Life Sciences, Vol. 50, pp. 1519-1528 Printed in the USA

ANTIPUNISHMENT

Pergamon Press

EFFECTS OF ACUTE AND REPEATED A D M I N I S T R A T I O N PHENCYCLIDINE AND NPC 12626 IN RATS

Jenny L. Wiley I, Joseph H. Porter I, Amelia and Robert L. Balster 2

OF

D. Compton I,

Departments of Ipsychology and 2Pharmacology and Toxicology, V i r g i n i a Commonwealth University, Richmond, VA 23284, USA (Received in final form March 4, 1992)

Summary The effects of phencyclidine (PCP) and NPC 12626 on punished responding were examined using a modified G e l l e r - S e i f t e r procedure in rats. Both drugs are known to antagonize N-methyl-D-aspartate (NMDA) receptor m e d i a t e d neurotransmission, albeit at different sites on the NMDA receptor complex. Rats were trained to lever press for food reinforcement under a multiple schedule, with responding in one component reinforced under a fixed-interval 60-sec schedule, while each response in the other component resulted in both food and brief electric shock. Both PCP and NPC 12626 produced selective increases in punished responding, although the effects were not as large as those produced by chlordiazepoxide. Repeated daily a d m i n i s t r a t i o n of each of these drugs for 6 days resulted in increases in punished responding during different portions of the treatment. A 5 m g / k g dose of chlordiazepoxide produced increases over the last 2 days of administration. PCP (2 mg/kg) produced an increase only during the second session, whereas NPC 12626 (30 mg/kg) produced increases for all but the first and fifth days of the 6-day regimen. Both competitive and noncompetitive NMDA antagonists can have antipunishment effects in this model. Antagonists of excitatory amino acid neurotransmission mediated by N - m e t h y l - D - a s p a r t a t e (NMDA) receptors are being evaluated for a number of therapeutic indications. Among these are n e u r o p r o t e c t i o n following ischemic or traumatic brain injury and treatment of n e u r o d e g e n e r a t i v e diseases (i). NMDA antagonists also have a n t i c o n v u l s a n t effects (2) and share a number of other p h a r m a c o l o g i c a l properties with classical CNS depressant drugs such as the b e n z o d i a z e p i n e s and barbiturates (3,4,5). This overlap in the p h a r m a c o l o g y of NMDA antagonists and depressants has led to the suggestion that they may have utility for the treatment of anxiety disorders (6,7). Correspondence: Dr. Robert L. Balster, Dept. of Pharmacology/ Toxicology, Medical College of Virginia, Virginia Commonwealth University, Richmond, VA 23298-0613 FAX (804) 371-7519. 0024-3205/92 $5.00 + .00 Copyright o 1992 Pergamon Press Ltd All rights reserved.

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The m o s t w i d e l y studied NMDA receptor is p r e s e n t l y considered to be part of a cation channel a s s o c i a t e d r e c e p t o r complex, in w h i c h a g o n i s t b i n d i n g to the N M D A site opens a channel gating the influx of Ca ++ and Na ÷, r e s u l t i n g in c e l l u l a r e x c i t a t i o n (8,9). T h e r e are at least two d i f f e r e n t sites at which a n t a g o n i s t s might b l o c k a c t i v a t i o n of this complex. P h e n c y c l i d i n e (PCP)-like drugs have been shown to block the channel and act as n o n c o m p e t i t i v e NMDA a n t a g o n i s t s (i0). R e c e p t o r a c t i v a t i o n can also be b l o c k e d by c o m p e t i t i v e a n t a g o n i s t s acting at the NMDA site itself (ii). It is of p a r t i c u l a r interest to compare the b e h a v i o r a l effects of these two classes of NMDA a n t a g o n i s t s (for review, see 12). The p o t e n t i a l a n t i a n x i e t y effects of NMDA a n t a g o n i s t s have only been e v a l u a t e d to a limited extent using animal models. Drugs acting at the PCP site have been studied the most comprehensively. PCP, or its analog ketamine, have been shown in a number of animal m o d e l s to increase rates of s c h e d u l e - c o n t r o l l e d b e h a v i o r suppressed by punishment. The effects in pigeons are quite robust (13,14,15). In rats, the results have been less consistent. Sanger and Jackson (16) did not find evidence for increased rates of punished responding with PCP or the PCP-receptor agonist (+)-Nallylnormetazocine. On the other hand, the potent and selective P C P - r e c e p t o r agonist d i z o c i l p i n e did increase p u n i s h e d responding, but only at a dose that also d e c r e a s e d rates of u n p u n i s h e d responding. The m a g n i t u d e of the effect of d i z o c i l p i n e was less than o n e - t h i r d that p r o d u c e d by c h l o r d i a z e p o x i d e (CDP). We (17) studied a number of n o n c o m p e t i t i v e NMDA a n t a g o n i s t s acting at the PCP site for their effects on p u n i s h e d r e s p o n d i n g in rats using a p r o c e d u r e very similar to that of Geller and Seifter (18). PCP, (+)-N-allylnormetazocine, etoxadrol, and (-)-~-cyclazocine all p r o d u c e d selective increases in rates of p u n i s h e d responding, in this case, of a m a g n i t u d e c o m p a r a b l e to those p r o d u c e d by CDP. The p u r p o s e of the present study was to extend this w o r k by examining the effects of repeated a d m i n i s t r a t i o n of PCP and to compare its effects to those of a c o m p e t i t i v e NMDA a n t a g o n i s t 2 - a m i n o - 4 , 5 - ( l , 2 c y c l o h e x y l ) - 7 - p h o s p h o n o h e p t a n o i c acid (NPC 12626). The results should be helpful in d e t e r m i n i n g the u s e f u l n e s s of the standard G e l l e r - S e i f t e r p r o c e d u r e for e v a l u a t i n g this class of potential a n t i a n x i e t y agents. The c o m p e t i t i v e NMDA a n t a g o n i s t l - a m i n o - 7 - p h o s p h o n o h e p t a n o i c acid (APH) has been shown in two studies to p r o d u c e increases in rates of p u n i s h e d r e s p o n d i n g in rats, although it was much less e f f e c t i v e than d i a z e p a m (19,20). A n o t h e r c o m p e t i t i v e antagonist, cis-4-phosphonomethyl-2-piperidine-carboxylic acid (CGS 19755), also i n c r e a s e d p u n i s h e d responding, and the m a g n i t u d e of the effects after i.p. a d m i n i s t r a t i o n were similar in m a g n i t u d e to those p r o d u c e d by d i a z e p a m (4). NPC 12626 has been shown to act competitively at NMDA receptors in vitro and to have NMDA a n t a g o n i s t effects in vivo (21,22). A l t h o u g h it fails to increase rates of p u n i s h e d r e s p o n d i n g in squirrel monkeys, n e i t h e r does PCP in this model (23). Thus, it was of interest to compare the effects of PCP and NPC 12626 under c o n d i t i o n s w h e r e PCP has been shown to have a n t i p u n i s h m e n t effects (17). A p r e l i m i n a r y report of these results was made elsewhere (24). Methods Subjects.

Fourteen male S p r a g u e - D a w l e y

rats

(260-320g)

obtained

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from D o m i n i o n Breeders (Dublin, VA) were h o u s e d i n d i v i d u a l l y in an animal colony room m a i n t a i n e d at 22°C with a 6:00 a.m. light/ 6:00 p.m. dark cycle. The rats were m a i n t a i n e d at 80% of their freefeeding w e i g h t s by a d j u s t i n g their daily ration of food. W a t e r was a v a i l a b l e a_ddlibitum in the home cages t h r o u g h o u t the study. These animals had p r i o r training and testing with c h l o r d i a z e p o x i d e and other drugs on the schedule d e s c r i b e d in the p r o c e d u r e section. The animals were 13 months old at the b e g i n n i n g of the present study. Apparatus. Four standard operant chambers (Model SEC-002, BRS/LVE, Laurel, MD) were housed in s o u n d - a t t e n u a t i n g cubicles. A lever was m o u n t e d in these chambers on the left side of the right wall, 5 cm above the floor. A pellet d i s p e n s e r (PDC/PPD series, BRS/LVE) d e l i v e r e d 45-mg BIO SERV (Frenchtown, NJ) food p e l l e t s to a food cup located in the center of the right wall, 1.6 cm above the grid floor. Fan motors and white noise p r o v i d e d m a s k i n g noise for each chamber. A 7-w h o u s e l i g h t was located 24 cm above the floor in the center of the right wall. Direct constant current shock was p r o v i d e d by a shock source (Model 26170, Stolting Co., Chicago, IL) and p a s s e d t h r o u g h a shock scrambler (Model 26171, Stolting Co.) b e f o r e being sent to the grid floor of the operant chamber. Solidstate p r o g r a m m i n g e q u i p m e n t which c o n t r o l l e d the experimental c o n t i n g e n c i e s and recorded lever presses was located in an adjacent room. Procedure. Training procedures similar to those p r e v i o u s l y d e s c r i b e d (17) were used. Lever presses were r e i n f o r c e d according to a m u l t i p l e fixed interval (FI) 60-sec fixed ratio (FR) 1 schedule in which three 7-min FI c o m p o n e n t s a l t e r n a t e d with 3-min FR c o m p o n e n t s to yield a total session length of 30 min. The h o u s e l i g h t was illuminated t h r o u g h o u t the sessions and an auditory stimulus (1850 Hz tone) was p r e s e n t only during the FR components. During FI c o m p o n e n t s (i.e., u n p u n i s h e d responding), r e i n f o r c e m e n t was d e l i v e r e d c o n t i n g e n t upon the first lever press after a period of 60 sec had elapsed since delivery of prior reinforcement. Every lever press d u r i n g the FR components resulted in both the delivery of a food pellet and the d e l i v e r y of mild e l e c t r i c shock (i.e., p u n i s h e d responding). The shock amperage was adjusted for each rat until lever p r e s s i n g during the FR c o m p o n e n t s was s u p p r e s s e d to b e t w e e n 1 and i0 responses for the entire session. Shock levels ranged from 0.2 to 1.0 mA. During acute d o s e - e f f e c t curve determinations, test sessions were c o n d u c t e d 5 days a w e e k with drugs u s u a l l y a d m i n i s t e r e d on T u e s d a y and Friday. There was a m i n i m u m 2-day n o n d r u g period b e t w e e n test sessions. Also, drug t r e a t m e n t was not a d m i n i s t e r e d unless, on the p r e c e d i n g control day, the rat met the criteria of m a k i n g 1 to i0 responses during the FR c o m p o n e n t s for the entire session and of earning more than 14 (of 21 possible) reinforcers d u r i n g the FI components. On weekends, when the rats were not tested, they were m a i n t a i n e d at 80% of their f r e e - f e e d i n g body weights. During acute d o s e - e f f e c t d e t e r m i n a t i o n s for each drug, the doses were a d m i n i s t e r e d in a c o u n t e r b a l a n c e d order using a r a n d o m i z e d Latin Square design. The first acute d o s e - e f f e c t curve d e t e r m i n a t i o n was with CDP with doses of 0, 2.5, 5.0, and i0.0 mg/kg. Then, PCP was tested with doses of 0, 1.0, 2.0, and 4.0 mg/kg. F o l l o w i n g acute testing

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with CDP and PCP, a repeated dosing p r o c e d u r e was implemented. F o l l o w i n g 3 sessions with vehicle injections (pre-drug), 2.0 mg/kg PCP was a d m i n i s t e r e d for 6 c o n s e c u t i v e test sessions, and this was followed by 3 additional sessions with v e h i c l e injections (postdrug). An identical repeated dosing p r o c e d u r e was then conducted with 5.0 m g / k g CDP. A f t e r testing with CDP and PCP was completed, an acute doseeffect d e t e r m i n a t i o n with NPC 12626 was c o n d u c t e d with doses of 0, i0.0, 30.0, 56.0, and i00.0 mg/kg (N=I3; a sick animal was removed from the study). Finally, the repeated dosing p r o c e d u r e was c o n d u c t e d w i t h 30.0 mg/kg NPC 12626 (N=I2; a sick animal was removed from the study). Data Analyses. During the acute dose determination, each session that i m m e d i a t e l y preceded a drug day served as a control session. During the repeated dosage procedure, the three p r e - d r u g vehicle sessions served as control sessions. The mean number of responses for the control sessions for each drug was c a l c u l a t e d separately for p u n i s h e d (FR) responding and u n p u n i s h e d (FI) r e s p o n d i n g for the acute and repeated dosage procedures, respectively. For the purposes of data analysis, response rates on drug days were c o n v e r t e d to a p e r c e n t a g e of mean control response rates during the testing of that drug. During repeated dosing, response rates on p r e - d r u g and p o s t - d r u g days were also c o n v e r t e d to a p e r c e n t a g e of mean control response rates. Each d o s e - e f f e c t curve or repeated dosage regimen was analyzed separately with a repeated measures (treatments-by-subjects) analysis of variance. For significant (p < .05) m a i n effects, post hoc comparisons were made with Duncan's m u l t i p l e - r a n g e tests (25). Drugs. C h l o r d i a z e p o x i d e HCL (CDP) (Sigma Chemical Co., St. Louis, MO) and p h e n c y c l i d i n e HCL (PCP) (NIDA, Rockville, MD) were dissolved in 0.9% saline. NPC 12626 (Nova Pharmaceuticals, Baltimore, MD) was dissolved in e q u i m o l a r sodium hydroxide. Doses for CDP and PCP refer to the salts. CDP and NPC 12626 were a d m i n i s t e r e d 30 min before test sessions; PCP was a d m i n i s t e r e d 15 min before test sessions. All injections were a d m i n i s t e r e d i.p. in a total volume of 1 ml/kg. Results Figure 1 shows the results of the acute d o s e - e f f e c t curve d e t e r m i n a t i o n s for each drug. The 5 m g / k g and i0 m g / k g doses of CDP and the highest dose of PCP (4 mg/kg) p r o d u c e d s i g n i f i c a n t (~