The septohippocampal cholinergic system and classical conditioning of the rabbit's nictitating membrane response.

Rabbits received bilateral microinjections of scopolamine or saline into either the dorsal hippocampus (Experiment 1) or the medial septal nucleus (Experiment 2). The animals then underwent classical conditioning of the nictitating membrane response in which a light served as a conditioned stimulus and eye shock served as the unconditioned stimulus. The results indicated that whereas hippocampal injections of scopolamine had no effect on conditioning, scopolamine injected into the medial septum retarded acquisition of the response. A third experiment indicated that this retardation of conditioning was not due to changes in sensitivity to either the conditioned or the unconditioned stimulus. The results are discussed in terms of accumulating evidence indicating that manipulations which produce certain patterns of activity in the hippocampus are detrimental to acquisition of the conditioned nictitating membrane response.