Acute stress and re-exposure to the stressful context suppress spontaneous unit activity in the basolateral amygdala via NMDA receptor activation.

Exposure to an acute stressor of intermittent tail-shocks enhances acquisition of the classically conditioned eyeblink response and the enhancement is dependent on NMDA receptor activation in the basolateral nucleus of the amygdala. In the present study, multiple units (spikes/s) were recorded from the basolateral amygdala in response to the stressor of intermittent tailshocks (thirty, 1 mA, 1 s, 1/min) and upon re-exposure to the context in which the stress was administered. Exposure to the stressor suppressed multiple unit activity in the basolateral/lateral amygdala (67% of baseline) which, in some cases, persisted for 48 h after stressor cessation. Re-exposure to the stressful context reactivated the suppression in unit activity (69% of baseline). In a second experiment, it was determined that the stress-induced suppression of neuronal activity was prevented by NMDA receptor antagonism during stressor exposure. It is proposed that the stress-induced suppression of background unit activity enhances the neural representation of environmental cues by enhancing their signal/background noise ratio and thereby facilitates the formation of associations between those cues.