The variation of nitric oxide synthase positive neurons in the medial amygdaloid nuclei during the estrous cycle in female rats

Abstract

Estrogen receptor-β mRNA expression and estrogen positive neurons were found in the medial amygdaloid nuclei (ME), and neuronal nitric oxide synthase (nNOS) positive neurons were found in the amygdala in rats. We hypothesized that the expression of nNOS in the amygdala is associated with the estrogen level and exhibits periodicity during estrous cycle in female rats. 40 rats were divided into preoestrus, estrus, metoestrus, diestrus and control groups. The nNOS positive neurons were found in most amygdala regions. The ME contained a large number of densely stained and medium-sized (20~35μM) pyramidal cells. No nNOS positive structures were found in the control. The nNOS stain was stronger in the cytoplasm of neurons in preoestrus and metoestrus groups than in estrus and diestrus groups during the estrus cycle. The nNOS positive prominences were shorter in the ME than in other nuclei of the amgdala during whole estrous cycle. Most nNOS positive neurons were found in preoestrus groups (22.03±2.99), and some nNOS positive neurons were found in metoestrus groups (21.73±3.17), and few nNOS positive neurons were found in estrus groups (7.33±1.42) and diestrus groups (7.10±1.81). The number of nNOS positive neurons in preoestrus was higher than in estrus (p<0.01) and diestrus (p<0.01), and the number of nNOS positive neurons in metoestrus was higher than in estrus (p<0.01) and diestrus (p<0.01). The results indicate that the distribution of nNOS positive neurons in the ME varies with the estrogen level during whole estrus cycle. The estrogen level upregulates the amount of nNOS positive neurons in the ME. Interaction of estrogen and nitric oxide is involved in the neuroendocrine and sexual activity modulated partly by the amygdala.