Sex differences in the basolateral amygdala: serotonin and dopamine release and their responses to restraint stress in rats

The sex difference in emotional response to stress suggests a sex-specific stress response in the amygdala. To examine the sex difference in serotonin and dopamine release response to stress in the basolateral amygdala (BLA), in vivo microdialysis studies were performed in male and female rats. In experiment I, dialysates were collected from the BLA at 15-min intervals under the freely moving condition. Mean serotonin or dopamine release in the BLA were higher in male rats than in female rats. In experiment II, rats were subjected to restraint stress for 60 min to examine the stress response of serotonin or dopamine release. Although restraint stress significantly increased serotonin release in both sexes of rats, female rats showed a greater response than male rats. Moreover, restraint stress significantly increased dopamine release in female rats, but not in male rats. In experiment III, rats were subjected to restraint stress for 30 min to examine behavioral responses. Although no sex difference was observed in the number of audible vocalizations, male rats defecated a larger number of fecal pellets than female rats. In experiment IV, rats were tested for freezing behavior to examine contextual fear responses. Conditioned male rats showed a longer freezing time than conditioned female rats. We found sex differences in the serotonin and dopamine release in the BLA and their responses to restraint stress, which may be involved in the sex-specific emotional response to stress in rats. [J Physiol Sci. 2007;57 Suppl:S170]