Stress‐induced activation of distinct subpopulations of neurons in the basolateral amygdala of the rat

Previous studies showed that repeated exposure to 6h restraint stress causes hippocampal plasticity and shifts the profile of activated basolateral amygdala (BLA) neurons, suggesting alterations in mechanisms that affect learning and memory in repeatedly stressed rats. The purpose of this study was to determine whether a lesser stress exposure can induce similar consequences, and whether the effects are sex‐specific. Adult male and female rats were acutely (A; 30min x 1d) or repeatedly (R; 30min x 14d) restraint stressed and compared to unstressed controls (C). Stress occurred near the beginning of the light cycle (0900h). Series of perfused brain sections (30μm) were stained immunohistochemically for Fos, and the number of Fos‐expressing cells was quantified in the BLA. The number of Fos‐positive BLA cells tended to be higher in females than males in all groups, and varied by group: C/Male=47±19, A/Male=251±57, R/Male=152±44; C/Female=169±79, A/Female=151±83, R/Female=235±41. One significant difference was seen between C and A males (p<0.05). The data suggest that BLA responses to short‐term emotional stress vary according to sex and stress exposure. Further analyses will be done using fluorescent immunohistochemistry to quantify the specific types of stress‐activated BLA neurons in both sexes. Supported by: UTEP's COURI Program, NIH/NCRR 5G12RR008124, and the Egbert Endowment (to KLG).