NMDA-induced lesions of the amygdaloid complex block the retention-enhancing effect of posttraining epinephrine

Rats with either bilateral amygdaloid complex (AC) lesions (produced by injection of the excito-toxin NMDA) or control surgery were trained on a one-trial step-through inhibitory-avoidance task and given immediate posttraining injections of either epinephrine (100 μg/kg, ip) or saline. Epinephrine significantly enhanced retention performance (measured 24 h after training) in rats that received the control surgery. The enhancement was completely blocked, however, in the AC-lesioned subjects. Furthermore, the lesions themselves significantly impaired learning of the task. The results are discussed in the context of evidence suggesting that the AC is involved in mediating the effects of endogenous hormones on memory processes.