The effect of pre- and post-trial amphetamine injections on avoidance responses of rats

Abstract

Rats were trained in a shuttle-box to avoid shocks, and then re-tested 5 days later for retention. A pre-trial injection of 2 mg/kg amphetamine increased the performance of conditioned responses (CR's) on the first day, but it did not improve retention beyond control levels. A similar post-trial injection, on the other hand, caused a marked enhancement of retention, even in rats which had received a pre-trial amphetamine treatment. Atropine potentiated the effect of pre-trial amphetamine on performance during the first-day session, but it partly antagonised that of post-trial amphetamine on retention. The effect of pre-trial amphetamine, and its interaction with atropine were similar to previously reported observations on pseudoconditioning. Thus, amphetamine was considered to have a dual effect on behaviour: on one hand, an enhancing effect on pseudoconditioning, which could be potentiated by atrophie; on the other, another stimulant action on memory consolidation, which was counteracted by atropine. Under the conditions of the present experiment, it was to be expected that the effect of pre-trial amphetamine on the performance of avoidance responses on the first-day would be due to an increase of pseudoconditioned responses, and therefore would not improve retention of CRs over control levels.

A higher dose (5 mg/kg) of amphetamine lacked all facilitatory action on learning. The effects of atropine by itself were dose-dependent on pre-trial injection (a low dose depressed, a higher dose enhanced performance on both sessions), and was stimulant upon retention upon post-trial treatment.