Abstract
Our previous study showed that estrogen modulated the activation of nitric oxide-producing neurons in the parvocellular paraventricular hypothalamic nucleus (pPVN) induced by cage-switch stress. In this study, we investigated whether estrogen affects the stress-induced activation of oxytocinergic and corticotoropin releasing hormone (CRH) containing neurons through nitric oxide in the pPVN in ovariectomized (OVX) rats by comparison of c-Fos expressions using immunohistochemistry. Nine-week-old female rats were ovariectomized and divided randomly into placebo-treated (OVX+Pla) and estrogen-treated (OVX+E2) groups. The rats were subcutaneously implanted with pellets containing 17 β -estradiol or a placebo 4 weeks after OVX. Four weeks later, the rats underwent cage-switch stress for 30 min with or without pretreatment of L-NAME. At 60 min after the cessation of this stress, the rats were anesthetized and perfused. The brain sections were processed for c-Fos and oxytocin, and CRH immunohistochemistry. Cage-switch stress increased activation in oxytocinergic neurons in the pPVN in OVX+Pla, but not in that of OVX+E2, rats. These findings suggest that estrogen may attenuate the activation of oxytocinergic neurons, via at least in part, nitric oxide. [J Physiol Sci. 2008;58 Suppl:S107]
