Abstract
Recently we showed that chronic estrogen replacement in ovariectomized rats significantly attenuates cardiovascular responses to mild psychological stress induced by cage-switch. Our hypothesis is that these estrogen effects are mediated by nitric oxide (NO) in the brain involved in decreasing sympathetic output. In this study, we investigated whether estrogen affects the stress-induced activation of nitric oxide-producing neurons in the paraventricular hypothalamic nucleus (PVN) in ovariectomized rat. Female rats aged 9 wk were ovariectomized and assigned randomly to 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 4 wk, each group of rats underwent cage-switch for 30 min and was sacrificed at 60 min after the cessation of the stress. The rats were perfused, and the brain sections were processed for c-Fos immunohistochemistry and NADPH-diaphorase histochemistry. In the medial parvocellular PVN (mpPVN), cage-switch stress significantly increased c-Fos positive neurons with a greater extent in the P than E group. Moreover, stress-induced elevation in the percentage of double-stained neurons (c-Fos + NADPH-d positive neurons) was significantly larger in the E than P group. These findings suggest that estrogen modulates the activation of nitric oxide-producing neurons in the mpPVN. [J Physiol Sci. 2007;57 Suppl:S193]
