KETAMINE - ACQUISITION AND RETENTION OF CLASSICALLY-CONDITIONED RESPONSES DURING TREATMENT WITH LARGE DOSES

Two experiments were conducted in rabbits to examine the effects of ke tamine (0, 100, and 200 mg/kg) on the acquisition and retention of the classically conditioned nictitating membrane response (NMR). Classica l conditioning of the NMR was accomplished by pairing tone and light c onditioned stimuli (CS) with paraorbital shock as the unconditioned st imulus (UCS). Experiment 1 assessed the effects of the drug on acquisi tion and retention of conditioned responses (CR) and determined the ro le of previous exposure to the experimental environment. Ketamine bloc ked the display of CR. However, data from subsequent retention testing under nondrug conditions revealed that rabbits that had previously re ceived 100 mg/kg ketamine learned faster than saline-treated rabbits d uring the acquisition phases. Rabbits that received 100 mg/kg ketamine and were placed in the experimental chambers, but not presented with stimuli during the acquisition phase, did not learn faster during the retention phase than naive rabbits. Experiment 2 controlled further fo r the effects of nonassociative, unlearned processes. Control groups w ere presented with unpaired CS and UCS training after drug administrat ion, and subsequently received conventional acquisition sessions under nondrug conditions. Their data indicated that the ketamine group's ra pid acquisition during retention testing could not be attributed to no nassociative factors. We conclude that, although it was impossible dir ectly to observe acquisition in rabbits under the influence of ketamin e, it was possible that learning occurred as manifested by ''savings'' in subsequent learning trials.