The rodent amygdala under acute psychological stress: a review.

Abstract

Stress is a common experience in everyday life. Exposure of organisms to threat stimuli requires adaptive mechanisms to maintain homeostasis. Thus, animals possess integrated circuits to generate defensive responses appropriate to the threat and to approach responses proportional to potential gains. The amygdala is a brain structure critical for the stress response. It is subdivided into nuclei that, due to their connections and cytoarchitecture, specifically modulate stress-related behavior. This review focuses on the role of the major amygdala nuclei in response to acute stressors that elicit emotional responses in rodents. Of the two nuclei, central and medial (Me), which constitute the main amygdala output to hypothalamic and brainstem stress-related regions, it is Me appears to be most important in generating anxiety-related responses to an acute psychological stressor. The Me neurons can influence the functioning of the hormonal and the autonomic systems, thereby regulating the defensive and reproductive behavior under stress conditions. The Me not only plays a role in integrating and relaying sensory cues to downstream targets, but also controls behavioral output itself and represents the earliest stage at which specific behavioral responses are determined. The basolateral complex (BLC) appears to play less direct, more 'analytical' functions such as evaluating the valence of stimuli or regulating behavior in situations involving an uncertainty or unpredictability. Moreover, under stress, the BLC may influence regional stress-induced immune and metabolic changes in other limbic structures. The role of the remaining amygdala nuclei involved in stress response is less examined and awaits further research.