Sex differences in the stress responses in the amygdala

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To examine the effect of the restriction of environmental space on the stress response of the hippocampal acetylcholine (ACh) release, an in vivo microdialysis study was performed in male and female rats after 4-day housing in a large cylindrical cage (diameter = 35 cm) or a small cylindrical cage (diameter =19 cm). Dialysates and blood samples were taken from 1100 h to 1600 h in freely moving rats, but restraint stress was applied from 1200 h to 1300 h. Male rats living in a large cage showed greater stress response of the A Ch release than female rats living in a large cage. In addition, the stress response of ACh release in the hippocampus was attenuated in male rats living in a small cage, while female rats showed a significant increase in the ACh release in female rats living in a small cage. We surmise that there may be a sex difference in the effect of housing condition in the stress response of ACh release in the hippocampus.To examine the sex difference in the stress response of serotonin (5HT) and dopamine (DA) release in the basolateral amygdala (BLA), an in vivo microdialysis study was performed in intact male and cycling female (diestrus 2) rats. Basal 5HT release in the BLA was low without sex difference. Although the 5HT release promptly increased with the onset of the restraint stress in both sexes, the magnitude of the stress response in male rats was significantly less than in female rats. In contrast, male rats showed higher basal DA release in the BLA than female rats. Although the DA release promptly increased with the onset of the restraint stress in female rats, male rats showed no significant stress response. These results indicate that sex and/or gonadal steroid hormone environment can affect the stress response of 5HT and DA release in the BLA in rats.