NIMODIPINE FACILITATES RETENTION OF THE CLASSICALLY-CONDITIONED NICTITATING-MEMBRANE RESPONSE IN AGED RABBITS OVER LONG RETENTION INTERVALS

Aged rabbits initially underwent 18 days of acquisition of the classic ally conditioned nictitating membrane response (NMR) using a tone cond itioned stimulus (CS) and an air puff unconditioned stimulus (UCS). Th ey were then treated with a low or high dose of nimodipine or a vehicl e for 90 days. During this time no further CS-UCS pairings were presen ted. They underwent testing for retention of the conditioned response (CR) at 30 and 90 days. Retention testing consisted of 20 presentation s of the CS alone. Rabbits in the control condition retained 46.4% of their predrug levels of conditioned responding and rabbits receiving t he low dose of nimodipine retained 37.3% of their predrug levels after 30 days. After 90 days, retention in these animals declined to 8.1% a nd 14.1%, respectively. In contrast, rabbits receiving the high dose o f nimodipine retained 85% of their predrug learning at 30 days with li ttle decline at 90 days (77.1%). Nonassociative factors such as sensit ivity to the CS or UCS could not explain these effects.