Posttraining brain norepinephrine concentrations: Correlation with retention performance of avoidance training and with peripheral epinephrine modulation of memory processing

Posttrial epinephrine injections can enhance or impair later retention performance of inhibitory (passive) avoidance training in rats. The findings reported here indicate that the effects on retention of epinephrine injections and of footshock level are closely related to transient posttraining decreases in whole brain norepinephrine concentrations. Posttraining norepinephrine levels, as measured 10 min after training and treatment, predict the later retention performance of groups of rats trained with high or low footshock and, in addition, predict the retroactive effects (enhancement or impairment) of posttrial epinephrine injections. These findings are consistent with the view that hormonal responses to training may modulate memory storage processing. In addition, the results suggest that memory modulation may involve neuroendocrine mechanisms that include the central noradrenergic system.