Peripheral epinephrine modulates the effects of post-training amygdala stimulation on memory.

The present study investigated the role of adrenal epinephrine in the memory modulatory effects of post-training amygdala stimulation. Adrenal demedullated (ADMX) or sham demedullated (SHAM) rats received electrical stimulation of the amygdala immediately after training on inhibitory and active avoidance tasks. With both tasks, the stimulation impaired retention only in the rats with intact adrenal medullae: the retention performance of the ADMX in the rats with intact adrenal medullae: the retention performance of the ADMX rats given post-training stimulation was better than that of the unstimulated ADMX group with implanted electrodes. However, ADMX rats given post-training epinephrine (1.0 mg/kg, s.c.) immediately before the amygdala stimulation had retention deficits comparable to those of the SHAM group given amygdala stimulation. If epinephrine was administered a short time after rather than before the post-training amygdala stimulation, retention of the ADMX animals was not impaired. The findings are interpreted as indicating that circulating epinephrine present at the time of amygdala stimulation modulates the effects of amygdala stimulation on memory.