The distribution of nitric oxide synthase positive neurons in the amygdala in ovariectomized rats

Abstract

The neuronal nitric oxide synthase (nNOS) is located in the amygdala. Gonadal hormone receptor were found in many neurons in the amygdala. Neurons in the basal amygdaloid nuclei (BA) and the medial amygdaloid nuclei (ME) exhibit strong expression of estrogen, and the amygdala might be related to neuroendocrine and sexual activity. We hypothesized that estrogen influence the distribution of nNOS positive neurons in the amygdala. 30 female rats underwent ovariectomy or SHAM surgery. All rats were studied two months later. In the SHAM rats, most of nNOS positive neurons in the BA were medium-sized (20~35μM), pyramidal shape, strongly stained cytoplasm, and a little of fine fibers were found in background, and nNOS positive neurons in the ME were small (<20μM), pyramidal shape. In ovariectomized (OVX) rats, nNOS positive neurons in the BA exhibited different size, all kinds of shape, slightly stainned cytoplasm and short prominences, and no positive fibers were found in background, and nNOS positive neurons in the ME were ovoid shape, larger than the SHAM. The amount of nNOS positive neurons in the BA in the OVX rats decreased than in SHAM rats (2.63±1.33 vs 4.23±1.89, p<0.01), and so did in the ME (3.67±1.42 vs 7.67±1.52, p<0.01). The results suggest that the distribution of nNOS positive neurons in the BA and ME varies with the change of endogenous estrogen level. Endogenous estrogen may be involved in nNOS neurons-mediated modulation of the amygdala.