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Repeated stressful experiences differently affect brain dopamine receptor subtypes
Life Sciences, Vol. 48, pp. 1263-1268 Printed in the U.S.A.
Pergamon Press
REPEATED STRESSFUL EXPERIENCES DIFFERENTLY AFFECT BRAIN DOPAMINE RECEPTOR SUBTYPES Stefano Pughsi-Allegra,
Ehane Kempf* Carmen Schleef* and Simona Cablb
I s t l t u t o dl P s l c o b l o l o g l a e P s l c o f a r m a c o l o g l a (CNR), v i a R e n o I, 1 - 0 0 1 9 8 R o m a , I t a l y a n d * C e n t r e d e N e u r o c h l m l e (CNRS/INSERM), 5 r u e B l a i s e P a s c a l , S t r a s b o u r g 6 7 0 8 4 , France
(Received in flnal form January 22, 1991)
The binding of trltlated splperone (D2 antagonist) and trltlated SCH 23390 (DI a n t a g o n i s t ) , i n v l v o , w a s i n v e s t i g a t e d in the caudatus p u t a m e n (CP) a n d n u c l e u s a c c u m b e n s s e p t l (NAS) of m i c e s u b m i t t e d t o t e n d a i l y r e s t r a i n t s t r e s s s e s s i o n s Mice s a c r i f i c e d 2 4 h r a f t e r t h e l a s t s t r e s s f u l e x p e r i e n c e p r e s e n t e d a 64% d e c r e a s e of D2 r e c e p t o r d e n s i t y ( B m a x ) b u t n o c h a n g e s m DI r e c e p t o r d e n s i t y i n t h e NAS I n t h e CP a m u c h s m a l l e r (I I%) r e d u c t i o n of D2 r e c e p t o r d e n s i t y w a s a c c o m p a n i e d b y a I0% i n c r e a s e of DI r e c e p t o r s T h e s e r e s u l t s s h o w t h a t t h e t w o t y p e s of d o p a m m e (DA) r e c e p t o r s a d a p t in d i f f e r e n t or e v e n o p p o s i t e w a y s to environmental p r e s s u r e , l e a d i n g to I m b a l a n c e b e t w e e n t h e m
T h e d o p a m m e r g l c s y s t e m is o n e of t h e k e y n e u r o t r a n s m l t t e r systems involved in the c e n t r a l r e s p o n s e t o s t r e s s T h e m e s o c o r t l c a l , t h e m e s o h m b l c a n d , to a l e s s e r e x t e n t , t h e m g r o s t r l a t a l DA s y s t e m s a r e all k n o w n to b e a c t i v a t e d b y m o s t f o r m s of s t r e s s ( I , 2, 3, 4, 5, 6, 7) M o r e o v e r , a l t e r a t i o n of b r a i n DA s y s t e m s h a s b e e n i n d i c a t e d as r e s p o n s i b l e f o r s e v e r a l b e h a v i o r a l e f f e c t s of c h r o n i c s t r e s s i n l a b o r a t o r y a n i m a l s (8, 9) A l t h o u g h e v i d e n c e e x l s t s t h a t c h r o m c s t r e s s is c a p a b l e of a l t e r i n g b r a i n DA r e c e p t o r s e n s l t l v l t y ( I 0 , I I , 12, 13, 14,), t h i s h y p o t h e s i s h a s n o t y e t b e e n e x p l o r e d b y b i n d i n g s t u d i e s DA r e c e p t o r s h a v e b e e n d l v l d e d i n t w o d i s t i n c t s u b t y p e s each possessing unique pharmacologlcal and blochemlcal properties (15) A number of r e s u l t s i n d i c a t e t h a t t h e s e n s i t i v i t y of t h e s e t w o t y p e s of r e c e p t o r m a y b e i n d e p e n d e n t l y r e g u l a t e d ( 1 6 , 17, 18, 19, 2 0 ) G i v e n t h e p o t e n t i a l c h m c a l s i g n i f i c a n c e o f s t r e s s i n d u c e d a l t e r a t i o n of b r a i n DA r e c e p t o r s e n s l t l v l t y , s t u d i e s of t h i s p h e n o m e n o n should provide Informatlons about DI/D2 receptor balance m stressed animals W e h a v e r e c e n t l y s h o w n t h a t C 5 7 B L / 6 m l c e s u b ) e c t e d t o t e n d a l l y s e s s l o n s of r e s t r a i n t s t r e s s e x h l b l t a l t e r e d b e h a v l o r a l r e s p o n s e s a n d c h a n g e s m b r a i n DA m e t a b o h s m when challenged wlth t h e DA r e c e p t o r a g o m s t a p o m o r p h m e , whlch suggest an a l t e r e d s e n s i t i v i t y of b r a i n DA r e c e p t o r s (9, I I, 12) T h e p r e s e n t s t u d y w a s d e s l g n e d to e v a l u a t e w e t h e r c h r o m c s t r e s s a f f e c t s t h e d e n s i t y of D1 a n d D2 DA r e c e p t o r s i n t h e c a u d a t u s p u t a m e n a n d n u c l e u s a c c u m b e n s s e p t l , t w o brain areas that appear to be dlfferently involved m the response to stress in the m o u s e (6, 7, 9, 2 I )
0024-3205/91 $3.00 +.00 Copyright (c) 1991 Pergamon Press plc
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Methods M a l e m i c e of t h e C 5 7 B L / 6 s t r a i n w e i g h i n g 2 3 - 2 5 g w e r e o b t a i n e d f r o m C h a r l e s R i v e r L a b s (Calco, Como, I t a l y ) T h e y w e r e m a i n t a i n e d w i t h f o o d a n d w a t e r a d llb i n a 1 2 / 1 2 h r h g h t - d a r k c y c l e ( l i g h t s o n f r o m 0 7 00 to 19 00 h r ) Mice w e r e s t r e s s e d b y r e s t r a i n i n g t h e m in a s n u g - f l t a p p a r a t u s (6, 11, 12) f o r t w o hours daily for ten consecutive days 24 hr after the last stressful experience, animals were sacrificed following drug administration S a c r l f l c e w a s c a r r i e d o u t In a r o o m a d j a c e n t t o t h e b r e e d i n g r o o m w h e r e all a n i m a l s h a d b e e n p r e v i o u s l y h a n d l e d to h a b i t u a t e t h e m to t h e s a c r i f i c e p r o c e d u r e (6, I I , 12) T h e e x p e r i m e n t s w e r e c a r r i e d o u t b e t w e e n 12 00 a n d 18 00 h r T r l t l a t e d S p l p e r o n e , 3H-SP (25 C i / m m o l ) a n d t r l t l a t e d S C H 2 3 3 9 0 , 3H-SCH ( 7 2 C i / m m o l ) w e r e o b t a i n e d f r o m A m e r s h a m Corp S p i p e r o n e , SCH 2 3 3 9 0 a n d K e t a n s e r m ( s o l u t i o n i n 0 9 NaCI, l a c t l c acid 2% w a s a d d e d i n s p l p e r o n e s o l u t i o n ) w e r e p u r c h a s e d f r o m RBI Drugs were rejected intravenously ( i v , t a l l v e t o ) , w i t h e x c e p t i o n of K e t a n s e r m which was given intraperltoneally (Ip) I n } e c t l o n v o l u m e s w e r e 0 2 ( I v ) or 0 25 m l (Ip) I n w v o 3H-SP a n d 3H-SCH i n t h e b r a i n w a s 2 a n d 1 h r e s p e c t i v e l y a f t e r I v I n } e c t l o n of 3H-SCH= 150 u C i / k g ) c o m b i n e d w i t h v a r i o u s s p l p e r o n e ( I 0 - I 0 0 0 n m o l / k g ) a n d SCH 2 3 3 9 0
d e t e r m i n e d f r o m r a d l o a c t i v R y c o n t e n t at a c o n s t a n t t r a c e r d o s e (3H=SP= 50 u C i / k g , d o s e s (6 m i c e f o r e a c h d o s e ) of u n l a b e l l e d (400- 1800 nmol/kg)
After decapitation the brain was rapidly removed and frozen by being placed in p r o x i m i t y ( 0 5 c m ) w i t h t h e s u r f a c e of l i q u i d n i t r o g e n c o n t a i n e d i n a t h e r m l c b o x T h e c e r e b e l l u m w a s c u t off a n d s t o r e d i n h q u l d n i t r o g e n u n t i l a n a l y z e d a n d t h e b r a i n w a s t h e n f i x e d v e r t l c a l I y o n t h e f r e e z e p l a t e of a f r e e z i n g m l c r o t o m e T h e f r e e z e p l a t e was used as a refrlgerat~ng table for punching, wlth the temperature being m a i n t a i n e d a t - 1 0 °C P u n c h e s w e r e o b t a l n e d f r o m b r a i n s h c e s ( f r o n t a l s e c t i o n s ) n o t h i c k e r t h a n 3 0 0 u m (6, 7) S t a i n l e s s s t e e l t u b e s of 1 3 or 2 0 m m i n s i d e d i a m e t e r w e r e u s e d T w o b r a i n a r e a s w e r e p u n c h e d N u c l e u s A c c u m b e n s S e p t l (NAS) a n d C a u d a t u s Putamen (CP) T h e c o o r d i n a t e s w e r e m e a s u r e d a c c o r d i n g to t h e a t l a s of S i d m a n , A n g e v i n e a n d P i e r c e ( 2 2 ) ( c o r o n a l s e c t i o n s ) , as f o l l o w s NAS= 4 slices f r o m s e c t i o n 141 to s e c t i o n 2 1 0 (I 3 m m t u b e ) , CP= 5 slices f r o m s e c t i o n 141 to s e c t i o n 2 3 0 ( 2 0 m m tube) The brain areas were stored in liquid nitrogen until analyzed B r a i n t i s s u e s a m p l e s w e r e d i s s o l v e d m I ml S o l u e n e ( P a c k a r d ) a n d c o u n t e d i n a h q u l d s c i n t i l l a t i o n c o u n t e r u s i n g D y n a g e l (JT B a k e r , I0 m l c o n t a i n i n g I% A c e t i c A c i d ) as scintillation liquid T h e m a x l m a l s a t u r a b l e b i n d i n g ( B m a x ) of t h e h g a n d s i n t h e t w o b r a i n r e g i o n s w a s d e r i v e d f r o m t h e r e l a t l o n s h l p b e t w e e n Its a c c u m u l a t i o n i n t h e r e g i o n , m e a s u r e d a t v a r i o u s d o s e s , a n d t h e c o r r e s p o n d i n g c e r e b e l l a r l e v e l s (23, 24, 2 5 ) R e g r e s s i o n l i n e s were calculated (from paired data for separate anlmals) from the levels m the brain r e g i o n s (Yi) a n d t h o s e i n t h e c e r e b e l l u m (XI), a t r e c e p t o r - s a t u r a t l n g doses The i n t e r c e p t w i t h t h e Y - a x l s e q u a l s B m a x T h e s t a n d a r d d e v l a t l o n ( S D ) of B m a x w a s c a l c u l a t e d f r o m t h e r e s i d u a l s ( n = 1 8 ) of t h e r e g r e s s l o n h n e a n d t h e m e a s u r e d d a t a b y a weighed procedure (24) The hgand levels in various brain regions were calculated f r o m r a d l o a c t i v ~ t y c o n c e n t r a t l o n a n d s p e c i f i c a c t l v l t y at t h e c o r r e s p o n d i n g d o s e (23, 24, 2 5 ) T h u s B m a x v a l u e s w e r e c a l c u l a t e d f r o m d a t a o b t a i n e d at d o s e s of 2 0 0 , 5 0 0 , a n d 8 0 0 n m o l / k g ( s p l p e r o n e ) , a n d 8 0 0 , 1 3 0 0 , a n d 1 8 0 0 n m o l / k g (SCH 2 3 3 9 0 ) Six a n i m a l s p e r d o s e w e r e u s e d f o r e a c h e x p e r i m e n t a l g r o u p (n= 4 C o n t r o l 3H-SP, S t r e s s e d 3H-SP, C o n t r o l 3H-SCH, S t r e s s e d 3H-SCH) In a further experiment a g r o u p of u n s t r e s s e d mice recelvmg t h r e e d o s e s of s p l p e r o n e ( n = 6 f o r e a c h d o s e ) c o m b i n e d w l t h a c o n s t a n t t r a c e r d o s e of 3 H - S P ( 5 0
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u C l / k g ) r e c e l v e d t w o m l e c t l o n s (5 m g / k g . , p e a c h ) of k e t a n s e r m 15 m m b e f o r e a n d 60 m , n a f t e r s p l p e r o n e p l u s 3H-SP, r e s p e c t l v e l y , a n d w a s c o m p a r e d w l t h a g r o u p of a n i m a l s s u b l e c t e d to the s a m e t r e a t m e n t b u t rece~vlng t w o m ] e c U o n s of sallne R e s u l t s a r e e x p r e s s e d in f m o l / m g w e t w e i g h t t , s s u e Data w e r e a n a l y z e d b y S t u d e n t ' s t -test (two-talled) P,e s u l t s I n VlVO B m a x v a l u e s of 3H-SP a n d 3H-SCH m t h e CP a n d NAS of c h r o n l c a l l y s t r e s s e d and control mlce are summarlzed in h g u r e I Chron,cally stressed mice are c h a r a c t e r l z e d b y a s h g h t b u t s l g n l f l c a n t r e d u c t l o n of B m a x v a l u e s of 3H-SP m t h e CP a n d b y a d r a m a t l c d e c r e a s e of t h e s e v a l u e s ,n t h e NAS B m a x v a l u e s f o r 3H-SCH w e r e s l g n l f l c a n t l y * * c r e a s e d m t h e CP a n d u n c h a n g e d m t h e NAS Ketanserm produced a elght percent f o u r t e e n p e r c e n t d e c r e a s e m NAS
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F l ~ u r e I. E f f e c t s of c h r o n i c s t r e s s o n D2 r e c e p t o r d e n s l t l e s (A) as c a l c u l a t e d f r o m In vlvo 3H-Splperone accumulatlon a n d DI r e c e p t o r densltles (B) as c a l c u l a t e d f r o m In v l v o 3H-SCH 2 3 3 9 0 a c c u m u l a t l o n in t h e s t r l a t u m (CP) a n d n u c l e u s a c c u m b e n s s e p t l (NAS) B m a x v a l u e s ( f m o l / m g +_ S D ) w e r e c a l c u l a t e d as d e s c r l b e d i n t h e M e t h o d s e c t l o n E a c h e x p e r l m e n t a l g r o u p ( n = 4 ) c o n s l s t e d of 18 m i c e *= p < 0 1 a n d **= p < 0 0 1 m c o m p a r l s o n w l t h controls (Student s l-test, two-talled)
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Dtscusslon I n t h e p r e s e n t s t u d y m w v o s p l p e r o n e a n d SCH 2 3 3 9 0 b i n d i n g w a s u s e d to e v a l u a t e t h e e f f e c t s of c h r o n i c s t r e s s o n D1 a n d D2 DA r e c e p t o r i n t w o b r a i n a r e a s of t h e m o u s e T h e m e t h o d c h o s e n w a s b e e n r e c e n t l y d e v e l o p e d (23, 24, 25), m a y a v o i d s o m e of t h e a r t i f a c t s a s s o c i a t e d w i t h r e c e p t o r s t u d i e s m w t r o (26, 27), a n d it is e x t r e m e l y u s e f u l w h e n v e r y s m a l l a m o u n t s of t i s s u e a r e to b e u s e d f o r a n a l y s i s , as m t h e c a s e of m i c e NAS M o r e o v e r , it h a s b e e n s h o w n t h a t B m a x v a l u e s of 3 H - S P o b t a i n e d b y t h i s m e t h o d m a y b e u s e d to e v a l u a t e D2 DA r e c e p t o r d e n s i t i e s i n s e v e r a l b r a i n a r e a s ( 2 5 ) 3 H - S P b i n d i n g w a s e v a l u a t e d 2 h r s a f t e r m j e c t l o n to o b t a i n r e s u l t s c o m p a r a b l e w i t h t h o s e r e p o r t e d b y p r e v i o u s s t u d i e s (23, 24, 2 5 ) By t h i s w a y , B m a x v a l u e s f o r 3 H - S P i n our experiments using mice were very similar to those obtained in rats (strlatum= 72 9 pmol/g, nucleus accumbens= 47 8 pmol/g) (25) However, since specific strlatal 3H-SP binding reaches a maximum only by 4 hrs after the mjectlon (28) the involvement of c h a n g e s i n r e g i o n a l b l o o d f l o w i n t h e r e d u c t i o n o f D2 b i n d i n g observed following chronic stress, although unlikely, cannot be completely ruled out B m a x v a l u e s f o r 3H-SCH h a v e n o t y e t b e e n e v a l u a t e d b y t h i s in v l v o m e t h o d H o w e v e r , s t u d i e s u s i n g d i f f e r e n t m e t h o d s h a v e s h o w n t h a t t h i s h g a n d b i n d s s p e c i f i c a l l y to DA D1 r e c e p t o r i n v i v Q (29, 3 0 ) T h e l e v e l of 3H-SCH r a d i o a c t i v i t y h a s b e e n s h o w n to r e a c h a p l a t e a u w i t h i n o n e h r a f t e r m j e c t l o n ( 2 9 ) T h e d i f f e r e n t k i n e t i c s of t h e DI a n d D2 a n t a g o n i s t s c o u l d r i s e p r o b l e m s in t h e i n t e r p r e t a t i o n of t h e e f f e c t s of c h r o n i c s t r e s s o n t h e b i n d i n g of t h e t w o h g a n d s H o w e v e r , it s h o u l d b e n o t e d t h a t t h e r a t i o of 3H-Sp/3H-SCH Bmax values obtained 2 h r s a f t e r t h e m } e c t l o n of t h e D1 l l g a n d a n d 4 h r s a f t e r t h e m } e c t l o n of t h e D2 h g a n d i n r a t s t r l a t a is 0 17 (29), a v a l u e v e r y c l o s e to t h e 0 2 c a l c u l a t e d o n t h e b a s i s of o u r d a t a T h e a i m of t h l s r e s e a r c h w a s to e v a l u a t e p o s s i b l e a l t e r a t i o n s i n b r a i n DA r e c e p t o r s densities induced by repeated stressful experiences The results obtained clearly i n d i c a t e t h a t r e p e a t e d s t r e s s f u l e x p e r i e n c e s a l t e r b r a i n DA r e c e p t o r d e n s i t i e s a n d t h a t t h e s e a l t e r a t l o n s d e p e n d o n t h e b r a i n a r e a a n d o n DA r e c e p t o r s u b t y p e S t r e s s e d m i c e e x h i b i t , In f a c t , a m o d e s t r e d u c t i o n of D2 r e c e p t o r density accompanied by a c o m p a r a b l e i n c r e a s e i n t h e d e n s i t y of t h e D1 r e c e p t o r s i n t h e CP By c o n t r a s t , d a t a o b t a i n e d m t h e NAS i n d i c a t e a d r a m a t i c d e c r e a s e of D2 r e c e p t o r d e n s i t y m t h e a b s e n c e of c h a n g e s m D1 r e c e p t o r d e n s i t y A n u m b e r of s t u d i e s h a v e s h o w n t h a t s e n s i t i v i t y of D1 a n d D2 DA r e c e p t o r s u b t y p e s m a y b e i n d e p e n d e n t l y modulated by chronic treatment w i t h c l a s s l c DA a g o m s t s a n d a n t a g o n i s t s (16, 17, 18, 19, 2 0 ) Moreover, studies conducted post-mortem on schizophrenic brains have shown o p p o s i t e a l t e r a t i o n s of D1 a n d D2 r e c e p t o r i n t h e s t r i a t u m ( 3 1 ) Our r e s u l t s i n d i c a t e t h a t t h e t w o s u b t y p e s of DA r e c e p t o r s m a y a d a p t in d i f f e r e n t or e v e n o p p o s i t e w a y s to environmental pressure, suggesting a possible adaptive r o l e of t h i s f u n c t l o n a l independence D i f f e r e n t a l t e r a t l o n of t h e B m a x of t h e t w o h g a n d s u s e d m t h l s s t u d y also r u l e s o u t t h e p o s s l b l h t y t h a t t h e s e c h a n g e s d e p e n d o n m o d l f l c a t l o n of 5 - H T 2 r e c e p t o r s I n f a c t , m b o t h a r e a s s t r e s s p r o d u c e d c h a n g e s m B m a x f o r 3 H - S P ( d e c r e a s e ) d i f f e r e n t or e v e n o p p o s l t e to t h o s e p r o d u c e d f o r 3H-SCH ( n o c h a n g e or i n c r e a s e ) S i n c e b o t h s p l p e r o n e a n d SCH 2 3 3 9 0 b r a d to 5 - H T 2 r e c e p t o r (29, 30, 32, 33 3 4 ) , I f t h e e f f e c t s o b s e r v e d m o u r s t u d y w e r e d e p e n d e n t of t h i s k i n d of r e c e p t o r o n e w o u l d e x p e c t p a r a l l e l c h a n g e s In t h e b i n d i n g of t h e t w o h g a n d s Moreover, animals m}ected with ketanserm showed a d e c r e a s e of 3 H - S P b i n d i n g w h i c h c a n n o t a c c o u n t f o r t h e s t r e s s - r e d u c e d changes observed F i n a l l y , it is w o r t h n o t i n g t h a t n o c h a n g e s m 5 - H T I , 5 - H T I a a n d 5 - H T 2 r e c e p t o r b i n d i n g h a v e b e e n r e p o r t e d i n r a t s f o l l o w i n g t e n d a y s of c h r o n i c f o o t s h o c k s t r e s s {35) Contrasting differences
results have been reported which indicate elther that inter-sub}ect m e n d o g e n o u s DA c o n c e n t r a t l o n s a f f e c t 3 H - S P s t r l a t a l b i n d i n g ( 3 6 ) , or
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t h a t i n v l v o b i n d i n g of 3H-SCH a n d 3 H - S P to s t r l a t u m is n o t a f f e c t e d b y i n c r e a s e d synaptlc concentrations of DA ( 2 9 ) However, a possible role of changed DA a v a i l a b i l i t y i n t h e e f f e c t s o b s e r v e d i n o u r s t u d y c a n b e r u l e d o u t s i n c e as p r e v i o u s l y s h o w n (12, 37), s t r e s s e d m i c e do n o t s h o w d i f f e r e n c e s i n DA a n d its m e t a b o h t e s i n CP a n d NAS 2 4 h r a f t e r t h e l a s t of t e n r e s t r a i n t e x p e r i e n c e s H o w e v e r , t h e p o s s i b i l i t y of s e l e c t l v e a l t e r a t i o n of 3H-SP binding in stressed mice by other endogenous s u b s t a n c e s ( 3 8 ) , a l t h o u g h u n l i k e l y , c a n n o t b e r u l e d o u t o n t h e b a s i s of t h e p r e s e n t data In previous studies we have demonstrated that chronically stressed C57BL/6 mice t e s t e d 2 4 h r s a f t e r t h e l a s t s t r e s s f u l e x p e r i e n c e e x h i b i t a l t e r a t i o n s of t h e b e h a v l o r a l and biochemical e f f e c t s of t h e DA r e c e p t o r agonlst apomorphlne suggesting hypersensitivity of m e s o h m b l c DA a u t o r e c e p t o r s a n d a p o s s i b l e h y p o s e n s l t l v l t y of p o s t s y n a p t l c DA r e c e p t o r s i n t h e NAS of s t r e s s e d m i c e (9, 11, 12) T h e b r a i n a r e a dissected in the present study contains both postsynaptlc DA r e c e p t o r s and autoreceptors located o n t h e a x o n s o f DA n e u r o n s pro)ectlng to the area C o n s e q u e n t l y , b o t h t y p e s of r e c e p t o r s c o u l d b e i n v o l v e d i n t h e o b s e r v e d e f f e c t s of chronic stress H o w e v e r , it h a s r e c e n t l y been shown that there exists a reserve for strlatal p r e s y n a p t l c DA r e c e p t o r s t h a t m a y b e a c t l v a t e d b y l o w d o s e s of DA a g o n l s t s w h e n all r e c e p t o r s a r e b l o c k e d b y i r r e v e r s i b l e DA r e c e p t o r a n t a g o n i s t EEDQ ( 3 9 ) It is p o s s i b l e t h a t a s i m i l a r r e s e r v e of a u t o r e c e p t o r s c o u l d b e a c t i v a t e d in t h e NAS of c h r o n i c a l l y s t r e s s e d m i c e M o r e o v e r , a l a r g e n u m b e r of DA r e c e p t o r s a r e l o c a t e d in t h e t e g m e n t a l a r e a m o d u l a t i n g p r e s y n a p t l c a l l y DA t r a n s m i s s i o n in t h e NAS T h e s e r e c e p t o r s c o u l d b e of t h e DI t y p e ( 1 5 ) or t h e r e c o u l d b e r e c e p t o r s t h a t a d a p t to c h r o n i c s t r e s s in a d i f f e r e n t w a y t h a n t h o s e l o c a t e d in t h e p r o j e c t i n g a r e a On t h e b a s i s of t h e s e r e s u l t s it m a y b e s u g g e s t e d t h a t t h e d e c r e a s e of D2 r e c e p t o r d e n s i t y o b s e r v e d i n t h e NAS of chronically stressed m i c e is r e l a t e d t o p o s t s y n a p t l c hyposensttlvlty shown by p r e v i o u s p h a r m a c o l o g i c a l s t u d i e s (9, 12) In conclusion, the present results strongly suggest that repeated stressful e x p e r i e n c e s i n d u c e i m b a l a n c e b e t w e e n DA r e c e p t o r s of t h e DI a n d D2 t y p e s i n t h e NAS a n d , less m a r k e d l y , in t h e s t r l a t u m of m i c e S i n c e t h e DA m e s o h m b l c s y s t e m p l a y s a n i m p o r t a n t r o l e In t h e e m o t i o n a l t u n i n g u n d e r l y i n g r e s p o n s l v l t y t o b o t h a v e r s i o n a n d p l e a s u r e (40, 41), t h e s t r e s s - l n d u c e d a l t e r a t i o n i n DA r e c e p t o r s r e p o r t e d h e r e m a y b e r e l a t e d t o t h e e x p r e s s i o n of b e h a v i o r a l s t r a t e g i e s of i n d i v i d u a l s f a c i n g e i t h e r p o s i t i v e or a v e r s l v e e x p e r i e n c e s Acknowledgements T h i s w o r k w a s s u p p o r t e d b y a g r a n t f r o m t h e I t a l i a n CNR a n d t h e F r e n c h INSERM (CNR/INSERM T w i n n i n g g r a n t n 7, 1 9 8 9 - 9 0 ) A p r e l i m i n a r y a c c o u n t of t h e s e f i n d i n g s w a s p r e s e n t e d a t t h e R e g i o n a l C o n g r e s s of the World Federation of S o c l e t l e s of B i o l o g i c a l P s y c h i a t r y , C a s a b l a n c a , M o r o c c o , February 1990
References I 2 3 4
F FADDA, A ARGIOLAS, M R MELIS, A H TISSARI, P L ONALI a n d P L GESSA, Life Scl 23 2 2 1 9 - 2 2 2 4 ( 1 9 7 8 ) D HERVE, J - P TASSIN, BARTHELEMY, G BLANC, S L A V I E L L E a n d J GLOWINSKY, Life Scl 25 1 6 5 9 - 1 6 6 4 ( 1 9 7 9 ) J P HERMAN, D GUILLONEAU, R DANTZER, B SCATTON, J SEMERDJION-ROUQIER, a n d M LE MOAL, Life Scl 3_0=2 2 0 7 - 2 2 1 4 ( 1 9 8 2 ) A J D U N N , S FILE, P h y s t o l Behav=3=]. 5 1 1 - 5 1 3 ( 1 9 8 3 )
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A IMPERATO, S PUGLISI-ALLEGRA, P CASOLINI, A ZOCCHI and L ANGELUCCI, Eur J Pharmacol 16~ 337=338 (1989) S CABIB, E KEMPF, C SCHLEEF, A OLIVERIO and S PUGLISI-ALLEGRA, Brain Res 441 153-160 (1988) S PUGLISI-ALLEGRA and S CABIB, Aggr Behav, 16 271-284 (1990) T E ROBINSON In P W K A L I V A S and C BARNES, Sensitization of the nervous system, CaldwellNJ pp 145-173 (1988) S PUGLISI-ALLEGRA, E K E M P F and S CABIB, Neuroscl Blobehav Rev 14 (4) 523528 (1990) S M ANTELMANandLA CHIODO, Blol Psichlat 16717-727 (1981) S CABIB, S PUGLISI-ALLEGRA and A OLIVERIO, Behav Neural Biol 44 239-248 (1985) S CABIB and S PUGLISI-ALLEGRA, Bram Res in press (1991) j P HERMAN, L STINUS and M LEMOAL, P s y c h o p h a r m a c o l o g y 8 4 4 3 1 - 4 3 5 (1984) R MUSCAT, A TOWELL and P WILLNER, P s y c h o p h a r m a c o l o g y 94 5 4 5 - 5 5 0 (I 988) D CLARK a n d F J WHITE, S y n a p s e 1 3 4 7 = 3 8 8 (1987) RE CHIPKIN, RD McQUADE and L C IORIO, Pharmacol Blochem Behav 28 4 7 7 - 4 8 2 (1987) AD LEVY, J J KIM, GD ELLISON, LIfeScl 4.3 1207-1213 (1988) P McGONIGLE, SJ BOYSON, S REUTER and PB MOLINOFF, S y n a p s e 3_74-82 (1989) P VEZINA and J STEWART, Braln Res 499 I 0 8 - 1 2 0 (1989) RE SEE, M ARAVAGIRI, G D ELLISON, LtfeScl 44 2 2 9 - 2 3 6 (1989) S CABIB, A OLIVERIOandS PUGLISI-ALLEGRA, LIfeScl 45 1 0 3 1 - 1 0 3 7 (1989) RL SIDMAN, JB ANGEVINE, and ET PIERCE, Atlas of the Mouse Brain and Spinal Cord, H a r v a r d Unlvers~ty Press, Cambridge (1970) J F VAN DER WERF, JB SEBENS, W VAALBURG AND J KORF, Eur J P h a r m a c o l 78 259-270 (1983) J F VAN DER WERF, F VAN HET SCHIP, JB SEBENS and J KORF, Eur J P h a r m a c o l , 102 387-399 (1984) J F VANDERWERF, JB S E B E N S a n d j KORF, LIfeScl 3=9= 155-160 (1986) SE LEEFand I CREESE Nature 306 586-589 (1983) NG BACOPOULOS Life SCl ~4 307-315 (1984) CA LESLIE, J P BENNETJr B r a l n R e s 407 2 5 3 - 2 6 2 (1987) CA LESLIE, J P BENNETJr B r a l n R e s 41~ 90-97 (1987) PH ANDERSEN and FC GRONVALD, LIfeScl 38 1507-1514 (1986) EJ HESS, SH BRACHA, JE KLEINMANANDI CREESE, L~eSc~ 40 1 4 8 7 - 1 4 9 7 (1987) JE LEYSEN, CGE NIEMEGEERS, JPTOLLENAERE, and P M LADURON, N a t u r e 2 7 2 163-166 (1978) I CREESE, SH SNYDER, Eur J P h a r m a c o l 29 2 0 1 - 2 0 2 (1978) J J FROST, AC SMITH, M J KUHAR, R F DANNALIS and HN WAGNER, Life Scl 40 987-995 (1987) K OHI, M MIKUNI, K TAKAHASHI, P h a r m a c o l B l o c h e m Behav 34 6 0 3 - 6 0 8 (1989) OT DE JESUS, GJC VAN MOFFAERT, R J DINERSTEIN and A M FRIEDMAN, Life Scl .39 341-349 (1986) S CABIB, E KEMPF, C SCHLEEF, A MELE and S PUGLISI-ALLEGRA, Physlol Behav 43 223-227 (1988) S J ENNA IN A LAJTHA ( E d ) H a n d b o o k of N e u r o c h e m e s t r y (2nd e d i t i o n ) v 6 Receptors in the Nervous S y s t e m pp 6 2 9 - 6 3 8 (1984) E MELLER, E HELMER-MATYJEK, K BOHMAKER, CH ADLER, A J FRIEDHOFF and M GOLDSTEIN, Eur J Pharmacol 123 3 1 1 - 3 1 4 (1986) RJ BENINGER, DC HOFFMA, EJ MAZURSKI, Neuroscl Blobehav Rev 13 ( I / 3 ) 113122 (1989) RN SWERDLOW, GF KOOB, Behav B r a i n S c i I0 197-245 (1987)
Pergamon Press
REPEATED STRESSFUL EXPERIENCES DIFFERENTLY AFFECT BRAIN DOPAMINE RECEPTOR SUBTYPES Stefano Pughsi-Allegra,
Ehane Kempf* Carmen Schleef* and Simona Cablb
I s t l t u t o dl P s l c o b l o l o g l a e P s l c o f a r m a c o l o g l a (CNR), v i a R e n o I, 1 - 0 0 1 9 8 R o m a , I t a l y a n d * C e n t r e d e N e u r o c h l m l e (CNRS/INSERM), 5 r u e B l a i s e P a s c a l , S t r a s b o u r g 6 7 0 8 4 , France
(Received in flnal form January 22, 1991)
The binding of trltlated splperone (D2 antagonist) and trltlated SCH 23390 (DI a n t a g o n i s t ) , i n v l v o , w a s i n v e s t i g a t e d in the caudatus p u t a m e n (CP) a n d n u c l e u s a c c u m b e n s s e p t l (NAS) of m i c e s u b m i t t e d t o t e n d a i l y r e s t r a i n t s t r e s s s e s s i o n s Mice s a c r i f i c e d 2 4 h r a f t e r t h e l a s t s t r e s s f u l e x p e r i e n c e p r e s e n t e d a 64% d e c r e a s e of D2 r e c e p t o r d e n s i t y ( B m a x ) b u t n o c h a n g e s m DI r e c e p t o r d e n s i t y i n t h e NAS I n t h e CP a m u c h s m a l l e r (I I%) r e d u c t i o n of D2 r e c e p t o r d e n s i t y w a s a c c o m p a n i e d b y a I0% i n c r e a s e of DI r e c e p t o r s T h e s e r e s u l t s s h o w t h a t t h e t w o t y p e s of d o p a m m e (DA) r e c e p t o r s a d a p t in d i f f e r e n t or e v e n o p p o s i t e w a y s to environmental p r e s s u r e , l e a d i n g to I m b a l a n c e b e t w e e n t h e m
T h e d o p a m m e r g l c s y s t e m is o n e of t h e k e y n e u r o t r a n s m l t t e r systems involved in the c e n t r a l r e s p o n s e t o s t r e s s T h e m e s o c o r t l c a l , t h e m e s o h m b l c a n d , to a l e s s e r e x t e n t , t h e m g r o s t r l a t a l DA s y s t e m s a r e all k n o w n to b e a c t i v a t e d b y m o s t f o r m s of s t r e s s ( I , 2, 3, 4, 5, 6, 7) M o r e o v e r , a l t e r a t i o n of b r a i n DA s y s t e m s h a s b e e n i n d i c a t e d as r e s p o n s i b l e f o r s e v e r a l b e h a v i o r a l e f f e c t s of c h r o n i c s t r e s s i n l a b o r a t o r y a n i m a l s (8, 9) A l t h o u g h e v i d e n c e e x l s t s t h a t c h r o m c s t r e s s is c a p a b l e of a l t e r i n g b r a i n DA r e c e p t o r s e n s l t l v l t y ( I 0 , I I , 12, 13, 14,), t h i s h y p o t h e s i s h a s n o t y e t b e e n e x p l o r e d b y b i n d i n g s t u d i e s DA r e c e p t o r s h a v e b e e n d l v l d e d i n t w o d i s t i n c t s u b t y p e s each possessing unique pharmacologlcal and blochemlcal properties (15) A number of r e s u l t s i n d i c a t e t h a t t h e s e n s i t i v i t y of t h e s e t w o t y p e s of r e c e p t o r m a y b e i n d e p e n d e n t l y r e g u l a t e d ( 1 6 , 17, 18, 19, 2 0 ) G i v e n t h e p o t e n t i a l c h m c a l s i g n i f i c a n c e o f s t r e s s i n d u c e d a l t e r a t i o n of b r a i n DA r e c e p t o r s e n s l t l v l t y , s t u d i e s of t h i s p h e n o m e n o n should provide Informatlons about DI/D2 receptor balance m stressed animals W e h a v e r e c e n t l y s h o w n t h a t C 5 7 B L / 6 m l c e s u b ) e c t e d t o t e n d a l l y s e s s l o n s of r e s t r a i n t s t r e s s e x h l b l t a l t e r e d b e h a v l o r a l r e s p o n s e s a n d c h a n g e s m b r a i n DA m e t a b o h s m when challenged wlth t h e DA r e c e p t o r a g o m s t a p o m o r p h m e , whlch suggest an a l t e r e d s e n s i t i v i t y of b r a i n DA r e c e p t o r s (9, I I, 12) T h e p r e s e n t s t u d y w a s d e s l g n e d to e v a l u a t e w e t h e r c h r o m c s t r e s s a f f e c t s t h e d e n s i t y of D1 a n d D2 DA r e c e p t o r s i n t h e c a u d a t u s p u t a m e n a n d n u c l e u s a c c u m b e n s s e p t l , t w o brain areas that appear to be dlfferently involved m the response to stress in the m o u s e (6, 7, 9, 2 I )
0024-3205/91 $3.00 +.00 Copyright (c) 1991 Pergamon Press plc
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Methods M a l e m i c e of t h e C 5 7 B L / 6 s t r a i n w e i g h i n g 2 3 - 2 5 g w e r e o b t a i n e d f r o m C h a r l e s R i v e r L a b s (Calco, Como, I t a l y ) T h e y w e r e m a i n t a i n e d w i t h f o o d a n d w a t e r a d llb i n a 1 2 / 1 2 h r h g h t - d a r k c y c l e ( l i g h t s o n f r o m 0 7 00 to 19 00 h r ) Mice w e r e s t r e s s e d b y r e s t r a i n i n g t h e m in a s n u g - f l t a p p a r a t u s (6, 11, 12) f o r t w o hours daily for ten consecutive days 24 hr after the last stressful experience, animals were sacrificed following drug administration S a c r l f l c e w a s c a r r i e d o u t In a r o o m a d j a c e n t t o t h e b r e e d i n g r o o m w h e r e all a n i m a l s h a d b e e n p r e v i o u s l y h a n d l e d to h a b i t u a t e t h e m to t h e s a c r i f i c e p r o c e d u r e (6, I I , 12) T h e e x p e r i m e n t s w e r e c a r r i e d o u t b e t w e e n 12 00 a n d 18 00 h r T r l t l a t e d S p l p e r o n e , 3H-SP (25 C i / m m o l ) a n d t r l t l a t e d S C H 2 3 3 9 0 , 3H-SCH ( 7 2 C i / m m o l ) w e r e o b t a i n e d f r o m A m e r s h a m Corp S p i p e r o n e , SCH 2 3 3 9 0 a n d K e t a n s e r m ( s o l u t i o n i n 0 9 NaCI, l a c t l c acid 2% w a s a d d e d i n s p l p e r o n e s o l u t i o n ) w e r e p u r c h a s e d f r o m RBI Drugs were rejected intravenously ( i v , t a l l v e t o ) , w i t h e x c e p t i o n of K e t a n s e r m which was given intraperltoneally (Ip) I n } e c t l o n v o l u m e s w e r e 0 2 ( I v ) or 0 25 m l (Ip) I n w v o 3H-SP a n d 3H-SCH i n t h e b r a i n w a s 2 a n d 1 h r e s p e c t i v e l y a f t e r I v I n } e c t l o n of 3H-SCH= 150 u C i / k g ) c o m b i n e d w i t h v a r i o u s s p l p e r o n e ( I 0 - I 0 0 0 n m o l / k g ) a n d SCH 2 3 3 9 0
d e t e r m i n e d f r o m r a d l o a c t i v R y c o n t e n t at a c o n s t a n t t r a c e r d o s e (3H=SP= 50 u C i / k g , d o s e s (6 m i c e f o r e a c h d o s e ) of u n l a b e l l e d (400- 1800 nmol/kg)
After decapitation the brain was rapidly removed and frozen by being placed in p r o x i m i t y ( 0 5 c m ) w i t h t h e s u r f a c e of l i q u i d n i t r o g e n c o n t a i n e d i n a t h e r m l c b o x T h e c e r e b e l l u m w a s c u t off a n d s t o r e d i n h q u l d n i t r o g e n u n t i l a n a l y z e d a n d t h e b r a i n w a s t h e n f i x e d v e r t l c a l I y o n t h e f r e e z e p l a t e of a f r e e z i n g m l c r o t o m e T h e f r e e z e p l a t e was used as a refrlgerat~ng table for punching, wlth the temperature being m a i n t a i n e d a t - 1 0 °C P u n c h e s w e r e o b t a l n e d f r o m b r a i n s h c e s ( f r o n t a l s e c t i o n s ) n o t h i c k e r t h a n 3 0 0 u m (6, 7) S t a i n l e s s s t e e l t u b e s of 1 3 or 2 0 m m i n s i d e d i a m e t e r w e r e u s e d T w o b r a i n a r e a s w e r e p u n c h e d N u c l e u s A c c u m b e n s S e p t l (NAS) a n d C a u d a t u s Putamen (CP) T h e c o o r d i n a t e s w e r e m e a s u r e d a c c o r d i n g to t h e a t l a s of S i d m a n , A n g e v i n e a n d P i e r c e ( 2 2 ) ( c o r o n a l s e c t i o n s ) , as f o l l o w s NAS= 4 slices f r o m s e c t i o n 141 to s e c t i o n 2 1 0 (I 3 m m t u b e ) , CP= 5 slices f r o m s e c t i o n 141 to s e c t i o n 2 3 0 ( 2 0 m m tube) The brain areas were stored in liquid nitrogen until analyzed B r a i n t i s s u e s a m p l e s w e r e d i s s o l v e d m I ml S o l u e n e ( P a c k a r d ) a n d c o u n t e d i n a h q u l d s c i n t i l l a t i o n c o u n t e r u s i n g D y n a g e l (JT B a k e r , I0 m l c o n t a i n i n g I% A c e t i c A c i d ) as scintillation liquid T h e m a x l m a l s a t u r a b l e b i n d i n g ( B m a x ) of t h e h g a n d s i n t h e t w o b r a i n r e g i o n s w a s d e r i v e d f r o m t h e r e l a t l o n s h l p b e t w e e n Its a c c u m u l a t i o n i n t h e r e g i o n , m e a s u r e d a t v a r i o u s d o s e s , a n d t h e c o r r e s p o n d i n g c e r e b e l l a r l e v e l s (23, 24, 2 5 ) R e g r e s s i o n l i n e s were calculated (from paired data for separate anlmals) from the levels m the brain r e g i o n s (Yi) a n d t h o s e i n t h e c e r e b e l l u m (XI), a t r e c e p t o r - s a t u r a t l n g doses The i n t e r c e p t w i t h t h e Y - a x l s e q u a l s B m a x T h e s t a n d a r d d e v l a t l o n ( S D ) of B m a x w a s c a l c u l a t e d f r o m t h e r e s i d u a l s ( n = 1 8 ) of t h e r e g r e s s l o n h n e a n d t h e m e a s u r e d d a t a b y a weighed procedure (24) The hgand levels in various brain regions were calculated f r o m r a d l o a c t i v ~ t y c o n c e n t r a t l o n a n d s p e c i f i c a c t l v l t y at t h e c o r r e s p o n d i n g d o s e (23, 24, 2 5 ) T h u s B m a x v a l u e s w e r e c a l c u l a t e d f r o m d a t a o b t a i n e d at d o s e s of 2 0 0 , 5 0 0 , a n d 8 0 0 n m o l / k g ( s p l p e r o n e ) , a n d 8 0 0 , 1 3 0 0 , a n d 1 8 0 0 n m o l / k g (SCH 2 3 3 9 0 ) Six a n i m a l s p e r d o s e w e r e u s e d f o r e a c h e x p e r i m e n t a l g r o u p (n= 4 C o n t r o l 3H-SP, S t r e s s e d 3H-SP, C o n t r o l 3H-SCH, S t r e s s e d 3H-SCH) In a further experiment a g r o u p of u n s t r e s s e d mice recelvmg t h r e e d o s e s of s p l p e r o n e ( n = 6 f o r e a c h d o s e ) c o m b i n e d w l t h a c o n s t a n t t r a c e r d o s e of 3 H - S P ( 5 0
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u C l / k g ) r e c e l v e d t w o m l e c t l o n s (5 m g / k g . , p e a c h ) of k e t a n s e r m 15 m m b e f o r e a n d 60 m , n a f t e r s p l p e r o n e p l u s 3H-SP, r e s p e c t l v e l y , a n d w a s c o m p a r e d w l t h a g r o u p of a n i m a l s s u b l e c t e d to the s a m e t r e a t m e n t b u t rece~vlng t w o m ] e c U o n s of sallne R e s u l t s a r e e x p r e s s e d in f m o l / m g w e t w e i g h t t , s s u e Data w e r e a n a l y z e d b y S t u d e n t ' s t -test (two-talled) P,e s u l t s I n VlVO B m a x v a l u e s of 3H-SP a n d 3H-SCH m t h e CP a n d NAS of c h r o n l c a l l y s t r e s s e d and control mlce are summarlzed in h g u r e I Chron,cally stressed mice are c h a r a c t e r l z e d b y a s h g h t b u t s l g n l f l c a n t r e d u c t l o n of B m a x v a l u e s of 3H-SP m t h e CP a n d b y a d r a m a t l c d e c r e a s e of t h e s e v a l u e s ,n t h e NAS B m a x v a l u e s f o r 3H-SCH w e r e s l g n l f l c a n t l y * * c r e a s e d m t h e CP a n d u n c h a n g e d m t h e NAS Ketanserm produced a elght percent f o u r t e e n p e r c e n t d e c r e a s e m NAS
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F l ~ u r e I. E f f e c t s of c h r o n i c s t r e s s o n D2 r e c e p t o r d e n s l t l e s (A) as c a l c u l a t e d f r o m In vlvo 3H-Splperone accumulatlon a n d DI r e c e p t o r densltles (B) as c a l c u l a t e d f r o m In v l v o 3H-SCH 2 3 3 9 0 a c c u m u l a t l o n in t h e s t r l a t u m (CP) a n d n u c l e u s a c c u m b e n s s e p t l (NAS) B m a x v a l u e s ( f m o l / m g +_ S D ) w e r e c a l c u l a t e d as d e s c r l b e d i n t h e M e t h o d s e c t l o n E a c h e x p e r l m e n t a l g r o u p ( n = 4 ) c o n s l s t e d of 18 m i c e *= p < 0 1 a n d **= p < 0 0 1 m c o m p a r l s o n w l t h controls (Student s l-test, two-talled)
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Dtscusslon I n t h e p r e s e n t s t u d y m w v o s p l p e r o n e a n d SCH 2 3 3 9 0 b i n d i n g w a s u s e d to e v a l u a t e t h e e f f e c t s of c h r o n i c s t r e s s o n D1 a n d D2 DA r e c e p t o r i n t w o b r a i n a r e a s of t h e m o u s e T h e m e t h o d c h o s e n w a s b e e n r e c e n t l y d e v e l o p e d (23, 24, 25), m a y a v o i d s o m e of t h e a r t i f a c t s a s s o c i a t e d w i t h r e c e p t o r s t u d i e s m w t r o (26, 27), a n d it is e x t r e m e l y u s e f u l w h e n v e r y s m a l l a m o u n t s of t i s s u e a r e to b e u s e d f o r a n a l y s i s , as m t h e c a s e of m i c e NAS M o r e o v e r , it h a s b e e n s h o w n t h a t B m a x v a l u e s of 3 H - S P o b t a i n e d b y t h i s m e t h o d m a y b e u s e d to e v a l u a t e D2 DA r e c e p t o r d e n s i t i e s i n s e v e r a l b r a i n a r e a s ( 2 5 ) 3 H - S P b i n d i n g w a s e v a l u a t e d 2 h r s a f t e r m j e c t l o n to o b t a i n r e s u l t s c o m p a r a b l e w i t h t h o s e r e p o r t e d b y p r e v i o u s s t u d i e s (23, 24, 2 5 ) By t h i s w a y , B m a x v a l u e s f o r 3 H - S P i n our experiments using mice were very similar to those obtained in rats (strlatum= 72 9 pmol/g, nucleus accumbens= 47 8 pmol/g) (25) However, since specific strlatal 3H-SP binding reaches a maximum only by 4 hrs after the mjectlon (28) the involvement of c h a n g e s i n r e g i o n a l b l o o d f l o w i n t h e r e d u c t i o n o f D2 b i n d i n g observed following chronic stress, although unlikely, cannot be completely ruled out B m a x v a l u e s f o r 3H-SCH h a v e n o t y e t b e e n e v a l u a t e d b y t h i s in v l v o m e t h o d H o w e v e r , s t u d i e s u s i n g d i f f e r e n t m e t h o d s h a v e s h o w n t h a t t h i s h g a n d b i n d s s p e c i f i c a l l y to DA D1 r e c e p t o r i n v i v Q (29, 3 0 ) T h e l e v e l of 3H-SCH r a d i o a c t i v i t y h a s b e e n s h o w n to r e a c h a p l a t e a u w i t h i n o n e h r a f t e r m j e c t l o n ( 2 9 ) T h e d i f f e r e n t k i n e t i c s of t h e DI a n d D2 a n t a g o n i s t s c o u l d r i s e p r o b l e m s in t h e i n t e r p r e t a t i o n of t h e e f f e c t s of c h r o n i c s t r e s s o n t h e b i n d i n g of t h e t w o h g a n d s H o w e v e r , it s h o u l d b e n o t e d t h a t t h e r a t i o of 3H-Sp/3H-SCH Bmax values obtained 2 h r s a f t e r t h e m } e c t l o n of t h e D1 l l g a n d a n d 4 h r s a f t e r t h e m } e c t l o n of t h e D2 h g a n d i n r a t s t r l a t a is 0 17 (29), a v a l u e v e r y c l o s e to t h e 0 2 c a l c u l a t e d o n t h e b a s i s of o u r d a t a T h e a i m of t h l s r e s e a r c h w a s to e v a l u a t e p o s s i b l e a l t e r a t i o n s i n b r a i n DA r e c e p t o r s densities induced by repeated stressful experiences The results obtained clearly i n d i c a t e t h a t r e p e a t e d s t r e s s f u l e x p e r i e n c e s a l t e r b r a i n DA r e c e p t o r d e n s i t i e s a n d t h a t t h e s e a l t e r a t l o n s d e p e n d o n t h e b r a i n a r e a a n d o n DA r e c e p t o r s u b t y p e S t r e s s e d m i c e e x h i b i t , In f a c t , a m o d e s t r e d u c t i o n of D2 r e c e p t o r density accompanied by a c o m p a r a b l e i n c r e a s e i n t h e d e n s i t y of t h e D1 r e c e p t o r s i n t h e CP By c o n t r a s t , d a t a o b t a i n e d m t h e NAS i n d i c a t e a d r a m a t i c d e c r e a s e of D2 r e c e p t o r d e n s i t y m t h e a b s e n c e of c h a n g e s m D1 r e c e p t o r d e n s i t y A n u m b e r of s t u d i e s h a v e s h o w n t h a t s e n s i t i v i t y of D1 a n d D2 DA r e c e p t o r s u b t y p e s m a y b e i n d e p e n d e n t l y modulated by chronic treatment w i t h c l a s s l c DA a g o m s t s a n d a n t a g o n i s t s (16, 17, 18, 19, 2 0 ) Moreover, studies conducted post-mortem on schizophrenic brains have shown o p p o s i t e a l t e r a t i o n s of D1 a n d D2 r e c e p t o r i n t h e s t r i a t u m ( 3 1 ) Our r e s u l t s i n d i c a t e t h a t t h e t w o s u b t y p e s of DA r e c e p t o r s m a y a d a p t in d i f f e r e n t or e v e n o p p o s i t e w a y s to environmental pressure, suggesting a possible adaptive r o l e of t h i s f u n c t l o n a l independence D i f f e r e n t a l t e r a t l o n of t h e B m a x of t h e t w o h g a n d s u s e d m t h l s s t u d y also r u l e s o u t t h e p o s s l b l h t y t h a t t h e s e c h a n g e s d e p e n d o n m o d l f l c a t l o n of 5 - H T 2 r e c e p t o r s I n f a c t , m b o t h a r e a s s t r e s s p r o d u c e d c h a n g e s m B m a x f o r 3 H - S P ( d e c r e a s e ) d i f f e r e n t or e v e n o p p o s l t e to t h o s e p r o d u c e d f o r 3H-SCH ( n o c h a n g e or i n c r e a s e ) S i n c e b o t h s p l p e r o n e a n d SCH 2 3 3 9 0 b r a d to 5 - H T 2 r e c e p t o r (29, 30, 32, 33 3 4 ) , I f t h e e f f e c t s o b s e r v e d m o u r s t u d y w e r e d e p e n d e n t of t h i s k i n d of r e c e p t o r o n e w o u l d e x p e c t p a r a l l e l c h a n g e s In t h e b i n d i n g of t h e t w o h g a n d s Moreover, animals m}ected with ketanserm showed a d e c r e a s e of 3 H - S P b i n d i n g w h i c h c a n n o t a c c o u n t f o r t h e s t r e s s - r e d u c e d changes observed F i n a l l y , it is w o r t h n o t i n g t h a t n o c h a n g e s m 5 - H T I , 5 - H T I a a n d 5 - H T 2 r e c e p t o r b i n d i n g h a v e b e e n r e p o r t e d i n r a t s f o l l o w i n g t e n d a y s of c h r o n i c f o o t s h o c k s t r e s s {35) Contrasting differences
results have been reported which indicate elther that inter-sub}ect m e n d o g e n o u s DA c o n c e n t r a t l o n s a f f e c t 3 H - S P s t r l a t a l b i n d i n g ( 3 6 ) , or
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t h a t i n v l v o b i n d i n g of 3H-SCH a n d 3 H - S P to s t r l a t u m is n o t a f f e c t e d b y i n c r e a s e d synaptlc concentrations of DA ( 2 9 ) However, a possible role of changed DA a v a i l a b i l i t y i n t h e e f f e c t s o b s e r v e d i n o u r s t u d y c a n b e r u l e d o u t s i n c e as p r e v i o u s l y s h o w n (12, 37), s t r e s s e d m i c e do n o t s h o w d i f f e r e n c e s i n DA a n d its m e t a b o h t e s i n CP a n d NAS 2 4 h r a f t e r t h e l a s t of t e n r e s t r a i n t e x p e r i e n c e s H o w e v e r , t h e p o s s i b i l i t y of s e l e c t l v e a l t e r a t i o n of 3H-SP binding in stressed mice by other endogenous s u b s t a n c e s ( 3 8 ) , a l t h o u g h u n l i k e l y , c a n n o t b e r u l e d o u t o n t h e b a s i s of t h e p r e s e n t data In previous studies we have demonstrated that chronically stressed C57BL/6 mice t e s t e d 2 4 h r s a f t e r t h e l a s t s t r e s s f u l e x p e r i e n c e e x h i b i t a l t e r a t i o n s of t h e b e h a v l o r a l and biochemical e f f e c t s of t h e DA r e c e p t o r agonlst apomorphlne suggesting hypersensitivity of m e s o h m b l c DA a u t o r e c e p t o r s a n d a p o s s i b l e h y p o s e n s l t l v l t y of p o s t s y n a p t l c DA r e c e p t o r s i n t h e NAS of s t r e s s e d m i c e (9, 11, 12) T h e b r a i n a r e a dissected in the present study contains both postsynaptlc DA r e c e p t o r s and autoreceptors located o n t h e a x o n s o f DA n e u r o n s pro)ectlng to the area C o n s e q u e n t l y , b o t h t y p e s of r e c e p t o r s c o u l d b e i n v o l v e d i n t h e o b s e r v e d e f f e c t s of chronic stress H o w e v e r , it h a s r e c e n t l y been shown that there exists a reserve for strlatal p r e s y n a p t l c DA r e c e p t o r s t h a t m a y b e a c t l v a t e d b y l o w d o s e s of DA a g o n l s t s w h e n all r e c e p t o r s a r e b l o c k e d b y i r r e v e r s i b l e DA r e c e p t o r a n t a g o n i s t EEDQ ( 3 9 ) It is p o s s i b l e t h a t a s i m i l a r r e s e r v e of a u t o r e c e p t o r s c o u l d b e a c t i v a t e d in t h e NAS of c h r o n i c a l l y s t r e s s e d m i c e M o r e o v e r , a l a r g e n u m b e r of DA r e c e p t o r s a r e l o c a t e d in t h e t e g m e n t a l a r e a m o d u l a t i n g p r e s y n a p t l c a l l y DA t r a n s m i s s i o n in t h e NAS T h e s e r e c e p t o r s c o u l d b e of t h e DI t y p e ( 1 5 ) or t h e r e c o u l d b e r e c e p t o r s t h a t a d a p t to c h r o n i c s t r e s s in a d i f f e r e n t w a y t h a n t h o s e l o c a t e d in t h e p r o j e c t i n g a r e a On t h e b a s i s of t h e s e r e s u l t s it m a y b e s u g g e s t e d t h a t t h e d e c r e a s e of D2 r e c e p t o r d e n s i t y o b s e r v e d i n t h e NAS of chronically stressed m i c e is r e l a t e d t o p o s t s y n a p t l c hyposensttlvlty shown by p r e v i o u s p h a r m a c o l o g i c a l s t u d i e s (9, 12) In conclusion, the present results strongly suggest that repeated stressful e x p e r i e n c e s i n d u c e i m b a l a n c e b e t w e e n DA r e c e p t o r s of t h e DI a n d D2 t y p e s i n t h e NAS a n d , less m a r k e d l y , in t h e s t r l a t u m of m i c e S i n c e t h e DA m e s o h m b l c s y s t e m p l a y s a n i m p o r t a n t r o l e In t h e e m o t i o n a l t u n i n g u n d e r l y i n g r e s p o n s l v l t y t o b o t h a v e r s i o n a n d p l e a s u r e (40, 41), t h e s t r e s s - l n d u c e d a l t e r a t i o n i n DA r e c e p t o r s r e p o r t e d h e r e m a y b e r e l a t e d t o t h e e x p r e s s i o n of b e h a v i o r a l s t r a t e g i e s of i n d i v i d u a l s f a c i n g e i t h e r p o s i t i v e or a v e r s l v e e x p e r i e n c e s Acknowledgements T h i s w o r k w a s s u p p o r t e d b y a g r a n t f r o m t h e I t a l i a n CNR a n d t h e F r e n c h INSERM (CNR/INSERM T w i n n i n g g r a n t n 7, 1 9 8 9 - 9 0 ) A p r e l i m i n a r y a c c o u n t of t h e s e f i n d i n g s w a s p r e s e n t e d a t t h e R e g i o n a l C o n g r e s s of the World Federation of S o c l e t l e s of B i o l o g i c a l P s y c h i a t r y , C a s a b l a n c a , M o r o c c o , February 1990
References I 2 3 4
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Chronic Stress on Dopamlne Receptors
Vol. 48, No. 13, 1991
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