IMPAIRMENTS PRODUCED BY AMPHETAMINE AND STRESS ON MEMORY STORAGE ARE REDUCED FOLLOWING A CHRONIC STRESSFUL EXPERIENCE

Post-training administration of the psychostimulant, amphetamine or po st-trial exposure to restraint stress impaired retention of an inhibit ory avoidance response in DBA/2 (DBA) mice. The effect of amphetamine was dose-dependent (1-3 mg/kg) whilst the effect of stress depended on restraint duration (15, 30, or 60 min). Both effects on retention per formance appeared to be due to an effect on memory consolidation. In f act, they were observed when the drug and the stressor were experience d at short, but not long, periods of time after training, which is whe n the memory trace is susceptible to modulation. Moreover, these effec ts could not be ascribed to a rewarding or non-specific action of the two treatments on retention performance, as the latencies during the r etention test of those mice that had not received a footshock during t he training, were not affected by the post-training treatments. Admini stration of either D1(SCH23390) or D2 [(-)-sulpiride] dopamine (DA) re ceptor antagonists prior to amphetamine injection or stress exposure a ntagonized the impairing effects of both treatments. These data indica te that brain dopamine was involved in both cases. Finally, when mice were food restricted for 13 days than allowed free access to food for 24 h before training, either the effects of amphetamine or restraint s tress were reduced. Food restricted mice did not differ from control f or stepthrough latencies either on the training or the test days, indi cating the absence of amnesic or otherwise impairing effects of the ex perimental procedure per se. Instead, the results indicated hyposensit ization to the effects of amphetamine and stress on memory consolidati on in food restricted animals.