Retrieval enhancement in mice by pretest amphetamine injection after a long retention interval

Abstract

Mice were trained to avoid one compartment of a shuttlebox using the procedures of Pavlovian fear conditioning, and retention was measured 1 day later and 1 month later using an active avoidance test. Good retention was evident at 1 day, but substantial forgetting occurred after 1 month, performance levels in this group being equivalent to those exhibited by sham-conditioned animals. Treatment with d-amphetamine (2.0 mg/kg) before testing restored retention to levels shown by mice tested 1 day after conditioning. When retention was tested with a passive avoidance test, amphetamine increased rather than decreased latencies of animals tested 1 month after conditioning. Amphetamine did not decrease latencies of sham-conditioned mice tested in active avoidance and did not enhance the performance of those with strong memory tested 1 day following training in either active or passive tests. Amphetamine also enhanced retrieval in mice in which conditioning was weakened by a reduction in shock level rather than by imposition of a long retention interval. These findings add to the growing evidence that retention of weak memories can be facilitated by monoaminergic stimulation of retrieval mechanisms. © 1983, Psychonomic Society, Inc.. All rights reserved.