Facilitation of time-dependent memory processes with posttrial epinephrine injections

This experiment examined the effect of posttraining epinephrine injections on memory-storage processes. Rats were trained with a weak footshock (0.7 mA, 0.35 sec) on a one-trial inhibitory avoidance task. The animals received epinephrine injections immediately, 10 min, 30 min, or 2 hr after training. On a retention test 24 hr after training, animals which received subcutaneous injections of epinephrine (0.01, 0.05, or 0.1 mg/kg) immediately after training had retention performance which was significantly better than that of saline control animals. A lower (0.001 mg/kg) or a higher (0.5 mg/kg) dose did not affect retention performance. Epinephrine injections (0.1 mg/kg) given 10 min after training also significantly facilitated retention, but injections given 30 min or 2 hr after training did not affect retention performance significantly. These findings suggest that the hormonal consequences of a training experience (e.g., epinephrine release) may normally modulate memory-storage processes in untreated animals.