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 classically conditioned nictitating membrane response (NMR) using a tone conditioned stimulus (CS) and an air puff unconditioned stimulus (UCS). They were then treated with a low or high dose of nimodipine or a vehicle for 90 days. During this time no further CS-UCS pairings were presented. They underwent testing for retention of the conditioned response (CR) at 30 and 90 days. Retention testing consisted of 20 presentations of the CS alone. Rabbits in the control condition retained 46.4% of their predrug levels of conditioned responding and rabbits receiving the low dose of nimodipine retained 37.3% of their predrug levels after 30 days. After 90 days, retention in these animals declined to 8.1076 and 14.1070, respectively. In contrast, rabbits receiving the high dose of nimodipine retained 85% of their predrug learning at 30 days with little decline at 90 days (77.1%). Nonassociative factors such as sensitivity to the CS or UCS could not explain these effects.