Ag/AgCl r e f e r e n c e e l e c t r o d e . The s e n s i t i v i t y was s e t a t 10-20nA/V f u l l s c a l e , d e p e n d i n g on c o n c e n t r a t i o n o f t h e compounds. The m o b i l e phase was a 0.1 M KH2PO4 b u f f e r , pH 3.6, c o n t a i n i n g 0.2 mM sodium o c t a n e s u l f o n i c a c i d , 0.15 mM Na2EDTA and 9.5% m e t h a n o l . The c o n c e n t r a t i o n o f each compound was e s t a b l i s h e d by c o m p a r i n g t h e peak a r e a s w i t h known s t a n d a r d s and were e x p r e s s e d i n nmol/g p r o t e i n . The d e t e c t i o n l i m i t f o r DA and i t s m e t a b o l i t e s was about 0.5 pmol/20 u.1 t i s s u e sample. Results and Discussion A l l r a t s a c q u i r e d t h e t a s k and by t h e 5 t h s e s s i o n were p e r f o r m i n g a t l e a s t 100 c o m p l e t e r o t a t i o n s i n a 20 min s e s s i o n . Once t h e y had a c q u i r e d t h e c o r r e c t r e s p o n s e , c i r c l i n g i n t h e i n a p p r o p r i a t e d i r e c t i o n was r a r e l y o b s e r v e d . Mean r o t a t i o n s p e r m i n u t e o b t a i n e d d u r i n g t h e t e s t s e s s i o n a r e p r e s e n t e d i n F i g u r e 1. An a n a l y s i s o f v a r i a n c e (ANOVA) w i t h one w i t h i n -s u b j e c t f a c t o r ( t e n 2 min b l o c k s ) was c o n d u c t e d on t h e b e h a v i o r a l d a t a o b t a i n e d d u r i n g t h e t e s t s e s s i o n . Degrees o f freedom a p p r o p r i a t e t o t h e G e i s s e r - G r e e n h o u s e C o n s e r v a t i v e F t e s t were u s e d f o r t h i s a n a l y s i s and a l l s ubsequent a n a l y s e s i n v o l v i n g r e p e a t e d measures w i t h more t h a n two l e v e l s ( K i r k , 1968). R a t e o f c i r c l i n g d e c r e a s e d p r o g r e s s i v e l y d u r i n g t h e s e s s i o n : F ( l , 7 ) = 19.07, p < .05. W h i l e t h e maximal r a t e s o f r e s p o n d i n g o b t a i n e d i n t h e p r e s e n t i n v e s t i g a t i o n were s i m i l a r t o t h o s e r e p o r t e d by Yamamoto & F r e e d ( 1 9 8 2 ) , a n i m a l s i n t h e p r e s e n t s t u d y e x h i b i t e d a g r e a t e r d e c l i n e i n r e s p o n d i n g w i t h i n a s e s s i o n . -19-F i g u r e 1. Mean (± 8EM) number o f r o t a t i o n s p e r minu t e o b t a i n e d d u r i n g t e s t s e s s i o n s a r e p r e s e n t e d i n b l o c k s o f two m i n u t e s . S o l i d c i r c l e s r e p r e s e n t t e s t d a t a o f r a t s t r a i n e d t o c i r c l e u s i n g a c o n t i n u o u s s c h e d u l e o f r e i n f o r c e m e n t ( E x p e r i m e n t I ; n=8). Mean r e s p o n s e r a t e s o f r a t s t r a i n e d t o c i r c l e u s i n g a FR-2 s c h e d u l e a r e d e p i c t e d w i t h open c i r c l e s ( E x p e r i m e n t I I ; n=5). i i 1 1 1 1 1 1 1 r 1 2 3 4 5 6 7 8 9 10 BLOCKS OF TWO MINUTES -21-To d e t e r m i n e whether r e i n f o r c e d c i r c l i n g s e l e c t i v e l y i n f l u e n c e d t h e c o n c e n t r a t i o n s o f DA and i t s m e t a b o l i t e s w i t h i n t h e s t r i a t u m and n u c l e u s accumbens c o n t r a l a t e r a l t o t h e d i r e c t i o n i n w h i c h t h e y c i r c l e d , ANOVAs w i t h one b e t w e e n - s u b j e c t f a c t o r (Group) and one w i t h i n - s u b j e c t f a c t o r ( i p s i l a t e r a l v s c o n t r a l a t e r a l s t r u c t u r e ) were c o n d u c t e d f o r each compound measured by HPLC-ED. S i n c e t h e r e i s e v i d e n c e o f n e u r o c h e m i c a l a symmetries i n n a i v e a n i m a l s ( J e r u s s i & T a y l o r , 1982; Rosen, F i n k e l s t e i n , S t o l l , Y u t z e y & Denenberg, 1984), t h e l e f t and r i g h t t i s s u e samples o b t a i n e d f r o m c o n t r o l s u b j e c t s were randomly d e s i g n a t e d as i p s i l a t e r a l and c o n t r a l a t e r a l s u c h t h a t h a l f o f t h e " i p s i l a t e r a l " samples were o b t a i n e d f r o m t h e r i g h t h e misphere and h a l f f r o m t h e l e f t . One e x p e r i m e n t a l s u b j e c t was o m i t t e d f r o m t h e n u c l e u s accumbens a n a l y s e s because o f an e r r o r made d u r i n g t h e p r e p a r a t i o n o f t h e c o n t r a l a t e r a l n u c l e u s accumbens sample. ANOVAs were a l s o c o n d u c t e d on t h e r a t i o o f each m e t a b o l i t e t o DA as i t has been s u g g e s t e d t h a t s u c h r a t i o s a r e a s e n s i t i v e i n d i c a t o r o f amine u t i l i z a t i o n ( e . g . L a v i e l l e , T a s s i n , T h i e r r y , B l a n c , H e r v e , B a r t h a l e m y & G l o w i n s k i , 1978). C i r c l i n g was n o t f o u n d t o i n f l u e n c e t h e a b s o l u t e c o n c e n t r a t i o n s o f DA, DOPAC o r HVA i n e i t h e r t h e s t r i a t u m o r n u c l e u s accumbens ( s e e T a b l e 1 ) . I n a d d i t i o n , t h e r a t i o s o f DOPAC o r HVA t o DA ( d a t a n o t shown) were n o t a f f e c t e d by c o n d i t i o n e d c i r c l i n g i n e i t h e r s t r u c t u r e . These d a t a f a i l t o c o n f i r m t h e r e p o r t s o f Yamamoto & F r e e d (1982, 1984) t h a t c o n d i t i o n e d c i r c l i n g p r o d u c e s l a t e r a l i z e d i n c r e a s e s i n t h e c o n c e n t r a t i o n s o f DA and DOPAC i n t h e s t r i a t u m and n u c l e u s accumbens. M o r e o v e r , c o n c e n t r a t i o n s o f HVA and t h e m e t a b o l i t e : D A r a t i o s were n o t i n f l u e n c e d by c o n d i t i o n e d c i r c l i n g . One p o s s i b l e e x p l a n a t i o n f o r t h i s d i s c r e p a n c y i s t h a t t h e t e r m i n a l r a t e o f r e s p o n d i n g i n t h e p r e s e n t s t u d y -22-T a b l e 1. Mean (± 3EM) c o n c e n t r a t i o n s o f DA, DOPAC and HVA (nmol/g p r o t e i n ) i n t h e s t r i a t u m and n u c l e u s accumbens i p s i l a t e r a l and c o n t r a l a t e r a l t o t h e d i r e c t i o n o f t u r n i n g i n r a t s t r a i n e d t o c i r c l e u s i n g a CRF s c h e d u l e and i n n o n - c i r c l i n g c o n t r o l s . DOPAMINE DOPAC HVA I p s i C o n t r a I p s i C o n t r a I p s i C o n t r a S t r i a t u m Controls' 1" 814.13 811.63 123.83 128.98 50.51 51.01 (n-8) 41.32 35.84 5.46 5.69 2.29 2.45 C i r c l e r s 793.75 792.00 130.79 137.93 54.86 54.19 (n-U) lO.IO Z l . /<i O.OZ /.J3 Z.<±/ 1.30 N u c l e u s Accumbens C o n t r o l s 570.75 531.83 133.10 136.95 42.53 42.50 (n~/) Z<± . / / 4) .OO 4.<iO O.UO 2.03 Z.Z3 C i r c l e r s 569.75 513.00 140.60 133.19 44.00 ( n — o ) z / . u u o / . o u 4.00 / .OO z . z u 1. L e f t and r i g h t t i s s u e samples o b t a i n e d f r o m c o n t r o l s u b j e c t s were randomly d e s i g n a t e d i p s i l a t e r a l and c o n t r a l a t e r a l . -23-was l o w e r t h a n t h a t o b t a i n e d by Yamamoto & F r e e d ( 1 9 8 2 ) . W h i l e t h e maximal r a t e s o f c i r c l i n g were s i m i l a r a c r o s s t h e two s t u d i e s , a n i m a l s i n t h e p r e s e n t s t u d y d i s p l a y e d a s u b s t a n t i a l r e d u c t i o n i n t u r n i n g b e h a v i o r w i t h i n t h e 20 min s e s s i o n s u c h t h a t , f o r t h e l a s t 6 min o f t h e s e s s i o n , t h e r a t s o n l y c i r c l e d an a v e r a g e o f 2-4 t i m e s p e r min. I t i s p o s s i b l e , t h e r e f o r e , t h a t l a t e r a l i z e d n e u r o c h e m i c a l changes a r e e v i d e n t o n l y i n s u b j e c t s e x h i b i t i n g h i g h e r o v e r a l l r a t e s o f c i r c l i n g . EXPERIMENT II Effects of Conditioned Circling Maintained by an Intermittent Schedule of Reinforcement on Mesotelencephalic DA Metabolism The f i r s t e x p e r i m e n t f a i l e d t o d e m o n s t r a t e an e f f e c t o f c o n d i t i o n e d c i r c l i n g on DA m e t a b o l i s m w i t h i n e i t h e r t h e s t r i a t u m o r n u c l e u s accumbens. As i n d i c a t e d above, i t seemed p o s s i b l e t h a t n e u r o c h e m i c a l changes were n o t o b t a i n e d b ecause o f t h e low t e r m i n a l l e v e l o f r e s p o n d i n g e x h i b i t e d by r a t s . A c c o r d i n g l y , a s econd e x p e r i m e n t was u n d e r t a k e n t o d e t e r m i n e t h e n e u r o c h e m i c a l consequences o f h i g h r a t e s o f c o n d i t i o n e d c i r c l i n g . To t h i s end, an i n t e r m i t t e n t s c h e d u l e o f r e i n f o r c e m e n t , r e s u l t i n g i n h i g h e r r e s p o n s e r a t e s , was employed. I f r e s p o n s e r a t e s a r e c r i t i c a l i n d e t e r m i n i n g t h e n e u r o c h e m i c a l c o r r e l a t e s o f c o n d i t i o n e d c i r c l i n g , t h e n l a t e r a l i z e d changes s h o u l d be r e a d i l y a p p a r e n t i n t h e p r e s e n t i n v e s t i g a t i o n . Materials and Methods S u b j e c t s and A p p a r a t u s N a i v e , male Sprague-Dawley r a t s , as d e s c r i b e d i n E x p e r i m e n t I , s e r v e d as s u b j e c t s . The a p p a r a t u s u s e d f o r b e h a v i o r a l t e s t i n g was as d e s c r i b e d p r e v i o u s l y . -24-P r o c e d u r e F i v e r a t s were randomly a s s i g n e d t o be t r a i n e d t o c i r c l e e i t h e r t o t h e l e f t o r t o t h e r i g h t . S u b j e c t s were w a t e r - d e p r i v e d f o r 23 h b e f o r e commencement o f t r a i n i n g . Food was a v a i l a b l e ad l i b i t u m i n t h e home cage. Each r a t r e c e i v e d 5 d a i l y 20 min t r a i n i n g s e s s i o n s d u r i n g w h i c h each c o m p l e t e c i r c l e was r e i n f o r c e d . On t h e 6 t h day o f t r a i n i n g , t h e f i r s t 10 r o t a t i o n s were r e i n f o r c e d a c c o r d i n g t o a CRF s c h e d u l e . T h e r e a f t e r , t h e s c h e d u l e o f r e i n f o r c e m e n t was s w i t c h e d t o a F i x e d R a t i o o f 2 ( F R - 2 ) , whereby e v e r y s e c o n d r o t a t i o n i n t h e a p p r o p r i a t e d i r e c t i o n was r e i n f o r c e d . T r a i n i n g c o n t i n u e d u n t i l e v e r y s u b j e c t was c o n s i s t e n t l y making a minimum o f 300 r o t a t i o n s w i t h i n a 20 min s e s s i o n ( i . e . e i t h e r 15 o r 21 s e s s i o n s ) . T r a i n i n g was i n t e r r u p t e d f o r 5 days f o l l o w i n g t h e 5 t h FR-2 s e s s i o n as t h e imposed s c h e d u l e o f w a t e r d e p r i v a t i o n r e s u l t e d i n t o o s e v e r e a degree o f w e i g h t l o s s ( i . e . 75% o f c o n t r o l w e i g h t s ) . D u r i n g t h i s 5 day p e r i o d , f o o d and w a t e r were a v a i l a b l e ad l i b i t u m . I m m e d i a t e l y f o l l o w i n g c o m p l e t i o n o f t h e l a s t s e s s i o n (Day 15 o r 21 o f FR-2 t r a i n i n g ) a n i m a l s were d e c a p i t a t e d . The b r a i n s were r a p i d l y removed and f r o z e n . L e f t and r i g h t s t r i a t u m , n u c l e u s accumbens and o l f a c t o r y t u b e r c l e were d i s s e c t e d f r o m t h e a p p r o p r i a t e t i s s u e s l i c e s , weighed and p r e p a r e d f o r a n a l y s i s by HPLC-ED as d e s c r i b e d i n E x p e r i m e n t 1. Three a d d i t i o n a l r a t s s e r v e d as c o n t r o l s u b j e c t s , as d e s c r i b e d p r e v i o u s l y . F o r p u r p o s e s o f a n a l y s i n g t h e n e u r o c h e m i c a l d a t a , t h e l e f t and r i g h t t i s s u e samples o b t a i n e d from c o n t r o l s u b j e c t s were randomly d e s i g n a t e d i p s i l a t e r a l and c o n t r a l a t e r a l . -25-Results B e h a v i o r R e l a t i v e t o t h e r a t e s o f r e s p o n d i n g o b t a i n e d when a CRF s c h e d u l e was employed ( E x p e r i m e n t I ) , i n t e r m i t t e n t r e i n f o r c e m e n t o f c i r c l i n g r e s u l t e d i n a marked i n c r e a s e i n r a t e s o f r e s p o n d i n g t h r o u g h o u t t h e s e s s i o n ( F i g u r e 1 ) . As i n t h e f i r s t e x p e r i m e n t , r e s p o n s e r a t e s were f o u n d t o d e c l i n e w i t h i n a s e s s i o n : F ( l , 4 ) = 3.713, p < .05. The mean m i n i m a l r e s p o n s e r a t e o b s e r v e d i n t h e t e s t s e s s i o n was, however, s l i g h t l y g r e a t e r t h a n t h e mean maximal r a t e s r e p o r t e d by Yamamoto & F r e e d ( 1 9 8 2 ) . N e u r o c h e m i s t r y S t r i a t u m . ANOVAs c o n d u c t e d on s t r i a t a l c o n c e n t r a t i o n s o f DA, DOPAC and HVA f a i l e d t o r e v e a l any s t a t i s t i c a l l y s i g n i f i c a n t e f f e c t s ( s e e T a b l e 2 ) . W h i l e DOPAC:DA r a t i o s d i d n o t d i f f e r between g r o u p s , a n a l y s i s o f t h e HVA:DA r a t i o s i n d i c a t e d t h a t t h e c o n v e r s i o n o f DA t o HVA was augmented b i l a t e r a l l y i n r a t s t r a i n e d t o c i r c l e f o r w a t e r r e i n f o r c e m e n t : F ( l , 5 ) = 7.264, p < .05 ( s e e F i g u r e 2 ) . T h i s f i n d i n g s u g g e s t s t h a t h i g h r a t e s o f c i r c l i n g , i n d u c e d and m a i n t a i n e d by w a t e r r e i n f o r c e m e n t , can r e s u l t i n an enhancement o f s t r i a t a l d o p a m i n e r g i c a c t i v i t y . However, t h i s n e u r o c h e m i c a l e f f e c t i s n o t r e s t r i c t e d t o t h e c o n t r a l a t e r a l s t r i a t u m , as s u g g e s t e d by Yamamoto & F r e e d (1982, 1984). N u c l e u s Accumbens. A n a l y s i s o f DA c o n c e n t r a t i o n s w i t h i n t h e n u c l e u s accumbens y i e l d e d a s t a t i s t i c a l l y s i g n i f i c a n t i n t e r a c t i o n : F ( l , 6 ) = 6.402, p < .05 ( T a b l e 2 ) . Newman-Keuls' p a i r - w i s e c o m p a r i s o n s ( a = .05) i n d i c a t e d t h a t t h e i n t e r a c t i o n r e f l e c t s an asymmetry i n DA c o n c e n t r a t i o n s i n a n i m a l s t r a i n e d t o c i r c l e , whereas i p s i l a t e r a l and c o n t r a l a t e r a l c o n c e n t r a t i o n s o f DA do n o t d i f f e r i n c o n t r o l s u b j e c t s . The d i r e c t i o n o f t h e asymmetry ( e . g . a d e c r e a s e i n c o n t r a l a t e r a l n u c l e u s accumbens as opposed t o an i n c r e a s e i n -26-T a b l e 2. Mean (± 3EM) c o n c e n t r a t i o n s o f DA, DOPAC and HVA (nmol/g p r o t e i n ) i n t h e s t r i a t u m , n u c l e u s accumbens and o l f a c t o r y t u b e r c l e i p s i l a t e r a l and c o n t r a l a t e r a l t o d i r e c t i o n o f t u r n i n g i n r a t s t r a i n e d t o c i r c l e u s i n g a FR-2 s c h e d u l e and i n n o n - c i r c l i n g c o n t r o l s . DOPAMINE DOPAC HVA I p s i C o n t r a I p s i C o n t r a I p s i C o n t r a S t r i a t u m C o n t r o l s 1 848.33 822.25 141.67 135.67 56.38 55.90 (n=3) 45.41 43.19 6.33 12.35 3.50 3.47 C i r c l e r s 822.25 777.00 134.25 122.00 63.23 61.05 (n=4) 24.12 12.92 3.97 3.53 5.23 1.91 N u c l e u s Accumbens C o n t r o l s 677.33 698.67 152.00 159.67 45.13 49.30 (n=3) 44.12 33.50 4.73 3.13 1.27 3.28 C i r c l e r s 623.20 619.30 157.00 152.00 62.40* 58.76* it it (n=5) 32.83 14.99 6.91 3.16 3.59 2.96 O l f a c t o r y T u b e r c l e C o n t r o l s 426.67 468.00 87.37 92.03 21.80 24.47 (n=3) 21.99 28.71 6.71 6.97 4.30 2.67 C i r c l e r s 424.00 393.40 92.33 82.40 23.43 26.42 (n=5) 28.95 24.08 10.04 4.49 1.95 2.13 1. L e f t and r i g h t t i s s u e samples o b t a i n e d f r o m c o n t r o l s u b j e c t s were randomly d e s i g n a t e d i p s i l a t e r a l and c o n t r a l a t e r a l . * — d i f f e r s f r o m a p p r o p r i a t e c o n t r o l v a l u e , p < .05. ** — d i f f f e r s f r o m own i p s i l a t e r a l v a l u e , p < .05. -27-F i g u r e 2. R a t i o s (± SEM) o f DOPAC and HVA t o DA i n s t r i a t u m i p s i l a t e r a l and c o n t r a l a t e r a l t o d i r e c t i o n o f t u r n i n g . R a t s were t r a i n e d t o c i r c l e a c c o r d i n g t o a FR-2 s c h e d u l e o f w a t e r r e i n f o r c e m e n t . R a t s were e i t h e r t e s t e d f o r 20 min ( c i r c l e r s ; n=4) o r were g i v e n a c c e s s t o w a t e r i n t h e i r home cage f o r 20 min ( c o n t r o l s ; n=3) b e f o r e b e i n g d e c a p i t a t e d . I p s i l a t e r a l / c o n t r a l a t e r a l d e s i g n a t i o n o f c o n t r o l v a l u e s was random. * d i f f e r s f r o m r e s p e c t i v e c o n t r o l v a l u e . i p s i l a t e r a l n u c l e u s accumbens) c a n n o t , however, be s t a t i s t i c a l l y d e t e r m i n e d s i n c e n e i t h e r o f t h e e x p e r i m e n t a l v a l u e s d i f f e r e d f r o m t h e a p p r o p r i a t e c o n t r o l v a l u e s . I n s p e c t i o n o f t h e d a t a does, however, i n d i c a t e t h a t c o n c e n t r a t i o n s t e n d t o be l o w e r i n t h e c o n t r a l a t e r a l n u c l e u s accumbens, r e l a t i v e t o b o t h t h e i p s i l a t e r a l n u c l e u s accumbens and c o n t r o l v a l u e s . The o v e r a l l a n a l y s i s c o n d u c t e d on DOPAC c o n c e n t r a t i o n s i n t h e n u c l e u s accumbens d i d n o t y i e l d any s t a t i s t i c a l l y s i g n i f i c a n t d i f f e r e n c e s . However, a n a l y s i s o f HVA c o n c e n t r a t i o n s y i e l d e d a s i g n i f i c a n t i n t e r a c t i o n t e r m : F ( l , 6 ) = 16.83, p < .01. P a i r - w i s e c o m p a r i s o n s ( a = .05) i n d i c a t e d t h a t , r e l a t i v e t o c o n t r o l v a l u e s , HVA was i n c r e a s e d b i l a t e r a l l y i n r a t s t r a i n e d t o c i r c l e . The c o n c e n t r a t i o n o f HVA i n t h e c o n t r a l a t e r a l n u c l e u s accumbens o f c i r c l e r s was, however, l o w e r t h a n w i t h i n t h e i p s i l a t e r a l n u c l e u s accumbens ( s ee T a b l e 2 ) . W h i l e t h e b i l a t e r a l enhancement o f DA m e t a b o l i s m i n r a t s t r a i n e d t o c i r c l e was f u r t h e r r e f l e c t e d i n t h e HVA:DA r a t i o s : F ( l , 6 ) = 20.99, p < .01, t h e r a t i o s d i d n o t i n d i c a t e a s y m m e t r i c a l l e v e l s o f DA a c t i v i t y ( F i g u r e 3 ) . O l f a c t o r y T u b e r c l e . As i n d i c a t e d i n T a b l e 2, t h e c o n c e n t r a t i o n s o f DA, DOPAC and HVA i n t h e o l f a c t o r y t u b e r c l e were n o t i n f l u e n c e d by p e r f o r m a n c e o f t h e c o n d i t i o n e d c i r c l i n g r e s p o n s e . I n a d d i t i o n , t h e r e was no e v i d e n c e o f a l t e r e d l e v e l s o f a c t i v i t y when r a t i o s o f t h e m e t a b o l i t e s t o DA were a n a l y z e d . D i s c u s s i o n Taken t o g e t h e r , t h e r e s u l t s o f t h i s e x p e r i m e n t i n d i c a t e t h a t h i g h r a t e s o f c i r c l i n g b e h a v i o r i n d u c e d and m a i n t a i n e d by p o s i t i v e r e i n f o r c e m e n t can p r o d u c e s e l e c t i v e n e u r o c h e m i c a l changes i n i n t a c t r a t s . S p e c i f i c a l l y , t h e t u r n o v e r o f DA, as e s t i m a t e d by HVA:DA r a t i o s , i s i n c r e a s e d b i l a t e r a l l y i n b o t h t h e s t r i a t u m and t h e n u c l e u s accumbens o f r a t s t r a i n e d t o c i r c l e , -30-F i g u r e 3. R a t i o s (± SEM) o f DOPAC and HVA t o DA i n n u c l e u s accumbens i p s i l a t e r a l and c o n t r a l a t e r a l t o d i r e c t i o n o f c i r c l i n g . See F i g u r e 2 f o r p r o c e d u r a l d e t a i l s ( C o n t r o l s - n = 3; C i r c l e r s - n = 5 ) . * d i f f e r s f rom r e s p e c t i v e c o n t r o l v a l u e . • IPSILATERAL m CONTRALATERAL Controls Circlers -32-r e l a t i v e t o n o n - c i r c l i n g c o n t r o l s . The p r e s e n t r e s u l t s a l s o i n d i c a t e t h a t c o n d i t i o n e d c i r c l i n g , a b e h a v i o r t h a t i s c o n s i d e r e d t o be a l a t e r a l i z e d r e s p o n s e , p r o d u c e s some a s y m m e t r i c a l changes i n t h e m e s o l i m b i c DA system b u t n o t i n t h e m e s o s t r i a t a l DA p r o j e c t i o n . W h i l e i t i s e v i d e n t t h a t accumbens DA f u n c t i o n was b i l a t e r a l l y enhanced r e l a t i v e t o n o n - c i r c l i n g c o n t r o l s u b j e c t s , t h e l o w e r c o n c e n t r a t i o n s o f DA and HVA i n t h e c o n t r a l a t e r a l n u c l e u s accumbens, r e l a t i v e t o t h e i p s i l a t e r a l n u c l e u s accumbens, a r e s u g g e s t i v e o f an asymmetry i n t h e e x t e n t t o w h i c h D A e r g i c a c t i v i t y i s enhanced by c i r c l i n g . The s i g n i f i c a n c e o f t h i s f i n d i n g i s n o t i m m e d i a t e l y c l e a r . I f t h e d e c r e a s e i n DA r e f l e c t s an i n c r e a s e i n r e l e a s e and/or m e t a b o l i s m t h e n one would e x p e c t t o o b s e r v e a c o n c o m i t a n t i n c r e a s e i n m e t a b o l i t e c o n c e n t r a t i o n s . W h i l e c o n t r a l a t e r a l c o n c e n t r a t i o n s o f HVA were i n c r e a s e d w i t h r e s p e c t t o t h e c o n t r o l s u b j e c t s , t h e y were l o w e r w i t h r e s p e c t t o c o n c e n t r a t i o n s w i t h i n t h e i p s i l a t e r a l n u c l e u s accumbens. One p o s s i b l e e x p l a n a t i o n i s t h a t t r a n s p o r t o f t h e m e t a b o l i t e s was a l s o enhanced (see H e f f n e r , e t a l . , 1984). I f t h i s were t h e c a s e , t h e l o w e r HVA c o n c e n t r a t i o n s w i t h i n t h e c o n t r a l a t e r a l n u c l e u s accumbens may have been due t o an a s y m m e t r i c a l i n c r e a s e i n t r a n s p o r t mechanisms. The p r e s e n t r e s u l t s p r o v i d e f u r t h e r e v i d e n c e t h a t DA i s i n v o l v e d i n t h e p e r f o r m a n c e o f t h e c o n d i t i o n e d c i r c l i n g r e s p o n s e . A l t h o u g h some e v i d e n c e o f a s y m m e t r i c a l changes i n DA a c t i v i t y was o b t a i n e d i n a n i m a l s t r a i n e d t o c i r c l e u s i n g an i n t e r m i t t e n t s c h e d u l e o f r e i n f o r c e m e n t , t h e r e s u l t s a r e q u a l i t a t i v e l y and q u a n t i t a t i v e l y d i f f e r e n t f r o m t h o s e r e p o r t e d by Yamamoto & F r e e d (1982; 1984). F i r s t , as p r e v i o u s l y i n d i c a t e d , a s y m m e t r i c a l n e u r o c h e m i c a l changes were e v i d e n t o n l y w i t h i n t h e n u c l e u s accumbens i n t h e p r e s e n t e x p e r i m e n t s . M o r e o v e r , DA and HVA c o n c e n t r a t i o n s t e n d e d t o be l o w e r i n t h e n u c l e u s accumbens c o n t r a l a t e r a l t o t h e a n i m a l s ' -33-d i r e c t i o n o f t u r n i n g . I n c o n t r a s t , t h e f o r m e r r e p o r t s i n d i c a t e d t h a t c i r c l i n g r e s u l t e d i n i n c r e a s e d c o n c e n t r a t i o n s o f DA and DOPAC i n t h e n u c l e u s accumbens and s t r i a t u m c o n t r a l a t e r a l t o d i r e c t i o n o f c i r c l i n g . W h i l e no e f f e c t s on t h e a b s o l u t e c o n c e n t r a t i o n s o f e i t h e r DOPAC o r HVA were o b s e r v e d i n t h e s t r i a t a and o l f a c t o r y t u b e r c l e , HVA i n t h e n u c l e u s accumbens was e l e v a t e d b i l a t e r a l l y . The e x t e n t o f t h e i n c r e a s e was, as j u s t m e n t i o n e d , l e s s i n t h e n u c l e u s accumbens c o n t r a l a t e r a l t o t h e d i r e c t i o n o f t u r n i n g . E v i d e n c e f o r b i l a t e r a l l y enhanced u t i l i z a t i o n was a l s o o b t a i n e d when HVA:DA r a t i o s were examined. I t s h o u l d be n o t e d t h a t when t h e r a t i o s were a n a l y z e d t h e r e was no i n d i c a t i o n o f a s y m m e t r i c a l l e v e l s o f a c t i v i t y w i t h i n t h e n u c l e u s accumbens. One p o s s i b l e e x p l a n a t i o n f o r t h e s e d i f f e r e n t r e s u l t s c o n c e r n s t h e r e l a t i v e l e v e l o f r e s p o n d i n g o b t a i n e d a t t h e t i m e when a n i m a l s were d e c a p i t a t e d . That i s , w h i l e Yamamoto & F r e e d r e p o r t e d maximal n e u r o c h e m i c a l changes f o l l o w i n g 20 min o f c i r c l i n g , t h e n e u r o c h e m i c a l c o r r e l a t e s o f c i r c l i n g may be c r i t i c a l l y dependent upon t h e p r o f i l e o f r e s p o n d i n g . I n b o t h E x p e r i m e n t s I and I I r a t e s o f r e s p o n d i n g had d e c l i n e d by t h e end o f t h e t e s t i n g s e s s i o n . As s u c h , i t i s p o s s i b l e t h a t a d i f f e r e n t n e u r o c h e m i c a l p r o f i l e w o u l d have been o b t a i n e d had a n i m a l s been s a c r i f i c e d a t ^ t h e t i m e when maximal l e v e l s o f r e s p o n d i n g o c c u r r e d . I n c o n c l u s i o n , t h e r e s u l t s o f t h e second e x p e r i m e n t s u p p o r t p r e v i o u s s u g g e s t i o n s t h a t DA systems a r e i n v o l v e d i n c i r c l i n g . However, t h e f a i l u r e t o o b s e r v e r o b u s t a s y m m e t r i c a l changes i n DA a c t i v i t y i s i n c o n s i s t e n t w i t h t h e h y p o t h e s i s t h a t c i r c l i n g i s m e d i a t e d by an asymmetry i n DA f u n c t i o n i n g . I t i s p o s s i b l e t h a t d i f f e r e n t n e u r a l p r o c e s s e s u n d e r l y c i r c l i n g i n d u c e d w i t h d i f f e r e n t p a r a d i g m s ( e . g . c o n d i t i o n e d c i r c l i n g and d r u g - i n d u c e d c i r c l i n g ) . To t h i s end, i t i s i n t e r e s t i n g t o n o t e t h a t t h e o v e r a l l -34-n e u r o c h e m i c a l p r o f i l e a s s o c i a t e d w i t h c i r c l i n g i n d u c e d by i n t r a c r a n i a l e l e c t r i c a l s t i m u l a t i o n i s s u b s t a n t i a l l y d i f f e r e n t f r o m t h e r e s u l t s o b t a i n e d i n t h i s s e c o n d e x p e r i m e n t ( S z o s t a k , J a k u b o v i c , P h i l l i p s and F i b i g e r , 1986). S p e c i f i c a l l y , s t i m u l a t i o n - i n d u c e d c i r c l i n g was a s s o c i a t e d w i t h an i n c r e a s e i n DA m e t a b o l i s m w i t h i n t h e s t r i a t u m c o n t r a l a t e r a l t o t h e d i r e c t i o n o f c i r c l i n g . No changes were d e t e c t e d w i t h i n t h e n u c l e u s accumbens ( S z o s t a k , e t a l . , 1986). EXPERIMENT III Effects of Conditioned Circling on Synthesis of Mesotelencephalic DA The r e s u l t s o f E x p e r i m e n t I I i n d i c a t e d a b e h a v i o r a l l y - i n d u c e d b i l a t e r a l a u g m e n t a t i o n i n t h e m e t a b o l i s m o f s t r i a t a l and accumbens DA. G i v e n t h a t DA m e t a b o l i s m i s t i g h t l y c o u p l e d t o i t s r a t e o f s y n t h e s i s ( s e e Cooper, Bloom & R o t h , 1982), one would e x p e c t t h a t DA s y n t h e s i s w o u l d a l s o be i n c r e a s e d b i l a t e r a l l y i n r a t s e x h i b i t i n g h i g h r a t e s o f c o n d i t i o n e d c i r c l i n g . However, i t has been r e p o r t e d p r e v i o u s l y t h a t t h e r a t e o f DA s y n t h e s i s i s u n i l a t e r a l l y augmented i n t h e s t r i a t u m o f r a t s t r a i n e d t o c i r c l e f o r s u c r o s e r e i n f o r c e m e n t ( B e n n e t t & F r e e d , 1986; Morgan, Yamamoto & F r e e d , 1984). F o r example, t h e a c t i v i t y o f t y r o s i n e h y d r o x y l a s e , t h e r a t e -l i m i t i n g enzyme i n c a t e c h o l a m i n e b i o s y n t h e s i s , was r e p o r t e d t o be enhanced o n l y i n t h e s t r i a t u m c o n t r a l a t e r a l t o t h e d i r e c t i o n o f r e i n f o r c e d c i r c l i n g (Morgan, e t a l . , 1984). S i m i l a r l y , f o l l o w i n g t h e a d m i n i s t r a t i o n o f [°H]tyrosine, B e n n e t t & F r e e d (1986) r e p o r t e d an a s y m m e t r i c a l i n c r e a s e i n c o n c e n t r a t i o n s o f [°H]dopamine w i t h i n t h e c o n t r a l a t e r a l s t r i a t u m . The t h i r d e x p e r i m e n t was u n d e r t a k e n t o d e t e r m i n e t h e e f f e c t s o f c o n d i t i o n e d c i r c l i n g on t h e b i o s y n t h e s i s o f DA, under c o n d i t i o n s a s s o c i a t e d w i t h a b i l a t e r a l a u g m e n t a t i o n o f DA m e t a b o l i s m . I t has p r e v i o u s l y been d e m o n s t r a t e d t h a t t h e b i o s y n t h e s i s o f DA can be e s t i m a t e d by m e a s u r i n g t h e -35-a c c u m u l a t i o n o f DOPA f o l l o w i n g t h e i n h i b i t i o n o f a r o m a t i c - L - a m i n o a c i d d e c a r b o x y l a s e ( C a r l s s o n , D a v i s , K e h r , L i n d g y i s t & A t a c k , 1972). As s u c h , i n E x p e r i m e n t I I I , r a t s were t r a i n e d t o c i r c l e f o r w a t e r , a c c o r d i n g t o a FR-2 s c h e d u l e o f r e i n f o r c e m e n t . Upon e s t a b l i s h m e n t o f s t a b l e r a t e s o f r e s p o n d i n g , s i m i l a r t o t h o s e o b t a i n e d i n E x p e r i m e n t I I , r a t s were a d m i n i s t e r e d NSD-1015 ( m - h y d r o x y b e n z y l h y d r a z i n e d i h y d r o c h l o r i d e ) , a DOPA d e c a r b o x y l a s e i n h i b i t o r , and t h e n t e s t e d f o r c o n d i t i o n e d c i r c l i n g . C o n c e n t r a t i o n s o f DOPA were d e t e r m i n e d i n t h e s t r i a t u m , n u c l e u s accumbens and o l f a c t o r y t u b e r c l e u s i n g HPLC-ED. Materials and Methods S u b j e c t s and A p p a r a t u s E i g h t e e n , n a i v e male Sprague-Dawley r a t s , as d e s c r i b e d i n t h e f i r s t e x p e r i m e n t , s e r v e d as s u b j e c t s . The b e h a v i o r a l a p p a r a t u s was as d e s c r i b e d p r e v i o u s l y . P r o c e d u r e E i g h t r a t s were randomly a s s i g n e d t o be t r a i n e d t o c i r c l e e i t h e r t o t h e l e f t o r t o t h e r i g h t f o r w a t e r r e i n f o r c e m e n t . The t r a i n i n g p r o t o c o l was as d e s c r i b e d i n E x p e r i m e n t I I . Upon e s t a b l i s h m e n t o f s t a b l e r a t e s o f c i r c l i n g (15 days o f FR-2 t r a i n i n g ) , r a t s r e c e i v e d a 20 min t e s t s e s s i o n . E x p e r i m e n t a l c o n t i n g e n c i e s were i d e n t i c a l t o t h o s e i n e f f e c t d u r i n g t r a i n i n g ( i . e . FR-2 s c h e d u l e o f r e i n f o r c e m e n t ) . R a t s r e c e i v e d an i n t r a p e r i t o n e a l i n j e c t i o n o f NSD-1015 (50 mg/kg/ml o f s a l i n e ) 10 min b e f o r e b e i n g t e s t e d . I m m e d i a t e l y f o l l o w i n g t h e t e s t s e s s i o n ( i . e . 30 min p o s t -i n j e c t i o n ) , r a t s were d e c a p i t a t e d , t h e i r b r a i n s r a p i d l y removed and f r o z e n . The l e f t and r i g h t s t r i a t u m , n u c l e u s accumbens and o l f a c t o r y t u b e r c l e were d i s s e c t e d , as d e s c r i b e d i n t h e f i r s t e x p e r i m e n t . A l l t i s s u e samples were p r e p a r e d f o r t h e a n a l y s i s o f DOPA c o n c e n t r a t i o n s u s i n g HPLC-ED, as -36-d e s c r i b e d i n E x p e r i m e n t I . A l o w e r c o n c e n t r a t i o n o f m e t h a n o l (2%) was, however, u s e d i n t h e b u f f e r s o l u t i o n t o p e r m i t t h e d e t e r m i n a t i o n o f DOPA c o n c e n t r a t i o n s . The r e m a i n i n g 10 r a t s s e r v e d as c o n t r o l s u b j e c t s . Each r a t was w a t e r -d e p r i v e d f o r t h e d u r a t i o n o f t h e e x p e r i m e n t , as d e s c r i b e d p r e v i o u s l y . On t h e t e s t day, 5 o f t h e r a t s r e c e i v e d an i n j e c t i o n o f NSD-1015 (50 mg/kg, i p ) w h i l e t h e r e m a i n i n g r a t s were i n j e c t e d w i t h t h e v e h i c l e s o l u t i o n 10 min b e f o r e b e i n g g i v e n a c c e s s t o w a t e r . B o t h c o n t r o l groups were s a c r i f i c e d a f t e r h a v i n g a c c e s s t o w a t e r f o r a 20 min p e r i o d i n t h e i r home c a g e s . F o r p u r p o s e s o f a n a l y s i n g t h e n e u r o c h e m i c a l d a t a , t h e l e f t and r i g h t t i s s u e samples o b t a i n e d f r o m t h e c o n t r o l g r o u p s were randomly d e s i g n a t e d i p s i l a t e r a l and c o n t r a l a t e r a l . Results B e h a v i o r . To d e t e r m i n e t h e e f f e c t s o f NSD-1015 on p e r f o r m a n c e o f c o n d i t i o n e d c i r c l i n g , r e s p o n d i n g d u r i n g t h e l a s t t r a i n i n g s e s s i o n ( B a s e l i n e ) was compared w i t h t h a t e x h i b i t e d d u r i n g t h e t e s t s e s s i o n ( s e e F i g u r e 4 ) . An ANOVA w i t h two r e p e a t e d f a c t o r s (Drug; B l o c k s o f two m i n u t e s ) y i e l d e d s i g n i f i c a n t main e f f e c t s o f b o t h f a c t o r s : Drug - F ( l , 7 ) = 6.06, p < .05, and B l o c k - F ( l , 7 ) = 7.61, p < .05. The a d m i n i s t r a t i o n o f NSD-1015 r e s u l t e d i n an a t t e n u a t i o n o f r e s p o n d i n g . W h i l e i n s p e c t i o n o f F i g u r e 4 s u g g e s t s t h a t r e s p o n d i n g was n o t i n f l u e n c e d by t h e d r u g i n i t i a l l y , t h e Drug x B l o c k i n t e r a c t i o n was n o t s i g n i f i c a n t . A l t h o u g h r e s p o n d i n g was s i g n i f i c a n t l y d e c r e a s e d , i t s h o u l d be n o t e d t h a t t h e m i n i m a l r e s p o n s e r a t e was s i m i l a r t o t h e maximal r a t e r e p o r t e d by Yamamoto & F r e e d ( 1 9 8 2 ) . A c c o r d i n g l y , t h e e x t e n t o f t h e r e s p o n s e s u p p r e s s i o n i n d u c e d by a d m i n i s t r a t i o n o f NSD-1015 woul d n o t be e x p e c t e d t o p r e c l u d e d e t e c t i o n o f -37-F i g u r e 4. Mean (± 3EM) number o f r o t a t i o n s p e r m i n u t e o b t a i n e d d u r i n g b a s e l i n e and t e s t s e s s i o n s a r e p r e s e n t e d i n b l o c k s o f two m i n u t e s (n=8). S o l i d c i r c l e s r e p r e s e n t d a t a o f r a t s o b t a i n e d d u r i n g t h e l a s t t r a i n i n g s e s s i o n . Mean r e s p o n s e r a t e s o f r a t s f o l l o w i n g an i n j e c t i o n o f NSD-1015, a DOPA d e c a r b o x y l a s e i n h i b i t o r , a r e d e p i c t e d w i t h open c i r c l e s . Lul 25-i a: b J 2 0 . z g O 10 on 15 H m i 0 0 I BASELINE O NSP-1015 (50 mg/kg) 5H < UJ " T ~ 2 T " 4 T 5 6 7 T " 8 10 BLOCKS OF TWO MINUTES -39-b e h a v i o r a l l y - i n d u c e d changes i n DA s y n t h e s i s . The s i g n i f i c a n t B l o c k e f f e c t c o n f i r m s t h e o b s e r v a t i o n i n E x p e r i m e n t I I t h a t r a t e o f r e s p o n d i n g p r o g r e s s i v e l y d e c r e a s e s w i t h i n a s e s s i o n , a l b e i t t h e r a t e and e x t e n t o f d e c l i n e was c o n s i d e r a b l y l e s s i n t h e p r e s e n t e x p e r i m e n t . N e u r o c h e m i s t r y . C o n c e n t r a t i o n s o f DOPA c o u l d n o t be d e t e c t e d w i t h i n t h e s t r i a t a , n u c l e u s accumbens and o l f a c t o r y t u b e r c l e s o f r a t s t h a t r e c e i v e d a v e h i c l e i n j e c t i o n p r i o r t o b e i n g d e c a p i t a t e d . T h e r e f o r e , f o r p u r p o s e s o f s t a t i s t i c a l a n a l y s i s , t h e d a t a from t h i s group were o m i t t e d . A c c o r d i n g l y , ANOVAs w i t h one between s u b j e c t f a c t o r (Group - 2 l e v e l s ) and one r e p e a t e d measure (Hemisphere) were c o n d u c t e d upon c o n c e n t r a t i o n s o f DOPA o b t a i n e d w i t h i n each s t r u c t u r e examined. No s i g n i f i c a n t d i f f e r e n c e s were d e t e c t e d i n any o f t h e t h r e e r e g i o n s examined. However, as i n d i c a t e d i n T a b l e 3, t h e r e was a t r e n d f o r DOPA c o n c e n t r a t i o n s t o be b i l a t e r a l l y e l e v a t e d w i t h i n t h e s t r i a t a and n u c l e u s accumbens o f r a t s t r a i n e d t o c i r c l e f o r w a t e r r e i n f o r c e m e n t . Discussion H i g h r a t e s o f c o n d i t i o n e d c i r c l i n g were n o t o b s e r v e d t o i n f l u e n c e s i g n i f i c a n t l y t h e b i o s y n t h e s i s o f DA, as e s t i m a t e d by t h e a c c u m u l a t i o n o f DOPA f o l l o w i n g i n h i b i t i o n o f DOPA d e c a r b o x y l a s e , w i t h i n t h e s t r i a t u m , n u c l e u s accumbens o r o l f a c t o r y t u b e r c l e . I t s h o u l d be n o t e d , however, t h a t c o n c e n t r a t i o n s t e n d e d t o be e l e v a t e d i n t h e s t r i a t u m and accumbens o f r a t s t r a i n e d t o c i r c l e . T h i s t r e n d was b i l a t e r a l i n n a t u r e . G i v e n t h a t DA m e t a b o l i s m w i t h i n t h e s e two s t r u c t u r e s was o b s e r v e d t o be b i l a t e r a l l y i n c r e a s e d by c o n d i t i o n e d c i r c l i n g ( E x p e r i m e n t I I ) , i t was e x p e c t e d t h a t s y n t h e s i s w o u l d a l s o be b i l a t e r a l l y enhanced. I t i s p o s s i b l e t h a t a l a r g e r sample s i z e w o u l d r e s u l t i n d e c r e a s e d v a r i a n c e w h i c h , i n t u r n , c o u l d p e r m i t -40-T a b l e 3. Mean (± 3.E.M.) c o n c e n t r a t i o n s o f DOPA (nmol/g p r o t e i n ) i n t h e s t r i a t u m , n u c l e u s accumbens and o l f a c t o r y t u b e r c l e i p s i l a t e r a l and c o n t r a l a t e r a l t o t h e d i r e c t i o n o f t u r n i n g i n r a t s t r a i n e d t o c i r c l e u s i n g a FR-2 s c h e d u l e o f r e i n f o r c e m e n t and i n n o n - c i r c l i n g c o n t r o l s . DOPA I p s i C o n t r a S t r i a t u m C o n t r o l s 1 10.86 10.69 (n=5) U . 3 _ L 1.70 C i r c l e r s _ L O . _ L U 12.81 <n=8) U . 3 J 0.95 N u c l e u s Accumbens C o n t r o l s 24.28 23.84 (n=5) ~» r" r\ Z . D U 1 |—i r~ X . O D C i r c l e r s 26.98 26.24 (n=8) -I A r- 2.02 O l f a c t o r y T u b e r c l e C o n t r o l s 20.94 20.70 (n=5) *1 A O 1.58 C i r c l e r s 21.13 21.34 (n=8) ±. uz 1.21 1. L e f t and r i g h t t i s s u e samples o b t a i n e d f r o m c o n t r o l s u b j e c t s were randomly d e s i g n a t e d i p s i l a t e r a l and c o n t r a l a t e r a l . -41-t h e d e t e c t i o n o f a s i g n i f i c a n t i n c r e a s e . A l t e r n a t i v e l y , i t i s p o s s i b l e t h a t a t i m e l a g e x i s t s between t h e e f f e c t s o f c o n d i t i o n e d c i r c l i n g on DA m e t a b o l i s m and on t h e b i o s y n t h e s i s o f DA. I n E x p e r i m e n t I I , t h e r e was a t r e n d f o r c o n c e n t r a t i o n s o f DA t o be l o w e r i n r a t s t r a i n e d t o c i r c l e , r e l a t i v e t o n o n - c i r c l i n g c o n t r o l s u b j e c t s . A c c o r d i n g l y , DA u t i l i z a t i o n may be p r e f e r e n t i a l l y i n f l u e n c e d by c o n d i t i o n e d c i r c l i n g . However, an i n c r e a s e i n b i o s y n t h e s i s c o u l d s u b s e q u e n t l y o c c u r i n r e s p o n s e t o a f e e d b a c k mechanism. C o n v e r s e l y , i t i s p o s s i b l e t h a t s y n t h e s i s was shut-down due t o t h e s t i m u l a t i o n o f a u t o r e c e p t o r s f o l l o w i n g an i n c r e a s e i n t h e r e l e a s e o f DA. F u r t h e r e x p e r i m e n t s a r e r e q u i r e d t o c h a r a c t e r i z e more f u l l y t h e e f f e c t s o f c o n d i t i o n e d c i r c l i n g on t h e b i o s y n t h e s i s and m e t a b o l i s m o f DA w i t h i n b o t h t h e s t r i a t u m and n u c l e u s accumbens. The r e s u l t s o f t h i s e x p e r i m e n t f a i l e d t o c o n f i r m p r e v i o u s r e p o r t s t h a t c o n d i t i o n e d c i r c l i n g i s a s s o c i a t e d w i t h a u n i l a t e r a l i n c r e a s e i n s t r i a t a l DA s y n t h e s i s . As i n d i c a t e d above, w h i l e a t r e n d f o r i n c r e a s e d s y n t h e s i s was o b s e r v e d , t h e r e was no e v i d e n c e f o r an a s y m m e t r i c a l e f f e c t o f c o n d i t i o n e d c i r c l i n g on DOPA c o n c e n t r a t i o n s . The b a s i s f o r t h e s e d i s c r e p a n t r e s u l t s i s u n c l e a r . EXPERIMENT IV Influence of Inherent Directional Biases on Neurochemical Consequences of Conditioned Circling The r e s u l t s o f E x p e r i m e n t I I s u g g e s t t h a t DA mechanisms w i t h i n b o t h t h e i p s i - and c o n t r a l a t e r a l m e s o t e l e n c e p h a l i c DA p r o j e c t i o n s s u b s e r v e c o n d i t i o n e d c i r c l i n g ( s e e a l s o S c h w a r t i n g & H u s t o n , 1987). These o b s e r v a t i o n s a r e i n c o n s i s t e n t w i t h t h e h y p o t h e s i s t h a t an asymmetry i n s t r i a t a l DA a c t i v i t y u n d e r l i e s DA-mediated c i r c l i n g ( f o r r e v i e w see P y c o c k , 1930). I t i s p o s s i b l e t h a t an asymmetry i n DA m e t a b o l i s m was n o t d e t e c t e d -42-because i n h e r e n t d i r e c t i o n a l b i a s e s were n o t c o n t r o l l e d f o r i n E x p e r i m e n t I I ( G l i c k , J e r u s s i & F l e i s c h e r , 1976). F o r example, t h e magnitude and d i r e c t i o n o f amphetamine-induced c i r c l i n g e x h i b i t e d by r a t s w i t h u n i l a t e r a l l e s i o n s o f t h e s u b s t a n t i a n i g r a a r e dependent upon whether t h e "dominant" o r "non-dominant" ( w i t h r e s p e c t t o DA a c t i v i t y ) system i s l e s i o n e d ( R o b i n s o n & B e c k e r , 1983). A c c o r d i n g l y , t h e n e u r o c h e m i c a l consequences o f c o n d i t i o n e d c i r c l i n g may v a r y as a f u n c t i o n o f t h e d i r e c t i o n o f t u r n i n g i n r e l a t i o n t o t h e dominant m e s o t e l e n c e p h a l i c DA p r o j e c t i o n . G l i c k & H i n d s (1984) have r e p o r t e d t h a t r a t s a r e a b l e t o a c q u i r e t h e c o n d i t i o n e d c i r c l i n g r e s p o n s e when t h e d i r e c t i o n i s i n a c c o r d w i t h t h e i r b i a s . However, a p p r o x i m a t e l y t w o - t h i r d s o f t h e i r s u b j e c t s were u n a b l e t o a c q u i r e t h e r e s p o n s e when d i r e c t e d a g a i n s t t h e i r p r e f e r r e d d i r e c t i o n o f t u r n i n g . I t s h o u l d be n o t e d however t h a t Yamamoto & F r e e d (1934) have n o t o b s e r v e d any e f f e c t o f i n h e r e n t d i r e c t i o n a l p r e f e r e n c e s on t h e a c q u i s i t i o n o f t h e c o n d i t i o n e d c i r c l i n g r e s p o n s e . I n f a c t , t h e y r e p o r t e d t h a t d i r e c t i o n a l b i a s e s c o u l d be r e v e r s e d by o p e r a n t c o n d i t i o n i n g . Two e x p e r i m e n t s were c o n d u c t e d t o c l a r i f y t h e i n f l u e n c e o f i n n a t e d i r e c t i o n a l b i a s e s on t h e a c q u i s i t i o n and p e r f o r m a n c e o f c o n d i t i o n e d c i r c l i n g . I n a d d i t i o n , i t was d e t e r m i n e d whether d i r e c t i o n a l p r e f e r e n c e s a l t e r t h e e f f e c t s o f c o n d i t i o n e d c i r c l i n g on DA m e t a b o l i s m w i t h i n t h e s t r i a t u m , n u c l e u s accumbens and o l f a c t o r y t u b e r c l e . Experiment IVa Assessment of Rat's Inherent Directional Biases I n t a c t , n a i v e r a t s i n j e c t e d s y s t e m i c a l l y w i t h e i t h e r amphetamine o r apomorphine a r e r e p o r t e d t o c i r c l e p r e d o m i n a n t l y i n one d i r e c t i o n ( J e r u s s i & G l i c k , 1976; Szechtman & P i s a , 1986; see a l s o , R o b i n s o n , B e c k e r & Camp, 1983). T h i s b e h a v i o r a l asymmetry has been c o r r e l a t e d w i t h i n c r e a s e d c o n c e n t r a t i o n s o f DA i n t h e c o n t r a l a t e r a l s t r i a t u m o f f e m a l e r a t s . W h i l e a s i m i l a r asymmetry has n o t been c o n s i s t e n t l y d e t e c t e d i n male r a t s , i t has been s u g g e s t e d t h a t d i r e c t i o n a l b i a s e s a r e r e l a t e d t o an asymmetry i n s t r i a t a l DA a c t i v i t y ( G l i c k & S h a p i r o , 1985; S h a p i r o , e t a l . , 1986). A c c o r d i n g l y , t h i s p r o c e d u r e i s commonly u s e d t o d e t e r m i n e d i r e c t i o n a l b i a s e s ( e . g . G l i c k & K i n d s , 1984; Yamamoto & F r e e d , 1984b). However, t h e a c u t e a d m i n i s t r a t i o n o f amphetamine ca n have l o n g l a s t i n g n e u r 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 ( R o b i n s o n , 1984; R o b i n s o n , B e c k e r & P r e s t y , 1982). These l o n g - t e r m consequences o f amphetamine may t h e r e f o r e l i m i t t h e u s e f u l n e s s o f t h i s p a r a d i g m as a method f o r d e t e r m i n i n g d i r e c t i o n a l b i a s e s . F o r example, e x p o s u r e t o amphetamine c o u l d a l t e r t h e n e u r o c h e m i c a l changes a s s o c i a t e d w i t h c o n d i t i o n e d c i r c l i n g . I t has been s u g g e s t e d t h a t d i r e c t i o n a l b i a s e s can a l s o be d e t e c t e d i n r a t s by o b s e r v i n g t h e spontaneous c i r c l i n g t h a t o c c u r s d u r i n g t h e d a r k phase o f t h e d i u r n a l c y c l e . The p r e f e r r e d d i r e c t i o n o f s p o n t a n e o u s , n o c t u r n a l c i r c l i n g has been r e p o r t e d t o be c o n s i s t e n t w i t h t h a t o b s e r v e d f o l l o w i n g t h e a d m i n i s t r a t i o n o f amphetamine ( G l i c k & Cox, 1978). A l t h o u g h t h e r a t e s o f spontaneous c i r c l i n g a r e o f t e n l o w , p r o h i b i t i n g t h e r e l i a b l e d e t e r m i n a t i o n o f d i r e c t i o n a l b i a s e s , i t i s p o s s i b l e t o i n c r e a s e t h e r a t e o f c i r c l i n g by r e i n f o r c i n g each r o t a t i o n e m i t t e d , r e g a r d l e s s o f d i r e c t i o n ( i . e . n o n - d i f f e r e n t i a l r e i n f o r c e m e n t ) ( G l i c k , 1982). T h i s p a r a d i g m may be b e n e f i c i a l i n t h e assessment o f d i r e c t i o n a l b i a s e s p r i o r t o t r a i n i n g r a t s t o c i r c l e as i t i n v o l v e s r o t a t i o n , t h e r e s p o n s e i n v o l v e d i n c o n d i t i o n e d c i r c l i n g , b u t does n o t r e q u i r e t h e a d m i n i s t r a t i o n o f p s y c h o t r o p i c a g e n t s . E x p e r i m e n t I V a d e t e r m i n e d t h e e x t e n t t o w h i c h t h e d i r e c t i o n a l b i a s o b t a i n e d w i t h t h e n o n - d i f f e r e n t i a l r e i n f o r c e m e n t o f c i r c l i n g p a r a d i g m c o r r e l a t e s w i t h t h e p r e f e r e n c e e x h i b i t e d u s i n g t h e t r a d i t i o n a l amphetamine -44-s c r e e n i n g p r o t o c o l . I n a d d i t i o n , t h e e x t e n t t o w h i c h d i r e c t i o n a l b i a s e s c o r r e l a t e w i t h a s y m m e t r i e s i n s t r i a t a l and m e s o l i m b i c DA c o n c e n t r a t i o n s f o l l o w i n g t h e a d m i n i s t r a t i o n o f amphetamine was examined. Materials and Methods S u b j e c t s and A p p a r a t u s N a i v e , male Sprague-Dawley r a t s ( C h a r l e s R i v e r L a b o r a t o r i e s ) , as d e s c r i b e d i n E x p e r i m e n t I , were used i n t h e p r e s e n t e x p e r i m e n t . A n i m a l s were a c c l i m a t i z e d t o t h e l a b o r a t o r y f o r one week p r i o r t o t h e commencement o f t h e e x p e r i m e n t . T e s t i n g was c o n d u c t e d i n one o f two a p p a r a t i . The a p p a r a t u s d e s c r i b e d i n E x p e r i m e n t I was u s e d f o r t h e n o n - d i f f e r e n t i a l r e i n f o r c e m e n t p a r a d i g m . Amphetamine-induced c i r c l i n g was a s s e s s e d u s i n g a s e m i - s p h e r i c a l aluminum c o n t a i n e r ( d i a m e t e r 40 cm, h e i g h t 20 cm). P r o c e d u r e s The p r e f e r r e d d i r e c t i o n o f c i r c l i n g f o r each r a t was d e t e r m i n e d u s i n g two i n d e p e n d e n t p a r a d i g m s . The o r d e r o f t e s t i n g was c o u n t e r - b a l a n c e d , s u c h t h a t h a l f o f t h e a n i m a l s were i n i t i a l l y t e s t e d w i t h t h e n o n - d i f f e r e n t i a l r e i n f o r c e m e n t (NDR) p a r a d i g m w h i l e t h e r e m a i n i n g s u b j e c t s were f i r s t t e s t e d u s i n g t h e amphetamine-induced c i r c l i n g p a r a d i g m . To m i n i m i z e t h e e f f e c t s o f amphetamine on subsequent NDR t e s t i n g , t h e two s e s s i o n s were s e p a r a t e d by a one week p e r i o d . N o n - d i f f e r e n t i a l R e i n f o r c e m e n t . R a t s were h a b i t u a t e d t o t h e t e s t a p p a r a t u s f o r 20 m i n u t e s . D u r i n g t h i s t i m e no r e i n f o r c e m e n t was d e l i v e r e d . I m m e d i a t e l y f o l l o w i n g t h i s s e s s i o n , t h e r a t s were r e t u r n e d t o t h e i r home cage and t h e i r w a t e r b o t t l e s removed. T w e n t y - f o u r h o u r s l a t e r , t h e y were t e s t e d f o r d i r e c t i o n a l b i a s e s u s i n g t h e n o n - d i f f e r e n t i a l r e i n f o r c e m e n t p r o c e d u r e whereby each c i r c l e e m i t t e d by t h e a n i m a l , r e g a r d l e s s o f t h e -45-d i r e c t i o n , was f o l l o w e d by t h e p r e s e n t a t i o n o f a drop o f w a t e r . The t o t a l number o f c i r c l e s e m i t t e d i n each d i r e c t i o n was r e c o r d e d . T e s t i n g c o n t i n u e d f o r 20 min. Upon c o m p l e t i o n o f t h e s e s s i o n , t h e a n i m a l s were g i v e n c o n t i n u o u s a c c e s s t o w a t e r . Amphetamine-induced C i r c l i n g . A n i m a l s were weighed and t h e n p l a c e d i n t h e t e s t a p p a r a t u s f o r a 15 min h a b i t u a t i o n p e r i o d . They were t h e n i n j e c t e d i . p . w i t h d-amphetamine s u l f a t e (1.25 mg/kg d i s s o l v e d i n s a l i n e ) and i m m e d i a t e l y r e t u r n e d t o t h e a p p a r a t u s . The number o f r o t a t i o n s e m i t t e d i n each d i r e c t i o n was r e c o r d e d i n 5 min b l o c k s . Each a n i m a l was o b s e r v e d f o r 1 h r f o l l o w i n g t h e i n j e c t i o n . N e u r o c h e m i s t r y To d e t e r m i n e whether r a t s 1 d i r e c t i o n a l b i a s e s a r e c o r r e l a t e d w i t h a s ymmetries i n n i g r o s t r i a t a l and/or m e s o l i m b i c DA c o n c e n t r a t i o n s a f i n a l t e s t s e s s i o n was c o n d u c t e d two weeks f o l l o w i n g t h e c o m p l e t i o n o f b e h a v i o r a l t e s t i n g . A t t h i s t i m e , each r a t was i n j e c t e d w i t h amphetamine (1.25 mg/kg) and t e s t e d f o r c i r c l i n g , as d e s c r i b e d above. I m m e d i a t e l y f o l l o w i n g t h e t e s t s e s s i o n , t h e r a t s were d e c a p i t a t e d and t h e i r b r a i n s r a p i d l y removed, mounted on a m i c r o t o m e , and f r o z e n . The l e f t and r i g h t s t r i a t u m , n u c l e u s accumbens and o l f a c t o r y t u b e r c l e were d i s s e c t e d f r o m t h e a p p r o p r i a t e s l i c e s and p r e p a r e d f o r a n a l y s i s o f DA c o n c e n t r a t i o n s by HPLC-ED, as p r e v i o u s l y d e s c r i b e d . Results and Discussion The d i r e c t i o n a l b i a s o f each i n d i v i d u a l s u b j e c t , as d e t e r m i n e d by t h e amphetamine p r o t o c o l and t h e n o n - d i f f e r e n t i a l r e i n f o r c e m e n t p r o c e d u r e a r e p r e s e n t e d i n T a b l e 4. The p r e f e r r e d d i r e c t i o n o f c i r c l i n g was g e n e r a l l y c o n s i s t e n t a c r o s s t h e two measures. W h i l e t h e o v e r a l l s t r e n g t h o f t h e b i a s d e t e c t e d w i t h t h e n o n - d i f f e r e n t i a l r e i n f o r c e m e n t p a r a d i g m was n o t as s t r o n g - 4 6 -T a b l e 4. D i r e c t i o n a l b i a s e s measured u s i n g amphetamine and non-d i f f e r e n t i a l r e i n f o r c e m e n t s c r e e n i n g p a r a d i g m s . -1 S u b j e c t ^ N o n - d i f f e r e n t i a l Amphetamine I Amphetamine I I r e i n f o r c e m e n t ( 1 . 2 5 mg/kg) ( 1 . 25 mg/kg) 10 .14 .19 . X X i n I O .22 .14 -I r-. xo i -i -L J . . zx 0 .00 i —i X O .13 .32 r- 1 . O X 15 . O O . 16 -» -i . O X 17 .75 1.00 .30 19 . / o 1.00 .93 1 A X < ± •"7 4 . / <± .93 .95 27 . O O .07 . 06 25 —» *-\ . oz .08 . z z 20 .73 . xz . U O 22 .26 .03 . 08 29 —i . O O . 56 I 1 . D O zx .68 .95 r i . O O zo .80 .44 —7 r\ . / U 24 .60 .79 1.00 1. D a t a r e p r e s e n t t h e number o f c i r c l e s e m i t t e d t o t h e l e f t d i v i d e d by t h e t o t a l number o f c i r c l e s e m i t t e d i n t h e t e s t s e s s i o n . P r e f e r e n c e s t o c i r c l e t o t h e l e f t a r e i n d i c a t e d by v a l u e s g r e a t e r t h a n .50 w h i l e v a l u e s l e s s t h a n .50 i n d i c a t e p r e f e r e n c e s t o c i r c l e t o t h e r i g h t . 2 . Order o f t e s t i n g was c o u n t e r - b a l a n c e d s u c h t h a t s u b j e c t s 10 - 19 were i n i t i a l l y s c r e e n e d f o r d i r e c t i o n a l p r e f e r e n c e s u s i n g t h e amphetamine s c r e e n i n g p r o c e d u r e w h i l e s u b j e c t s 20 - 29 were t e s t e d i n i t i a l l y u s i n g t h e n o n - d i f f e r e n t i a l r e i n f o r c e m e n t p a r a d i g m . 3. A l l s u b j e c t s were t e s t e d f o r amphetamine-induced c i r c l i n g a second t i m e two weeks f o l l o w i n g c o m p l e t i o n o f b e h a v i o r a l t e s t i n g . -47-as t h a t o b t a i n e d w i t h amphetamine, t h e d i r e c t i o n was g e n e r a l l y c o n s i s t e n t a c r o s s t h e two p a r a d i g m s . S t a t i s t i c a l a n a l y s i s ( P e a r s o n product-moment c o r r e l a t i o n ) c o n f i r m e d t h e s e o b s e r v a t i o n s and d e m o n s t r a t e d t h a t t h e two measurements c o r r e l a t e d w i t h one a n o t h e r ( r = .08; p < .01). I t i s a l s o n o t e w o r t h y t h a t t h e d i r e c t i o n a l b i a s e x h i b i t e d d u r i n g t h e two amphetamine t e s t s c o r r e l a t e d h i g h l y w i t h one a n o t h e r ( r = .93, p < .01). G i v e n t h e l o n g - t e r m b e h a v i o r a l and n e u r o c h e m i c a l consequences o f amphetamine ( R o b i n s o n , 1984; R o b i n s o n , e t a l . , 1982), i t a p p e a r s t h a t i t may be more a p p r o p r i a t e t o use t h e n o n - d i f f e r e n t i a l r e i n f o r c e m e n t p a r a d i g m i n d e t e r m i n i n g d i r e c t i o n a l b i a s e s , e s p e c i a l l y i n t h o s e s i t u a t i o n s where i t i s i m p o r t a n t t h a t a n i m a l s a r e d r u g - n a i v e a t t h e t i m e o f t e s t i n g . I t s h o u l d be n o t e d t h a t t h e magnitude o f t h e b i a s d e t e c t e d u s i n g t h e NDR p r o t o c o l can be enhanced by n o t h a b i t u a t i n g r a t s t o t h e a p p a r a t u s p r i o r t o t e s t i n g ( u n p u b l i s h e d o b s e r v a t i o n s ) . T h i s i n c r e a s e i n magnitude a p p e a r s t o r e f l e c t t h e i n c r e a s e d l e v e l o f a c t i v i t y o b s e r v e d when r a t s a r e i n i t i a l l y e x posed t o a n o v e l e n v i r o n m e n t . To d e t e r m i n e whether amphetamine-induced c i r c l i n g was a s s o c i a t e d w i t h i n c r e a s e d c o n c e n t r a t i o n s o f DA i n s t r u c t u r e s c o n t r a l a t e r a l t o t h e p r e f e r r e d d i r e c t i o n o f t u r n i n g , c o r r e l a t e d t - t e s t s were c o n d u c t e d c o m p a r i n g DA c o n c e n t r a t i o n s w i t h i n t h e i p s i l a t e r a l and c o n t r a l a t e r a l s t r i a t u m (987.6 ± 13.1 v s 965.7 ± 14.5 nmol/g p r o t e i n ) , n u c l e u s accumbens (902.8 ± 22.0 vs 906.6 ± 20.5) and o l f a c t o r y t u b e r c l e (639.0 + 11.6 vs 626.2 i 1 7 . 5 ) . These a n a l y s e s f a i l e d t o r e v e a l any s t a t i s t i c a l l y s i g n i f i c a n t d i f f e r e n c e s . T h i s o b s e r v a t i o n i s c o n s i s t e n t w i t h p r e v i o u s r e p o r t s t h a t amphetamine-i n d u c e d c i r c l i n g i n i n t a c t , male r a t s i s n o t a s s o c i a t e d w i t h i n c r e a s e d c o n c e n t r a t i o n s o f DA i n t h e s t r i a t u m c o n t r a l a t e r a l t o t h e p r e f e r r e d d i r e c t i o n o f t u r n i n g ( R o b i n s o n , B e c k e r & Camp, 1985). -48-I t has r e c e n t l y been s u g g e s t e d t h a t t h e r e l a t i o n s h i p between DA a c t i v i t y and d i r e c t i o n a l b i a s e s i s n o t as s i m p l e as o r i g i n a l l y h y p o t h e s i z e d . R a t h e r , S h a p i r o , G l i c k & Hough (1986) have r e p o r t e d t h a t i t i s t h e a b s o l u t e asymmetry i n DA a c t i v i t y , r e g a r d l e s s o f l e f t / r i g h t o r i p s i l a t e r a l / c o n t r a l a t e r a l r e l a t i o n s h i p s , t h a t c r i t i c a l l y u n d e r l i e s t h e magnitude o f r a t s ' d i r e c t i o n a l b i a s e s . To t e s t t h i s h y p o t h e s i s , t h e p r e s e n t d a t a were s u b j e c t e d t o two f u r t h e r a n a l y s e s . F i r s t , a c o r r e l a t e d t - t e s t was c o n d u c t e d t o d e t e r m i n e whether o r n o t t h e r e were any a b s o l u t e d i f f e r e n c e s ( i . e . h i g h v s low c o n c e n t r a t i o n s o f DA) i n any o f t h e t h r e e s t r u c t u r e s examined. S t a t i s t i c a l l y s i g n i f i c a n t d i f f e r e n c e s were d e t e c t e d i n each s t r u c t u r e ( s t r i a t u m : 1000.0 ± 11.9 v s 953.3 ± 13.5 nmol/ g p r o t e i n , t ( 1 5 ) = 5.472, p < .001; n u c l e u s accumbens: 938.2 ± 21.2 v s 871.1 ± 17.5, t ( 1 5 ) = 6.439, p < .001; o l f a c t o r y t u b e r c l e : 653.4 ± 13.6 v s 611.9 ± 14.3, t ( 1 5 ) = 6.324, p < .001). P e a r s o n ' s product-moment c o r r e l a t i o n t e s t s were t h e n c o n d u c t e d i n o r d e r t o d e t e r m i n e whether t h e s e asymmetries were c o r r e l a t e d w i t h t h e magnitude o f t h e d i r e c t i o n a l b i a s . 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 (p's > .10). Thus, w h i l e n e u r o c h e m i c a l a s ymmetries c a n be d e t e c t e d w i t h i n v a r i o u s t e r m i n a l f i e l d s o f t h e m e s o t e l e n c e p h a l i c DA p r o j e c t i o n , t h e s e a symmetries do n o t appear t o be r e l a t e d t o t h e d i r e c t i o n a l b i a s e s o f r a t s . Experiment IVb Effects of Directional Biases on Neurochemical Consequences of Conditioned Circling The r e s u l t s o f E x p e r i m e n t I V a c o n f i r m p r e v i o u s r e p o r t s t h a t r a t s have a p r e f e r r e d d i r e c t i o n o f c i r c l i n g ( J e r u s s i & G l i c k , 1976). A l t h o u g h t h e i r d i r e c t i o n a l b i a s was n o t a s s o c i a t e d w i t h an asymmetry i n DA c o n c e n t r a t i o n s f o l l o w i n g t h e a d m i n i s t r a t i o n o f amphetamine, i t r e m a i n s p o s s i b l e t h a t s u c h b i a s e s can i n f l u e n c e t h e p e r f o r m a n c e o f c o n d i t i o n e d c i r c l i n g and t h a t t h e n e u r o c h e m i c a l changes a s s o c i a t e d w i t h t h i s b e h a v i o r v a r y i n r e l a t i o n t o i n n a t e d i r e c t i o n a l b i a s e s . I n E x p e r i m e n t IVb, r a t s were t r a i n e d t o c i r c l e i n e i t h e r t h e i r p r e f e r r e d d i r e c t i o n o r i n t h e o p p o s i t e d i r e c t i o n f o r w a t e r r e i n f o r c e m e n t . Upon e s t a b l i s h m e n t o f s t a b l e r a t e s o f r e s p o n d i n g , t h e n e u r o c h e m i c a l consequences o f c o n d i t i o n e d c i r c l i n g were d e t e r m i n e d i n t h e s e two g r o u p s . Materials and Methods S u b j e c t s and A p p a r a t u s N a i v e , male Sprague-Dawley r a t s ( C h a r l e s R i v e r L a b o r a t o r i e s ) , as d e s c r i b e d i n E x p e r i m e n t I , s e r v e d as s u b j e c t s . The t e s t a p p a r a t u s was t h e same as t h a t u s e d i n E x p e r i m e n t I . P r o c e d u r e s R a t s were w a t e r - d e p r i v e d f o r 20 - 24 h b e f o r e b e i n g t e s t e d f o r d i r e c t i o n a l b i a s e s . They were t h e n p l a c e d i n d i v i d u a l l y i n t h e t e s t a p p a r a t u s f o r 20 min and d u r i n g t h i s t i m e , each c o m p l e t e r o t a t i o n e m i t t e d (360°) was r e i n f o r c e d w i t h w a t e r , r e g a r d l e s s o f i t s d i r e c t i o n ( l e f t o r r i g h t ) . The number o f r o t a t i o n s e m i t t e d i n e ach d i r e c t i o n was r e c o r d e d and t h e p r e f e r r e d d i r e c t i o n o f t u r n i n g was d e t e r m i n e d by d i v i d i n g t h e number o f r o t a t i o n s t o t h e l e f t by t h e t o t a l number, i r r e s p e c t i v e o f d i r e c t i o n . The r a t s were s u b s e q u e n t l y p l a c e d i n t o one o f 4 groups (n=6): N o n - d e p r i v e d C o n t r o l s (NDC); Water D e p r i v e d C o n t r o l s (WDC); P r e f e r r e d D i r e c t i o n C i r c l e r s ( P R ) ; N o n - p r e f e r r e d D i r e c t i o n C i r c l e r s (NPR). Each group was matched a c c o r d i n g t o t h e s t r e n g t h o f p r e f e r e n c e , d i r e c t i o n o f p r e f e r e n c e and t o t a l number o f c i r c l e s e m i t t e d . R a t s i n t h e NDC group had c o n t i n u o u s a c c e s s t o f o o d and w a t e r f o r t h e d u r a t i o n o f t h e e x p e r i m e n t . The second c o n t r o l group (WDC) was i n c l u d e d so t h a t t h e e f f e c t s o f c o n s u m p t i o n o f non-c o n t i n g e n t l y p r e s e n t e d w a t e r on DA m e t a b o l i s m c o u l d be d e t e r m i n e d . To t h i s end, r a t s were m a i n t a i n e d on a s c h e d u l e o f w a t e r d e p r i v a t i o n s i m i l a r t o t h a t employed w i t h t h e PR and NPR g r o u p s . Each r a t r e c e i v e d a c c e s s t o w a t e r f o r a 20 min p e r i o d d a i l y . R a t s i n b o t h c o n t r o l groups were h a n d l e d d a i l y . On t h e t e s t day, s u b j e c t s i n t h e WDC group were k i l l e d i m m e d i a t e l y a f t e r t h e i r 20 min d r i n k i n g s e s s i o n . R a t s i n t h e PR and t h e NPR groups were t r e a t e d i d e n t i c a l l y , e x c e p t t h a t PR r a t s were t r a i n e d t o c i r c l e i n t h e i r p r e f e r r e d d i r e c t i o n , whereas NPR r a t s were t r a i n e d t o t u r n i n t h e o p p o s i t e d i r e c t i o n . Each r a t r e c e i v e d 5 s e s s i o n s whereby each r o t a t i o n e m i t t e d i n t h e a p p r o p r i a t e d i r e c t i o n was r e i n f o r c e d . Upon e s t a b l i s h m e n t o f t h e r e s p o n s e , t h e s c h e d u l e o f r e i n f o r c e m e n t was changed t o a FR-2. T r a i n i n g c o n s i s t e d o f 12 FR-2 s e s s i o n s . A l l s e s s i o n s were o f 20 min d u r a t i o n and t h e a n i m a l s were t e s t e d 6 days/week. On t h e 7 t h day o f each week, a l l r a t s were g i v e n a c c e s s t o w a t e r f o r a 30 min p e r i o d . One NPR s u b j e c t was e l i m i n a t e d f r o m t h e e x p e r i m e n t due t o i l l n e s s . On t h e day f o l l o w i n g t h e f i n a l t r a i n i n g s e s s i o n , e ach s u b j e c t r e c e i v e d one t e s t s e s s i o n . The e x p e r i m e n t a l c o n t i n g e n c i e s u s e d f o r FR-2 t r a i n i n g c o n t i n u e d t o be i n e f f e c t d u r i n g t h i s s e s s i o n . I m m e d i a t e l y f o l l o w i n g c o m p l e t i o n o f t h e t e s t s e s s i o n , r a t s were d e c a p i t a t e d and t h e b r a i n s r a p i d l y removed. The s t r i a t u m , n u c l e u s accumbens and o l f a c t o r y t u b e r c l e were d i s s e c t e d and t h e a n a l y s i s o f DA, DOPAC and HVA c o n c e n t r a t i o n s was c o n d u c t e d , as d e s c r i b e d i n E x p e r i m e n t I . Results B e h a v i o r I n s p e c t i o n o f F i g u r e 5 i n d i c a t e s t h a t t h e d i r e c t i o n o f r e i n f o r c e d c i r c l i n g , w i t h r e s p e c t t o i n h e r e n t d i r e c t i o n a l p r e f e r e n c e s , d i d n o t i n f l u e n c e a s y m p t o t i c r a t e s o f r e s p o n d i n g . I t s h o u l d be n o t e d t h a t a l l r a t s -51-F i g u r e 5. Number o f r o t a t i o n s e m i t t e d p e r m i n u t e by r a t s d u r i n g t h e t e s t s e s s i o n i n E x p e r i m e n t I V a . V a l u e s r e p r e s e n t means (± S.E.M.) and a r e p r e s e n t e d i n b l o c k s o f 2 min. R a t s were t r a i n e d t o c i r c l e f o r w a t e r a c c o r d i n g t o a FR-2 s c h e d u l e o f r e i n f o r c e m e n t . R a t s were r e q u i r e d t o c i r c l e i n t h e i r p r e f e r r e d d i r e c t i o n ( s o l i d c i r c l e s ; n=6) o r a g a i n s t t h e i r d i r e c t i o n a l b i a s (open c i r c l e s ; n=6). • REINFORCED: PREFERRED O REINFORCED: NON-PREFERRED ~ i 1 1 1 1 1 1 1 r 2 3 4 5 6 7 8 9 10 BLOCKS OF TWO MINUTES were a b l e t o a c q u i r e t h e a p p r o p r i a t e r e s p o n s e and t h a t a l l s u b j e c t s r e c e i v e d an e q u i v a l e n t amount o f t r a i n i n g . ANOVA w i t h one between s u b j e c t f a c t o r (Group) and one r e p e a t e d measure ( B l o c k s o f 2 M i n u t e s ) c o n f i r m e d t h a t t h e r e were no Group o r Group x B l o c k d i f f e r e n c e s . U s i n g d e g r e e s o f freedom a p p r o p r i a t e t o t h e G e i s s e r - G r e e n h o u s e C o n s e r v a t i v e F t e s t , a s i g n i f i c a n t B l o c k e f f e c t was o b t a i n e d : F ( l , 9 ) = 20.72, p < .001. T h i s e f f e c t r e f l e c t s t h e p r o g r e s s i v e d e c r e a s e i n t h e r a t e o f r e s p o n d i n g t h a t o c c u r r e d as t h e s e s s i o n p r o g r e s s e d . N e u r o c h e m i s t r y I n o r d e r t o d e t e r m i n e t h e n e u r o c h e m i c a l changes a s s o c i a t e d w i t h c o n d i t i o n e d c i r c l i n g and w a t e r - d e p r i v a t i o n , ANOVAs w i t h 1 between s u b j e c t f a c t o r (Group) and 1 w i t h i n s u b j e c t f a c t o r (Hemisphere, r e l a t i v e t o d i r e c t i o n a l b i a s ) were c o n d u c t e d f o r each compound and m e t a b o l i t e ' . t r a n s m i t t e r r a t i o measured i n each o f t h e t h r e e a n a t o m i c a l s t r u c t u r e s ( s t r i a t u m , n u c l e u s accumbens and o l f a c t o r y t u b e r c l e ) . No s i g n i f i c a n t e f f e c t s o f Hemisphere o r Group x Hemisphere i n t e r a c t i o n s were o b s e r v e d f o r any compound o r r a t i o measured w i t h i n t h e s t r i a t u m , n u c l e u s accumbens o r o l f a c t o r y t u b e r c l e . M o r e o ver, c o n c e n t r a t i o n s o f DA and DOPAC were n o t a f f e c t e d by e i t h e r c o n d i t i o n e d c i r c l i n g o r w a t e r d e p r i v a t i o n i n any o f t h e t h r e e b r a i n r e g i o n s examined. S i m i l a r l y , t h e r a t i o o f DOPAC t o DA d i d n o t v a r y a c r o s s g r o u p s . S t r i a t u m . A n a l y s i s o f HVA c o n c e n t r a t i o n s y i e l d e d a s i g n i f i c a n t Group main e f f e c t : F ( 3 , 1 9 ) = 7.58, p = .002 (s e e upper p a n e l o f F i g . 6 ) . Newman K e u l s p a i r - w i s e c o m p a r i s o n s ( a = .05) i n d i c a t e d t h a t t h e two c o n t r o l group ( i . e . NDC and WDC) d i d n o t d i f f e r f r o m one a n o t h e r . I n a d d i t i o n , no d i f f e r e n c e s were o b s e r v e d between t h e two groups o f r a t s t r a i n e d t o c i r c l e ( i . e . PR and NPR). However, c o n c e n t r a t i o n s o f HVA were g r e a t e r i n t h e -54-F i g u r e 6. S t r i a t a l c o n c e n t r a t i o n s o f HVA (nmol/ g p r o t e i n ) (upper p a n e l ) and t h e r a t i o s o f HVA t o DA ( l o w e r p a n e l ) a r e p r e s e n t e d f o r n o n - d e p r i v e d c o n t r o l s (NDC; n=6), w a t e r - d e p r i v e d c o n t r o l s (WDC; n=6), r a t s t r a i n e d t o c i r c l e i n t h e i r p r e f e r r e d d i r e c t i o n (PR; n=6), and r a t s r e q u i r e d t o c i r c l e i n t h e d i r e c t i o n o p p o s i t e t o t h e i r b i a s (NPR; n=6). R a t s i n t h e PR and NPR groups were t e s t e d f o r 20 min. C o n d i t i o n e d c i r c l i n g was m a i n t a i n e d u s i n g a FR-2 s c h e d u l e o f w a t e r r e i n f o r c e m e n t . S u b j e c t s i n t h e WDC g roup were g i v e n a c c e s s t o w a t e r f o r 20 min i n t h e i r home cage p r i o r t o b e i n g s a c r i f i c e d . * s i g n i f i e s s t a t i s t i c a l l y d i f f e r e n t f r o m c o r r e s p o n d i n g NDC and WDC v a l u e s , p < .05. -55--56-s t r i a t u m o f r a t s t r a i n e d t o c i r c l e , r e l a t i v e t o c o n t r o l s u b j e c t s . A s i m i l a r p r o f i l e was o b t a i n e d when t h e r a t i o o f HVA t o DA was a n a l y z e d : F (3,19) = 11.90, p < .001 (see l o w e r p a n e l o f F i g . 6 ) . These r e s u l t s c o n f i r m and e x t e n d e a r l i e r r e p o r t s t h a t c o n d i t i o n e d c i r c l i n g i s a s s o c i a t e d w i t h a b i l a t e r a l a u g m e n t a t i o n o f s t r i a t a l DA m e t a b o l i s m ( S c h w a r t i n g & Hu s t o n , 1987; see a l s o E x p e r i m e n t I I ) . The p r e s e n t r e s u l t s a l s o i n d i c a t e t h a t i n h e r e n t d i r e c t i o n a l b i a s e s do n o t i n f l u e n c e t h e n e u r o c h e m i c a l p r o f i l e a s s o c i a t e d w i t h h i g h r a t e s o f c o n d i t i o n e d c i r c l i n g . N u c l e u s Accumbens. C o n c e n t r a t i o n s o f HVA c o u l d n o t be d e t e r m i n e d f o r two s u b j e c t s i n each o f t h e two c o n t r o l g r o u p s due t o sample c o n t a m i n a t i o n . A n a l y s i s o f HVA c o n c e n t r a t i o n s w i t h i n t h e n u c l e u s accumbens f a i l e d 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 ( s e e up p e r p a n e l . F i g . 7 ) . However, t h e r a t i o o f HVA t o DA was f o u n d t o v a r y as a f u n c t i o n o f Group: F(3,15) = 5.22, p = .011. P a i r - w i s e c o m p a r i s o n s r e v e a l e d t h a t t h e two c o n t r o l groups d i d n o t d i f f e r f r o m one a n o t h e r . S i m i l a r HVA:DA r a t i o s were o b t a i n e d f o r t h e two e x p e r i m e n t a l g r o u p s . DA m e t a b o l i s m was, however, o n l y s i g n i f i c a n t l y augmented i n t h e n u c l e u s accumbens o f r a t s t r a i n e d t o c i r c l e i n t h e i r p r e f e r r e d d i r e c t i o n , r e l a t i v e t o b o t h c o n t r o l g r o u p s . W h i l e a s i m i l a r t r e n d was o b s e r v e d when r a t s i n t h e NPR group were compared w i t h t h e c o n t r o l s , t h e s e d i f f e r e n c e s d i d n o t a c h i e v e s t a t i s t i c a l s i g n i f i c a n c e . O l f a c t o r y T u b e r c l e . No s i g n i f i c a n t d i f f e r e n c e s were o b t a i n e d when e i t h e r HVA c o n c e n t r a t i o n s o r HVA:DA r a t i o s were a n a l y z e d ( s e e F i g . 8 ) . These o b s e r v a t i o n s a r e c o n s i s t e n t w i t h t h e o b s e r v a t i o n i n E x p e r i m e n t I I t h a t DA m e t b o l i s m w i t h i n t h e o l f a c t o r y t u b e r c l e i s n o t i n f l u e n c e d by c o n d i t i o n e d c i r c l i n g . -57-F i g u r e 7. C o n c e n t r a t i o n s o f HVA (nmol/ g p r o t e i n ) (upper p a n e l ) and t h e r a t i o s o f HVA t o DA ( l o w e r p a n e l ) d e t e c t e d w i t h i n t h e n u c l e u s accumbens a r e p r e s e n t e d f o r n o n - d e p r i v e d c o n t r o l s (NDC; n=6), w a t e r - d e p r i v e d c o n t r o l s (WDC; n=6), r a t s t r a i n e d t o c i r c l e i n t h e i r p r e f e r r e d d i r e c t i o n (PR; n=6), and r a t s r e q u i r e d t o c i r c l e i n t h e d i r e c t i o n o p p o s i t e t o t h e i r b i a s (NPR; n=6). See F i g u r e 6 and Methods f o r d e s c r i p t i o n o f e x p e r i m e n t a l p r o c e d u r e s . * s i g n i f i e s s t a t i s t i c a l l y d i f f e r e n t f r o m c o r r e s p o n d i n g NDC and WDC v a l u e s , p < .05. -58--59-F i g u r e 8. C o n c e n t r a t i o n s o f HVA (nmol/ g p r o t e i n ) (upper p a n e l ) and t h e r a t i o s o f HVA t o DA ( l o w e r p a n e l ) d e t e c t e d w i t h i n t h e o l f a c t o r y t u b e r c l e a r e p r e s e n t e d f o r n o n - d e p r i v e d c o n t r o l s (NDC; n=6), w a t e r - d e p r i v e d c o n t r o l s (WDC; n=6), r a t s t r a i n e d t o c i r c l e i n t h e i r p r e f e r r e d d i r e c t i o n (PR; n=6), and r a t s r e q u i r e d t o c i r c l e i n t h e d i r e c t i o n o p p o s i t e t o t h e i r b i a s (NPR; n=6). See F i g u r e 6 and Methods f o r d e s c r i p t i o n o f e x p e r i m e n t a l p r o c e d u r e s . -60--61-Discussion The a c q u i s i t i o n and p e r f o r m a n c e o f c o n d i t i o n e d c i r c l i n g was n o t i n f l u e n c e d by t h e d i r e c t i o n a l b i a s e s . S p e c i f i c a l l y , r a t s t r a i n e d t o c i r c l e i n t h e d i r e c t i o n o p p o s i t e t o t h e i r b i a s r e s p o n d e d a t r a t e s s i m i l a r t o t h o s e e x h i b i t e d by r a t s r e i n f o r c e d f o r c i r c l i n g i n t h e i r p r e f e r r e d d i r e c t i o n . W h i l e t h e s e r e s u l t s a r e c o n s i s t e n t w i t h t h e b e h a v i o r a l o b s e r v a t i o n s o f Yamamoto & F r e e d ( 1 9 8 4 ) , t h e y a r e a t odds w i t h G l i c k & H i n d s (1982) who r e p o r t e d t h a t a m a j o r i t y o f r a t s were u n a b l e t o a c q u i r e t h e c o n d i t i o n e d c i r c l i n g r e s p o n s e when i t i s d i r e c t e d a g a i n s t t h e i r b i a s . The b a s i s f o r t h i s d i s c r e p a n c y i s n o t c l e a r . One p o s s i b l e e x p l a n a t i o n c o n c e r n s t h e t e s t a p p a r a t i employed by t h e v a r i o u s e x p e r i m e n t e r s . I t has been d e m o n s t r a t e d t h a t r a t e s o f c i r c l i n g a r e dependent upon t h e t y p e o f a p p a r a t u s employed ( G l i c k , e t a l . , 1976; G l i c k , J e r u s s i & Zimmerberg, 1976). I n t h e r e p o r t by G l i c k & H i n d s (1984) r a t s were t r a i n e d t o c i r c l e i n s t a n d a r d o p e r a n t chambers. I n c o n t r a s t , r a t s i n t h e p r e s e n t e x p e r i m e n t were t r a i n e d i n a c i r c u l a r a p p a r a t u s w i t h a f l a t f l o o r ( s e e a l s o Yamamoto & F r e e d , 1984). I t i s p o s s i b l e t h a t a c q u i s i t i o n o f t h e c o n t r a - p r e p a r e d r e s p o n s e i s more s e n s i t i v e t o e n v i r o n m e n t a l f a c t o r s s u c h t h a t a c q u i s i t i o n w i l l be i m p a i r e d when t e s t e d i n an e n v i r o n m e n t t h a t i s n o t c o n d u c i v e t o c i r c l i n g . I t i s a l s o p o s s i b l e t h a t t h e d i f f e r e n t i a l b e h a v i o r a l r e s u l t s r e f l e c t s e x d i f f e r e n c e s . I t has been r e p o r t e d t h a t d i r e c t i o n a l b i a s e s a r e s t r o n g e r i n f e m a l e r a t s t h a n i n males ( s ee R o b i n s o n , e t a l . , 1983 f o r r e v i e w ) . As s u c h , i t may be more d i f f i c u l t t o d i s r u p t t h e d i r e c t i o n a l b i a s e s o f f e m a l e r a t s . The r e s u l t s o f E x p e r i m e n t IVb p r o v i d e f u r t h e r e v i d e n c e f o r t h e b i l a t e r a l i n v o l v e m e n t o f t h e m e s o t e l e n c e p h a l i c DA system i n c o n d i t i o n e d c i r c l i n g ( S c h w a r t i n g & H u s t o n , 1987; see a l s o E x p e r i m e n t I I ) . The n e u r o c h e m i c a l changes a s s o c i a t e d w i t h c o n d i t i o n e d c i r c l i n g were a l s o f o u n d n o t t o v a r y as a f u n c t i o n o f d i r e c t i o n a l b i a s . S p e c i f i c a l l y , i t was o b s e r v e d t h a t DA m e t a b o l i s m was i n c r e a s e d b i l a t e r a l l y w i t h i n t h e s t r i a t u m , r e g a r d l e s s o f whether r a t s were r e q u i r e d t o c i r c l e i n r e g i s t e r w i t h t h e i r b i a s o r i n t h e i r n o n - p r e f e r r e d d i r e c t i o n . As o b s e r v e d i n E x p e r i m e n t I I , c o n d i t i o n e d c i r c l i n g was a l s o a s s o c i a t e d w i t h a b i l a t e r a l a u g m e n t a t i o n i n DA m e t a b o l i s m w i t h i n t h e n u c l e u s accumbens. However, t h e magnitude o f t h e i n c r e a s e w i t h i n t h e n u c l e u s accumbens a p p e a r s t o depend upon whether r a t s a r e c i r c l i n g i n t h e d i r e c t i o n o f t h e i r i n h e r e n t p r e f e r e n c e o r n o t . I t i s not c l e a r why r a t s t r a i n e d t o c i r c l e i n t h e d i r e c t i o n o p p o s i t e t o t h e i r b i a s d i d n o t e x h i b i t an i n c r e a s e i n n u c l e u s accumbens DA m e t a b o l i s m . G i v e n t h a t comparable r a t e s o f c i r c l i n g were e x h i b i t e d by t h e two g r o u p s , t h e changes o b s e r v e d i n t h e PR group do n o t appear t o be r e l a t e d t o l e v e l s o f l o c o m o t o r a c t i v i t y . EXPERIMENT V Neurochemical Consequences of Conditioned Circling Maintained by Food Reinforcement To d a t e , e x p e r i m e n t s e x a m i n i n g t h e n e u r o c h e m i c a l c o r r e l a t e s o f c o n d i t i o n e d c i r c l i n g have u s e d e i t h e r w a t e r o r s u c r o s e s o l u t i o n s as t h e r e i n f o r c e r ( S c h w a r t i n g & Hus t o n , 1987; Yamamoto & F r e e d , 1982; 1984; see a l s o p r e c e d i n g E x p e r i m e n t s ) . Due t o t h e r e l a t i v e l y l e n g t h y t r a i n i n g p r o t o c o l i n v o l v e d i n t h o s e e x p e r i m e n t s u s i n g i n t e r m i t t e n t r e i n f o r c e m e n t s c h e d u l e s , a n i m a l s a r e pr o n e t o s e v e r e w e i g h t l o s s u n l e s s p e r i o d i c a l l y g i v e n a d d i t i o n a l , n o n - c o n t i n g e n t a c c e s s t o w a t e r ( s e e a l s o S c h w a r t i n g & Hu s t o n , 1987). S e v e r e w e i g h t l o s s and d e h y d r a t i o n a l s o o c c u r s when a h y p e r t o n i c s u c r o s e s o l u t i o n , as u s e d by Yamamoto & F r e e d ( 1 9 8 2 ) , i s employed as t h e r e i n f o r c i n g s t i m u l u s f o r w a t e r - d e p r i v e d r a t s ( u n p u b l i s h e d o b s e r v a t i o n s ) . G i v e n t h e pr o b l e m s a s s o c i a t e d w i t h w a t e r d e p r i v a t i o n , i t i s i m p o r t a n t t o i d e n t i f y a n o t h e r r e i n f o r c i n g s t i m u l u s t h a t can be u s e d t o e s t a b l i s h and m a i n t a i n h i g h r a t e s o f c o n d i t i o n e d c i r c l i n g . A c c o r d i n g l y , E x p e r i m e n t V d e t e r m i n e d whether f o o d - d e p r i v e d r a t s w o u l d r e a d i l y a c q u i r e t h e c o n d i t i o n e d c i r c l i n g r e s p o n s e when f o o d p e l l e t s s e r v e d as t h e r e i n f o r c e r . M o r e o v e r , t h i s e x p e r i m e n t a s s e s s e d whether t h e n e u r o c h e m i c a l e f f e c t s p r e v i o u s l y a s s o c i a t e d w i t h c i r c l i n g m a i n t a i n e d by w a t e r r e i n f o r c e m e n t w o u l d be i n f l u e n c e d by c h a n g i n g t h e r e i n f o r c i n g s t i m u l u s . Materials and Methods S u b j e c t s and A p p a r a t u s N a i v e , male Sprague-Dawley r a t s ( C h a r l e s R i v e r L a b o r a t o r i e s ) , as d e s c r i b e d i n E x p e r i m e n t I , s e r v e d as s u b j e c t s . The b e h a v i o r a l a p p a r a t u s was t h e same e x c e p t t h a t t h e w a t e r hopper was r e p l a c e d w i t h a s t a n d a r d f o o d hopper w h i c h d i s p e n s e d 45 mg f o o d p e l l e t s . P r o c e d u r e s The e x p e r i m e n t a l p r o t o c o l employed i n t h i s e x p e r i m e n t was i d e n t i c a l t o t h a t d e s c r i b e d i n E x p e r i m e n t IVb e x c e p t t h a t , r a t h e r t h a n r e c e i v i n g l i m i t e d a c c e s s t o w a t e r , t h e r a t s were f o o d d e p r i v e d . B i o s e r v e P r e c i s i o n f o o d p e l l e t s (45 mg) were u s e d as r e i n f o r c e m e n t . A l l r a t s were h a b i t u a t e d t o t h e f o o d p e l l e t s 24 h r s b e f o r e b e i n g t e s t e d f o r d i r e c t i o n a l p r e f e r e n c e . R a t s i n t h e FDC group ( i . e . F o o d - d e p r i v e d c o n t r o l group) r e c e i v e d 15-20 g o f f o o d ( P u r i n a Lab chow) d a i l y . As i n E x p e r i m e n t I I , FDC s u b j e c t s were g i v e n f o o d 20 min p r i o r t o b e i n g s a c r i f i c e d on t h e t e s t day. R a t s i n t h e PR ( r e i n f o r c e d f o r c i r c l i n g i n p r e f e r r e d d i r e c t i o n ) and NPR ( r e i n f o r c e d f o r c i r c l i n g i n t h e i r n o n - p r e f e r r e d d i r e c t i o n ) groups were g i v e n 10-15 g o f f o o d a f t e r t e s t i n g . Comparable w e i g h t s were m a i n t a i n e d f o r r a t s i n t h e 3 -64-g r o u p s i n v o l v i n g f o o d d e p r i v a t i o n ( a p p r o x i m a t e l y 35-90% o f f r e e f e e d i n g w e i g h t s o f t h e N o n - d e p r i v e d C o n t r o l group - NDC). Results B e h a v i o r As i n d i c a t e d i n F i g u r e 9, t h e d i r e c t i o n o f r e i n f o r c e d c i r c l i n g , r e l a t i v e t o i n h e r e n t b i a s e s , d i d n o t i n f l u e n c e t h e r a t e o f r e s p o n d i n g e x h i b i t e d on t h e t e s t day. S t a t i s t i c a l a n a l y s i s o f t h e s e d a t a c o n f i r m e d t h i s o b s e r v a t i o n : Group - F ( l , 1 0 ) = 3.11, p > .10; Group x B l o c k s - F < 1. The r a t e s o f r e s p o n d i n g w i t h i n t h e t e s t s e s s i o n were c o n s t a n t f o r b o t h g r o u p s : F < 1. As s u c h , i t i s e v i d e n t t h a t a s y m p t o t i c r a t e s o f c o n d i t i o n e d c i r c l i n g a r e n o t dependent upon d i r e c t i o n a l b i a s e s . F u r t h e r m o r e , a l l s u b j e c t s r e c e i v e d an e q u i v a l e n t amount o f t r a i n i n g , i n d i c a t i n g , as i n E x p e r i m e n t I V b , t h a t a c q u i s i t i o n d i d n o t v a r y as a f u n c t i o n o f t h e d i r e c t i o n a l p r e f e r e n c e . N e u r o c h e m i s t r y The n e u r o c h e m i c a l d a t a were a n a l y z e d as d e s c r i b e d i n E x p e r i m e n t IVb. DA c o n c e n t r a t i o n s were n o t o b s e r v e d t o be i n f l u e n c e d by e i t h e r c o n d i t i o n e d c i r c l i n g o r f o o d d e p r i v a t i o n i n t h e s t r i a t u m o r n u c l e u s accumbens. However, c o n c e n t r a t i o n s o f DA were s i g n i f i c a n t l y a l t e r e d w i t h i n t h e o l f a c t o r y t u b e r c l e ( s e e b e l o w ) . No s i g n i f i c a n t e f f e c t s o f Hemisphere o r Group x Hemisphere i n t e r a c t i o n s were o b s e r v e d f o r e i t h e r o f t h e m e t a b o l i t e s o r m e t a b o l i t e : t r a n s m i t t e r r a t i o s i n t h e s t r i a t u m , n u c l e u s accumbens o r o l f a c t o r y t u b e r c l e . S t r i a t u m . DOPAC c o n c e n t r a t i o n s d i d n o t d i f f e r a c r o s s g r o u p s . S i m i l a r l y , DOPAC:DA r a t i o s were n o t a l t e r e d by c o n d i t i o n e d c i r c l i n g o r f o o d d e p r i v a t i o n . However, a s i g n i f i c a n t main e f f e c t o f Groups was o b t a i n e d when c o n c e n t r a t i o n s o f HVA were a n a l y z e d : F ( 3 ,17) = 5.14, p = .01. P a i r --65-F i g u r e 9. Number o f r o t a t i o n s e m i t t e d p e r m i n u t e by r a t s d u r i n g t h e t e s t s e s s i o n i n E x p e r i m e n t V. V a l u e s r e p r e s e n t means (± S.E.M.) and a r e p r e s e n t e d i n b l o c k s o f 2 min. R a t s were t r a i n e d t o c i r c l e f o r f o o d a c c o r d i n g t o a FR-2 s c h e d u l e o f r e i n f o r c e m e n t . R a t s were r e q u i r e d t o c i r c l e i n t h e i r p r e f e r r e d d i r e c t i o n ( s o l i d c i r c l e s ; n=6) o r a g a i n s t t h e i r d i r e c t i o n a l b i a s (open c i r c l e s ; n=6). 16-r ID z OC Ld Ld 10 >£ CO z o I a: 14-12-10-8 -6-I OH Ld m < Ld 4-2-• REINFORCED: PREFERRED O REINFORCED: NON-PREFERRED ~T~ 2 3 4 " T 5 T 6 " T 8 T " 9 BLOCKS OF TWO MINUTES 10 -67-w i s e c o m p a r i s o n s r e v e a l e d t h a t a n i m a l s w i t h i n t h e FDC, PR and NPR groups had s i g n i f i c a n t l y g r e a t e r HVA c o n c e n t r a t i o n s t h a n d i d r a t s w i t h i n t h e NDC group ( s e e F i g u r e 1 0 ) . No o t h e r group d i f f e r e n c e s were o b t a i n e d . A s i m i l a r p r o f i l e was o b t a i n e d when HVA:DA r a t i o s were a n a l y z e d : F ( 3,17) = 11.45, p < .001. As s u c h , t h e e f f e c t s o f f o o d d e p r i v a t i o n / c o n s u m p t i o n appear t o mask any changes i n DA m e t a b o l i s m a s s o c i a t e d w i t h c o n d i t i o n e d c i r c l i n g . N u c l e u s Accumbens. DOPAC c o n c e n t r a t i o n s d i d n o t d i f f e r between g r o u p s . However, a n a l y s i s o f DOPAC:DA r a t i o s r e v e a l e d t h a t t h e s e were g r e a t e r i n t h e n u c l e u s accumbens o f FDC, PR and NPR r a t s , r e l a t i v e t o t h e NDC group: F(3,19) = 5.76, p- .006. A s i m i l a r p a t t e r n was d e t e c t e d upon a n a l y z i n g HVA c o n c e n t r a t i o n s and HVA:DA r a t i o s : F(3,19) = 4.38, p = .011; F(3,19) = 7.33, p = .002, r e s p e c t i v e l y . P a i r - w i s e c o m p a r i s o n s i n d i c a t e d t h a t m e t a b o l i s m was b i l a t e r a l l y augmented i n t h e FDC, PR and NPR g r o u p s , r e l a t i v e t o t h e NDC group (see F i g u r e 1 1 ) . No f u r t h e r group d i f f e r e n c e s were e v i d e n t , s u g g e s t i n g t h a t any e f f e c t s o f c o n d i t i o n e d c i r c l i n g on m e s o l i m b i c DA m e t a b o l i s m a r e a l s o masked by t h e use o f f o o d d e p r i v a t i o n / c o n s u m p t i o n . O l f a c t o r y T u b e r c l e . A n a l y s i s o f DA c o n c e n t r a t i o n s y i e l d e d a s i g n i f i c a n t Group x Hemisphere i n t e r a c t i o n : F ( 3 ,17) = 3.33, p < .03. Newman-Keuls p a i r - w i s e c o m p a r i s o n s ( a = .05) i n d i c a t e d t h a t none o f t h e i n d i v i d u a l c o m p a r i s o n s were s i g n i f i c a n t l y d i f f e r e n t . I n s p e c t i o n o f t h e means c o m p r i s i n g t h i s i n t e r a c t i o n s u g g e s t s a t r e n d t o w a r d s i n c r e a s e d DA c o n c e n t r a t i o n s i n t h e o l f a c t o r y t u b e r c l e c o n t r a l a t e r a l t o t h e d i r e c t i o n o f r e i n f o r c e d c i r c l i n g , i r r e s p e c t i v e o f r a t s ' d i r e c t i o n a l b i a s e s (NDC: I p s i l a t e r a l - 434.6 + 24.1 v s C o n t r a l a t e r a l - 473.6 ± 19.1 nmol/g p r o t e i n ; -68-F i g u r e 10. S t r i a t a l c o n c e n t r a t i o n s o f HVA (nmol/ g p r o t e i n ) (upper p a n e l ) and t h e r a t i o s o f HVA t o DA ( l o w e r p a n e l ) a r e p r e s e n t e d f o r n o n - d e p r i v e d c o n t r o l s (NDC; n=5), f o o d - d e p r i v e d c o n t r o l s (FDC; n - 6 ) , r a t s t r a i n e d t o c i r c l e i n t h e i r p r e f e r r e d d i r e c t i o n (PR; n=6), and r a t s r e q u i r e d t o c i r c l e i n t h e d i r e c t i o n o p p o s i t e t o t h e i r b i a s (NPR; n=6). R a t s i n t h e PR and NPR g r o u p s were t e s t e d f o r 20 min. C o n d i t i o n e d c i r c l i n g was m a i n t a i n e d u s i n g a FR-2 s c h e d u l e o f f o o d r e i n f o r c e m e n t . S u b j e c t s i n t h e FDC group were g i v e n a c c e s s t o a matched amount o f f o o d f o r 20 min p r i o r t o b e i n g s a c r i f i c e d . * i n d i c a t e s s t a t i s t i c a l l y d i f f e r e n t from c o r r e s p o n d i n g NDC v a l u e s , p < .05. -69--70-F i g u r e 11. C o n c e n t r a t i o n s o f HVA (nmol / g p r o t e i n ) (upper p a n e l ) and t h e r a t i o s o f HVA t o DA ( l o w e r p a n e l ) d e t e c t e d w i t h i n t h e n u c l e u s accumbens a r e p r e s e n t e d f o r n o n - d e p r i v e d c o n t r o l s (NDC; n - 6 ) , f o o d - d e p r i v e d c o n t r o l s (FDC; n=6), r a t s t r a i n e d t o c i r c l e i n t h e i r p r e f e r r e d d i r e c t i o n (PR; n=6), and r a t s r e q u i r e d t o c i r c l e i n t h e d i r e c t i o n o p p o s i t e t o t h e i r b i a s (NPR; n=5). See F i g u r e 10 and Methods ( E x p e r i m e n t V) f o r d e s c r i p t i o n o f e x p e r i m e n t a l p r o c e d u r e s . * i n d i c a t e s s t a t i s t i c a l l y d i f f e r e n t f r o m c o r r e s p o n d i n g NDC v a l u e s , p < .05. -71--72-FDC: 473.7 ± 17.1 v s 458.7 ± 25.5; PR: 444.2 ± 28.3 vs 480.7 ± 28.9; NPR: 442.3 ± v s 499.2 ± 2 4 . 2 ) . A b s o l u t e c o n c e n t r a t i o n s o f DOPAC and HVA were not s i g n i f i c a n t l y d i f f e r e n t a c r o s s g r o u p s . However, b o t h D0PAC:DA and HVA:DA r a t i o s were b i l a t e r a l l y i n c r e a s e d i n t h e o l f a c t o r y t u b e r c l e o f FDC, PR and NPR g r o u p s , r e l a t i v e t o t h e NDC: F{3,17) = 4.46, p = .017; F(3,17) = 6.76, p = .003, r e s p e c t i v e l y ( s e e F i g . 1 2 ) . D i s c u s s i o n E x p e r i m e n t V d e t e r m i n e d t h e e f f e c t s o f u s i n g f o o d as t h e r e i n f o r c i n g s t i m u l u s on a c q u i s i t i o n and p e r f o r m a n c e o f c o n d i t i o n e d c i r c l i n g and, as w e l l , t h e n e u r o c h e m i c a l p r o f i l e a s s o c i a t e d w i t h t h i s r e s p o n s e . A l l r a t s were a b l e t o a c q u i r e t h e r e s p o n s e when i t was r e i n f o r c e d w i t h f o o d p e l l e t s . As i n E x p e r i m e n t I V b , d i r e c t i o n a l b i a s e s were n o t f o u n d t o i n f l u e n c e t h e pe r f o r m a n c e o f t h i s r e s p o n s e . W h i l e t h e o v e r a l l r a t e s o f c i r c l i n g were s i m i l a r between E x p e r i m e n t s IVb and t h e p r e s e n t s t u d y , t h e w i t h i n - s e s s i o n r e s p o n s e p r o f i l e v a r i e d as a f u n c t i o n o f t h e r e i n f o r c i n g s t i m u l u s . S p e c i f i c a l l y , t h e use o f w a t e r r e s u l t e d i n an i n i t i a l l y h i g h e r r a t e o f r e s p o n d i n g and a l o w e r t e r m i n a l r a t e o f r e s p o n d i n g , r e l a t i v e t o r a t s t h a t were r e i n f o r c e d w i t h f o o d ( s ee F i g u r e s . 5 & 9 ) . These d i f f e r e n t r e s p o n s e p r o f i l e s may r e f l e c t d i f f e r e n c e s i n d e p r i v a t i o n s c h e d u l e s . F o r example, t h e p r o g r e s s i v e d e c r e a s e i n r e s p o n d i n g f o r w a t e r may r e f l e c t s a t i a t i o n . When w a t e r - d e p r i v e d c o n t r o l s a r e g i v e n a c c e s s t o w a t e r i n t h e i r home cage f o r a 20 mi n u t e p e r i o d , t h e y a r e o b s e r v e d t o i n g e s t w a t e r c o n t i n u o u s l y f o r a p p r o x i m a t e l y 10 m i n u t e s . T h e r e a f t e r , t h e a n i m a l s a p p r o a c h t h e b o t t l e p e r i o d i c a l l y and consume s m a l l amounts o f w a t e r . As a r e s u l t , t h e p a t t e r n o f i n g e s t i o n and t h e volume o f w a t e r consumed under t h e s e two c o n d i t i o n s a r e s i m i l a r . -73-F i g u r e 12. C o n c e n t r a t i o n s o f HVA (nmol/ g p r o t e i n ) (upper p a n e l ) and t h e r a t i o s o f HVA t o DA ( l o w e r p a n e l ) d e t e c t e d w i t h i n t h e o l f a c t o r y t u b e r c l e a r e p r e s e n t e d f o r n o n - d e p r i v e d c o n t r o l s (NDC; n=5), f o o d - d e p r i v e d c o n t r o l s (FDC; n=6), r a t s t r a i n e d t o c i r c l e i n t h e i r p r e f e r r e d d i r e c t i o n (PR; n=4), and r a t s r e q u i r e d t o c i r c l e i n t h e d i r e c t i o n o p p o s i t e t o t h e i r b i a s (NPR; n=6). See F i g u r e 10 and Methods ( E x p e r i m e n t V) f o r d e s c r i p t i o n o f e x p e r i m e n t a l p r o c e d u r e s . * i n d i c a t e s s i g n i f i c a n t l y d i f f e r e n t f r o m c o r r e s p o n d i n g NDC v a l u e s , p < .05. \ -74--75-A l t h o u g h r a t s were a b l e t o a c q u i r e t h e c o n d i t i o n e d c i r c l i n g r e s p o n s e when f o o d was u s e d as t h e r e i n f o r c e r , n e u r o c h e m i c a l changes s p e c i f i c t o t h e p e r f o r m a n c e o f t h i s r e s p o n s e were n o t d e t e c t e d w i t h i n t h e s t r i a t u m , n u c l e u s accumbens o r o l f a c t o r y t u b e r c l e . That i s , w h i l e c o n t r o l s u b j e c t s t h a t had been f o o d - d e p r i v e d b u t g i v e n a meal 20 min p r i o r t o b e i n g s a c r i f i c e d and t h e two groups t r a i n e d t o c i r c l e c o u l d be d i s t i n g u i s h e d f r o m t h e non-d e p r i v e d c o n t r o l g r o u p , t h e s e 3 groups e x h i b i t e d comparable b i l a t e r a l i n c r e a s e s i n s t r i a t a l and accumbens DA m e t a b o l i s m . These r e s u l t s a r e c o n s i s t e n t w i t h a p r e v i o u s r e p o r t t h a t s t r i a t a l and m e s o l i m b i c DA m e t a b o l i s m i s b i l a t e r a l l y i n c r e a s e d i n r a t s g i v e n a c c e s s t o f o o d p e l l e t s o r a n u t r i t i v e l i q u i d d i e t f o r a one hour p e r i o d ( B l a c k b u r n , P h i l l i p s , J a k u b o v i c and F i b i g e r , 1986). I t i s a p p a r e n t t h e n t h a t t h e e f f e c t s o f f o o d d e p r i v a t i o n / c o n s u m p t i o n must be t a k e n i n t o a c c o u n t when t h e i n v o l v e m e n t o f t h e m e s o t e l e n c e p h a l i c DA sytem i s examined i n t a s k s u s i n g t h e s e c o n d i t i o n s . W h i l e changes i n s t r i a t a l and accumbens DA m e t a b o l i s m s p e c i f i c t o c o n d i t i o n e d c i r c l i n g were n o t d e t e c t e d when f o o d was employed as t h e r e i n f o r c e r , a t r e n d f o r i n c r e a s e d c o n c e n t r a t i o n s o f DA w i t h i n t h e o l f a c t o r y t u b e r c l e c o n t r a l a t e r a l t o r e i n f o r c e d d i r e c t i o n o f c i r c l i n g was e v i d e n t . W h i l e c o n c e n t r a t i o n s o f DA w i t h i n t h e o l f a c t o r y t u b e r c l e have n o t p r e v i o u s l y been o b s e r v e d t o be i n f l u e n c e d by c o n d i t i o n e d c i r c l i n g ( s e e E x p e r i m e n t s I I and I V b ) , a r o l e f o r t u b e r c l e DA i n c i r c l i n g has p r e v i o u s l y been p o s i t e d . F o r example, Szewczak, C o r n f e l d t & F i e l d i n g (1985) have r e p o r t e d t h a t c o n t r a v e r s i v e c i r c l i n g c an be i n d u c e d by u n i l a t e r a l i n f u s i o n s o f DA i n t o t h e o l f a c t o r y t u b e r c l e . M o r e o v e r , i n c r e a s e s i n DA m e t a b o l i s m w i t h i n t h e c o n t r a l a t e r a l o l f a c t o r y t u b e r c l e have been a s s o c i a t e d w i t h s t i m u l a t i o n - i n d u c e d c i r c l i n g ( S z o s t a k , e t a l . , 1986). A c c o r d i n g l y , i t i s p o s s i b l e t h a t t h e c o n t r a l a t e r a l o l f a c t o r y t u b e r c l e i s i n v o l v e d i n t h e -76-m e d i a t i o n o f c i r c l i n g . F u r t h e r e x p e r i m e n t s a r e r e q u i r e d t o e l u c i d a t e t h e r o l e o f t u b e r c l e DA i n t h i s b e h a v i o r . EXPERIMENT VI Neurochemical Correlates of Conditioned Circling Within Localized Regions of the Striatum I t i s p o s s i b l e t h a t c o n d i t i o n e d c i r c l i n g i s m o d ulated by r e s t r i c t e d p o r t i o n s o f t h e s t r i a t u m and t h a t d i f f e r e n t r e g i o n s s u b s e r v e d i s c r e t e components o f t h e r e s p o n s e . J o y c e , D a v i s & van H a r t e s v e l d t (1981) have o b s e r v e d t h a t i n f u s i o n s o f DA i n t o t h e d o r s a l s t r i a t u m r e s u l t i n s t r o n g c o n t r a v e r s i v e c i r c l i n g ( i . e . away f r o m t h e s i t e o f i n f u s i o n ) whereas i n j e c t i o n s i n t o v e n t r a l r e g i o n s a r e a s s o c i a t e d w i t h o n l y weak c o n t r a v e r s i v e c i r c l i n g . These f i n d i n g s have been e x t e n d e d by W o l f s o n & Brown (1983) who have d e m o n s t r a t e d t h a t r o t a t i o n i n d u c e d by i n t r a s t r i a t a l DA i n j e c t i o n s i s dependent upon t h e c o n c e n t r a t i o n o f DA w i t h i n t h e d o r s a l s t r i a t u m . Subsequent r e s e a r c h by J o y c e & van H a r t e s v e l d t (1984) has f u r t h e r i n d i c a t e d t h a t i t i s t h e m e d i a l p o r t i o n o f d o r s a l s t r i a t u m t h a t s u b s e r v e s r o t a t i o n w h i l e p o s t u r a l d e v i a t i o n ( i . e . b e h a v i o r s d i r e c t e d t o t h e e n v i r o n m e n t i p s i v e r s i v e o r c o n t r a v e r s i v e t o t h e i n j e c t i o n s i t e ) i s s e l e c t i v e l y s u b s e r v e d by t h e l a t e r a l d o r s a l s t r i a t u m . C o n d i t i o n e d c i r c l i n g may a l s o be a s s o c i a t e d w i t h d e c r e a s e s i n DA m e t a b o l i s m w i t h i n r e s t r i c t e d s t r i a t a l r e g i o n s , t h e d i r e c t i o n and magnitude o f t h e n e u r o c h e m i c a l changes b e i n g dependent upon t h e s i d e o f t h e s t r i a t u m i n r e l a t i o n s h i p t o t h e d i r e c t i o n o f t u r n i n g ( i . e . i p s i v e r s i v e v s c o n t r a v e r s i v e ) . F o r example, V a c c a r i n o & F r a n k l i n (1984) have s u g g e s t e d t h a t t h e m e d i a l and l a t e r a l s u b s t a n t i a n i g r a p a r s compacta (SNC) a r e f u n c t i o n a l l y a n t a g o n i s t i c w i t h r e s p e c t t o t h e i r i n v o l v e m e n t i n c i r c l i n g . I n c o m b i n a t i o n w i t h s y s t e m i c d-amphetamine, i n f u s i o n s o f apomorphine i n t o -77-t h e m e d i a l 3NC e l i c i t i p s i v e r s i v e c i r c l i n g , whereas s i m i l a r i n j e c t i o n s i n t o t h e l a t e r a l SNC a r e w i t h o u t e f f e c t . I n c o n t r a s t , i n f u s i o n s o f a l p h a -f l u p e n t h i x o l , a DA r e c e p t o r a n t a g o n i s t , a r e a s s o c i a t e d w i t h c o n t r a l a t e r a l r o t a t i o n when i n j e c t e d m e d i a l l y , b u t p r o d u c e i p s i v e r s i v e c i r c l i n g when i n f u s e d l a t e r a l l y . The d e t e c t i o n o f s u c h an i n t r a s t r i a t a l i n t e r p l a y i s p r e c l u d e d when o v e r a l l s t r i a t a l DA and m e t a b o l i t e c o n c e n t r a t i o n s a r e a n a l y z e d . A c c o r d i n g l y , t h e b i l a t e r a l i n c r e a s e s i n s t r i a t a l DA m e t a b o l i s m o b s e r v e d i n t h e p r e c e d i n g e x p e r i m e n t s may n o t a c c u r a t e l y r e f l e c t t h e i n v o l v e m e n t o f t h e s t r i a t u m i n c o n d i t i o n e d c i r c l i n g . F o r example, assuming t h a t c o n d i t i o n e d c i r c l i n g i s dependent upon an i m b a l a n c e i n s t r i a t a l DA a c t i v i t y , t h e b i l a t e r a l i n c r e a s e s p r e v i o u s l y o b s e r v e d c o u l d r e f l e c t i n c r e a s e s w i t h i n t h e c o n t r a l a t e r a l d o r s a l s t r i a t u m and t h e i p s i l a t e r a l v e n t r a l s t r i a t u m . To t e s t t h i s h y p o t h e s i s , two e x p e r i m e n t s were c o n d u c t e d . The f i r s t e x p e r i m e n t examined t h e d i s t r i b u t i o n o f DA, DOPAC and HVA c o n c e n t r a t i o n s w i t h i n t h e s t r i a t u m o f u n t r e a t e d , c o n t r o l r a t s . The e x t e n t t o w h i c h t h e c o n c e n t r a t i o n s o f t h e s e t h r e e compounds and t h e r a t i o s o f t h e m e t a b o l i t e s t o DA v a r i e d a l o n g t h e dominant axes ( a n t e r i o r - p o s t e r i o r ; m e d i a l - l a t e r a l ; d o r s a l - v e n t r a l ) was d e t e r m i n e d . I n a d d i t i o n , i n t e r a c t i o n s between t h e s e axes were a s s e s s e d . The second e x p e r i m e n t examined t h e e x t e n t t o w h i c h DA m e t a b o l i s m w i t h i n d i s c r e t e s u b - r e g i o n s o f t h e s t r i a t u m i s d i f f e r e n t i a l l y i n f l u e n c e d by c o n d i t i o n e d c i r c l i n g . Experiment Via Regional Distribution of DA and Its Two Primary Metabolites P r e v i o u s s t u d i e s have i n d i c a t e d t h a t DA c o n c e n t r a t i o n s d e c r e a s e a l o n g t h e a n t e r i o r - p o s t e r i o r a x i s ( B e a l & M a r t i n , 1985; T a s s i n , Cheramy, B l a n c , T h i e r r y & G l o w i n s k i , 1976). A s i m i l a r p a t t e r n o f d i s t r i b u t i o n has been d e s c r i b e d f o r DA m e t a b o l i t e s ( S e a l & M a r t i n , 1985). W h i l e t h e s e e x p e r i m e n t s have c l e a r l y d e m o n s t r a t e d s u b - r e g i o n a l v a r i a t i o n s i n DA a c t i v i t y , t h e y have n o t a s s e s s e d more s u b t l e r e g i o n a l d i f f e r e n c e s . B e a l & M a r t i n (1985) have r e p o r t e d t h a t c o n c e n t r a t i o n s o f DA, DOPAC and HVA do n o t v a r y a l o n g t h e m e d i a l - l a t e r a l a x i s . However, t h e i r s t a t i s t i c a l t r e a t m e n t o f t h e d a t a d i d n o t p e r m i t assessment o f p o t e n t i a l i n t e r a c t i o n s between t h e v a r i o u s a x e s . The p r e s e n t e x p e r i m e n t was d e s i g n e d so t h a t t h e d i s t r i b u t i o n s o f DA, DOPAC and HVA c o u l d be a s s e s s e d u s i n g h i g h e r - o r d e r s t a t i s t i c a l t e s t s t h a t w o u l d be more s e n s i t i v e t o d e t e c t i n g t h e v a r i o u s g r a d i e n t s o f c o n c e n t r a t i o n s and t h e i n t e r p l a y between t h e s e g r a d i e n t s . I n a d d i t i o n , DOPAC:DA and HVA:DA r a t i o s were a n a l y z e d i n t h e same f a s h i o n . Materials and Methods S u b j e c t s N a i v e , male Sprague-Dawley r a t s ( 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=17), as d e s c r i b e d i n E x p e r i m e n t I , were u s e d i n t h e p r e s e n t e x p e r i m e n t . P r o c e d u r e On t h e t e s t d a y s , r a t s were removed f r o m t h e i r home c a g e s , t a k e n t o a s e p a r a t e room and d e c a p i t a t e d . B r a i n s were r a p i d l y removed, a c o r o n a l c u t was made s l i g h t l y c a u d a l t o t h e o p t i c c h i a s m and t h e a n t e r i o r s e c t i o n f r o z e n on a mic r o t o m e . Three c o n s e c u t i v e c o r o n a l s e c t i o n s , 1 mm t h i c k , were o b t a i n e d and p l a c e d on i c e . The d e c u s s a t i o n o f t h e c o r p u s c a l l o s u m s e r v e d t o d e f i n e t h e r o s t r a l e x t e n t o f t h e a n t e r i o r s l i c e , and c o r r e s p o n d e d a p p r o x i m a t e l y t o l e v e l A8920 u o f K o n i g and K l i p p e l ( 1 9 6 3 ) . The a n t e r i o r b o r d e r s o f t h e se c o n d and t h i r d s l i c e s c o r r e s p o n d e d a p p r o x i m a t e l y t o l e v e l s A7890 a and A6860 yx, r e s p e c t i v e l y . The two a n t e r i o r s l i c e s were p l a c e d on i c e so t h a t t h e r o s t r a l s u r f a c e s were f a c e up. L e f t and r i g h t s t r i a t u m -79-were d i s s e c t e d f r o m t h e s e two s e c t i o n s by i n i t i a l l y making a h o r i z o n t a l c u t a t t h e l e v e l o f t h e a n t e r i o r commissure. The d o r s o l a t e r a l b o r d e r s were d e f i n e d by t h e c o r p u s c a l l o s u m w h i l e t h e m e d i a l e x t e n t was d e f i n e d by t h e l a t e r a l v e n t r i c l e s and septum. Each s t r i a t a l sample was t h e n d i v i d e d i n t o 4 q u a d r a n t s by making a h o r i z o n t a l and a v e r t i c a l c u t midway. The t h i r d s l i c e was p l a c e d on i c e so t h a t t h e c a u d a l s u r f a c e was f a c e up. A h o r i z o n t a l c u t was made a t t h e l e v e l o f t h e f o r n i x w h i c h s e r v e d t o d e f i n e t h e v e n t r a l e x t e n t o f t h e s t r i a t u m . The m e d i a l b o r d e r o f t h e t a i l o f t h e s t r i a t u m was d e f i n e d by t h e g l o b u s p a l l i d u s whereas t h e c o r p u s c a l l o s u m marked t h e l a t e r a l l i m i t . T h i s s t r u c t u r e was t h e n d i v i d e d i n t o two e q u a l p a r t s by c u t t i n g midway a l o n g t h e d o r s a l / v e n t r a l a x i s . The t i s s u e samples were n o t weighed b u t were i n s t e a d i m m e d i a t e l y p l a c e d i n 200 u l h o m o g e n i z i n g s o l u t i o n and p r e p a r e d f o r a n a l y s i s o f DA, DOPAC and HVA by HPLC-ED, as d e s c r i b e d i n E x p e r i m e n t I . The c o n c e n t r a t i o n o f each compound was e x p r e s s e d as nmol/ g p r o t e i n . S t a t i s t i c a l A n a l y s e s I n o r d e r t o d e t e r m i n e whether t h e r e were any c o n s i s t e n t l e f t - r i g h t d i f f e r e n c e s , one-way ANOVAs were c o n d u c t e d f o r each compound measured w i t h i n e ach s u b - r e g i o n . To m i n i m i z e t h e p r o b a b i l i t y o f making a Type I e r r o r , w h i c h would be i n c r e a s e d due t o t h e number o f i n t e r - d e p e n d e n t a n a l y s e s c o n d u c t e d , t h e a c c e p t a b l e l e v e l o f s i g n i f i c a n c e p e r c o m p a r i s o n was s e t a t a < .001 ( K i r k , 1968). As no c o n s i s t e n t l e f t - r i g h t d i f f e r e n c e s were o b s e r v e d f o r any o f t h e compounds o r r a t i o s , l e f t and r i g h t v a l u e s were p o o l e d and t h e mean o f t h e two s e c t i o n s u s e d f o r p u r p o s e s o f a s s e s s i n g r e g i o n a l v a r i a t i o n s . The 4 r e g i o n s w i t h i n t h e a n t e r i o r s l i c e were i n i t i a l l y compared w i t h t h e c o r r e s p o n d i n g a r e a s o b t a i n e d f r o m t h e second c o r o n a l s e c t i o n ( i . e . p o s t e r i o r ) . The t h i r d s e c t i o n , c o n t a i n i n g t h e t a i l -30-o f t h e s t r i a t u m , was n o t i n c l u d e d i n t h i s a n a l y s i s as comparable sub-r e g i o n s were n o t o b t a i n e d . A c c o r d i n g l y , t h r e e - w a y ANOVAs, w i t h each f a c t o r b e i n g a r e p e a t e d measure h a v i n g two l e v e l s ( a n t e r i o r / p o s t e r i o r ; d o r s a l / v e n t r a l ; m e d i a l / l a t e r a l ) , were c o n d u c t e d f o r each compound and r a t i o . Unique e r r o r terms were u s e d i n d e t e r m i n i n g t h e s i g n i f i c a n c e o f each main e f f e c t and i n t e r a c t i o n t e r m ( K i r k , 1968). T e s t s o f s i m p l e i n t e r a c t i o n s and p a i r - w i s e c o m p a r i s o n s (Newman-Keuls) were c o n d u c t e d when a p p r o p r i a t e i n o r d e r t o i d e n t i f y t h e s o u r c e o f s i g n i f i c a n t two-way and thre e - w a y i n t e r a c t i o n s . The a c c e p t a b l e l e v e l o f s i g n i f i c a n c e was s e t a t a < .01 f o r a l l o v e r a l l a n a l y s e s and subsequent c o m p a r i s o n s . To d e t e r m i n e whether c o n c e n t r a t i o n s v a r i e d w i t h i n t h e t a i l o f t h e s t r i a t u m , one-way ANOVAs w i t h r e p e a t e d measures ( d o r s o m e d i a l v s v e n t r o l a t e r a l ) were c o n d u c t e d f o r each compound and r a t i o . I n a d d i t i o n , t h e e x i s t e n c e o f a n t e r i o r - p o s t e r i o r g r a d i e n t s was f u r t h e r a s s e s s e d by co m p a r i n g t h e o v e r a l l c o n c e n t r a t i o n s o f each compound w i t h i n t h e t a i l o f t h e s t r i a t u m ( i . e . mean o f i t s two s u b - r e g i o n s ) w i t h t h e a v e r a g e c o n c e n t r a t i o n s f o u n d i n each o f t h e o t h e r two c o r o n a l s e c t i o n s o f t h e s t r i a t u m . ANOVAs w i t h one r e p e a t e d measure ( a n t e r i o r v s p o s t e r i o r v s t a i l ) were c o n d u c t e d f o r each compound and r a t i o . The s o u r c e o f s i g n i f i c a n t main e f f e c t s was i d e n t i f i e d u s i n g Newman-Keuls p a i r - w i s e c o m p a r i s o n s . I n c a s e s o f i n c o m p l e t e d a t a s e t s due t o s p o r a d i c c o n t a m i n a t i o n o f HVA samp l e s , t h e d a t a f o r t h a t s u b j e c t were e l i m i n a t e d from t h e o v e r a l l a n a l y s i s o f HVA c o n c e n t r a t i o n s and HVA:DA r a t i o s ( f i n a l n=8). Results Dopamine A n a l y s i s o f DA c o n c e n t r a t i o n s y i e l d e d a s i g n i f i c a n t 3-way i n t e r a c t i o n : F ( l , 1 6 ) = 3.95, p = .009 ( s e e T a b l e 5 ) . I n o r d e r t o i d e n t i f y - 3 1 -T a b l e 5. Mean (± 3.E.M.) c o n c e n t r a t i o n s (nmol/g p r o t e i n ) o f DA, DOPAC and HVA w i t h i n d i s c r e t e s u b - r e g i o n s o f t h e s t r i a t u m . Dopamine D o r s a l A n t e r i o r : (n-17) P o s t e r i o r : (n=17) T a i l : (n-16) L a t e r a l 851.09 24.33 663.00 M e d i a l 913.56 20.79 675.79 14.32 336.69 8.90 V e n t r a l L a t e r a l M e d i a l 378.91 23.06 739.71 19.90 424.09 15.15 770.29 20.69 702.03 39.11 DOPAC D o r s a l L a t e r a l M e d i a l V e n t r a l L a t e r a l M e d i a l A n t e r i o r : (n=17) P o s t e r i o r : (n-17) i a i i : (n=16) 133.15 6.32 116.56 5.96 170.24 6.59 130.41 3.43 77.47 2.71 171.13 7.04 126.94 5.44 86.98 o r- -l Z . 31 202.33 7.53 163.06 r-i O "> O . OZ HVA A n t e r i o r : <n=8) P o s t e r i o r : (n-8) T a i l : (n=8) D o r s a l L a t e r a l M e d i a l 62.97 53.42 54.46 46. 69 26 V e n t r a l j a t e r a l M e d i a l 77.43 4.03 63.71 4.97 37.73 1.71 64.39 4.18 t h e n a t u r e o f t h i s i n t e r a c t i o n , t e s t s o f t h e s i m p l e i n t e r a c t i o n s composing t h e 3-way t e r m were c o n d u c t e d . A n a l y s i s o f t h e AP x DV i n t e r a c t i o n w i t h i n t h e l a t e r a l s t r i a t u m i n d i c a t e d t h a t t h e a n t e r i o r s t r i a t u m c o n t a i n e d more DA t h a n t h e p o s t e r i o r s t r i a t u m , i r r e s p e c t i v e o f t h e d o r s a l - v e n t r a l a x i s : F ( l , 1 6 ) = 91.16, p < .001. C o n c e n t r a t i o n s were a l s o g r e a t e r i n t h e v e n t r o l a t e r a l s t r i a t u m , r e l a t i v e t o t h e d o r s o l a t e r a l s t r i a t u m : F ( l , 1 6 ) = 9.30, p < .01. W i t h i n t h e m e d i a l s t r i a t u m , t h e AP x DV i n t e r a c t i o n t e r m was s i g n i f i c a n t : F ( l , 1 6 ) = 24.45, p < .001. P a i r - w i s e c o m p a r i s o n s r e v e a l e d t h a t t h e a n t e r i o r -p o s t e r i o r g r a d i e n t was o n l y s i g n i f i c a n t w i t h i n t h e d o r s o m e d i a l s t r i a t u m and n o t i n t h e v e n t r o m e d i a l s t r i a t u m a l t h o u g h a t r e n d i n t h e same d i r e c t i o n was e v i d e n t (.05 > p > .01). W i t h i n t h e a n t e r o m e d i a l s t r i a t u m , DA c o n c e n t r a t i o n s were g r e a t e r i n t h e d o r s a l r e g i o n t h a n i n t h e v e n t r a l r e g i o n . I n c o n t r a s t , no d i f f e r e n c e s between d o r s a l and v e n t r a l c o n c e n t r a t i o n s were e v i d e n t w i t h i n t h e p o s t e r o m e d i a l s t r i a t u m . A n a l y s i s o f t h e AP x ML s i m p l e i n t e r a c t i o n s y i e l d e d s i g n i f i c a n t main e f f e c t s o f t h e AP a x i s , i n d i c a t i n g t h a t c o n c e n t r a t i o n s were g r e a t e s t i n t h e r o s t r a l r e g i o n s o f t h e s t r i a t u m , r e l a t i v e t o more c a u d a l r e g i o n s : F ' s ( l , 1 6 ) = 181.51 and 43.03, p's < .001, f o r d o r s a l and v e n t r a l r e g i o n s , r e s p e c t i v e l y . No m e d i a l - l a t e r a l d i f f e r e n c e s were d e t e c t e d w i t h i n t h e d o r s a l s t r i a t u m . However, a m e d i a l - l a t e r a l g r a d i e n t was e v i d e n t w i t h i n t h e v e n t r a l s t r i a t u m : F ( l , 1 6 ) = 21.42, p < .001. S p e c i f i c a l l y , c o n c e n t r a t i o n s w i t h i n t h e v e n t r o l a t e r a l s t r i a t u m were g r e a t e r t h a n t h o s e d e t e c t e d w i t h i n t h e v e n t r o m e d i a l s t r i a t u m . A n a l y s i s o f t h e DV x ML i n t e r a c t i o n w i t h i n t h e a n t e r i o r s t r i a t u m y i e l d e d a s i g n i f i c a n t i n t e r a c t i o n : F ( l , 1 6 ) = 25.53, p < .001. P a i r - w i s e c o m p a r i s o n s i n d i c a t e d t h a t c o n c e n t r a t i o n s were h i g h e r i n t h e - o j -a n t e r o d o r s o m e d i a l s t r i a t u m , r e l a t i v e t o t h o s e o b t a i n e d w i t h i n t h e a n t e r o v e n t r o m e d i a l s t r i a t u m . No d o r s a l - v e n t r a l d i f f e r e n c e s were d e t e c t e d w i t h i n t h e a n t e r o l a t e r a l r e g i o n o f t h e s t r i a t u m . The i n t e r a c t i o n a l s o r e f l e c t e d a m e d i a l - l a t e r a l g r a d i e n t w i t h i n t h e a n t e r o v e n t r a l s t r i a t u m , w i t h c o n c e n t r a t i o n s b e i n g h i g h e s t l a t e r a l l y . " I n c o n t r a s t , a n a l y s i s o f t h i s i n t e r a c t i o n w i t h i n t h e p o s t e r i o r s t r i a t u m y i e l d e d o n l y an e f f e c t o f t h e d o r s a l - v e n t r a l a x i s w i t h c o n c e n t r a t i o n s b e i n g g r e a t e s t w i t h i n t h e p o s t e r o v e n t r a l s t r i a t u m : F ( l , 1 6 ) = 9.24, p< .01. A n a l y s i s o f DA c o n c e n t r a t i o n s w i t h i n t h e t a i l o f t h e s t r i a t u m i n d i c a t e d t h a t c o n c e n t r a t i o n s were g r e a t e s t w i t h i n t h e v e n t r o l a t e r a l t a i l , r e l a t i v e t o t h e d o r s o m e d i a l r e g i o n : F ( l , 1 5 ) = 37.80, p< .001. The o b s e r v a t i o n o f t h e a n t e r i o r - p o s t e r i o r g r a d i e n t was c o n f i r m e d and e x t e n d e d when o v e r a l l DA c o n c e n t r a t i o n s w i t h i n t h e t a i l were compared w i t h t h e a v e r a g e c o n c e n t r a t i o n s o b t a i n e d w i t h i n t h e a n t e r i o r and p o s t e r i o r s e c t i o n s : F ( l , 1 5 ) = 320.01, p < .001. P a i r - w i s e c o m p a r i s o n s i n d i c a t e d a p r o g r e s s i v e d e c r e a s e i n c o n c e n t r a t i o n s f r o m a n t e r i o r t o c a u d a l s e c t i o n s . To summarize, DA c o n c e n t r a t i o n s were f o u n d t o v a r y a l o n g t h e r o s t r a l -c a u d a l a x i s o f t h e s t r i a t u m . S p e c i f i c a l l y , c o n c e n t r a t i o n s were l o w e r i n t h e more c a u d a l r e g i o n s . T h i s g r a d i e n t was a p p a r e n t t h r o u g h o u t t h e s t r i a t u m , t h a t i s t o s a y , i r r e s p e c t i v e o f any m e d i a l - l a t e r a l o r d o r s a l -v e n t r a l d i f f e r e n c e s ( s e e F i g u r e 1 3 ) . The p r e s e n t r e s u l t s a l s o i n d i c a t e d t h a t DA c o n c e n t r a t i o n s v a r y a c r o s s t h e o t h e r a x e s . However, t h e m e d i a l -l a t e r a l and d o r s a l - v e n t r a l g r a d i e n t s a r e n o t as r o b u s t as t h e a n t e r i o r -p o s t e r i o r g r a d i e n t i n t h a t t h e d i r e c t i o n and magnitude o f t h e s e g r a d i e n t s v a r y a c r o s s s t r i a t a l s u b - r e g i o n s . I n g e n e r a l , c o n c e n t r a t i o n s a r e g r e a t e r i n t h e v e n t r a l r e g i o n s o f t h e s t r i a t u m , r e l a t i v e t o d o r s a l r e g i o n s . One e x c e p t i o n i s t h e a n t e r o m e d i a l s t r i a t u m . I n t h i s a r e a , t h e g r a d i e n t i s -84-F i g u r e 13. S c h e m a t i c r e p r e s e n t a t i o n o f t h e d i s t r i b u t i o n s o f DA, DOPAC and HVA w i t h i n 10 s u b - r e g i o n s o f t h e s t r i a t u m . R e l a t i v e d i f f e r e n c e s ( h i g h t o low) i n t h e i n t r a s t r i a t a l d i s t r i b u t i o n o f each compound a r e d e p i c t e d . Each g r a d a t i o n i s s i g n i f i c a n t l y d i f f e r e n t f r o m one a n o t h e r . The two a n t e r i o r s e c t i o n s o f t h e s t r i a t u m were d i v i d e d i n t o 4 q u a d r a n t s w h i l e t h e t a i l o f t h e s t r i a t u m was d i v i d e d i n t o two p a r t s ( s e e t e x t f o r d i s s e c t i o n p r o c e d u r e s ) . DOPAMINE D O P A C HVA High A7890 Low -36-r e v e r s e d , w i t h c o n c e n t r a t i o n s b e i n g g r e a t e s t i n t h e d o r s a l a s p e c t o f t h e a n t e r o m e d i a l s t r i a t u m . The l a t e r a l e x t e n t o f t h e v e n t r a l s t r i a t u m i s a l s o r i c h e r i n DA t h a n i s t h e m e d i a l c o u n t e r p a r t . I n c o n t r a s t , no m e d i a l -l a t e r a l d i f f e r e n c e s a r e d i s c e r n i b l e w i t h i n t h e d o r s a l s t r i a t u m . I n a d d i t i o n , c o n c e n t r a t i o n s w i t h i n t h e t a i l o f t h e s t r i a t u m v a r i e d s u c h t h a t t h e v e n t r o l a t e r a l r e g i o n c o n t a i n e d more DA t h a n d i d t h e d o r s o m e d i a l a r e a o f t h e t a i l . DOPAC and HVA The 3-way ANOVA c o n d u c t e d upon DOPAC c o n c e n t r a t i o n s y i e l d e d a s i g n i f i c a n t AP x DV i n t e r a c t i o n : F ( l , 1 6 ) = 9.71, p < .01. P a i r - w i s e c o m p a r i s o n s c o n d u c t e d t o i d e n t i f y t h e s o u r c e o f t h i s i n t e r a c t i o n i n d i c a t e d t h a t DOPAC c o n c e n t r a t i o n s v a r i e d a l o n g t h e a n t e r i o r - p o s t e r i o r g r a d i e n t . S p e c i f i c a l l y , c o n c e n t r a t i o n s were h i g h e s t i n t h e a n t e r i o r s t r i a t u m , i r r e s p e c t i v e o f t h e d o r s a l - v e n t r a l a x i s . I n a d d i t i o n , t h e v e n t r a l r e g i o n c o n t a i n e d more DOPAC t h a n t h e d o r s a l a s p e c t o f b o t h t h e a n t e r i o r and p o s t e r i o r s t r i a t u m . The o v e r a l l a n a l y s i s a l s o r e v e a l e d a s i g n i f i c a n t main e f f e c t o f t h e m e d i a l - l a t e r a l a x i s , r e f l e c t i n g g r e a t e r c o n c e n t r a t i o n s w i t h i n t h e m e d i a l s t r i a t u m : F ( l , 1 6 ) = 198.15, p < .001. DOPAC c o n c e n t r a t i o n s were g r e a t e r i n t h e v e n t r o l a t e r a l r e g i o n o f t h e t a i l o f t h e s t r i a t u m , r e l a t i v e t o t h e d o r s o m e d i a l a r e a : F ( l , 1 5 ) = 13.10, p = .003. A n a l y s i s o f HVA c o n c e n t r a t i o n s i n d i c a t e d t h a t a l l 3 main e f f e c t s were s i g n i f i c a n t : AP - F ( l , 7 ) = 13.20, p = .008; DV - F ( l , 7 ) = 52.29, p < .001; ML - F ( l , 7 ) = 19.13, p = .003. That i s , c o n c e n t r a t i o n s o f HVA were g r e a t e s t i n t h e a n t e r i o r s t r i a t u m , r e l a t i v e t o t h e p o s t e r i o r r e g i o n . The d o r s a l - v e n t r a l g r a d i e n t r e f l e c t e d i n c r e a s i n g c o n c e n t r a t i o n s v e n t r a l l y . F i n a l l y , c o n c e n t r a t i o n s were h i g h e r l a t e r a l l y t h a n m e d i a l l y . S u b - r e g i o n a l v a r i a t i o n s i n HVA c o n c e n t r a t i o n s were n o t d e t e c t e d w i t h i n t h e t a i l o f t h e s t r i a t u m . Comparison o f o v e r a l l c o n c e n t r a t i o n s o f DOPAC and HVA w i t h i n t h e t a i l o f t h e s t r i a t u m w i t h t h o s e d e t e c t e d i n t h e a n t e r i o r and p o s t e r i o r s e c t i o n s c o n f i r m e d t h e e x i s t e n c e o f t h e a n t e r i o r - p o s t e r i o r g r a d i e n t f o r b o t h m e t a b o l i t e s : F ( l , 1 5 ) = 139.90, p < .001; F ( l , 5 ) = 194.45, p < .001, r e s p e c t i v e l y . P a i r - w i s e c o m p a r i s o n s r e v e a l e d t h a t t h e a n t e r i o r s e c t i o n had more DOPAC and HVA t h a n d i d t h e p o s t e r i o r s e c t i o n . C o n c e n t r a t i o n s w i t h i n t h e t a i l were a l s o l e s s t h a n o b t a i n e d i n t h e o t h e r two r e g i o n s . I t s h o u l d be n o t e d t h a t t h e p a t t e r n o f d i s t r i b u t i o n o f HVA was v e r y s i m i l a r t o t h a t o f DOPAC ( s e e F i g u r e 1 3 ) . C o n c e n t r a t i o n s o f b o t h m e t a b o l i t e s were g r e a t e s t w i t h i n t h e a n t e r i o r r e g i o n o f t h e s t r i a t u m , r e l a t i v e t o t h e p o s t e r i o r r e g i o n and t h e t a i l o f t h e s t r i a t u m . A v e n t r a l t o d o r s a l , d e c r e a s i n g g r a d i e n t was a l s o o b s e r v e d f o r b o t h m e t a b o l i t e s . However, t h e p a t t e r n o f d i s t r i b u t i o n f o r t h e two m e t a b o l i t e s d i f f e r e d w i t h r e s p e c t t o t h e m e d i a l - l a t e r a l a x i s . S p e c i f i c a l l y , DOPAC c o n c e n t r a t i o n s were h i g h e s t i n t h e m e d i a l s t r i a t u m whereas a g r a d i e n t i n t h e o p p o s i t e d i r e c t i o n was d e t e c t e d f o r HVA. W h i l e t h e s i g n i f i c a n c e o f t h i s o b s e r v a t i o n i s n o t i m m e d i a t e l y c l e a r , i t s u g g e s t s t h a t DA m e t a b o l i s m may v a r y w i t h i n d i f f e r e n t r e g i o n s o f t h e s t r i a t u m . DOPAC:DA and HVA:DA The o v e r a l l a n a l y s i s o f DOPAC:DA r a t i o s y i e l d e d a s i g n i f i c a n t AP x DV i n t e r a c t i o n : F ( l , 1 6 ) = 33.23, p < .001 ( s e e F i g . 1 4 ) . P a i r - w i s e c o m p a r i s o n s i n d i c a t e d t h a t w i t h i n t h e d o r s a l s t r i a t u m , u t i l i z a t i o n o f DA (as e s t i m a t e d b y DOPAC:DA r a t i o s ) does n o t v a r y a l o n g t h e a n t e r i o r -p o s t e r i o r a x i s . However, m e t a b o l i s m i s augmented w i t h i n t h e a n t e r o v e n t r a l s t r i a t u m , r e l a t i v e t o t h a t o b s e r v e d w i t h i n t h e p o s t e r o v e n t r a l s t r i a t u m . A -38-F i g u r e 14. R a t i o s o f DOPAC and HVA t o DA i n 3 s u b - r e g i o n s o f t h e s t r i a t u m . V a l u e s r e p r e s e n t t h e mean (± S.E.M.) r a t i o s . N=17 f o r DOPAC:DA r a t i o s and n=8 f o r HVA:DA r a t i o s . See t e x t f o r d e t a i l e d d e s c r i p t i o n o f s i g n i f i c a n t d i f f e r e n c e s . -89-0.30 0.25 < Q 0.20 O Q 0.15 Q 0.10 0.05 ANTERIOR POSTERIOR 0.125 0.100 < Q < 0.075 0.050 0.025 MEDIAL LATERAL DORSAL VENTRAL ANTERIOR DORSAL VENTRAL POSTERIOR DORSAL VENTRAL DORSAL VENTRAL -90-d o r s a l - v e n t r a l g r a d i e n t was d e t e c t e d w i t h i n t h e a n t e r i o r s t r i a t u m ( m e t a b o l i s m b e i n g g r e a t e s t v e n t r a l l y ) . A s i m i l a r g r a d i e n t was not o b s e r v e d w i t h i n t h e p o s t e r i o r s t r i a t u m . DA m e t a b o l i s m was a l s o f o u n d t o v a r y a l o n g t h e m e d i a l - l a t e r a l a x i s : F ( l , 1 6 ) = 198.15, p < .001. S p e c i f i c a l l y , r a t i o s o f DOPAC t o DA were g r e a t e s t w i t h i n t h e m e d i a l s t r i a t u m . The DOPAC:DA r a t i o was h i g h e r i n t h e d o r s o r n e d i a l t a i l o f t h e s t r i a t u m , r e l a t i v e t o t h e v e n t r o l a t e r a l r e g i o n o f t h e t a i l : F ( l , 1 5 ) = 19.50, p = .001. O v e r a l l a n a l y s i s o f t h e HVA:DA r a t i o s y i e l d e d a s i g n i f i c a n t AP x ML i n t e r a c t i o n : F ( l , 7 ) = 12.08, p = .01 ( s e e F i g . 1 4 ) . P a i r - w i s e c o m p a r i s o n s c o n d u c t e d upon t h e means c o m p r i s i n g t h i s e f f e c t i n d i c a t e d t h a t m e t a b o l i s m was enhanced w i t h i n t h e p o s t e r o m e d i a l s t r i a t u m r e l a t i v e t o t h e a n t e r o m e d i a l s t r i a t u m . No o t h e r c o m p a r i s o n s w i t h i n t h i s i n t e r a c t i o n were s i g n i f i c a n t . The o v e r a l l a n a l y s i s a l s o r e v e a l e d t h a t m e t a b o l i s m was g r e a t e r w i t h i n t h e v e n t r a l s t r i a t u m when compared t o t h e d o r s a l s t r i a t u m : F ( l , 7 ) = 42.30, p < .001. No r e g i o n a l d i f f e r e n c e s were d e t e c t e d w i t h i n t h e t a i l o f t h e s t r i a t u m . A n a l y s i s o f b o t h D0PAC:DA and HVA:DA r a t i o s w i t h i n t h e a n t e r i o r , p o s t e r i o r and t a i l r e g i o n s o f t h e s t r i a t u m f a i l e d t o r e v e a l any s i g n i f i c a n t d i f f e r e n c e s . To summarize, an a n t e r i o r - p o s t e r i o r g r a d i e n t was o b s e r v e d i n r e s t r i c t e d r e g i o n s o f t h e s t r i a t u m f o r b o t h DOPAC:DA and HVA:DA r a t i o s ( i . e . D0PAC:DA - v e n t r a l s t r i a t u m ; HVA:DA - m e d i a l s t r i a t u m ) . However, t h e g r a d i e n t was r e v e r s e d f o r HVA:DA r a t i o s . That i s , t h e r e was p r o p o r t i o n a t e l y more HVA t h a n DA i n t h e p o s t e r i o r s t r i a t u m , r e l a t i v e t o t h e a n t e r i o r s t r i a t u m . A d o r s a l - v e n t r a l g r a d i e n t was e v i d e n t t h r o u g h o u t t h e s t r i a t u m w i t h DOPAC:DA and HVA:DA r a t i o s b e i n g h i g h e s t i n t h e v e n t r a l -91-r e g i o n s o f t h e s t r i a t u m . A m e d i a l - l a t e r a l g r a d i e n t was f o u n d f o r DOPAC:DA r a t i o s b u t n o t f o r HVA:DA. Discussion The r e s u l t s o f E x p e r i m e n t V i a d e m o n s t r a t e t h a t t h e m e s o s t r i a t a l DA syst e m i s v e r y complex w i t h r e s p e c t t o t h e t o p o g r a p h i c d i s t r i b u t i o n o f DA and i t s two p r i m a r y m e t a b o l i t e s . I n g e n e r a l , an a n t e r i o r - p o s t e r i o r g r a d i e n t was d e t e c t e d f o r each o f t h e compounds examined, i r r e s p e c t i v e o f m e d i a l - l a t e r a l and d o r s a l - v e n t r a l d i f f e r e n c e s . T h i s f i n d i n g c o n f i r m s and e x t e n d s p r e v i o u s r e p o r t s on t h e t o p o g r a p h i c a l d i s t r i b u t i o n o f DA and i t s m e t a b o l i t e s ( B e a l & M a r t i n , 1985; T a s s i n , e t a l . , 1976). C o n c e n t r a t i o n s o f DA, DOPAC and HVA were a l s o f o u n d t o v a r y as a f u n c t i o n o f t h e d o r s a l -v e n t r a l a x i s . However, t h e d i r e c t i o n o f t h i s g r a d i e n t was f o u n d t o depend upon t h e compound and t h e s p e c i f i c l o c u s w i t h i n t h e s t r i a t u m . D i f f e r e n c e s were a l s o n o t e d a l o n g t h e m e d i a l - l a t e r a l a x i s f o r e ach compound. The d i r e c t i o n and t h e magnitude o f DA's m e d i a l - l a t e r a l g r a d i e n t were dependent upon t h e p r e c i s e l o c u s w i t h r e s p e c t t o b o t h t h e a n t e r i o r - p o s t e r i o r and d o r s a l - v e n t r a l a x e s . DOPAC c o n c e n t r a t i o n s were g r e a t e s t w i t h i n t h e m e d i a l s t r i a t u m , r e g a r d l e s s o f e i t h e r t h e a n t e r i o r - p o s t e r i o r o r d o r s a l - v e n t r a l a x e s . The h i g h e s t c o n c e n t r a t i o n s o f HVA were, i n c o n t r a s t , f o u n d l a t e r a l l y . A g a i n , t h e m e d i a l - l a t e r a l g r a d i e n t d i d n o t v a r y as a f u n c t i o n o f t h e o t h e r a x e s . P r e v i o u s e v i d e n c e f o r e i t h e r d o r s a l - v e n t r a l o r m e d i a l - l a t e r a l g r a d i e n t s f o r DA, DOPAC and HVA has been i n c o n s i s t e n t . F o r example, B e a l & M a r t i n (1985) and T a s s i n and a s s o c i a t e s (1976) d i d n ot d e t e c t e i t h e r g r a d i e n t f o r any o f t h e compounds. I n c o n t r a s t , D i P a o l o , D a i g l e & Dupont (1982) r e p o r t e d r e g i o n a l v a r i a t i o n s w i t h i n a g i v e n c o r o n a l s e c t i o n . J o y c e , L o e s c h e n & M a r s h a l l (1985) r e p o r t e d t h a t DOPAC and HVA c o n c e n t r a t i o n s were -92-h i g h e r i n t h e v e n t r a l s t r i a t u m , r e l a t i v e t o t h e d o r s a l s t r i a t u m . These d i f f e r e n c e s were a l s o e v i d e n t when m e t a b o l i t e t o DA r a t i o s were examined. The r e s u l t s o f E x p e r i m e n t V i a c o n f i r m t h e l a t t e r o b s e r v a t i o n s . I t i s p o s s i b l e t h a t t h e d i s c r e p a n c i e s w i t h i n t h e l i t e r a t u r e r e f l e c t d i f f e r e n c e s i n b o t h e x p e r i m e n t a l d e s i g n and s t a t i s t i c a l t r e a t m e n t o f d a t a . The p r e s e n t e x p e r i m e n t u s e d e x p e r i m e n t a l p r o c e d u r e s and s t a t i s t i c a l methods t h a t w o u l d p e r m i t t h e d e t e c t i o n o f a x i a l v a r i a t i o n s , as w e l l as i n t e r a c t i o n s between t h e a x e s . The s i g n i f i c a n c e o f t h e v a r i o u s t o p o g r a p h i c a l d i s t r i b u t i o n s o b s e r v e d f o r DA, DOPAC and HVA i s per h a p s b e s t u n d e r s t o o d i n terms o f t h e r e g i o n a l v a r i a t i o n s i n DA u t i l i z a t i o n , as e s t i m a t e d by m e t a b o l i t e t o DA r a t i o s . F o r example, t h e a n t e r i o r - p o s t e r i o r g r a d i e n t s were f o u n d t o v a r y as a f u n c t i o n o f t h e o t h e r a x e s . Such a g r a d i e n t was o n l y e v i d e n t w i t h i n t h e v e n t r a l s t r i a t u m f o r t h e DOPAC:DA r a t i o and o n l y w i t h i n t h e m e d i a l s t r i a t u m f o r t h e HVA:DA r a t i o s . B o t h r a t i o s a l s o e x h i b i t e d d o r s a l - v e n t r a l d i f f e r e n c e s , w i t h m e t a b o l i s m b e i n g h i g h e r w i t h i n t h e v e n t r a l r e g i o n o f t h e s t r i a t u m . The m e d i a l - l a t e r a l g r a d i e n t d e t e c t e d w i t h DOPAC c o n c e n t r a t i o n s was c o n f i r m e d when t h e DOPAC:DA r a t i o s were a n a l y z e d . D e s p i t e t h e e x i s t e n c e o f a l a t e r a l - m e d i a l g r a d i e n t i n HVA c o n c e n t r a t i o n s , no d i f f e r e n c e s were d e t e c t e d when HVA:DA r a t i o s were examined. The f a c t t h a t t h e t o p o g r a p h i c a l d i s t r i b u t i o n s o f t h e r a t i o s a r e n o t t h e same as t h e d i s t r i b u t i o n p a t t e r n s d e s c r i b e d f o r t h e s p e c i f i c m e t a b o l i t e s o r f o r DA i n d i c a t e s t h a t t h e r e g i o n a l v a r i a t i o n s a r e n o t p r o p o r t i o n a t e a c r o s s compounds i n a l l o f t h e s u b - r e g i o n s . T h i s i n d i c a t e s t h a t t h e r e may e x i s t r e g i o n a l d i f f e r e n c e s i n t h e m e t a b o l i s m o f DA i n terms o f r a t e and, p e r h a p s , mechanism. The c o m p l e x i t y o f t h e s t r i a t a l DA sys t e m i s f u r t h e r i l l u s t r a t e d by c o n s i d e r i n g t h e t o p o g r a p h i c a l d i s t r i b u t i o n o f DA r e c e p t o r s . J o y c e and -93-a s s o c i a t e s have r e p o r t e d t h a t DA D2 r e c e p t o r s show a l a t e r a l t o m e d i a l g r a d i e n t w i t h i n t h e s t r i a t u m , and a r e w i t h o u t any o b v i o u s a n t e r i o r -p o s t e r i o r o r d o r s a l - v e n t r a l g r a d i e n t s ( J o y c e , e t a l . , 1985; J o y c e & M a r s h a l l , 1987). I t i s i n t e r e s t i n g t o n o t e t h a t t h e d i s t r i b u t i o n o f D2 r e c e p t o r s c o r r e s p o n d s w i t h t h e l a t e r a l - m e d i a l g r a d i e n t e x h i b i t e d by t h e m e t a b o l i t e HVA. The s i g n i f i c a n c e o f t h i s a s s o c i a t i o n i s n o t c l e a r a t t h i s t i m e . Taken t o g e t h e r , t h e r e s u l t s o f t h i s e x p e r i m e n t c l e a r l y i n d i c a t e t h a t t h e m e s o s t r i a t a l d o p a m i n e r g i c system i s n o t a u n i t a r y system. Complex r e g i o n a l v a r i a t i o n s i n c o n c e n t r a t i o n s o f DA and b o t h m e t a b o l i t e s a r e e v i d e n t . I t i s p a r t i c u l a r l y i m p o r t a n t t o n o t e t h a t t h e t o p o g r a p h i c a l d i s t r i b u t i o n o f each compound i s u n i q u e , s u g g e s t i n g t h a t DA may be r e l e a s e d and m e t a b o l i z e d d i f f e r e n t i a l l y w i t h i n d i s c r e t e r e g i o n s o f t h e s t r i a t u m . T h i s r e a l i z a t i o n may f a c i l i t a t e u n d e r s t a n d i n g o f t h e n e u r a l b a s i s o f t h e f u n c t i o n a l h e t e r o g e n e i t y o f t h e s t r i a t u m . S p e c i f i c a l l y , i t may a c c o u n t f o r t h e f a c t t h a t a v a r i e t y o f b e h a v i o r s known t o be m o d u l a t e d by DA a r e d i f f e r e n t i a l l y s e n s i t i v e t o p h a r m a c o l o g i c a l i n t e r v e n t i o n s ( e . g . Rebec & C u r t i s , 1983; Tombaugh, S z o s t a k & M i l l s , 1983). Experiment VIb Effects of Conditioned Circling on DA Metabolism within Sub-regions of the Striatum The d i v e r s e r e g i o n a l v a r i a t i o n s i n DA m e t a b o l i s m o b s e r v e d i n E x p e r i m e n t V i a p r o v i d e f u r t h e r e v i d e n c e f o r t h e f u n c t i o n a l h e t e r o g e n e i t y o f t h e s t r i a t u m . G i v e n t h i s h e t e r o g e n e i t y , i t i s c o n c e i v a b l e t h a t DA m e t a b o l i s m w i t h i n d i f f e r e n t s t r i a t a l r e g i o n s i s n o t u n i f o r m l y a f f e c t e d d u r i n g t h e e x e c u t i o n o f a g i v e n b e h a v i o r . Thus, i t i s p o s s i b l e t h a t t h e b i l a t e r a l changes p r e v i o u s l y o b s e r v e d do n o t a c c u r a t e l y p o r t r a y t h e r o l e o f -94-t h e s t r i a t u m i n c o n d i t i o n e d c i r c l i n g . The e x t e n t t o w h i c h v a r i o u s r e g i o n s o f t h e s t r i a t u m a r e d i f f e r e n t i a l l y i n v o l v e d i n c o n d i t i o n e d c i r c l i n g was a s s e s s e d i n E x p e r i m e n t V I b . Materials and Methods S u b j e c t s and a p p a r a t u s N a i v e , male Sprague-Dawley r a t s ( C h a r l e s R i v e r L a b o r a t o r i e s ) , as d e s c r i b e d i n E x p e r i m e n t I , were p l a c e d on a f o o d d e p r i v a t i o n s c h e d u l e t h a t r e s u l t e d i n t h e i r b e i n g m a i n t a i n e d a t 85-90 % o f t h e i r ad l i b i t u m w e i g h t s . F o r t h e f i n a l p h a s e s o f t r a i n i n g and t e s t i n g , r a t s were g i v e n r e s t r i c t e d a c c e s s t o w a t e r w h i l e f o o d was once a g a i n a v a i l a b l e f r e e l y i n t h e i r home ca g e s . T h i s change i n p r o c e d u r e was n e c e s s i t a t e d by t h e o b s e r v a t i o n o f b i l a t e r a l i n c r e a s e s i n DOPAC and HVA i n n o n - c i r c l i n g r a t s t h a t had consumed t h e same amount o f f o o d as r e c e i v e d by a n i m a l s t h a t were t r a i n e d t o c i r c l e f o r f o o d (see E x p e r i m e n t V ) . A l l b e h a v i o r a l t e s t i n g was c o n d u c t e d i n t h e a p p a r a t u s d e s c r i b e d i n E x p e r i m e n t V. D u r i n g t h e f i n a l phase o f t e s t i n g , t h e f o o d hopper was r e p l a c e d w i t h a m o t o r - d r i v e n w a t e r d i s p e n s e r ( S k i n n e r E l e c t r i c V a l v e D i v i s i o n ) c a l i b r a t e d t o d e l i v e r 0.07 - 0.09 ml o f wa t e r p e r r e i n f o r c e m e n t . R e i n f o r c e m e n t ( b o t h f o o d and w a t e r ) was d e l i v e r e d i n t o a t r o u g h l o c a t e d a t t h e p e r i m e t e r o f t h e a p p a r a t u s , 4 cm fr o m t h e f l o o r . P r o c e d u r e P r e - s c r e e n i n g . The d i r e c t i o n a l b i a s o f each s u b j e c t was d e t e r m i n e d u s i n g t h e n o n - d i f f e r e n t i a l r e i n f o r c e m e n t p a r a d i g m , whereby each c o m p l e t e r o t a t i o n e m i t t e d was r e i n f o r c e d , r e g a r d l e s s o f i t s d i r e c t i o n . The number o f c i r c l e s e m i t t e d i n each d i r e c t i o n d u r i n g a 20 min t e s t s e s s i o n were r e c o r d e d . D i r e c t i o n a l b i a s was d e t e r m i n e d by d i v i d i n g t h e number o f r o t a t i o n s t o t h e l e f t by t h e t o t a l number o f r o t a t i o n s . -95-T r a i n i n g . H a l f o f t h e r a t s (n-9) were t r a i n e d t o c i r c l e i n t h e i r p r e f e r r e d d i r e c t i o n f o r f o o d r e i n f o r c e m e n t . C i r c l i n g was i n i t i a l l y -e s t a b l i s h e d u s i n g a c o n t i n u o u s r e i n f o r c e m e n t s c h e d u l e , w h e r e i n each c o m p l e t e r o t a t i o n ( i . e . 360°), p e r f o r m e d i n t h e a p p r o p r i a t e d i r e c t i o n , was r e i n f o r c e d . F o l l o w i n g 3-6 d a i l y 20 min t r a i n i n g s e s s i o n s , t h e s c h e d u l e o f r e i n f o r c e m e n t was s w i t c h e d t o a FR-2. On t h e t e n t h FR-2 s e s s i o n , w a t e r was s u b s t i t u t e d f o r f o o d as t h e r e i n f o r c e r . Each r a t r e c e i v e d 6 a d d i t i o n a l 20 min t r a i n i n g s e s s i o n s d u r i n g w h i c h c i r c l i n g was r e i n f o r c e d w i t h w a t e r a c c o r d i n g t o a FR-2 s c h e d u l e o f r e i n f o r c e m e n t . The r e m a i n i n g s u b j e c t s (n=9) were m a i n t a i n e d on s i m i l a r s c h e d u l e s o f f o o d and w a t e r d e p r i v a t i o n and s e r v e d as n o n - c i r c l i n g c o n t r o l s . Each s u b j e c t was h a n d l e d d a i l y . T e s t i n g . Upon a t t a i n m e n t o f s t a b l e r a t e s o f c i r c l i n g , r a t s r e c e i v e d a s i n g l e t e s t s e s s i o n o f 20 min d u r i n g w h i c h t i m e e x p e r i m e n t a l c o n t i n g e n c i e s were as d e s c r i b e d above. I m m e d i a t e l y f o l l o w i n g t h e t e s t s e s s i o n , r a t s were d e c a p i t a t e d and t h e i r b r a i n s q u i c k l y removed. C o n t r o l s u b j e c t s were g i v e n a c c e s s t o w a t e r f o r 20 min i n t h e i r home cage b e f o r e b e i n g s a c r i f i c e d . A c o r o n a l c u t was made s l i g h t l y a n t e r i o r t o t h e o p t i c c h i a s m and t h e a n t e r i o r s e c t i o n f r o z e n on a microtome. The s t r i a t u m was removed and d i s s e c t e d as d e s c r i b e d i n E x p e r i m e n t Va. The t i s s u e samples were i m m e d i a t e l y p l a c e d i n 200 u l h o m o g e n i z i n g s o l u t i o n and p r e p a r e d f o r a n a l y s i s o f DA, DOPAC and HVA by HPLC-ED, as d e s c r i b e d p r e v i o u s l y . S t a t i s t i c a l a n a l y s e s Each r e g i o n was a n a l y z e d s e p a r a t e l y as i n c o m p l e t e d a t a s e t s , due t o s p o r a d i c sample c o n t a m i n a t i o n , p r e c l u d e d t h e use o f h i g h e r - o r d e r s t a t i s t i c a l d e s i g n s . A c c o r d i n g l y , e ach a n a l y s i s c o n s i s t e d o f one between -96-s u b j e c t f a c t o r (Group) and one w i t h i n s u b j e c t f a c t o r ( H e m i s p h e r e ) . The a c c e p t a b l e l e v e l o f s i g n i f i c a n c e was s e t a t a < .01. Results B e h a v i o r A l l r a t s e x h i b i t e d s t a b l e l e v e l s o f r e s p o n d i n g f o r w a t e r r e i n f o r c e m e n t f o l l o w i n g 6-7 t r a i n i n g s e s s i o n s . On t h e t e s t day, t h e mean t o t a l number o f r o t a t i o n s e m i t t e d was 230.2 (± 5.5). N e u r o c h e m i s t r y S t a t i s t i c a l a n a l y s e s f a i l e d t o r e v e a l any s i g n i f i c a n t e f f e c t s o f Hemisphere o r any i n t e r a c t i o n s between t h e Group and Hemisphere f a c t o r s . I n a d d i t i o n , c o n c e n t r a t i o n s o f DA were n o t i n f l u e n c e d by c i r c l i n g i n any o f t h e s u b - r e g i o n s a s s e s s e d . Of t h e 10 r e g i o n s t h a t were examined, o n l y t h e 4 a n t e r i o r r e g i o n s e x h i b i t e d s t a t i s t i c a l l y s i g n i f i c a n t changes i n m e t a b o l i t e c o n c e n t r a t i o n s and/or r a t i o s o f t h e m e t a b o l i t e s t o DA ( s e e F i g u r e s 15, 16 and T a b l e s 6, 7 & 8 ) . W i t h i n t h e a n t e r i o r d o r s o l a t e r a l s t r i a t u m , HVA c o n c e n t r a t i o n s and t h e r a t i o s o f b o t h HVA and DOPAC t o DA were i n c r e a s e d i n r a t s t r a i n e d t o c i r c l e : F ' s ( l , 1 4 ) = 13.290, 9.384, 10.597; p's = .003, .008, .006, r e s p e c t i v e l y ( s e e T a b l e 6; F i g u r e 1 5 ) . A s i m i l a r t r e n d was o b s e r v e d when a b s o l u t e c o n c e n t r a t i o n s o f DOPAC were a n a l y z e d (p = .02 ) . W i t h i n t h e a n t e r i o r d o r s o m e d i a l s t r i a t u m , o n l y DOPAC c o n c e n t r a t i o n s and t h e r a t i o o f DOPAC t o DA were augmented b i l a t e r a l l y i n r a t s t r a i n e d t o c i r c l e : F ( l , 1 3 ) = 11.061, p = .005; F ( l , 1 3 ) = 21.998, p < .001, r e s p e c t i v e l y . The d i f f e r e n t i a l s e n s i t i v i t i e s o f DOPAC and HVA i n t h e a n t e r i o r d o r s o m e d i a l and d o r s o l a t e r a l r e g i o n s o f t h e s t r i a t u m may r e f l e c t t h e d i f f e r e n t i a l d i s t r i b u t i o n s o f t h e s e two m e t a b o l i t e s . I n E x p e r i m e n t V i a , i t was o b s e r v e d t h a t HVA c o n c e n t r a t i o n s were g r e a t e r w i t h i n t h e l a t e r a l s t r i a t a l r e g i o n s -97-F i g u r e 15. R a t i o s o f DOPAC and HVA t o DA i n a n t e r o d o r s o m e d i a l (ADM), a n t e r o d o r s o l a t e r a l (ADL), a n t e r o v e n t r o m e d i a l (AVM) and a n t e r o v e n t r o l a t e r a l (AVL) s t r i a t u m o f r a t s t r a i n e d t o c i r c l e f o r w a t e r r e i n f o r c e m e n t (n=9, e x c e p t f o r AVL where n=7) and w a t e r - d e p r i v e d c o n t r o l s ( n - 7 , e x c e p t f o r AVL and AVM where n=6). V a l u e s r e p r e s e n t t h e mean (± S.E.M.) r a t i o s . R a t s were e i t h e r t e s t e d f o r 20 min ( c i r c l e r s ) o r g i v e n a c c e s s t o w a t e r i n t h e i r home cage f o r 20 min ( c o n t r o l s ) b e f o r e b e i n g d e c a p i t a t e d . * D i f f e r s f r o m r e s p e c t i v e c o n t r o l v a l u e . - 9 8 -O CONTROL ADM ADL AVM AVL ADM ADL AVM AVL -99-F i g u r e I D . R a t i o s o f DOPAC and HVA t o DA i n p o s t e r o d o r s o m e d i a l (PDM), p o s t e r o d o r s o l a t e r a l ( P D L ) , p o s t e r o v e n t r o m e d i a l (PVM) and p o s t e r o v e n t r o l a t e r a l (PVL) s t r i a t u m o f r a t s t r a i n e d t o c i r c l e f o r w a t e r r e i n f o r c e m e n t (PDL - n=7; PDM & PVL - n=6; PVM - n=8) and w a t e r - d e p r i v e d c o n t r o l s (PDL - n=8; PDM - n=7; PVL & PVM -n=6). V a l u e s r e p r e s e n t t h e mean (± S.E.M.) r a t i o s . R a t s were e i t h e r t e s t e d f o r 20 min ( c i r c l e r s ) o r g i v e n a c c e s s t o w a t e r i n t h e i r home cage f o r 20 min ( c o n t r o l s ) b e f o r e b e i n g d e c a p i t a t e d . * D i f f e r s f r o m r e s p e c t i v e c o n t r o l v a l u e . -100--101-T a b l e 6. Mean (± S.E.M.) c o n c e n t r a t i o n s (nmol/g p r o t e i n ) o f DA, DOPAC and HVA w i t h i n d i s c r e t e s u b - r e g i o n s o f t h e a n t e r i o r s t r i a t u m o f w a t e r - d e p r i v e d r a t s and r a t s t r a i n e d t o c i r c l e f o r w a t e r r e i n f o r c e m e n t . Dopamine C o n t r o l s : C i r c l e r s : D o r s a l L a t e r a l M e d i a l 982.29 1062.67 50.15 26.64 975.39 1055.28 50.14 29.72 V e n t r a l L a t e r a l M e d i a l 1103.75 921.83 46.92 74.59 1052.71 868.33 42.00 54.11 DOPAC D o r s a l L a t e r a l M e d i a l V e n t r a l L a t e r a l M e d i a l C o n t r o l s : 117.39 4.90 147.58 3.53 134.42 7.28 14 .84 C i r c l e r s : 143.39 7.34 180.39 7.62 205.71 i i i XX . xz izx 1 1 XX .67 .79 iVA D o r s a l j a t e r a l M e d i a l V e n t r a j l a t e r a l M e d i a l C o n t r o l s : 71.74 3.22 60.53 4.96 95.43 6.64 / 3 4 .71 .92 C i r c l e r s : 88.72 3.25 71.45 5.71 105.94 5.91 95, 8. 56 82 -102-T a b l e 7. Mean (± 3.E.M.) c o n c e n t r a t i o n s (nmol/g p r o t e i n ) o f DA, DOPAC and HVA w i t h i n d i s c r e t e s u b - r e g i o n s o f t h e p o s t e r i o r s t r i a t u m o f w a t e r - d e p r i v e d r a t s and r a t s t r a i n e d t o c i r c l e f o r w a t e r r e i n f o r c e m e n t . Dopamine D o r s a l L a t e r a l M e d i a l V e n t r a l L a t e r a l M e d i a l C o n t r o l s : 716.00 32.19 6 1 n *-r -\ X U . / X J x . o y 636.00 37.68 565.00 56.63 C i r c l e r s : 734.43 19.55 677.50 37.59 626.50 44.91 565.56 30.75 DOPAC D o r s a l L a t e r a l M e d i a l V e n t r a l L a t e r a l M e d i a l C o n t r o l s : 137.00 5.54 L59. 4. 132.40 13.24 C i r c l e r s : 148.86 8.32 154.67 8.50 170.20 16.06 136.31 3.06 HVA D o r s a l V e n t r a l L a t e r a l M e d i a l ^ a t e r a l M e d i a l C o n t r o l s : 67.07 55.79 3.49 71, 2. 49 30 51.43 6.92 C i r c l e r s : 79.75 4.34 60.90 2.38 69.60 6.58 56.52 3.30 -103-T a b l e S. Mean (± S.E.M.) c o n c e n t r a t i o n s (nmol/g p r o t e i n ) o f DA, DOPAC and HVA w i t h i n d i s c r e t e s u b - r e g i o n s o f t h e t a i l o f t h e s t r i a t u m o f w a t e r -d e p r i v e d r a t s and r a t s t r a i n e d t o c i r c l e f o r w a t e r r e i n f o r c e m e n t . Dopamine D o r s o m e d i a l V e n t r o l a t e r a l C o n t r o l s : 434.83 567.73 27.67 21.37 C i r c l e r s : 501.22 537.83 23.70 20. DOPAC D o r s o m e d i a l V e n t r o l a t e r a l C o n t r o l s : 31.05 9.57 95.02 C i r c l e r s : 90.09 4.47 95.09 5.59 HVA D o r s o m e d i a l V e n t r o l a t e r a l C o n t r o l s : 35.58 4.02 44.91 4.06 C i r c l e r s : 41.62 50.12 1.97 -104-when compared t o t h e m e d i a l e x t e n t . The r e v e r s e r e l a t i o n s h i p was o b s e r v e d w i t h DOPAC. I n t h e p r e s e n t e x p e r i m e n t , DOPAC was s e l e c t i v e l y i n c r e a s e d w i t h i n t h e d o r s o m e d i a l r e g i o n — t h e a r e a t h a t c o n t a i n s p r o p o r t i o n a t e l y more DOPAC t h a n HVA. C o n c u r r e n t l y , HVA was p r e f e r e n t i a l l y i n c r e a s e d i n t h e d o r s o l a t e r a l r e g i o n w h i c h c o n t a i n s p r o p o r t i o n a t e l y more HVA t h a n DOPAC. As p r e v i o u s l y s u g g e s t e d , t h e d i f f e r e n t p a t t e r n s o f d i s t r i b u t i o n may r e f l e c t d i f f e r e n t m e t a b o l i c p r o c e s s e s . I t i s a l s o p o s s i b l e t h a t t h e s e two r e g i o n s a r e a l s o i n v o l v e d i n d i f f e r e n t a s p e c t s o f t h e c i r c l i n g r e s p o n s e ( s ee J o y c e & van H a r t e s v e l d t , 1984). I n c o n t r a s t t o t h e e f f e c t s o b s e r v e d i n t h e d o r s a l r e g i o n s o f t h e a n t e r i o r s t r i a t u m , o n l y l i m i t e d d i f f e r e n c e s were o b s e r v e d i n t h e v e n t r a l s t r i a t a l a r e a s . C o n d i t i o n e d c i r c l i n g was a s s o c i a t e d w i t h a b i l a t e r a l i n c r e a s e i n DOPAC:DA r a t i o s w i t h i n t h e v e n t r o m e d i a l s t r i a t u m : F ( l , 1 3 ) = 23.117, p < .001. A s i m i l a r t r e n d was o b s e r v e d when t h e HVA:DA was a n a l y z e d (p = .03 ) . No s i g n i f i c a n t d i f f e r e n c e s were o b s e r v e d f o r any o f t h e dependent measures i n t h e v e n t r o l a t e r a l r e g i o n o f t h e s t r i a t u m a l t h o u g h t h e r e was a t r e n d f o r DOPAC:DA t o be b i l a t e r a l l y i n c r e a s e d i n a n i m a l s t r a i n e d t o c i r c l e (p = .05). Discussion These r e s u l t s c o n f i r m p r e v i o u s r e p o r t s o f b i l a t e r a l a u g m e n t a t i o n o f DA m e t a b o l i s m w i t h i n t h e s t r i a t u m ( S c h w a r t i n g & H u s t o n , 1987; see a l s o E x p e r i m e n t s I I and I V b ) . The b i l a t e r a l n a t u r e o f t h e p r e s e n t n e u r o c h e m i c a l e f f e c t s i s o f p a r t i c u l a r i n t e r e s t g i v e n t h a t t h e a n i m a l s were t r a i n e d t o c i r c l e i n t h e d i r e c t i o n c o n s i s t e n t w i t h t h e i r i n n a t e d i r e c t i o n a l b i a s , a p r o c e d u r e w h i c h s h o u l d enhance t h e l i k e l i h o o d o f d e t e c t i n g a s y m m e t r i c a l changes i n DA m e t a b o l i s m ( G l i c k , 1982; R o b i n s o n & B e c k e r , 1983). A c c o r d i n g l y , t h e s e r e s u l t s c o n f i r m t h e f i n d i n g s r e p o r t e d i n E x p e r i m e n t IVb. -105-I t i s a l s o i m p o r t a n t t o n o t e t h a t t h e i n c r e a s e s d e t e c t e d i n each s t r i a t u m o c u r r e d w i t h i n c omparable r e g i o n s . A c c o r d i n g l y , t h e r e was no e v i d e n c e o f an a n t a g o n i s t i c i n t e r p l a y between s t r i a t a l s u b r e g i o n s ( V a c c a r i n o & F r a n k l i n , 1984). The r e s u l t s o f t h i s e x p e r i m e n t f u r t h e r s u p p o r t t h e v i e w t h a t t h e s t r i a t u m i s f u n c t i o n a l l y h e t e r o g e n o u s . S p e c i f i c a l l y , b i l a t e r a l i n c r e a s e s i n DA m e t a b o l i s m were r e s t r i c t e d t o t h e a n t e r i o r p o r t i o n o f t h e s t r i a t u m , and i n p a r t i c u l a r , w i t h i n t h e d o r s a l a s p e c t o f t h e a n t e r i o r s t r i a t u m . The l o c a t i o n o f t h e s e changes i s c o n s i s t e n t w i t h r e p o r t s by J o y c e and a s s o c i a t e s ( J o y c e , e t a l . , 1981; J o y c e & van H a r t e s v e l d t , 1984) t h a t c i r c l i n g i s e l i c i t e d by i n j e c t i o n s o f DA i n t o t h e d o r s a l s t r i a t u m b u t n o t by i n f u s i o n s i n t o t h e v e n t r a l s t r i a t u m . D unnett and a s s o c i a t e s (1981a,b) have a l s o s u g g e s t e d t h a t t h e d o r s a l a n t e r i o r s t r i a t u m c r i t i c a l l y s u b s e r v e s r o t a t i o n . They r e p o r t e d t h a t f u n c t i o n a l r e c o v e r y , as measured by a t t e n u a t i o n o f amphetamine-induced c i r c l i n g , f o l l o w i n g e mbryonic g r a f t s i s dependent upon t h e l o c u s o f t h e g r a f t . S p e c i f i c a l l y , r o t a t i o n was a t t e n u a t e d f o l l o w i n g d o r s a l a n t e r i o r s t r i a t u m g r a f t s b u t n o t a f t e r t r a n s p l a n t s w h i c h r e i n n e r v a t e d t h e v e n t r a l o r v e n t r o l a t e r a l s t r i a t u m . W h i l e J o y c e & v a n H a r t e s v e l d t (1984) have s u g g e s t e d t h a t c i r c l i n g i s s u b s e r v e d s p e c i f i c a l l y by t h e m e d i a l d o r s a l s t r i a t u m , t h e 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 DA m e t a b o l i s m i s augmented t h r o u g h o u t t h e d o r s a l a n t e r i o r s t r i a t u m by c o n d i t i o n e d c i r c l i n g . The m e d i a l and l a t e r a l r e g i o n s a r e , however, d i f f e r e n t i a l l y a f f e c t e d . I t i s p o s s i b l e t h a t t h e changes o b s e r v e d w i t h i n t h e a n t e r i o r d o r s o m e d i a l s t r i a t u m a r e r e l a t e d s p e c i f i c a l l y t o t h e r o t a t i o n a l r e s p o n s e e x h i b i t e d . I n c o n t r a s t , t h o s e changes d e t e c t e d w i t h i n t h e a n t e r i o r d o r s o l a t e r a l s t r i a t u m , t h e r e g i o n p o s i t e d by J o y c e and a s s o c i a t e s t o s u b s e r v e s e n s o r i m o t o r f u n c t i o n i n g , may r e f l e c t t h e -106-i n v o l v e m e n t o f s e n s o r i m o t o r f u n c t i o n s i n t h e p e r f o r m a n c e o f t h e c o n d i t i o n e d c i r c l i n g r e s p o n s e . I f t h i s i s t h e c a s e , a n i m a l s t e s t e d i n t h e c o n d i t i o n e d c i r c l i n g p a r a d i g m m i g h t be e x p e c t e d t o e x h i b i t enhanced r e a c t i v i t y t o s e n s o r y s t i m u l a t i o n . A l t e r n a t i v e l y , t h e changes n o t e d i n t h e a n t e r i o r d o r s o l a t e r a l r e g i o n may a l s o be a d i r e c t consequence o f t h e r o t a t i o n a l r e s p o n s e i n v o l v e d i n c o n d i t i o n e d c i r c l i n g . I t i s n o t e w o r t h y t h a t Dunnett & I v e r s e n (1982) have f a i l e d t o o b s e r v e any e f f e c t o f l o c u s o f d i s c r e t e s t r i a t a l l e s i o n s on t h e o c c u r r e n c e o f subsequent d r u g - i n d u c e d c i r c l i n g . R a t h e r , s i m i l a r m agnitudes and d i r e c t i o n s o f c i r c l i n g were o b s e r v e d w i t h each l e s i o n s i t e . I t i s p o s s i b l e t h a t t h e p r e c i s e n e u r a l s u b s t r a t e o f c i r c l i n g i s dependent upon t h e s p e c i f i c p r o c e d u r e s u s e d t o e l i c i t c i r c l i n g . I f t h i s i s t h e c a s e , f u r t h e r e x p e r i m e n t a t i o n w i l l be r e q u i r e d t o d e t e r m i n e how t h e s e r e s p o n s e s d i f f e r b o t h b e h a v i o r a l l y and n e u r o c h e m i c a l l y . EXPERIMENT VII Effects of unilateral Lesions of the Mesotelencephalic DA Projection on Conditioned Circling I t has p r e v i o u s l y been r e p o r t e d t h a t h i g h r a t e s o f c o n d i t i o n e d c i r c l i n g a r e a s s o c i a t e d w i t h a b i l a t e r a l a u g m e n t a t i o n o f s t r i a t a l DA m e t a b o l i s m ( S c h w a r t i n g & H u s t o n , 1987; see a l s o e x p e r i m e n t s I I , IVb & V I b ) . These r e s u l t s have been i n t e r p r e t e d as i n d i c a t i n g t h e i n v o l v e m e n t o f b o t h s t r i a t a i n t h e m e d i a t i o n o f c o n d i t i o n e d c i r c l i n g . U s i n g a d i f f e r e n t a p p r o a c h , D u n n e t t & B j o r k l u n d (1983) have, however, p r o v i d e d e v i d e n c e f o r an a s y m m e t r i c a l i n v o l v e m e n t o f t h e m e s o t e l e n c e p h a l i c DA s y s t e m i n c o n d i t i o n e d c i r c l i n g . They r e p o r t e d t h a t u n i l a t e r a l l e s i o n s o f t h i s p r o j e c t i o n d i s r u p t e d c o n t r a v e r s i v e c i r c l i n g , whereas i p s i v e r s i v e c i r c l i n g was u n a f f e c t e d . The r e s u l t s o f t h e i r e x p e r i m e n t a r e , however, d i f f i c u l t t o -107-i n t e r p r e t as a n i m a l s were r e i n f o r c e d i n t e r m i t t e n t l y p r e o p e r a t i v e l y , w h i l e a c o n t i n u o u s s c h e d u l e o f r e i n f o r c e m e n t was i n e f f e c t p o s t o p e r a t i v e l y . M o r e o v er, t h e r a t s had r e c e i v e d l i m i t e d p r e o p e r a t i v e t r a i n i n g . As s u c h , i t i s n o t c l e a r whether t h e e x p e r i m e n t a l c o n d i t i o n s were s u f f i c i e n t t o i n d u c e n e u r o c h e m i c a l changes i n i n t a c t r a t s . I f t h e two s t r i a t a a r e d i f f e r e n t i a l l y i n v o l v e d , as s u g g e s t e d by Dunnett & B j o r k l u n d ( 1 9 8 3 ) , t h e n t h e p o s t o p e r a t i v e r e s p o n s e p r o f i l e s s h o u l d d i f f e r as a f u n c t i o n o f t h e l e s i o n e d s i d e . On t h e o t h e r hand, i f b o t h s t r i a t a a r e i n v o l v e d i n t h e p e r f o r m a n c e o f c o n d i t i o n e d c i r c l i n g , as i n d i c a t e d by t h e b i l a t e r a l changes i n DA m e t a b o l i s m p r e v i o u s l y r e p o r t e d ( S c h w a r t i n g & H u s t o n , 1987), t h e n comparable d e f i c i t s i n c i r c l i n g s h o u l d be e x h i b i t e d p o s t o p e r a t i v e l y , i r r e s p e c t i v e o f t h e l o c u s o f t h e l e s i o n . I t i s a l s o p o s s i b l e t h a t b o t h t h e i p s i l a t e r a l and c o n t r a l a t e r a l m e s o t e l e n c e p h a l i c DA systems a r e i n v o l v e d b u t t h a t each s u b s e r v e s a s e p a r a t e and d i s t i n c t component o f t h e r e s p o n s e . To t h i s end, R e i t e , R i c h a r d s & F r e e d (1986) have r e p o r t e d t h a t r e s p o n d i n g was a t t e n u a t e d f o l l o w i n g b o t h i p s i - and c o n t r a l a t e r a l l e s i o n s . However, t h e e x t e n t o f t h e d e f i c i t was f o u n d t o v a r y as a f u n c t i o n o f t h e s i d e o f t h e l e s i o n , r e l a t i v e t o t h e d i r e c t i o n o f t u r n i n g . The p r e s e n t e x p e r i m e n t f u r t h e r examined t h e e f f e c t s o f u n i l a t e r a l 6-hydroxydopamine (6-OHDA) l e s i o n s o f t h e m e s o t e l e n c e p h a l i c DA s y s t e m on c o n d i t i o n e d c i r c l i n g . A n i m a l s were t r a i n e d t o a l e v e l o f r e s p o n d i n g p r e v i o u s l y a s s o c i a t e d w i t h b i l a t e r a l changes i n s t r i a t a l and m e s o l i m b i c DA m e t a b o l i s m ( s e e E x p e r i m e n t I I ) . Upon a c q u i s i t i o n o f t h e r e s p o n s e , r a t s r e c e i v e d a u n i l a t e r a l l e s i o n o f t h e m e s o t e l e n c e p h a l i c DA p r o j e c t i o n , a t t h e l e v e l o f t h e l a t e r a l h y p o t h a l a m u s , t h a t was e i t h e r i p s i l a t e r a l o r c o n t r a l a t e r a l t o t h e r e i n f o r c e d d i r e c t i o n o f c i r c l i n g . -108-Haterials and Methods S u b j e c t s and A p p a r a t u s N a i v e , male Sprague-Dawley r a t s ( C h a r l e s R i v e r L a b o r a t o r i e s ) , as d e s c r i b e d i n E x p e r i m e n t I , were u s e d as s u b j e c t s . The b e h a v i o r a l a p p a r a t u employed was t h e same as t h a t d e s c r i b e d i n t h e f i r s t e x p e r i m e n t . E x p e r i m e n t a l P r o c e d u r e s T r a i n i n g . R a t s were w a t e r - d e p r i v e d f o r 24 h p r i o r t o s c r e e n i n g f o r d i r e c t i o n a l p r e f e r e n c e s . The d i r e c t i o n a l b i a s o f each s u b j e c t was d e t e r m i n e d u s i n g t h e n o n - d i f f e r e n t i a l r e i n f o r c e m e n t p a r a d i g m ( s e e E x p e r i m e n t I l l b ) . Each r a t was s u b s e q u e n t l y t r a i n e d t o c i r c l e f o r w a t e r r e i n f o r c e m e n t , as d e s c r i b e d p r e v i o u s l y . Water was a v a i l a b l e a c c o r d i n g t o F i x e d R a t i o 2 s c h e d u l e o f r e i n f o r c e m e n t f o l l o w i n g t h e i n i t i a l a c q u i s i t i o n o f t h e r e s p o n s e . R a t s r e c e i v e d 10 d a i l y FR-2 t r a i n i n g s e s s i o n s . Each s e s s i o n was 20 min. A l l r a t s were t r a i n e d t o c i r c l e i n t h e i r p r e f e r r e d d i r e c t i o n . S u r g e r y . Upon a c q u i s i t i o n o f t h e r e q u i r e d r e s p o n s e , r a t s were g i v e n f r e e a c c e s s t o f o o d and w a t e r f o r 5 days p r i o r t o s u r g e r y . R a t s were i n j e c t e d i . p . w i t h d e s m e t h y l i m i p r a m i n e (25 mg/kg, d i s s o l v e d i n 2 m l w a t e r / k g , C i b a - G e i g y ) 30 min p r i o r t o b e i n g a n a e s t h e t i z e d . Under Nembutal a n a e s t h e s i a (50 mg/ml/kg), r a t s were p l a c e d i n a s t a n d a r d Kopf s t e r e o t a x i c a p p a r a t u s , a m i d l i n e i n c i s i o n was made and a b u r r h o l e was d r i l l e d t h r o u g h t h e s k u l l above t h e l a t e r a l h y p o t h a l a m u s . R a t s r e c e i v e d a u n i l a t e r a l i n f u s i o n o f &-0HDA HBr (4 ug/ 2 u l d i s s o l v e d i n 0.1 mg/ml a s c o r b i c a c i d , dosage e x p r e s s e d as t h e b a s e ) , v i a a 30 gauge 5 u l H a m i l t o n s y r i n g e , i n t o t h e m e s o t e l e n c e p h a l i c DA system a t t h e l e v e l o f t h e l a t e r a l h y p o t h a l a m u s . The s t e r e o t a x i c c o o r d i n a t e s , t a k e n f r o m s t e r e o t a x i c z e r o , were: AP + 5.9 ; ML + 2.3; DV + 2.2. The i n c i s o r b a r was s e t a t -4.2. F o r h a l f o f t h e -109-r a t s , t h e l e s i o n was p l a c e d on t h e s i d e i p s i l a t e r a l t o t h e i r r e i n f o r c e d d i r e c t i o n o f c i r c l i n g ( ' I p s i l a t e r a l 1 g r o u p ) . The c o n t r a l a t e r a l s i d e was l e s i o n e d i n t h e r e m a i n i n g s u b j e c t s ( ' C o n t r a l a t e r a l ' g r o u p ) . The two grou p s were matched f o r p r e - o p e r a t i v e r a t e s o f c i r c l i n g . P o s t o p e r a t i v e T e s t i n g . B e h a v i o r a l t e s t i n g recommenced two weeks f o l l o w i n g s u r g e r y . R a t s were i n i t i a l l y w a t e r - d e p r i v e d f o r 24 h. F o r t h e f i r s t 5 days o f p o s t - o p e r a t i v e t e s t i n g ( N o n - R e v e r s a l ) , t h e e x p e r i m e n t a l c o n t i n g e n c i e s were i d e n t i c a l t o t h o s e i n e f f e c t i m m e d i a t e l y b e f o r e s u r g e r y ( i . e . a l l r a t s were r e q u i r e d t o t u r n i n t h e i r o r i g i n a l l y p r e f e r r e d d i r e c t i o n ) . That i s , r a t s i n t h e ' I p s i l a t e r a l ' group were r e i n f o r c e d f o r c i r c l i n g t o w a r d s t h e l e s i o n s i t e whereas t h e ' C o n t r a l a t e r a l ' group were r e q u i r e d t o t u r n away f r o m t h e l e s i o n i n o r d e r t o be r e i n f o r c e d . R a t s t h e n r e c e i v e d 10 a d d i t i o n a l t e s t s e s s i o n s ( R e v e r s a l ) w h e r e i n t h e e x p e r i m e n t a l c o n t i n g e n c i e s were r e v e r s e d . A c c o r d i n g l y , a l l r a t s were now r e q u i r e d t o c i r c l e i n t h e o p p o s i t e d i r e c t i o n ( i . e . a g a i n s t t h e i r i n i t i a l b i a s ) . However, r a t s i n t h e ' I p s i l a t e r a l ' group were now r e q u i r e d t o t u r n c o n t r a v e r s i v e t o t h e l e s i o n s i t e w h i l e t h e ' C o n t r a l a t e r a l ' group were now r e i n f o r c e d f o r t u r n i n g towards t h e l e s i o n ( s e e F i g . 1 7 ) . N e u r o c h e m i c a l V e r i f i c a t i o n o f L e s i o n . Upon c o m p l e t i o n o f b e h a v i o r a l t e s t i n g , r a t s were m a i n t a i n e d on ad l i b i t u m f o o d and w a t e r f o r a p p r o x i m a t e l y one week. A t t h i s t i m e , r a t s were d e c a p i t a t e d and t h e i r b r a i n s r a p i d l y removed. A c o r o n a l c u t was made s l i g h t l y a n t e r i o r t o t h e o p t i c c h i a s m and t h e a n t e r i o r s e c t i o n f r o z e n on a microtome. The s t r i a t u m , n u c l e u s accumbens and o l f a c t o r y t u b e r c l e were t h e n d i s s e c t e d as p r e v i o u s l y d e s c r i b e d . The t i s s u e samples o f t h e d i f f e r e n t b r a i n r e g i o n s were i m m e d i a t e l y weighed and p r e p a r e d f o r a n a l y s i s o f DA c o n c e n t r a t i o n s by HPLC-ED as d e s c r i b e d i n t h e f i r s t e x p e r i m e n t . -110-F i g u r e 17. S c h e m a t i c r e p r e s e n t a t i o n o f t h e e x p e r i m e n t a l d e s i g n . R a t s were i n i t i a l l y t r a i n e d t o c i r c l e f o r w a t e r r e i n f o r c e m e n t . H a l f o f t h e r a t s were t h e n l e s i o n e d i p s i l a t e r a l t o t h e r e i n f o r c e d d i r e c t i o n o f t u r n i n g ( upper p a n e l ) w h i l e t h e r e m a i n i n g s u b j e c t s were l e s i o n e d on t h e c o n t r a l a t e r a l s i d e . A p p r o x i m a t e l y h a l f o f t h e s u b j e c t s i n each group were l e s i o n e d on t h e l e f t s i d e . P o s t o p e r a t i v e l y , r a t s r e c e i v e d 5 days o f N o n - R e v e r s a l t e s t i n g . D u r i n g t h e s e s e s s i o n s , t h e e x p e r i m e n t a l c o n t i n g e n c i e s were i d e n t i c a l t o t h o s e i n e f f e c t p r e o p e r a t i v e l y . F o l l o w i n g t h e Non-R e v e r s a l p h a s e , e x p e r i m e n t a l c o n t i n g e n c i e s were r e v e r s e d ( R e v e r s a l ) f o r each s u b j e c t . > 1 1 1 -NON-REVERSAL 'IPSILATERAL* GROUP «0 o L R 51. o L R 'CONTRALATERAL' 0# GROUP ~ O .L R ID O L R REVERSAL o L R o L R I o L R o L R ^ Reinforced direction of circling ^ 1^ Non-Reinforced direction of circling - x l z -Results N e u r o c h e m i s t r y ANOVAs w i t h one between s u b j e c t f a c t o r (Group) and one r e p e a t e d measure ( N o n - l e s i o n e d / L e s i o n e d Hemisphere) were c o n d u c t e d on DA c o n c e n t r a t i o n s w i t h i n t h e s t r i a t u m , n u c l e u s accumbens and o l f a c t o r y t u b e r c l e . One s u b j e c t from t h e ' I p s i l a t e r a l ' group was e l i m i n a t e d from t h e n e u r o c h e m i c a l and a l l subsequent b e h a v i o r a l a n a l y s e s as t h e l e s i o n was c o n s i d e r e d i n s u f f i c i e n t l y c o m p l ete ( i . e . l e s s t h a n 90% d e p l e t i o n ) . DA c o n c e n t r a t i o n s were s i g n i f i c a n t l y l e s s i n a l l 3 s t r u c t u r e s i p s i l a t e r a l t o t h e l e s i o n , r e l a t i v e t o t h e c o n t r a l a t e r a l s t r u c t u r e s : F ( l , l l ) = 1550.47; F ( l , l l ) = 21.94; F ( l , l l ) - 215.82; p's < .001 f o r s t r i a t u m , n u c l e u s accumbens and o l f a c t o r y t u b e r c l e , r e s p e c t i v e l y (see T a b l e 9 ) . W h i l e i n s p e c t i o n o f T a b l e 9 s u g g e s t s t h a t t h e l e s i o n was more e x t e n s i v e i n t h e ' I p s i l a t e r a l ' g r o u p , no s i g n i f i c a n t group d i f f e r e n c e s were d e t e c t e d i n any o f t h e t h r e e r e g i o n s examined. M o r e o v e r , no i n t e r a c t i o n s between t h e two f a c t o r s were e v i d e n t . The r e l a t i v e l y h i g h c o n c e n t r a t i o n s o f DA i n t h e l e s i o n e d s t r u c t u r e s o f t h e ' C o n t r a l a t e r a l ' group a r e l a r g e l y a t t r i b u t a b l e t o one s u b j e c t whose d e p l e t i o n s were c o n s i s t e n t l y l e s s t h a n t h o s e o b s e r v e d f o r t h e o t h e r s u b j e c t s i n t h a t group. I t s h o u l d be n o t e d t h a t w h i l e i t i s p o s s i b l e t h a t t h e l e s i o n p r o c e d u r e p r o d u c e d s l i g h t c o n c u r r e n t damage t o t h e c o n t r a l a t e r a l s t r u c t u r e s , t h i s i s u n l i k e l y as t h e c o n t r a l a t e r a l v a l u e s were c o n s i s t e n t w i t h c o n t r o l c o n c e n t r a t i o n s o b t a i n e d i n p r e v i o u s e x p e r i m e n t s . R e i n f o r c e d R e s p o n d i n g A l l s u b j e c t s e x h i b i t e d a s y m p t o t i c r a t e s o f r e s p o n d i n g w i t h i n 10 days o f FR-2 t r a i n i n g . To d e t e r m i n e t h e s p e c i f i c e f f e c t s o f &-0HDA l e s i o n s on r e i n f o r c e d c o n d i t i o n e d c i r c l i n g , r e s p o n d i n g d u r i n g t h e l a s t p r e - o p e r a t i v e 1 1 - X J . O -T a b l e 9. Mean (± S.E.M.) c o n c e n t r a t i o n s (nmol/g p r o t e i n ) o f DA w i t h i n t h e s t r i a t u m , n u c l e u s accumbens and o l f a c t o r y t u b e r c l e o f r a t s f o l l o w i n g u n i l a t e r a l 6-0HDA-induced l e s i o n s o f t h e MFB. Striatum: Group I p s i l a t e r a l : (n-6) C o n t r a l a t e r a l : (n=7) Non-Lesioned 1074.17 47.37 1090.00 39.69 Lesioned 2.67* 1.54 19.86 16.69 % Non-Lesioned 0.25 1.82 Nucleus Accumbens: Group I p s i l a t e r a l : (n=6) C o n t r a l a t e r a l : <n=V) Non-Les ioned 295.33 I <i . O S 327.57 98.49 Lesioned 0.47* 0.47 22.71* 10.28 % Non-Lesioned u . ±o Olfactory Tubercle: Group Non-Lesioned I p s i l a t e r a l : (n-6) C o n t r a l a t e r a l : (n=7) 395.67 455.43 36.63 Lesioned 6.50* z. a i % Non-Lesioned 1.64 6.62 * denotes s i g n i f i c a n t l y l e s s t h a n v a l u e s o b t a i n e d f o r N o n - l e s i o n e d s t r u c t u r e , p < .001. -114-t e s t s e s s i o n ( b a s e l i n e ) was compared w i t h t h a t o b t a i n e d d u r i n g t h e f i r s t p o s t o p e r a t i v e s e s s i o n . A two-way ANOVA w i t h one between s u b j e c t f a c t o r (Group) and one w i t h i n s u b j e c t f a c t o r ( S e s s i o n ) y i e l d e d a s i g n i f i c a n t i n t e r a c t i o n : F ( l , l l ) = 9.15, p = .012. P a i r - w i s e c o m p a r i s o n s (Newman-K e u l ' s , a < .05) i n d i c a t e d t h a t , p r e o p e r a t i v e l y , comparable r a t e s o f c o n d i t i o n e d c i r c l i n g were e x h i b i t e d by b o t h g r o u p s ( s e e F i g u r e 1 3 ) . F o l l o w i n g u n i l a t e r a l 6-OHDA l e s i o n s , r e i n f o r c e d r e s p o n d i n g was a t t e n u a t e d . However, t h e e x t e n t o f t h e r e s p o n s e decrement was group dependent. That i s , r a t s l e s i o n e d c o n t r a l a t e r a l t o t h e d i r e c t i o n o f r e i n f o r c e d r e s p o n d i n g c i r c l e d l e s s f r e q u e n t l y t h a n r a t s w i t h l e s i o n s i p s i l a t e r a l t o t h e d i r e c t i o n o f c i r c l i n g . To d e t e r m i n e whether r e c o v e r y o f r e s p o n d i n g o c c u r r e d w i t h r e p e a t e d t e s t i n g a two-way ANOVA was c o n d u c t e d o v e r t h e 5 N o n - R e v e r s a l t e s t s e s s i o n s . Degrees o f freedom a p p r o p r i a t e t o t h e G e i s s e r - G r e e n h o u s e C o n s e r v a t i v e F t e s t were u s e d f o r t h i s and a l l subsequent a n a l y s e s i n v o l v i n g r e p e a t e d measures w i t h more t h a n 2 l e v e l s . T h i s a n a l y s i s y i e l d e d a s i g n i f i c a n t Group x S e s s i o n i n t e r a c t i o n : F ( l , l l ) - 5.59, p < .05. Newman-Keul's p a i r - w i s e c o m p a r i s o n s ( a < .05) were c o n d u c t e d t o i d e n t i f y t h e s o u r c e o f t h i s i n t e r a c t i o n . W i t h i n - g r o u p c o m p a r i s o n s d e m o n s t r a t e d t h a t , f o r t h e ' I p s i l a t e r a l ' g r o u p , r e s p o n d i n g was r e l a t i v e l y s t a b l e a c r o s s s e s s i o n s . The o n l y e x c e p t i o n was an i n c r e a s e i n r e s p o n d i n g o b s e r v e d d u r i n g t h e second day o f p o s t - o p e r a t i v e t e s t i n g . R e s p o n d i n g was n o t , however, m a i n t a i n e d a t t h i s h i g h e r l e v e l d u r i n g s u bsequent s e s s i o n s . I n c o n t r a s t , r a t s r e q u i r e d t o c i r c l e c o n t r a v e r s i v e t o t h e l e s i o n e x h i b i t e d a p r o g r e s s i v e d e c r e a s e i n r e s p o n d i n g a c r o s s s e s s i o n s . S p e c i f i c a l l y , c i r c l i n g o c c u r r e d more f r e q u e n t l y d u r i n g t h e f i r s t two N o n - R e v e r s a l s e s s i o n s , r e l a t i v e t o subsequent t e s t s e s s i o n s . Between group c o m p a r i s o n s i n d i c a t e d t h a t t h e -115-F i g u r e 18. The number o f r e i n f o r c e d r o t a t i o n s e m i t t e d p e r s e s s i o n a r e p l o t t e d f o r t h e ' I p s i l a t e r a l ' Group (open c i r c l e s ; n=6) and ' C o n t r a l a t e r a l ' Group ( s o l i d c i r c l e s ; n=7). Each d a t a p o i n t r e p r e s e n t s t h e mean (± S.E.M.) number o f r e s p o n s e s e m i t t e d w i t h i n a 20 min t e s t s e s s i o n . The l e f t hand p a n e l (B) r e f l e c t s r e s p o n d i n g d u r i n g t h e l a s t p r e - o p e r a t i v e s e s s i o n . The m i d d l e p a n e l ( N o n - R e v e r s a l ) r e p r e s e n t s t h e f i r s t 5 p o s t - o p e r a t i v e t e s t s e s s i o n s . D u r i n g t h e s e s e s s i o n s , e x p e r i m e n t a l c o n t i n g e n c i e s were i d e n t i c a l t o t h o s e i n e f f e c t p r e - o p e r a t i v e l y . The r e s p o n s e p r o f i l e s o b t a i n e d d u r i n g t h e 10 R e v e r s a l s e s s i o n s a r e p r e s e n t e d i n t h e r i g h t - h a n d p a n e l ( R e v e r s a l ) . D u r i n g t h e s e s e s s i o n s , e x p e r i m e n t a l c o n t i n g e n c i e s were r e v e r s e d s u c h t h a t r a t s p r e v i o u s l y r e q u i r e d t o c i r c l e t o t h e l e f t f o r r e i n f o r c e m e n t had t o c i r c l e t o t h e r i g h t and v i c e v e r s a . C i r c l i n g i n t h e a p p r o p r i a t e d i r e c t i o n was r e i n f o r c e d a c c o r d i n g t o a FR-2 s c h e d u l e f o r a l l e x p e r i m e n t a l s e s s i o n s . ^ 250-, Ld (/) c b CO 200 O B t) NON-REVERSAL 150H O on Q Ld O OH o Ld 100 a: ipsiversive rotations on Ld m 50H 4-^^ contraversive rotations 1 1 1 1 r 1 2 3 4 5 REVERSAL O 'Ipsilateral' Group • 'Contralateral' Group Ipsiversive rotations 1 2 3 4 5 6 7 8 9 10 SESSIONS -117-' C o n t r a l a t e r a l ' g roup c o n s i s t e n t l y e m i t t e d f e w e r r e s p o n s e s t h a n t h e ' I p s i l a t e r a l ' g r o u p . Upon r e v e r s a l o f e x p e r i m e n t a l c o n t i n g e n c i e s , r a t s l e s i o n e d c o n t r a l a t e r a l t o t h e o r i g i n a l d i r e c t i o n o f r e i n f o r c e d c i r c l i n g were o b s e r v e d t o r e s p o n d more f r e q u e n t l y f o r r e i n f o r c e m e n t t h a n r a t s i n t h e ' I p s i l a t e r a l ' group ( s e e r i g h t hand p a n e l o f F i g u r e 1 8 ) . Comparison o f t h e l a s t N o n - R e v e r s a l s e s s i o n w i t h t h e f i r s t R e v e r s a l s e s s i o n r e v e a l e d a s i g n i f i c a n t Group x S e s s i o n i n t e r a c t i o n : F ( l , l l ) = 122.01, p < .001. W i t h i n group c o m p a r i s o n s (Newman-Keul's, a < .05) r e v e a l e d t h a t r a t s i n t h e ' I p s i l a t e r a l ' group r e s p o n d e d l e s s f r e q u e n t l y d u r i n g t h e f i r s t R e v e r s a l s e s s i o n t h a n d u r i n g t h e l a s t N o n - R e v e r s a l s e s s i o n . The o p p o s i t e was o b s e r v e d w i t h r a t s l e s i o n e d c o n t r a l a t e r a l t o t h e o r i g i n a l d i r e c t i o n o f r e i n f o r c e d c i r c l i n g . That i s , r e v e r s a l o f t h e e x p e r i m e n t a l c o n t i n g e n c i e s r e s u l t e d i n i n c r e a s e d r e i n f o r c e d r e s p o n d i n g f o r t h e ' C o n t r a l a t e r a l ' g roup. Between group c o m p a r i s o n s c o n f i r m e d t h a t t h e ' I p s i l a t e r a l ' group e m i t t e d more r e s p o n s e s t h a n t h e ' C o n t r a l a t e r a l ' group d u r i n g t h e N o n - R e v e r s a l phase whereas t h e o p p o s i t e was t r u e once c o n t i n g e n c i e s were r e v e r s e d . Comparison o f c o n t r a v e r s i v e c i r c l i n g ( i . e . number o f r o t a t i o n s e m i t t e d by t h e ' C o n t r a l a t e r a l ' group d u r i n g N o n - R e v e r s a l v s p e r f o r m a n c e o f t h e ' I p s i l a t e r a l ' group d u r i n g R e v e r s a l ) r e v e a l e d no group d i f f e r e n c e s . T hat i s , b o t h groups e x h i b i t e d v e r y few c o n t r a v e r s i v e r e s p o n s e s , even when r e i n f o r c e m e n t was c o n t i n g e n t upon t h i s r e s p o n s e . Between group c o m p a r i s o n s o f r e i n f o r c e d , i p s i v e r s i v e c i r c l i n g i n d i c a t e d t h a t t h e ' I p s i l a t e r a l ' group t u r n e d i p s i v e r s i v e l y more f r e q u e n t l y on t h e l a s t day o f N o n - R e v e r s a l t e s t i n g t h a n t h e ' C o n t r a l a t e r a l ' group d i d on t h e f i r s t day o f R e v e r s a l t e s t i n g . An ANOVA w i t h two f a c t o r s (Group and S e s s i o n s ) was c o n d u c t e d a c r o s s t h e 10 R e v e r s a l s e s s i o n s i n o r d e r t o d e t e r m i n e whether r e p e a t e d t e s t i n g w o u l d i n f l u e n c e r e i n f o r c e d r e s p o n d i n g . A s i g n i f i c a n t main e f f e c t o f Group was o b s e r v e d : F ( l , l l ) - 102.61, p < .001, d e m o n s t r a t i n g t h a t t h e ' C o n t r a l a t e r a l ' group c i r c l e d more f r e q u e n t l y f o r r e i n f o r c e m e n t t h a n t h e ' I p s i l a t e r a l ' g r oup d u r i n g R e v e r s a l t e s t i n g . The e f f e c t s o f r e p e a t e d t e s t i n g c o u l d n o t be d e t e r m i n e d as s u c c e s s i v e s e s s i o n s were l i n e a r l y dependent upon t h e p r e c e d i n g ones. C o n s e q u e n t l y , a two-way ANOVA comparing t h e f i r s t and l a s t R e v e r s a l s e s s i o n s was c o n d u c t e d . T h i s a n a l y s i s y i e l d e d a s i g n i f i c a n t i n t e r a c t i o n t e r m : F ( l , l l ) = 9.23, p < .02. P a i r - w i s e c o m p a r i s o n s ( a < .05) c o n f i r m e d t h e between group d i f f e r e n c e s d e s c r i b e d above. Re p e a t e d t e s t i n g d i d n o t i n f l u e n c e t h e r a t e o f r e s p o n d i n g e x h i b i t e d by a n i m a l s i n t h e ' I p s i l a t e r a l ' g r oup. However, r e s p o n d i n g by t h e r a t s i n t h e ' C o n t r a l a t e r a l ' g roup was g r e a t e r i n t h e l a s t s e s s i o n , r e l a t i v e t o t h e i n i t i a l R e v e r s a l s e s s i o n . N o n - R e i n f o r c e d R e s p o n d i n g I n s p e c t i o n o f F i g u r e 19 i n d i c a t e s t h a t , p r e o p e r a t i v e l y , n e i t h e r group made v e r y many r e s p o n s e s i n t h e n o n - r e i n f o r c e d d i r e c t i o n . Comparison o f b a s e l i n e r e s p o n s e r a t e s w i t h t h o s e o b s e r v e d d u r i n g t h e f i r s t N o n - R e v e r s a l s e s s i o n y i e l d e d a s i g n i f i c a n t i n t e r a c t i o n : F ( l , l l ) - 8.97, p < .02. P a i r -w i s e c o m p a r i s o n s c o n f i r m e d t h a t t h e two group s d i d n o t d i f f e r f r o m one a n o t h e r p r e o p e r a t i v e l y . R a t s l e s i o n e d i p s i l a t e r a l t o t h e d i r e c t i o n o f r e i n f o r c e d c i r c l i n g ( i . e . c o n t r a l a t e r a l t o d i r e c t i o n o f n o n - r e i n f o r c e d r e s p o n d i n g ) d i d n o t e x h i b i t any change i n n o n - r e i n f o r c e d c i r c l i n g . I n c o n t r a s t , r a t s l e s i o n e d c o n t r a l a t e r a l t o t h e i r d i r e c t i o n o f r e i n f o r c e d t u r n i n g ( i . e . i p s i l a t e r a l t o n o n - r e i n f o r c e d d i r e c t i o n o f c i r c l i n g ) e x h i b i t e d an i n c r e a s e i n n o n - r e i n f o r c e d c i r c l i n g , r e l a t i v e t o t h e i r -119-F i g u r e 19. The number o f n o n - r e i n f o r c e d r o t a t i o n s p e r s e s s i o n a r e p l o t t e d f o r t h e ' I p s i l a t e r a l ' Group (open c i r c l e s ; n=6) and ' C o n t r a l a t e r a l ' Group ( s o l i d c i r c l e s ; n=7). Each d a t a p o i n t r e p r e s e n t s t h e mean (± S.E.M.) number o f r e s p o n s e s e m i t t e d w i t h i n a 20 min t e s t s e s s i o n . The l e f t hand p a n e l (B) r e f l e c t s r e s p o n d i n g d u r i n g t h e l a s t p r e - o p e r a t i v e s e s s i o n . The m i d d l e p a n e l ( N o n - R e v e r s a l ) r e p r e s e n t s t h e f i r s t 5 p o s t - o p e r a t i v e t e s t s e s s i o n s . The r i g h t - h a n d p a n e l d e p i c t s r e s p o n s e p r o f i l e s o b t a i n e d d u r i n g t h e 10 R e v e r s a l s e s s i o n s . D u r i n g t h e s e s e s s i o n s , e x p e r i m e n t a l c o n t i n g e n c i e s were r e v e r s e d s u c h t h a t r a t s t h a t had n o t been r e i n f o r c e d f o r t u r n i n g t o t h e l e f t d u r i n g t h e N o n - R e v e r s a l phase were now no l o n g e r r e i n f o r c e d f o r c i r c l i n g t o t h e r i g h t and v i c e v e r s a . 125 n B NON-REVERSAL ui in o OH 10<H a: P ui I O UI m < ui 5(H 25H Ipsiversive rotations contraversive rotations 1 2 3 4 5 REVERSAL O 'Ipsflaterql' Group • 'Contrqlaterql' Group A contraversive rotations 1 2 3 4 5 6 7 8 9 10 SESSIONS -121-b a s e l i n e r a t e s o f r e s p o n d i n g and t o t h e p o s t o p e r a t i v e r a t e s e x h i b i t e d by t h e ' I p s i l a t e r a l ' g r o u p . A n a l y s i s o f n o n - r e i n f o r c e d r e s p o n d i n g a c r o s s t h e f i v e N o n - R e v e r s a l s e s s i o n s y i e l d e d a s i g n i f i c a n t i n t e r a c t i o n t e r r a : F ( l , l l ) = 5.01, p < .05. T h i s i n t e r a c t i o n r e f l e c t e d t h e o b s e r v a t i o n t h a t r a t s i n t h e ' C o n t r a l a t e r a l ' g r oup made more r e s p o n s e s t h a n t h e ' I p s i l a t e r a l ' g r oup. M o reover, non-r e i n f o r c e d r e s p o n d i n g i n c r e a s e d f o l l o w i n g t h e f i r s t t e s t s e s s i o n f o r r a t s l e s i o n e d c o n t r a l a t e r a l t o t h e i r r e i n f o r c e d d i r e c t i o n o f c i r c l i n g . I t s h o u l d be emphasized t h a t t h i s c i r c l i n g was spontaneous i n t h a t i t was n o t m a i n t a i n e d by r e i n f o r c e m e n t . Upon r e v e r s a l o f t h e e x p e r i m e n t a l c o n t i n g e n c i e s , r a t s i n t h e ' I p s i l a t e r a l ' group e x h i b i t e d an i n c r e a s e i n n o n - r e i n f o r c e d c i r c l i n g whereas a d e c r e a s e was o b s e r v e d i n r a t s w i t h c o n t r a l a t e r a l l e s i o n s . T h i s f i n d i n g was c o n f i r m e d s t a t i s t i c a l l y : F ( l , l l ) = 104.27, p < .001. I n a d d i t i o n , i t was o b s e r v e d t h a t , d u r i n g t h e f i r s t R e v e r s a l s e s s i o n , t h e ' I p s i l a t e r a l ' group e m i t t e d more n o n - r e i n f o r c e d r e s p o n s e s t h a n t h e ' C o n t r a l a t e r a l ' g r o u p . G i v e n t h e i n t e r d e p e n d e n c e o f each R e v e r s a l t e s t s e s s i o n , t h e e f f e c t s o f r e p e a t e d R e v e r s a l t e s t i n g were d e t e r m i n e d by c o m p a r i n g r e s p o n d i n g w i t h i n t h e f i r s t s e s s i o n w i t h p e r f o r m a n c e o b t a i n e d d u r i n g t h e l a s t s e s s i o n . T h i s a n a l y s i s y i e l d e d a s i g n i f i c a n t i n t e r a c t i o n : F ( l , l l ) = 15.02, p < .003. P a i r - w i s e c o m p a r i s o n s d e m o n s t r a t e d t h a t r a t s i n t h e ' I p s i l a t e r a l ' group e x h i b i t e d a d e c r e a s e i n r e s p o n d i n g a c r o s s t e s t s e s s i o n s . I n c o n t r a s t , r e p e a t e d t e s t i n g d i d n o t i n f l u e n c e t h e r a t e o f non-r e i n f o r c e d r e s p o n d i n g e m i t t e d by t h e ' C o n t r a l a t e r a l ' g roup. Discussion The r e s u l t s o f t h i s s t u d y c o n f i r m p r e v i o u s r e p o r t s t h a t u n i l a t e r a l 6-OHDA l e s i o n s o f t h e m e s o t e l e n c e p h a l i c DA p r o j e c t i o n d i s r u p t t h e p e r f o r m a n c e -122-o f t h e c o n d i t i o n e d c i r c l i n g r e s p o n s e ( D u n n e t t & B j o r k l u n d , 1983; R e i t e , e t a l . , 1986). I n t h e p r e s e n t e x p e r i m e n t , r a t s were o b s e r v e d t o c i r c l e t o w a r d s t h e l e s i o n ( i . e . i p s i v e r s i v e ) more f r e q u e n t l y t h a n away f r o m t h e l e s i o n ( i . e . c o n t r a v e r s i v e ) , i r r e s p e c t i v e o f r e i n f o r c e m e n t c o n t i n g e n c i e s . I n f a c t , c o n t r a v e r s i v e r e s p o n d i n g was a l m o s t c o m p l e t e l y a b o l i s h e d . T h i s p r o f i l e o f p o s t o p e r a t i v e r e s p o n d i n g i s c o n s i s t e n t w i t h t h e h y p o t h e s i s t h a t c i r c l i n g i s d i r e c t e d away f r o m t h e s i d e o f t h e b r a i n t h a t p o s s e s s e s t h e g r e a t e s t DA a c t i v i t y ( s e e P y c o c k , 1980 f o r r e v i e w ) . A s y m p t o t i c r a t e s o f r e i n f o r c e d i p s i l a t e r a l c i r c l i n g were, however, a l s o r e d u c e d s i g n i f i c a n t l y . Thus, w h i l e t h e s i d e o f t h e l e s i o n , i n r e l a t i o n s h i p t o t h e d i r e c t i o n o f c i r c l i n g , was f o u n d t o be c r i t i c a l i n d e t e r m i n i n g t h e e x t e n t o f t h e b e h a v i o r a l d e f i c i t s , t h e 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 c o n d i t i o n e d c i r c l i n g i s s u b s e r v e d by b i l a t e r a l a c t i v i t y i n t h e m e s o t e l e n c e p h a l i c DA system. A c c o r d i n g l y , t h e p r e s e n t r e s u l t s a r e c o n s i s t e n t w i t h t h o s e r e p o r t e d by R e i t e , e t a l . , ( 1 9 8 6 ) . I n c o n t r a s t , however, Dunnett & B j o r k l u n d (1983) d i d n o t o b s e r v e i m p a i r e d r e s p o n d i n g f o l l o w i n g i p s i l a t e r a l l e s i o n s o f t h e m e s o t e l e n c e p h a l i c DA system. A l t h o u g h t h e b a s i s f o r t h i s d i s c r e p a n c y i s n o t known, i t may r e f l e c t t h e h i g h e r a s y m p t o t i c r a t e s o f r e s p o n d i n g e x h i b i t e d by t h e r a t s i n t h e p r e s e n t e x p e r i m e n t . The f i n d i n g s o f D unnett & B j o r k l u n d (1983) may a l s o r e f l e c t t h e f a c t t h a t t h e s c h e d u l e o f r e i n f o r c e m e n t i n e f f e c t p o s t o p e r a t i v e l y was d i f f e r e n t f r o m t h a t u s e d p r e o p e r a t i v e l y . I t i s n o t e w o r t h y t h a t , r e l a t i v e t o p r e - o p e r a t i v e r a t e s o f non-r e i n f o r c e d r e s p o n d i n g , i p s i v e r s i v e c i r c l i n g was i n c r e a s e d . I t i s l i k e l y t h a t t h e i n c r e a s e i n s p o n t a n e o u s , i p s i v e r s i v e c i r c l i n g r e f l e c t s an i n t e r a c t i o n between t h e r a t s 1 h i s t o r y o f r e i n f o r c e d l o c o m o t o r a c t i v i t y and t h e l e s i o n - i n d u c e d r e s t r i c t i o n i n r e s p o n s e r e p e r t o i r e . That i s , g i v e n t h e -123-h i g h p r e - o p e r a t i v e r a t e s o f l o c o m o t o r a c t i v i t y , i t i s u n l i k e l y t h a t t h e r a t s w o u l d r e m a i n i n a c t i v e f o r a 20 min t e s t p e r i o d . S i n c e t h e a n i m a l s were u n a b l e t o c i r c l e c o n t r a v e r s i v e l y and, g i v e n t h a t t h e o c c u r r e n c e o f spontaneous r o t a t i o n a l b e h a v i o r may be f a c i l i t a t e d by t h e t e s t a p p a r a t u s ( G l i c k , e t a l . , 1 9 7 6 ) , i t i s n o t s u r p r i s i n g t h a t r a t s e x h i b i t e d i p s i v e r s i v e c i r c l i n g , even when no t a s s o c i a t e d w i t h r e i n f o r c e m e n t . I n g e n e r a l , t h e t e s t i n g o r d e r d i d n o t i n f l u e n c e t h e e f f e c t s o f t h e l e s i o n s . C r o s s - g r o u p c o m p a r i s o n o f r e s p o n s e p r o f i l e s o b t a i n e d d u r i n g t h e l a s t 3 days o f each p o s t o p e r a t i v e t e s t i n g phase d e m o n s t r a t e s t h a t t h e C o n t r a l a t e r a l g r o u p s ' p a t t e r n o f r e s p o n d i n g d u r i n g N o n - R e v e r s a l t e s t i n g was a l m o s t i d e n t i c a l t o t h a t e x h i b i t e d by t h e ' I p s i l a t e r a l ' group d u r i n g t h e R e v e r s a l p h a s e . S i m i l a r l y , t h e p e r f o r m a n c e o f t h e ' I p s i l a t e r a l ' group d u r i n g N o n - R e v e r s a l was comparable t o t h a t e x h i b i t e d by t h e ' C o n t r a l a t e r a l ' group d u r i n g R e v e r s a l t e s t i n g . One d i f f e r e n c e t h a t was o b s e r v e d was t h a t r a t s i n t h e ' C o n t r a l a t e r a l ' group i n i t i a l l y c i r c l e d c o n t r a v e r s i v e l y f o r r e i n f o r c e m e n t d u r i n g t h e N o n - R e v e r s a l t e s t phase. The a d m i n i s t r a t i o n o f r e i n f o r c e m e n t was n o t , however, a b l e t o m a i n t a i n t h i s r e s p o n d i n g a c r o s s t e s t s e s s i o n s . S i n c e a s i m i l a r e f f e c t on c o n t r a v e r s i v e c i r c l i n g was n o t e x h i b i t e d by t h e ' I p s i l a t e r a l ' group d u r i n g t h e r e v e r s a l p h a s e , c e r t a i n e f f e c t s o f u n i l a t e r a l l e s i o n s o f t h e m e s o t e l e n c e p h a l i c DA s y s t e m on c o n d i t i o n e d c i r c l i n g may be dependent upon i n i t i a l p o s t o p e r a t i v e t e s t e x p e r i e n c e . W h i l e t h e s i g n i f i c a n c e o f t h i s o b s e r v a t i o n i s n o t known, i t i s i n t e r e s t i n g t o n o t e t h a t t h e p r o g r e s s i v e d e c r e a s e i s r e m i n i s c e n t o f t h e e f f e c t s o f r e p e a t e d a d m i n i s t r a t i o n o f n e u r o l e p t i c s on o p e r a n t r e s p o n d i n g (Tombaugh, Tombaugh & Anisman, 1979: W i s e , S p i n d l e r , deWit & G e r b e r , 1978). I t has been d e m o n s t r a t e d t h a t t h i s e f f e c t o f n e u r o l e p t i c s i s n o t due t o an a c c u m u l a t i o n o f t h e d r u g b u t i s , i n s t e a d , dependent upon e x p e r i e n c e i n t h e -124-t e s t e n v i r o n m e n t w h i l e i n t h e drugged s t a t e (Tombaugh, e t a l . , 1979; Wise, e t a l . , 1978). As m e n t i o n e d p r e v i o u s l y , h i g h r a t e s o f c o n d i t i o n e d c i r c l i n g have been a s s o c i a t e d w i t h a b i l a t e r a l a u g m e n t a t i o n i n DA m e t a b o l i s m w i t h i n b o t h t h e s t r i a t u m and t h e n u c l e u s accumbens ( S c h w a r t i n g & H u s t o n , 1987; E x p e r i m e n t I I , IVb and V I b ) . These r e s u l t s have been i n t e r p r e t e d as r e f l e c t i n g a s i m i l a r i n v o l v e m e n t o f t h e i p s i l a t e r a l and c o n t r a l a t e r a l m e s o t e l e n c e p h a l i c DA systems i n c o n d i t i o n e d c i r c l i n g . T h i s i n t e r p r e t a t i o n r e q u i r e s m o d i f i c a t i o n i n l i g h t o f t h e p r e s e n t r e s u l t s . W h i l e p r o v i d i n g f u r t h e r e v i d e n c e o f a b i l a t e r a l i n v o l v e m e n t o f t h i s p r o j e c t i o n i n c o n d i t i o n e d c i r c l i n g , t h e p r e s e n t d a t a a l s o i n d i c a t e t h a t t h e r e i s an asymmetry i n t h e r o l e o f t h e m e s o t e l e n c e p h a l i c DA system i n t h e c o n t r o l o f c o n d i t i o n e d t u r n i n g b e h a v i o r . D e t e c t i o n o f t h e u n d e r l y i n g asymmetry may be dependent upon t h e e x p e r i m e n t a l p a r a m e t e r s employed. F o r example, t h e t i m e c o u r s e o f t h e i n c r e a s e s i n m e t a b o l i s m may d i f f e r f o r t h e i p s i l a t e r a l and c o n t r a l a t e r a l p r o j e c t i o n s . F i r s t , an i n c r e a s e d i r e c t l y a s s o c i a t e d w i t h t h e a s y m m e t r i c a l p o s t u r e , o r p e r h a p s , t h e i n i t i a t i o n o f t h e a s y m m e t r i c a l r e s p o n s e , may o c c u r i n s t r u c t u r e s c o n t r a l a t e r a l t o t h e d i r e c t i o n o f c i r c l i n g . F o l l o w i n g t h i s i n i t i a l a s y m m e t r i c a l change i n DA m e t a b o l i s m , a g e n e r a l i z e d i n c r e a s e may o c c u r as a f u n c t i o n o f t h e o v e r a l l i n c r e a s e i n l o c o m o t o r a c t i v i t y . T h i s subsequent i n c r e a s e may mask t h e changes s p e c i f i c t o t h e asymmetx-ical p o s t u r i n g when t h e n e u r a l s u b s t r a t e o f c o n d i t i o n e d c i r c l i n g i s a s s e s s e d by m e a s u r i n g a b s o l u t e c o n c e n t r a t i o n s o f DA and i t s m e t a b o l i t e s a t t h e end o f a 20 min t e s t s e s s i o n . A c c o r d i n g l y , t h e n e u r o c h e m i c a l p r o f i l e a s s o c i a t e d w i t h c o n d i t i o n e d c i r c l i n g may v a r y as a f u n c t i o n o f t h e d u r a t i o n o f t h e t e s t s e s s i o n . -125-W h i l e i t a p p e a r s t h a t t h e i p s i l a t e r a l and c o n t r a l a t e r a l DA p r o j e c t i o n s p l a y d i f f e r e n t r o l e s i n t h e m e d i a t i o n o f c o n d i t i o n e d c i r c l i n g , t h e s p e c i f i c n a t u r e o f t h e i r i n v o l v e m e n t i s n o t p r e s e n t l y c l e a r . As s u g g e s t e d p r e v i o u s l y , t h e a t t e n u a t i o n o f c o n t r a v e r s i v e c i r c l i n g may r e f l e c t t h e c r i t i c a l i n v o l v e m e n t o f t h e c o n t r a l a t e r a l s t r i a t u m i n t h e m e d i a t i o n o f a s y m m e t r i c a l p o s t u r i n g ( K e l l y & Moore, 1976; Py c o c k & Marsden, 1978). C o n c u r r e n t l y , t h e d e c r e a s e d r a t e o f i p s i v e r s i v e r e s p o n d i n g may be a t t r i b u t a b l e t o t h e u n i l a t e r a l d e c r e a s e i n DA i n t h e n u c l e u s accumbens and/or o l f a c t o r y t u b e r c l e . There i s e v i d e n c e t h a t t h e r a t e o f c i r c l i n g i s d e t e r m i n e d by DA a c t i v i t y w i t h i n t h e n u c l e u s accumbens ( K e l l y & Moore, 1976; Pycock & Marsden, 1978). T h i s i s s u p p o r t e d by t h e o b s e r v a t i o n t h a t d r u g - i n d u c e d c i r c l i n g i s b l o c k e d by b i l a t e r a l l e s i o n s o f t h e n u c l e u s accumbens. However, u n i l a t e r a l l e s i o n s o f t h e n u c l e u s accumbens have n o t been f o u n d t o i n f l u e n c e r a t e o f d r u g - i n d u c e d c i r c l i n g when t h e l e s i o n i s on t h e same s i d e as t h e l e s i o n o f t h e s t r i a t u m ( P y c o c k & Marsden, 1978). W h i l e t h i s s u g g e s t s t h a t t h e d e c r e a s e d r a t e s o f i p s i v e r s i v e c i r c l i n g o b s e r v e d i n t h e p r e s e n t e x p e r i m e n t may n o t be a t t r i b u t a b l e t o t h e d e p l e t i o n o f l i m b i c DA, i t s h o u l d be n o t e d t h a t t h e l e s i o n s i n t h e p r e s e n t e x p e r i m e n t were more e x t e n s i v e t h a n t h o s e r e p o r t e d by P y c o c k & Marsden ( 1 9 7 8 ) . A c c o r d i n g l y , i n o r d e r t o c l a r i f y t h e r o l e o f t h e n u c l e u s accumbens i n c o n d i t i o n e d c i r c l i n g , t h e e f f e c t s o f e x t e n s i v e s i t e - s p e c i f i c l e s i o n s s h o u l d be d e t e r m i n e d . The a t t e n u a t i o n o f r e i n f o r c e d , i p s i v e r s i v e c i r c l i n g may a l s o be due t o a d e c r e a s e i n m o t i v a t i o n a l l e v e l s . However, a l l r a t s a p p r o a c h e d t h e hopper r e a d i l y and consumed t h e w a t e r i m m e d i a t e l y upon i t s p r e s e n t a t i o n . M o r e o v e r , a d m i n i s t r a t i o n o f r e i n f o r c e m e n t was o b s e r v e d t o i n f l u e n c e t h e r a t e o f c i r c l i n g . F o r example, r a t s i n t h e ' C o n t r a l a t e r a l ' group e x h i b i t e d -126-an i n c r e a s e i n t h e r a t e o f i p s i v e r s i v e c i r c l i n g when t h i s r e s p o n s e was r e i n f o r c e d d u r i n g t h e r e v e r s a l s e s s i o n s ( s e e F i g . 2 ) . I n c o n t r a s t , r a t s i n t h e ' I p s i l a t e r a l ' g r oup e x h i b i t e d e x t i n c t i o n o f i p s i v e r s i v e r e s p o n d i n g when t h i s r e s p o n s e was no l o n g e r r e i n f o r c e d d u r i n g t h e R e v e r s a l phase (see F i g . 3 ) . S p e c i f i c a l l y , t h e number o f r e i n f o r c e d r e s p o n s e s e m i t t e d by I p s i l a t e r a l s u b j e c t s d u r i n g t h e l a s t n o n - r e v e r s a l s e s s i o n was g r e a t e r t h a n t h e number o f n o n - r e i n f o r c e d r e s p o n s e s e m i t t e d d u r i n g t h e f i r s t r e v e r s a l s e s s i o n , even though t h e d i r e c t i o n o f t u r n i n g was i d e n t i c a l . M o r e o v e r , r e s p o n d i n g c o n t i n u e d t o d e c r e a s e w i t h r e p e a t e d t e s t s e s s i o n s . These o b s e r v a t i o n s c l e a r l y i n d i c a t e t h a t w h i l e r a t s w i t h u n i l a t e r a l l e s i o n s o f t h e m e s o t e l e n c e p h a l i c DA system w i l l s p o n t a n e o u s l y c i r c l e t o w a r d s t h e l e s i o n e d s i d e , t h e f r e q u e n c y o f t h i s r e s p o n s e can be m o d i f i e d by r e i n f o r c e m e n t . F i n a l l y , t h e d e c r e a s e d r a t e s o f c o n d i t i o n e d c i r c l i n g , i r r e s p e c t i v e o f d i r e c t i o n , may, i n p a r t , r e f l e c t an i m p a i r e d a b i l i t y t o i n i t i a t e r e s p o n d i n g , as s u g g e s t e d by R e i t e , e t a l . ( 1 9 8 6 ) . To t h i s end, r a t s i n b o t h g r o u p s e x h i b i t e d l o n g pauses between r e s p o n d i n g . However, once a r e s p o n s e was i n i t i a t e d , t h e r e s p o n s e was e x e c u t e d w i t h o u t any a p p a r e n t d i f f i c u l t y . I t i s n o t e w o r t h y t h a t t h e b e h a v i o r a l d e f i c i t s o b s e r v e d i n t h e p r e s e n t e x p e r i m e n t were o n l y e v i d e n t i n r a t s w i t h v e r y e x t e n s i v e l e s i o n s . I n f a c t , t h e one s u b j e c t whose d e p l e t i o n was l e s s t h a n 90 p e r c e n t e x h i b i t e d c o m p l e t e b e h a v i o r a l r e c o v e r y f o l l o w i n g s u r g e r y . M o r e o v e r , t h i s r a t was a b l e t o a c q u i r e t h e r e v e r s a l t a s k . I n c o n t r a s t , t h e b e h a v i o r a l p r o f i l e o f t h e one r a t whose l e s i o n was g r e a t e r t h a n 90 p e r c e n t b u t l e s s t h a n 95 p e r c e n t was s i m i l a r t o t h a t e x h i b i t e d by a l l o t h e r s u b j e c t s . T h i s o b s e r v a t i o n i s c o n s i s t e n t w i t h p r i o r r e p o r t s t h a t l e s i o n s g r e a t e r t h a n 90 p e r c e n t a r e o f t e n n e c e s s a r y i n o r d e r t o o b s e r v e b e h a v i o r a l d e f i c i t s ( s e e S t r i e k e r & Zigmond, 1986 f o r r e v i e w ) . I n summary, t h e p r e s e n t r e s u l t s p r o v i d e f u r t h e r e v i d e n c e t h a t c o n d i t i o n e d c i r c l i n g i s m o d u l a t e d by c e n t r a l d o p a m i n e r g i c a c t i v i t y ( S c h w a r t i n g & H u s t o n , 1987; Yamamoto & F r e e d , 1982; see a l s o E x p e r i m e n t s I I , I V b , V I b ) . M o r e o v e r , t h e a t t e n u a t i o n o f r e i n f o r c e d r e s p o n d i n g a f t e r i p s i l a t e r a l l y p l a c e d l e s i o n s , as w e l l as c o n t r a l a t e r a l l e s i o n s , s u g g e s t s t h a t b o t h m e s o t e l e n c e p h a l i c DA systems a r e c r i t i c a l l y i n v o l v e d i n t h i s r e s p o n s e . These o b s e r v a t i o n s a r e c o n s i s t e n t w i t h e a r l i e r r e p o r t s t h a t c o n d i t i o n e d c i r c l i n g i s a s s o c i a t e d w i t h a b i l a t e r a l a u g m e n t a t i o n i n DA m e t a b o l i s m ( S c h w a r t i n g & H u s t o n , 1987). However, t h e p r e s e n t r e s u l t s a l s o i n d i c a t e t h a t t h e i p s i l a t e r a l and c o n t r a l a t e r a l systems appear t o s u b s e r v e d i f f e r e n t components o f c o n d i t i o n e d c i r c l i n g . GENERAL DISCUSSION The r e s u l t s o f t h i s s e r i e s o f e x p e r i m e n t s i n d i c a t e t h a t c o n d i t i o n e d c i r c l i n g i s a s s o c i a t e d w i t h a b i l a t e r a l a u g m e n t a t i o n i n DA m e t a b o l i s m w i t h i n t h e n u c l e u s accumbens and w i t h i n d i s c r e t e r e g i o n s o f t h e s t r i a t u m . S p e c i f i c a l l y , DA m e t a b o l i s m was i n c r e a s e d o n l y w i t h i n r e s t r i c t e d r e g i o n s o f t h e a n t e r i o r s t r i a t u m ( E x p e r i m e n t I V b ) , a l t h o u g h i n c r e a s e s were r e l i a b l y d e t e c t e d f o l l o w i n g l e s s d i s c r e t e d i s s e c t i o n s o f t h e s t r i a t u m ( e . g . E x p e r i m e n t I I , I V b ) . DA m e t a b o l i s m w i t h i n t h e o l f a c t o r y t u b e r c l e was g e n e r a l l y n o t a f f e c t e d . The i n c r e a s e s i n DA m e t a b o l i s m appear t o be r a t e -dependent s i n c e no changes were d e t e c t e d i n c o n j u n c t i o n w i t h low r a t e s o f c i r c l i n g i n e i t h e r s t r u c t u r e ( E x p e r i m e n t I ) . I n c o n t r a s t , h i g h r a t e s o f r e s p o n d i n g e s t a b l i s h e d and m a i n t a i n e d by an i n t e r m i t t e n t s c h e d u l e o f r e i n f o r c e m e n t were a s s o c i a t e d w i t h a b i l a t e r a l a u g m e n t a t i o n o f s t r i a t a l and accumbens DA m e t a b o l i s m . R a t s ' i n h e r e n t d i r e c t i o n a l b i a s e s were n o t f o u n d -128-t o i n f l u e n c e t h e changes i n s t r i a t a l DA m e t a b o l i s m i n d u c e d by h i g h r a t e s o f c o n d i t i o n e d c i r c l i n g ( E x p e r i m e n t I V b ) . S p e c i f i c a l l y , DA m e t a b o l i s m was i n c r e a s e d b i l a t e r a l l y i n r a t s t r a i n e d t o c i r c l e i n a c c o r d w i t h t h e i r d i r e c t i o n a l b i a s , as w e l l as i n r a t s r e q u i r e d t o t u r n i n t h e i r non-p r e f e r r e d d i r e c t i o n . M e t a b o l i s m o f DA w i t h i n t h e n u c l e u s accumbens was i n c r e a s e d o n l y i n r a t s t h a t were r e i n f o r c e d f o r c i r c l i n g i n t h e i r p r e f e r r e d d i r e c t i o n . W h i l e a s i m i l a r t r e n d was o b s e r v e d i n t h e n u c l e u s accumbens o f r a t s t r a i n e d t o c i r c l e i n t h e i r n o n - p r e f e r r e d d i r e c t i o n , t h e i n c r e a s e was n o t s t a t i s t i c a l l y s i g n i f i c a n t . On t h e b a s i s o f t h e s e n e u r o c h e m i c a l r e s u l t s , c o n d i t i o n e d c i r c l i n g a p p e a r s t o be s u b s e r v e d by b o t h t h e i p s i l a t e r a l and c o n t r a l a t e r a l m e s o t e l e n c e p h a l i c DA p r o j e c t i o n s . The s y m m e t r i c a l n e u r o c h e m i c a l p r o f i l e s s u g g e s t s t h a t b o t h p r o j e c t i o n s a r e i n v o l v e d i n t h e m e d i a t i o n o f t h i s b e h a v i o r i n a s i m i l a r manner and, t o a s i m i l a r e x t e n t . The o b s e r v a t i o n t h a t u n i l a t e r a l l e s i o n s d i s r u p t b o t h i p s i - and c o n t r a v e r s i v e c i r c l i n g c o n f i m s t h e b i l a t e r a l i n v o l v e m e n t o f t h e m e s o t e l e n c e p h a l i c DA s y s t e m ( E x p e r i m e n t V I I ) . However, t h e r e s u l t s o f t h e l a t t e r e x p e r i m e n t a r e more c o n s i s t e n t w i t h t h e s u g g e s t i o n t h a t t h e two p r o j e c t i o n s s u b s e r v e d i f f e r e n t components o f c o n d i t i o n e d c i r c l i n g . That i s , f o l l o w i n g u n i l a t e r a l l e s i o n s o f t h e m e s o t e l e n c e p h a l i c DA p r o j e c t i o n c i r c l i n g was a t t e n u a t e d t o a g r e a t e r degree i n r a t s w i t h c o n t r a l a t e r a l l y p l a c e d l e s i o n s , r e l a t i v e t o i p s i l a t e r a l l e s i o n s . The p r e s e n t r e s u l t s a l s o p r o v i d e f u r t h e r e v i d e n c e o f t h e c o m p l e x i t y o f t h e m e s o t e l e n c e p h a l i c DA system. F i r s t , i t i s e v i d e n t t h a t n o t a l l neurones w i t h i n t h i s p r o j e c t i o n a r e i n f l u e n c e d i n a s i m i l a r f a s h i o n by c o n d i t i o n e d c i r c l i n g . I n p a r t i c u l a r , d e s p i t e c o n s i s t e n t a u g m e n t a t i o n o f DA m e t a b o l i s m w i t h i n t h e s t r i a t u m and n u c l e u s accumbens, i n c r e a s e s i n -129-o l f a c t o r y t u b e r c l e DA m e t a b o l i s m were g e n e r a l l y n o t o b s e r v e d i n a s s o c i a t i o n w i t h c o n d i t i o n e d c i r c l i n g . S e c o n d l y , t h e r e s u l t s o f E x p e r i m e n t V i a and VIb de m o n s t r a t e t h e c o m p l e x i t y o f t h e m e s o s t r i a t a l DA system ( e . g . B e a l & M a r t i n , 1985; J o y c e , e t a l . , 1985). E x p e r i m e n t V i a c o n f i r m e d and e x t e n d e d p r e v i o u s r e p o r t s o f t h e he t e r o g e n o u s d i s t r i b u t i o n o f DA w i t h i n t h e s t r i a t u m ( B e a l & M a r t i n , 1985; D i P a o l o , e t a l . , 1982). I n a d d i t i o n , i t was o b s e r v e d t h a t t h e d i s t r i b u t i o n s o f DA and i t s two p r i m a r y m e t a b o l i t e s , DOPAC and HVA, do n o t p a r a l l e l one a n o t h e r . T h i s f i n d i n g i s s u g g e s t i v e o f r e g i o n a l d i f f e r e n c e s i n terms o f r a t e , and p e r h a p s mechanism o f s t r i a t a l DA m e t a b o l i s m . The h e t e r o g e n o u s n a t u r e o f t h e m e s o s t r i a t a l DA system was c o n f i r m e d b e h a v i o r a l l y i n E x p e r i m e n t V I b . S p e c i f i c a l l y , DA m e t a b o l i s m was augmented o n l y w i t h i n d i s c r e t e r e g i o n s o f t h e a n t e r i o r s t r i a t u m . M o r e o v e r , DOPAC and HVA were d i f f e r e n t i a l l y s e n s i t i v e t o t h e c i r c l i n g r e s p o n s e as a f u n c t i o n o f s t r i a t a l l o c u s . I n v o l v e m e n t o f t h e M e s o t e l e n c e p h a l i c DA P r o j e c t i o n i n C o n d i t i o n e d C i r c l i n g W h i l e t h e r e s u l t s o f t h e p r e s e n t s e r i e s o f e x p e r i m e n t s s u p p o r t t h e h y p o t h e s i s t h a t c o n d i t i o n e d c i r c l i n g i s s u b s e r v e d by an i n c r e a s e i n a c t i v i t y w i t h i n t h e m e s o t e l e n c e p h a l i c DA system (Yamamoto & F r e e d , 1982; 1984a), t h e p r o f i l e o f t h e n e u r o c h e m i c a l changes o b t a i n e d i s s u b s t a n t i a l l y d i f f e r e n t from t h a t r e p o r t e d by F r e e d and a s s o c i a t e s ( B e n n e t t and F r e e d , 1986; Morgan, e t a l . , 1984; Yamamoto & F r e e d , 1982; 1984a). F o r example, Yamamoto & F r e e d (1982; 1984) r e p o r t e d t h a t c o n c e n t r a t i o n s o f DA and DOPAC were i n c r e a s e d w i t h i n t h e c o n t r a l a t e r a l s t r i a t u m and n u c l e u s accumbens, r e l a t i v e t o t h e i p s i l a t e r a l s t r u c t u r e s . Changes i n t h e a b s o l u t e c o n c e n t r a t i o n s o f DA were g e n e r a l l y n o t o b s e r v e d i n t h e p r e s e n t s e r i e s o f e x p e r i m e n t s . I n f a c t , i n o n l y one i n s t a n c e was t h e r e a s i g n i f i c a n t change i n DA c o n c e n t r a t i o n s ( E x p e r i m e n t I I ) . However, i n t h i s i n s t a n c e DA -130-c o n c e n t r a t i o n s t e n d e d t o be l o w e r i n t h e c o n t r a l a t e r a l n u c l e u s accumbens o f r a t s t r a i n e d t o c i r c l e , r e l a t i v e t o i p s i l a t e r a l c o n c e n t r a t i o n s and a l s o t o c o n t r o l v a l u e s . A l t h o u g h changes i n DA m e t a b o l i s m were c o n s i s t e n t l y o b s e r v e d , t h e y were n o t r e s t r i c t e d t o t h e c o n t r a l a t e r a l s t r u c t u r e s , as s u g g e s t e d by Yamamoto & F r e e d (1982; 1984a). M o reover, w h i l e DOPAC c o n c e n t r a t i o n s and t h e r a t i o o f DOPAC t o DA were i n c r e a s e d b i l a t e r a l l y i n some c a s e s , t h e changes i n m e t a b o l i s m were more r e l i a b l y i n d i c a t e d by HVA c o n c e n t r a t i o n s and t h e r a t i o o f HVA t o DA, v a r i a b l e s n o t a s s e s s e d by Yamamoto & F r e e d (1982; 1984a). The s y n t h e s i s o f DA has a l s o been r e p o r t e d t o be s e l e c t i v e l y enhanced w i t h i n t h e s t r i a t u m and n u c l e u s accumbens c o n t r a l a t e r a l t o t h e r a t s d i r e c t i o n o f t u r n i n g ( B e n n e t t and F r e e d , 1986; Morgan, e t a l . , 1984). I n c o n t r a s t , no s i g n i f i c a n t e f f e c t s o f c o n d i t i o n e d c i r c l i n g on DA s y n t h e s i s were o b s e r v e d i n E x p e r i m e n t I I I , a l t h o u g h a t r e n d f o r b i l a t e r a l i n c r e a s e s was e v i d e n t . The b a s i s f o r t h e s e d i s c r e p a n c i e s i s n o t c l e a r . I t i s p o s s i b l e t h a t d i f f e r e n t h o u s i n g p r o t o c o l s u n d e r l y t h e d i s c r e p a n t n e u r o c h e m i c a l p r o f i l e s . I n t h e p r e s e n t e x p e r i m e n t s , a l l s u b j e c t s were housed i n d i v i d u a l l y . I n c o n t r a s t , F r e e d and a s s o c i a t e s t y p i c a l l y m a i n t a i n t h e i r a n i m a l s i n group s o f t h r e e o r f o u r ( F r e e d , p e r s o n a l c o m m u n i c a t i o n ) . G i v e n t h e e v i d e n c e t h a t e n v i r o n m e n t a l f a c t o r s , s u c h as h o u s i n g c o n d i t i o n s , can i n f l u e n c e n e u r o c h e m i c a l v a r i a b l e s and b e h a v i o r ( S e g a l , Kapp, K u c z e n s k i & M a n d e l l , 1973; Thoa, T i z a b i & J a c o b o w i t z , 1 977), i t i s p o s s i b l e t h a t t h i s p r o c e d u r a l d i f f e r e n c e c o n t r i b u t e d t o t h e v a r i a n t r e s u l t s . I t s h o u l d be n o t e d , however, t h a t S c h w a r t i n g & Huston ( 1 9 8 7 ) , who have r e p o r t e d t h a t c o n d i t i o n e d c i r c l i n g i s a s s o c i a t e d w i t h b i l a t e r a l i n c r e a s e s i n s t r i a t a l DA m e t a b o l i s m , a l s o group-housed t h e i r a n i m a l s . A c c o r d i n g l y , i t does n o t appear t h a t h o u s i n g c o n d i t i o n s a r e a c r i t i c a l f a c t o r i n d e t e r m i n i n g t h e n e u r o c h e m i c a l consequences o f c o n d i t i o n e d c i r c l i n g . A n o t h e r p o s s i b i l i t y c o n c e r n s t h e use o f a h y p e r t o n i c s u c r o s e s o l u t i o n as t h e r e i n f o r c i n g s t i m u l u s i n w a t e r - d e p r i v e d r a t s ( s e e Yamamoto & F r e e d , 1982 f o r p r o c e d u r a l d e s c r i p t i o n ) . I t i s p o s s i b l e t h a t t h e n e u r o c h e m i c a l changes r e p o r t e d by F r e e d and a s s o c i a t e s r e f l e c t an i n t e r a c t i o n between t h e n e u r o c h e m i c a l consequences o f t h e c o n d i t i o n e d c i r c l i n g r e s p o n s e and t h a t o f t h e r e i n f o r c i n g s t i m u l u s . F o r example, r a t s m a i n t a i n e d on t h i s s c h e d u l e o f d e p r i v a t i o n become s e v e r e l y d e h y d r a t e d and e x h i b i t e x t e n s i v e w e i g h t l o s s (70-75% o f ad l i b i t u m w e i g h t s ) ( u n p u b l i s h e d o b s e r v a t i o n s ; see a l s o Morgan, e t a l . , 1 9 8 4), f a c t o r s t h a t by t h e m s e l v e s may i n f l u e n c e b r a i n c h e m i s t r y . Consumption o f t h e s u c r o s e s o l u t i o n under t h e s e e x p e r i m e n t a l c o n d i t i o n s h a s , i n f a c t , been f o u n d t o i n d u c e changes i n DA m e t a b o l i s m , i n d e p e n d e n t o f t h e c o n d i t i o n e d c i r c l i n g r e s p o n s e ( F r e e d , p e r s o n a l c o m m u n i c a t i o n ) . I t i s a l s o n o t e w o r t h y t h a t b i l a t e r a l i n c r e a s e s i n DA r e l e a s e , as i n d i c a t e d u s i n g m i c r o d i a l y s i s , w i t h i n t h e s t r i a t u m and n u c l e u s accumbens o f r a t s t r a i n e d t o c i r c l e f o r w a t e r r e i n f o r c e m e n t have been o b s e r v e d ( S a b o l & F r e e d , p e r s o n a l c o m m u n i c a t i o n ) . These r e s u l t s a r e c o n s i s t e n t w i t h t h e f i n d i n g s o f t h e p r e s e n t s e r i e s o f e x p e r i m e n t s . I n a d d i t i o n , as p r e v i o u s l y i n d i c a t e d , S c h w a r t i n g & Huston (1987) have a l s o r e p o r t e d a b i l a t e r a l i n c r e a s e i n DA m e t a b o l i s m i n r a t s t r a i n e d t o c i r c l e f o r w a t e r r e i n f o r c e m e n t . Thus, i t a p p e a r s t h a t c i r c l i n g m a i n t a i n e d by w a t e r r e i n f o r c e m e n t i s s u b s e r v e d by a b i l a t e r a l a u g m e n t a t i o n o f s t r i a t a l and accumbens DA m e t a b o l i s m . These changes a r e n o t r e l a t e d t o t h e co n s u m p t i o n o f w a t e r p e r s e , as i n t h e p r e s e n t s e r i e s o f e x p e r i m e n t s c o n t r o l s u b j e c t s consumed a s i m i l a r volume o f w a t e r i m m e d i a t e l y b e f o r e b e i n g s a c r i f i c e d . M o r e o v er, t h e ' -132-r e s u l t s o f E x p e r i m e n t s IVb d e m o n s t r a t e d t h a t t h e s e c o n t r o l s u b j e c t s do n o t d i f f e r n e u r o c h e m i c a l l y from n o n - d e p r i v e d c o n t r o l r a t s . F u n c t i o n a l S i g n i f i c a n c e o f t h e B i l a t e r a l I n c r e a s e s i n DA m e t a b o l i s m : I s  C o n d i t i o n e d C i r c l i n g a L a t e r a l i z e d B e h a v i o r ? The f a i l u r e t o o b s e r v e r o b u s t a s y m m e t r i c a l changes i n DA a c t i v i t y i s i n c o n s i s t e n t w i t h t h e h y p o t h e s i s t h a t c i r c l i n g i s m e d i a t e d by an asymmetry i n t h e f u n c t i o n i n g o f t h e i p s i l a t e r a l and c o n t r a l a t e r a l m e s o t e l e n c e p h a l i c DA p r o j e c t i o n s ( s e e P y c o c k , 1980; G l i c k , e t a l . , 1976). The l a c k o f a s y m m e t r i c a l changes i n DA m e t a b o l i s m may r e f l e c t t h e p o s s i b i l i t y t h a t t h e c i r c l i n g r e s p o n s e i s n o t a t r u l y l a t e r a l i z e d b e h a v i o r . W h i l e t h e two s i d e s o f t h e body a r e c l e a r l y n o t p e r f o r m i n g t h e same movements, i t i s i m p o r t a n t t o a p p r e c i a t e t h a t t h e i p s i l a t e r a l s i d e i s n o t i n a c t i v e d u r i n g c i r c l i n g — r a t h e r , b o t h s i d e s a r e a c t i v e l y i n v o l v e d i n t h e p e r f o r m a n c e o f t h e c i r c l i n g r e s p o n s e . To t h i s end, Szechtman & P i s a (1986) have r e p o r t e d t h a t an asymmetry i n i p s i l a t e r a l and c o n t r a l a t e r a l s t e p p i n g movements i s n o t a s s o c i a t e d w i t h a p o m o r p h i n e - i n d u c e d c i r c l i n g . As s u c h , t h e b i l a t e r a l e f f e c t s on DA m e t a b o l i s m o b t a i n e d i n E x p e r i m e n t s I I , IVb and V I b may be a t t r i b u t a b l e t o t h e g e n e r a l l y h i g h l e v e l s o f b i l a t e r a l motor a c t i v i t y e x h i b i t e d by t h e a n i m a l s . To d e t e r m i n e t h e e x t e n t t o w h i c h c o n d i t i o n e d c i r c l i n g i s a l a t e r a l i z e d b e h a v i o r , f i n e - g r a i n e d a n a l y s i s o f t h e r e s p o n s e i s r e q u i r e d . I f , on t h e o t h e r hand, t h e c i r c l i n g r e s p o n s e i s c o n s i d e r e d t o be a s t r o n g l y l a t e r a l i z e d b e h a v i o r , t h e 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 t h e m e s o t e l e n c e p h a l i c DA system i s b i l a t e r a l l y a c t i v a t e d d u r i n g h i g h r a t e s o f l a t e r a l i z e d r e s p o n d i n g . T h i s f i n d i n g i s open t o s e v e r a l i n t e r p r e t a t i o n s . I t c o u l d i n d i c a t e t h a t i n t h e awake, i n t a c t a n i m a l a c t i v a t i o n o f one d o p a m i n e r g i c s y s t e m d u r i n g l a t e r a l i z e d motor a c t i v i t y c a u s e s , by m u l t i s y n a p t i c mechanisms, t h e o t h e r s i d e t o be a c t i v a t e d as w e l l ( e . g . G e r f e n , S t a i n e s , A r b u t h n o t t & F i b i g e r , 1982). A l t e r n a t i v e l y , an i n i t i a l a s y m m e t r i c a l i n c r e a s e i n DA a c t i v i t y , d i r e c t l y a s s o c i a t e d w i t h t h e a s y m m e t r i c a l p o s t u r i n g , may be s u c c e e d e d by a g e n e r a l i z e d i n c r e a s e t h a t i s r e f l e c t i v e o f t h e o v e r a l l l e v e l o f motor a c t i v i t y . I f t h i s i s t h e c a s e , t h e a s y m m e t r i c a l d e f i c i t s o b s e r v e d f o l l o w i n g u n i l a t e r a l l e s i o n s ( E x p e r i m e n t V I I ) may r e f l e c t d i f f e r e n t i a l i n t e r r u p t i o n , as a f u n c t i o n o f t h e l o c u s o f t h e l e s i o n , i n t h i s t w o - s t e p n e u r a l p r o c e s s . That i s , t h e s i t e o f t h e l e s i o n , r e l a t i v e t o t h e d i r e c t i o n o f t u r n i n g , w o u l d be c r i t i c a l i n d e t e r m i n i n g t h e s e v e r i t y o f t h e b e h a v i o r a l d e f i c i t . I f t h e c o n t r a l a t e r a l s t r u c t u r e s a r e c r i t i c a l f o r t h e i n i t i a t i o n o f t h e a s y m m e t r i c a l r e s p o n s e ( e . g . K e l l y , 1977) t h e n l e s i o n s o f t h e p r o j e c t i o n i n n e r v a t i n g t h o s e s t r u c t u r e s w o u l d m i n i m i z e t h e o c c u r r e n c e o f c o n t r a v e r s i v e c i r c l i n g . I n c o n t r a s t , a l t h o u g h i p s i v e r s i v e c i r c l i n g c o u l d s t i l l o c c u r maximal r a t e s o f r e s p o n d i n g w o u l d be a t t e n u a t e d because o f t h e o v e r a l l l o w e r l e v e l o f m e s o t e l e n c e p h a l i c DA a c t i v i t y . The b i l a t e r a l a u g m e n t a t i o n i n DA m e t a b o l i s m c o u l d , a l t e r n a t i v e l y , i n d i c a t e t h a t t h e m e s o t e l e n c e p h a l i c DA p r o j e c t i o n m e d i a t e s o t h e r a s p e c t s o f t h e c i r c l i n g r e s p o n s e , s u c h as t h e h i g h l e v e l s o f a r o u s a l and/or m o t i v a t i o n t h a t a r e p r e s e n t d u r i n g c o n d i t i o n e d c i r c l i n g . W h i l e t h e i n c l u s i o n o f c o n t r o l s u b j e c t s t h a t consume a matched volume o f w a t e r i m m e d i a t e l y b e f o r e b e i n g s a c r i f i c e d d e m o n s t r a t e s t h a t t h e o b s e r v e d n e u r o c h e m i c a l changes a r e n o t a t t r i b u t a b l e t o c o n s u m p t i o n o f w a t e r p e r s e , i t r e m a i n s p o s s i b l e t h a t t h e i n c r e a s e s a r e r e l a t e d t o t h e r e s p o n s e - c o n t i n g e n t p r e s e n t a t i o n and c o n s u m p t i o n o f t h e r e i n f o r c i n g s t i m u l u s . -134-I d e n t i f i c a t i o n o f O t h e r N e u r a l P r o c e s s e s I n v o l v e d i n C o n d i t i o n e d C i r c l i n g I n o r d e r t o u n d e r s t a n d more c o m p l e t e l y t h e phenomenon o f c o n d i t i o n e d c i r c l i n g and how i t r e l a t e s t o o t h e r models o f r o t a t i o n a l b e h a v i o r , f u r t h e r c h a r a c t e r i z a t i o n o f t h e n e u r a l p r o c e s s e s i n v o l v e d i n t h e p e r f o r m a n c e o f t h e c o n d i t i o n e d r o t a t i o n a l r e s p o n s e i s r e q u i r e d . F o r example, t h e t o p o g r a p h y o f c i r c l i n g i n d u c e d by t h e a d m i n i s t r a t i o n o f amphetamine i s q u a l i t a t i v e l y d i f f e r e n t f r o m t h e c i r c l i n g e x h i b i t e d f o l l o w i n g an i n j e c t i o n o f apomorphine ( P y c o c k , 1980). The d i f f e r e n c e s i n r e s p o n s e t o p o g r a p h y a r e assumed t o r e f l e c t t h e d i f f e r e n t means t h r o u g h w h i c h amphetamine and apomorphine i n d u c e c i r c l i n g ( i . e . i n c r e a s e d p r e s y n a p t i c DA a c t i v i t y w i t h i n t h e i n t a c t s t r i a t u m vs p o s t s y n a p t i c s t i m u l a t i o n o f t h e s u p e r s e n s i t i v e r e c e p t o r s w i t h i n t h e l e s i o n e d s t r i a t u m , r e s p e c t i v e l y ) . The r e s p o n s e t o p o g r a p h y o f t h e w e l l -e s t a b l i s h e d c o n d i t i o n e d c i r c l i n g r e s p o n s e i s r e m i n i s c e n t o f t h e s t y l e o f c i r c l i n g i n d u c e d by t h e a d m i n i s t r a t i o n o f apomorphine t o l e s i o n e d s u b j e c t s ( i . e . t i g h t r a d i u s , h e a d - t o - t a i l c i r c l i n g ) ( s ee P y c o c k , 1980). A c c o r d i n g l y , i t w o u l d be o f i n t e r e s t t o d e t e r m i n e whether DA r e c e p t o r m o d i f i c a t i o n o c c u r s i n c o m p e n s a t i o n t o t h e a l t e r e d r e l e a s e o f DA i n d u c e d by c o n d i t i o n e d c i r c l i n g . I n a d d i t i o n , t h e use o f i n v i v o p r o c e d u r e s , s u c h as e l e c t r o c h e m i s t r y and m i c r o d i a l y s i s , c o u l d p r o v i d e f u r t h e r i n s i g h t i n t o DA's i n v o l v e m e n t i n c o n d i t i o n e d c i r c l i n g . I t i s p o s s i b l e t h a t s u c h p r o c e d u r e s w o u l d be more s e n s i t i v e t o t h e o c c u r r e n c e o f s u b t l e and t e m p o r a l l y d i s c r e t e c hanges, as h y p o t h e s i z e d above, t h a t may be a s s o c i a t e d w i t h c o n d i t i o n e d c i r c l i n g . W h i l e t h e p r e s e n t s e r i e s o f e x p e r i m e n t s has f o c u s s e d upon t h e i n v o l v e m e n t o f t h e m e s o t e l e n c e p h a l i c DA p r o j e c t i o n , i t must be e mphasized t h a t o t h e r n e u r o c h e m i c a l systems a r e a l s o c r i t i c a l l y i n v o l v e d i n t h e m e d i a t i o n o f t h i s r e s p o n s e . To t h i s end, Yamamoto & F r e e d (1984a) have r e p o r t e d i n c r e a s e s i n s e r o t o n i n m e t a b o l i s m w i t h i n t h e c o n t r a l a t e r a l s u b s t a n t i a n i g r a and amygdala. S e r o t o n i n m e t a b o l i s m was n o t , however, a f f e c t e d w i t h i n t h e s t r i a t u m o r n u c l e u s accumbens (Yamamoto & F r e e d , 1984a). I n c o n t r a s t , a b i l a t e r a l a u g m e n t a t i o n i n s e r o t o n i n m e t a b o l i s m was o b s e r v e d w i t h i n t h e s t r i a t u m , n u c l e u s accumbens and o l f a c t o r y t u b e r c l e u nder e x p e r i m e n t a l c o n d i t i o n s a s s o c i a t e d w i t h b i l a t e r a l i n c r e a s e s i n s t r i a t a l and accumbens DA m e t a b o l i s m ( S z o s t a k , J a k u b o v i c , P h i l l i p s and F i b i g e r , 1986b). O t h e r n e u r o c h e m i c a l systems ( e . g . c h o l i n e r g i c , G A B A e r g i c ) w h i c h have been i m p l i c a t e d i n t h e m e d i a t i o n o f r o t a t i o n a l b e h a v i o r i n d u c e d by o t h e r p r o t o c o l s ( s e e P y c o c k , 1980 f o r r e v i e w ) may a l s o s u b s e r v e c o n d i t i o n e d c i r c l i n g . The e x t e n t t o w h i c h t h e s e systems a r e i n f l u e n c e d by c o n d i t i o n e d c i r c l i n g r e m a i n s t o be d e t e r m i n e d . F u r t h e r u n d e r s t a n d i n g o f t h e i n v o l v e m e n t o f d o p a m i n e r g i c and non-d o p a m i n e r g i c systems i n c o n d i t i o n e d c i r c l i n g may be a t t a i n e d t h r o u g h t h e use o f p h a r m a c o l o g i c a l c h a l l e n g e s . However, t h e use o f drugs t o h e l p c h a r a c t e r i z e t h e i n v o l v e m e n t o f a n e u r o c h e m i c a l system may be l i m i t e d by t h e a p p a r e n t s e n s i t i v i t y o f t h e c o n d i t i o n e d c i r c l i n g r e s p o n s e t o t h e non-s p e c i f i c e f f e c t s o f d r u g s , e s p e c i a l l y m o t o r i c s i d e e f f e c t s . F o r example, i n t h e t h i r d e x p e r i m e n t , a d o p a - d e c a r b o x y l a s e i n h i b i t o r was a d m i n i s t e r e d t o w e l l - t r a i n e d r a t s i n an a t t e m p t t o d e t e r m i n e t h e e f f e c t s o f c o n d i t i o n e d c i r c l i n g on t h e s y n t h e s i s o f DA. No s i g n i f i c a n t e f f e c t s were o b s e r v e d . W h i l e i t i s p o s s i b l e t h a t s y n t h e s i s was n o t a f f e c t e d by c o n d i t i o n e d c i r c l i n g i t may a l s o be t h a t t h e l a c k o f s i g n i f i c a n t e f f e c t s r e f l e c t e d t h e d r u g - i n d u c e d a t t e n u a t i o n o f r e s p o n d i n g . S i m i l a r l y , t h e e f f e c t s o f c o n d i t i o n e d c i r c l i n g on t h e e f f l u x o f DA m e t a b o l i t e s c o u l d n o t be d e t e r m i n e d as r e s p o n d i n g was s e v e r e l y d i s r u p t e d by p a r g y l i n e , a monoamine o x i d a s e i n h i b i t o r ( u n p u b l i s h e d o b s e r v a t i o n s ) . G i v e n t h e a p p a r e n t r a t e --136-dependent e f f e c t s o f c o n d i t i o n e d c i r c l i n g on DA m e t a b o l i s m w i t h i n t h e s t r i a t u m and n u c l e u s accumbens, c a u t i o n i s w a r r a n t e d i n i n t e r p r e t i n g t h e r e s u l t s o f such e x p e r i m e n t s . The use o f l e s i o n i n g t e c h n i q u e s may a l s o be h e l p f u l i n i d e n t i f y i n g more c o m p l e t e l y t h e n e u r a l s u b s t r a t e o f c o n d i t i o n e d c i r c l i n g . F o r example, assessment o f t h e e f f e c t s o f u n i l a t e r a l l e s i o n s o f t h e m e s o t e l e n c e p h a l i c DA p r o j e c t i o n p r o v i d e d t h e o n l y e v i d e n c e f o r an a s y m m e t r i c a l i n v o l v e m e n t o f t h i s n e u r o c h e m i c a l s y s t e m i n c o n d i t i o n e d c i r c l i n g . The s i g n i f i c a n c e o f t h i s o b s e r v a t i o n c o u l d , p e r h a p s , be c l a r i f i e d by d e t e r m i n i n g t h e e f f e c t s o f l o c u s - s p e c i f i c l e s i o n s ( e . g . l e s i o n s o f t h e s t r i a t u m v s n u c l e u s accumbens). That i s , i s t h e r e d u c e d r a t e o f i p s i v e r s i v e c i r c l i n g a t t r i b u t a b l e t o t h e d e c r e a s e i n DA a c t i v i t y w i t h i n t h e n u c l e u s accumbens, o r i s t h e c o n t r a l a t e r a l s t r i a t u m c r i t i c a l l y i n v o l v e d i n t h i s b e h a v i o r . The use o f s e l e c t i v e l e s i o n s may a l s o h e l p t o i d e n t i f y t h e p r o j e c t i o n s a f f e r e n t and e f f e r e n t t o t h e s t r i a t u m t h a t a r e i n v o l v e d i n c o n d i t i o n e d c i r c l i n g . F o r example, c i r c l i n g i n d u c e d by apomorphine ( i n c o n j u n c t i o n w i t h u n i l a t e r a l l e s i o n s o f t h e m e s o t e l e n c e p h a l i c DA p r o j e c t i o n ) has been f o u n d t o be dependent upon t h e s t r i o n i g r a l p r o j e c t i o n ( M a r s h a l l & U n g e r s t e d t , 1977). I f c o n d i t i o n e d c i r c l i n g and d r u g - i n d u c e d c i r c l i n g a r e m e d i a t e d by t h e same n e u r a l p r o c e s s e s , t h e n c o n d i t i o n e d c i r c l i n g s h o u l d be d i s r u p t e d f o l l o w i n g s t r i o n i g r a l l e s i o n s . I t would a l s o be o f i n t e r e s t t o d e t e r m i n e whether b o t h i p s i v e r s i v e and c o n t r a v e r s i v e c i r c l i n g a r e d i s r u p t e d , as o b s e r v e d f o l l o w i n g u n i l a t e r a l l e s i o n s o f t h e m e s o t e l e n c e p h a l i c p r o j e c t i o n o r , i f an asymmetry i n n e u r a l f u n c t i o n i n g c a n be more r e a d i l y d e t e c t e d downstream f r o m t h e s t r i a t u m . -137-C i r c l i n q : I s i t a U n i t a r y Phenomenon? The p r e s e n t r e s u l t s r a i s e t h e p o s s i b i l i t y t h a t t h e n e u r a l s u b s t r a t e o f c i r c l i n g i s dependent upon t h e e x p e r i m e n t a l p a r a d i g m u s e d t o i n d u c e t h e r e s p o n s e ( e . g . c o n d i t i o n e d c i r c l i n g , d r u g - i n d u c e d c i r c l i n g , s t i m u l a t i o n -i n d u c e d c i r c l i n g ) . W h i l e t h e r e appear t o be some c o m m o n a l i t i e s a c r o s s p a r a d i g m s ( e . g . i n v o l v e m e n t o f t h e m e s o t e l e n c e p h a l i c DA p r o j e c t i o n ; r e s p o n s e t o p o g r a p h y ) , i n o r d e r t o u n d e r s t a n d more f u l l y t h e phenomenon o f c i r c l i n g , t h e d i f f e r e n c e s and s i m i l a r i t i e s need t o be d e t e r m i n e d . I t has been p r e v i o u s l y r e p o r t e d t h a t i n h e r e n t d i r e c t i o n a l b i a s e s i n f l u e n c e t h e magnitude and d i r e c t i o n o f d r u g - i n d u c e d c i r c l i n g f o l l o w i n g u n i l a t e r a l l e s i o n s o f t h e m e s o t e l e n c e p h a l i c DA p r o j e c t i o n ( J e r u s s i & G l i c k , 1975; R o b i n s o n & B e c k e r , 1983). I n c o n t r a s t , such b i a s e s d i d n o t i n f l u e n c e a c q u i s i t i o n o r p e r f o r m a n c e o f c o n d i t i o n e d c i r c l i n g . I n a d d i t i o n , t h e n e u r o c h e m i c a l consequences o f c o n d i t i o n e d t u r n i n g were i n d e p e n d e n t o f i n h e r e n t d i r e c t i o n a l p r e f e r e n c e s ( E x p e r i m e n t I V b ) . I t i s a l s o i n t e r e s t i n g t o n o t e t h a t , as p r e v i o u s l y m e n t i o n e d , t h e o v e r a l l n e u r o c h e m i c a l p r o f i l e a s s o c i a t e d w i t h c i r c l i n g i n d u c e d by i n t r a c r a n i a l e l e c t r i c a l s t i m u l a t i o n ( S z o s t a k , e t a l . , 1986) i s s u b s t a n t i a l l y d i f f e r e n t f r o m t h e p r o f i l e a s s o c i a t e d w i t h c o n d i t i o n e d c i r c l i n g . These o b s e r v a t i o n s s u g g e s t t h a t t h e n e u r a l s u b s t r a t e s o f c i r c l i n g depend upon t h e e x p e r i m e n t a l p r o c e d u r e s u s e d t o e s t a b l i s h c i r c l i n g . To d a t e , t h e t e n d e n c y has been t o v i e w c i r c l i n g as a u n i t a r y phenomenon. U n d e r s t a n d i n g o f b r a i n - b e h a v i o r i n t e r a c t i o n s may, however, be augmented by e x p l o r i n g how t h e v a r i o u s models d i f f e r f r o m one a n o t h e r , as w e l l a s , how t h e y a r e s i m i l a r . As p r e v i o u s l y i n d i c a t e d , t h e a s y m m e t r i c a l p o s t u r i n g i n d u c e d by u n i l a t e r a l l e s i o n s o f t h e m e s o t e l e n c e p h a l i c DA system i s g e n e r a l l y t h o u g h t t o r e f l e c t a c o m b i n a t i o n o f motor and s e n s o r y d e f i c i t s r e s t r i c t e d t o t h e body c o n t r a l a t e r a l t o t h e l e s i o n ( I v e r s e n , 1977). C i r c l i n g i n d u c e d by t h e s y s t e m i c a d m i n i s t r a t i o n o f amphetamine i s , a c c o r d i n g l y , t h o u g h t t o r e f l e c t enhanced l o c o m o t o r a c t i v i t y w h i c h i s a s y m m e t r i c a l l y d i r e c t e d due t o t h e u n d e r l y i n g b e h a v i o r a l d e f i c i t s p r o d u c e d by t h e l e s i o n ( I v e r s e n , 1977). S u p p o r t f o r t h i s c o n t e n t i o n has been p r o v i d e d i n d i r e c t l y by i n d e p e n d e n t r e p o r t s o f l e s i o n - i n d u c e d s e n s o r y n e g l e c t ( e . g . L j u n g b e r g & U n g e r s t e d t , 1976) and motor d e f i c i t s ( I v e r s e n , 1977). More r e c e n t l y , however, t h e i n v o l v e m e n t o f an u n d e r l y i n g asymmetry i n l o c o m o t o r a c t i v i t y has been q u e s t i o n e d . S p e c i f i c a l l y , Szechtman & P i s a (1986) have r e p o r t e d t h a t a l t h o u g h r a t s e x h i b i t an asymmetry i n s t e p p i n g p a t t e r n s , t h e d i r e c t i o n o f t h e asymmetry does n o t c o r r e l a t e w i t h t h e d i r e c t i o n o f d r u g - i n d u c e d c i r c l i n g . I n s u p p o r t o f t h e h y p o t h e s i s t h a t c i r c l i n g i s m e d i a t e d by an asymmetry i n s e n s o r y f u n c t i o n i n g , Szechtman (1983) has r e p o r t e d t h a t n e u r o l o g i c a l l y i n t a c t r a t s w i t h one s i d e o f t h e head bandaged w i l l c i r c l e when g i v e n apomorphine. Moreover, t h e d i r e c t i o n o f c i r c l i n g i s c o n t r a v e r s i v e t o t h e bandaged s i d e ( i . e . t o w a r d s t h e s e n s o r i l y i n t a c t s i d e ) . T h i s o b s e r v a t i o n i s c o n s i s t e n t w i t h t h a t o b s e r v e d u s i n g t h e DA a g o n i s t / l e s i o n p r e p a r a t i o n ( i . e . c i r c l i n g i s c o n t r a v e r s i v e t o t h e n e g l e c t e d s i d e o f t h e b o d y ) . To t h i s end, i t w o u l d be i n t e r e s t i n g t o d e t e r m i n e t h e e x t e n t t o w h i c h changes i n s e n s i t i v i t y t o s e n s o r y s t i m u l a t i o n o c c u r i n n e u r o l o g i c a l l y i n t a c t a n i m a l s t r a i n e d t o c i r c l e . I n p a r t i c u l a r , t h e e x t e n t t o w h i c h t h e s e changes a r e l a t e r a l i z e d w o u l d be o f s i g n i f i c a n c e t o u n d e r s t a n d i n g t h e r o l e o f t h e m e s o t e l e n c e p h a l i c DA system i n c o n d i t i o n e d c i r c l i n g . F o r example, i f , as s u g g e s t e d by t h e a s y m m e t r i c a l d e f i c i t s o b s e r v e d f o l l o w i n g u n i l a t e r a l l e s i o n s , a f u n c t i o n a l asymmetry w i t h i n t h e m e s o t e l e n c e p h a l i c DA s y s t e m s u b s e r v e s c o n d i t i o n e d c i r c l i n g , an i m b a l a n c e i n s e n s o r y f u n c t i o n i n g w o u l d be p r e d i c t e d . S p e c i f i c a l l y , t h e s i d e o f t h e body i p s i l a t e r a l t o t h e d i r e c t i o n o f t u r n i n g s h o u l d be h y p e r s e n s i t i v e t o s e n s o r y s t i m u l a t i o n , r e l a t i v e t o t h e c o n t r a l a t e r a l s i d e . I n a n e c d o t a l s u p p o r t o f such a h y p o t h e s i s , r a t s e x h i b i t i n g h i g h r a t e s o f c o n d i t i o n e d c i r c l i n g have been o b s e r v e d t o groom t h e i p s i l a t e r a l s i d e o f t h e body more f r e q u e n t l y t h a n t h e c o n t r a l a t e r a l h a l f o f t h e body. I n o r d e r t o s u b s t a n t i a t e t h i s o b s e r v a t i o n , q u a n t i t a t i v e and q u a l i t a t i v e assessment o f s e n s o r y f u n c t i o n i n r a t s t r a i n e d t o c i r c l e f o r w a t e r r e i n f o r c e m e n t i s r e q u i r e d . A l t e r n a t i v e l y , g i v e n t h e b i l a t e r a l a u g m e n t a t i o n i n s t r i a t a l DA m e t a b o l i s m , r a t s t r a i n e d t o c i r c l e may e x h i b i t a b i l a t e r a l , h y p e r s e n s i t i v i t y t o s e n s o r i m o t o r s t i m u l a t i o n , r e l a t i v e t o c o n t r o l s u b j e c t s . F u n c t i o n s S u b s e r v e d by t h e M e s o t e l e n c e p h a l i c DA P r o j e c t i o n : Beyond C i r c l i n g As i n d i c a t e d i n t h e I n t r o d u c t i o n , d i s r u p t i o n o f s e n s o r i m o t o r f u n c t i o n s i s t h o u g h t t o u n d e r l y r o t a t i o n a l b e h a v i o r . The l e s i o n - i n d u c e d d e f i c i t s i n s e n s o r i m o t o r i n t e g r a t i o n have been g e n e r a l l y c h a r a c t e r i z e d i n terms o f s e n s o r y i n a t t e n t i o n . More r e c e n t l y , however, C a r l i , Evenden & R o b b i n s (1985) p r o v i d e d e v i d e n c e t h a t t h e f a i l u r e t o o r i e n t t o c o n t r a l a t e r a l s e n s o r y e v e n t s may r e f l e c t an i n a b i l i t y t o r e s p o n d t o t h e s e n s o r y s t i m u l a t i o n , as opposed t o s e n s o r y i n a t t e n t i o n . S p e c i f i c a l l y , t h e y r e p o r t e d t h a t u n i l a t e r a l d e p l e t i o n o f s t r i a t a l DA d i s r u p t e d r a t s 1 a b i l i t y t o i n i t i a t e c o n t r a l a t e r a l motor a c t s , i n d e p e n d e n t o f t h e l o c u s o f t h e s e n s o r y e v e n t . 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 p r e v i o u s s u g g e s t i o n s t h a t t h e s t r i a t u m i s c r i t i c a l l y i n v o l v e d i n t h e i n i t i a t i o n o f movement ( e . g . R o l l s , 1983). I t has a l s o been r e c e n t l y d e m o n s t r a t e d t h a t t h e s t r i a t u m i s i n v o l v e d i n t h e e x e c u t i o n o f i n d e p e n d e n t l i m b movements (Whishaw, O'Connor & D u n n e t t , 1986). F o r example, u n i l a t e r a l l e s i o n s o f t h e s t r i a t u m have been o b s e r v e d t o d i s r u p t r e a c h i n g w i t h t h e c o n t r a l a t e r a l f o r e l i m b i n r a t s (Whishaw, O'Connor & D u n n e t t , 1986; see a l s o , P i s a , 1987). -140-These d e f i c i t s do n o t r e f l e c t a g e n e r a l i z e d motor i m p a i r m e n t o r p a r e s i s as o t h e r b e h a v i o r s i n v o l v i n g t h e f o r e l i m b s ( e . g . w a l k i n g , g r o o m i n g , h o l d i n g f o o d ) a r e n o t c o n c u r r e n t l y d i s r u p t e d . M o r e o v e r , r e a c h i n g w i t h t h e c o n t r a l a t e r a l l i m b i s e x h i b i t e d when use o f t h e " p r e f e r r e d " , i p s i l a t e r a l l i m b i s r e s t r i c t e d . I t s h o u l d be n o t e d t h a t t h e s e d e f i c i t s a r e i n d e p e n d e n t o f l e s i o n - i n d u c e d r o t a t i o n . That i s , w h i l e t h e s e r a t s e x h i b i t e d i p s i v e r s i v e c i r c l i n g when a d m i n i s t e r e d methamphetamine, t h e degree o f r o t a t i o n a l b i a s d i d n o t c o r r e l a t e w i t h t h e s e v e r i t y o f im p a i r m e n t i n l i m b use (Whishaw, e t a l . , 1986). G i v e n t h e v a r i e t y o f d i s c r e t e f u n c t i o n s s u b s e r v e d by t h e s t r i a t u m , i t i s p o s s i b l e t h a t t h e b i l a t e r a l a u g m e n t a t i o n i n s t r i a t a l DA m e t a b o l i s m a s s o c i a t e d w i t h c o n d i t i o n e d c i r c l i n g r e f l e c t s t h e i n v o l v e m e n t o f t h e s e p r o c e s s e s i n t h e e x e c u t i o n o f c o n d i t i o n e d c i r c l i n g . F o r example, c o n d i t i o n e d c i r c l i n g i s a t o p o g r a p h i c a l l y complex and c o o r d i n a t e d b e h a v i o r . I t i s p o s s i b l e t h a t t h e i n c r e a s e s i n DA m e t a b o l i s m r e f l e c t , i n p a r t , t h e s k i l l e d l i m b movements i n v o l v e d i n t h i s r e s p o n s e (Whishaw, e t a l . , 1986). F u r t h e r e x p e r i m e n t s a r e r e q u i r e d i n o r d e r t o c l a r i f y t h e n a t u r e o f t h e c o n d i t i o n e d c i r c l i n g r e s p o n s e and t h e i n v o l v e m e n t o f t h e m e s o t e l e n c e p h a l i c DA sy s t e m i n t h e d i s c r e t e components o f t h e c o n d i t i o n e d c i r c l i n g b e h a v i o r . Summary Taken t o g e t h e r , t h e p r e s e n t r e s u l t s d e m o n s t r a t e t h a t s p e c i f i c and d e t e c t a b l e n e u r o c h e m i c a l changes a r e a s s o c i a t e d w i t h t h e e x h i b i t i o n o f d i s c r e t e p a t t e r n s o f b e h a v i o r e s t a b l i s h e d w i t h o u t t h e use o f s u r g i c a l  i n t e r v e n t i o n s and/or t h e a d m i n i s t r a t i o n o f p s y c h o t r o p i c a g e n t s . S p e c i f i c a l l y , DA m e t a b o l i s m was b i l a t e r a l l y augmented i n t h e s t r i a t u m and n u c l e u s accumbens o f r a t s t r a i n e d t o c i r c l e f o r w a t e r r e i n f o r c e m e n t . E v i d e n c e o f an a s y m m e t r i c a l i n v o l v e m e n t o f t h e m e s o t e l e n c e p h a l i c DA sy s t e m -141-i n c o n d i t i o n e d c i r c l i n g was o n l y o b t a i n e d f o l l o w i n g u n i l a t e r a l l e s i o n s o f t h i s p r o j e c t i o n . That i s , r e s p o n d i n g was a t t e n u a t e d f o l l o w i n g b o t h i p s i -and c o n t r a l a t e r a l l e s i o n s . However, t h e r e s p o n s e d e f i c i t was g r e a t e r i n s u b j e c t s w i t h l e s i o n s o f t h e c o n t r a l a t e r a l m e s o t e l e n c e p h a l i c DA p r o j e c t i o n . The r e s u l t s o f t h e e x p e r i m e n t s i n v e s t i g a t i n g t h e e f f e c t s o f c o n d i t i o n e d c i r c l i n g on DA m e t a b o l i s m do n o t p r o v i d e any s u p p o r t f o r t h e c o n t e n t i o n by Yamamoto & F r e e d (1982; 1984) t h a t t h i s r e s p o n s e i s a s s o c i a t e d w i t h an a s y m m e t r i c a l i n c r e a s e i n s t r i a t a l and accumbens DA m e t a b o l i s m . R a t h e r , t h e p r e s e n t f i n d i n g s c l e a r l y d e m o n s t r a t e t h a t DA m e t a b o l i s m i s i n c r e a s e d i n a b i l a t e r a l and s y m m e t r i c a l manner w i t h i n t h e s t r i a t u m and n u c l e u s accumbens o f r a t s t r a i n e d t o c i r c l e . As s u c h , t h e 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 r o t a t i o n a l b e h a v i o r i s n o t n e c e s s a r i l y m e d i a t e d by an asymmetry i n m e s o t e l e n c e p h a l i c DA a c t i v i t y , as s u g g e s t e d by e x p e r i m e n t s i n v e s t i g a t i n g t h e n e u r a l b a s i s o f d r u g - i n d u c e d c i r c l i n g . I t i s s u g g e s t e d t h a t t h e n e u r a l s u b s t r a t e o f r o t a t i o n a l b e h a v i o r i s dependent upon t h e s p e c i f i c e x p e r i m e n t a l c o n d i t i o n s u s e d t o i n d u c e c i r c l i n g . F u r t h e r e x p e r i m e n t s a r e r e q u i r e d t o c l a r i f y t h e r e l a t i o n s h i p between c i r c l i n g and b a s a l g a n g l i a f u n c t i o n . - x 4 z -BIBLIOGRAPHY B e a l M.F. and M a r t i n J.B. (1985) T o p o g r a p h i c a l dopamine and s e r o t o n i n d i s t r i b u t i o n and t u r n o v e r i n r a t s t r i a t u m . B r a i n Res. 358; 10-B e n n e t t , B.A. and F r e e d , C.R. (1986) M o b i l i z a t i o n o f s t o r a g e p o o l dopamine and l a t e i p s i l a t e r a l a u g m e n t a t i o n o f s t r i a t a l dopamine s y n t h e s i s i n t h e t r a i n e d c i r c l i n g r a t . J . N e u r o c h e m i s t r y 47: 472-476. B l a c k b u r n , J.R., P h i l l i p s , A.G., J a k u b o v i c , A. and F i b i g e r , H.C. (1986) I n c r e a s e d dopamine m e t a b o l i s m i n t h e n u c l e u s accumbens and s t r i a t u m f o l l o w i n g c o n s u m p t i o n o f a n u t r i t i v e meal b u t n o t a p a l a t a b l e n o n - n u t r i t i v e s a c c h a r i n s o l u t i o n . P h a r m a c o l . Biochem. & Behav. 25: 1095 - 1100. B y e r , J.A. and D e x t e r , J.D. (1983) N e u r o l o g i c a l assessment. B r a i n Res. B u l l . 11: 143-147. C a r l i , M., Evenden, J . L . & R o b b i n s , T.W. (1985) D e p l e t i o n o f u n i l a t e r a l s t r i a t a l dopamine immpairs i n i t i a t i o n o f c o n t r a l a t e r a l a c t i o n s and n o t s e n s o r y i n a t t e n t i o n . N a t u r e 313: 679-681. C a r l s s o n , A., D a v i s , J.N., K e h r , W., L i n d g y i s t , M. and A t a c k , C.V. 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