Effect of estrogen on stress‐induced c‐Fos expression in catecholaminergic neurons of ovariectomized rat brain

Abstract

Recently we revealed that mild psychological stress evoked by cage-switch significantly increased c-Fos expression in ovariectomized rat brain areas: locus coeruleus (LC), the nucleus of the solitary tract (NTS), hypothalamic paraventricular nucleus, etc. The present study investigated whether estrogen affected the stress-induced expression of c-Fos in catecholaminergic neurons of ovariectomized rat brain through estrogen receptor (ER). Female rats aged 9wk were ovariectomized and randomly assigned placebo-treated (P) and estrogen-treated (E) groups. The P and E groups were implanted with pellets containing either placebo or 17 β-estradiol (1.5 mg/60-day release). After 4wk, each group rat underwent cage-switch for 30 min and was sacrificed at 60 min after the stress. The brains were immunohistochemically processed for c-Fos and tyrosine hydroxylase (TH) as an identifier of catecholaminergic neurons, and for ER. TH-positive neurons were found in LC, NTS, and rostral ventrolateral medulla (RVLM) in both P and E groups. In these areas, stress significantly increased c-Fos+TH double-labeled neurons in both groups. However, the c-Fos expression of catecholaminergic neurons was significantly suppressed in LC in the E group. In addition, ER immunoreactive neurons were observed in similar regions in LC. These findings suggest that estrogen affects c-Fos expression of catecholaminergic neurons in LC.