Epinephrine-induced learning under anesthesia: retention performance at several training-testing intervals.

While under deep barbiturate anesthesia, rats received a series of 10 classical conditioning trials in which white noise was paired with intramuscular shock. The anesthetized animals received either saline or epinephrine injections prior to the training trials. Independent sets of animals were tested for retention performance 2, 7, or 15 days after training. In these test trials, a conditioned suppression measure was used in which the white noise was turned on while the animals were drinking. The results indicated that the animals that had received saline while trained under anesthesia exhibited no evidence of later retention. Animals that had received epinephrine injections prior to training under anesthesia suppressed their drinking in the presence of the white noise when tested 2 or 7, but not 15, days later. Thus, the results indicate that epinephrine can enable learning under anesthesia and, in addition, forgetting occurs within 15 days.