Effects of posttraining injection of cholinergic agonists and antagonists into the amygdala on retention of passive avoidance training in rats.

Rats were given a single footshock while licking a water tube and tested 24 hr later for retention of the footshock experience. A single bilateral injection of a subseizure dose of physostigmine into the amygdala applied immediately, but not 18 hr, after the footshock imparied retention. This effect appeared to be somewhat localized, as physostigmine injected into the hippocampus or lateral ventricles did not disrupt retention. Conversely, a subseizure dose of atropine sulfate into the amygdala, given immediately or 18 hr after the footshock did not impair retention. Atropine injected concurrently with physostigmine into the same amygdaloid loci counteracted a potential physostigmine-induced retention deficit. Injection of carbachol into the amygdala also impaired retention; however, carbachol precipitated seizures and possibly exerted proactive consequences on performance. The time-dependent nature of the deficit following physostigmine is consistent with the view that injection of cholinergic agonists into the amygdala disrupts memory for the footshock experience.