Norepinephrine release in the amygdala in response to footshock stimulation.

Extensive evidence suggests that many drugs and hormones influence memory storage by modulating training-induced release of norepinephrine (NE) within the amygdala. This experiment used in vivo microdialysis and high-performance liquid chromatography to examine norepinephrine NE release in the amygdala induced by footshock stimulation typically used in inhibitory avoidance training. Sprague-Dawley rats were implanted bilaterally with cannulae aimed at the amygdala. One to two weeks later, microdialysis probes were inserted (unilaterally) and the animals were placed in a box with a stainless-steel grid floor through which a single footshock (0.55 mA, 1.0 s) was administered either 45.5 (N = 5) or 180.5 (N = 4) min later. Samples were collected and analyzed at 15-min intervals. In both groups, the footshock stimulation increased NE levels to approximately 75% above basal levels in the first sample collected after the footshock and the levels returned to baseline within 30 min. The findings are consistent with pharmacological evidence suggesting that NE released by arousing stimulation is involved in regulating memory storage.