Effects of posttraining epinephrine injections on retention of avoidance training in mice

These experiments examined the effects, on retention, of posttraining epinephrine injections in mice. Mice were trained in a one-trial inhibitory (passive) avoidance task and retention performance was measured 24 hr after training. In the first experiment, animals received an immediate posttraining injection of saline or epinephrine (3-1000 μg/kg). An intermediate epinephrine dose (30 μg/kg) enhanced later retention performance and the high dose (1000 μg/kg) impaired later retention performance. In a second experiment, an intermediate epinephrine dose (50 μg/kg) again enhanced later retention if the treatment was administered immediately after training but not if delayed by 10 or 30 min after training. A higher epinephrine dose (500 μg/kg) had no effect on retention performance if the drug was administered immediately after training or 30 min after training. However, this dose did enhance retention if administered 10 min after training. Thus, the dose-response characteristics of epinephrine enhancement of retention vary with time after training. These findings are consistent with the general view that hormonal consequences of training may modulate the storage of recent information and, furthermore, that posttraining treatments may affect memory through mechanisms which interact with the hormonal responses to training.