Neuronal activity in the sagittalis nucleus of the hypothalamus after ovarian steroid hormone manipulation and sexual behavior in female rat.

During extended observation of estrogen receptor (ER) α-immunoreactive neurons in the hypothalamus, we previously identified a novel nucleus, the Sagittalis Nucleus of the Hypothalamus (SGN), in the interstitial area between the arcuate nucleus and the ventromedial hypothalamic nucleus. The SGN exhibits sexual dimorphism in its volume and cell count, and estrous cycle related variations in ERα-immunoreactivity. These characteristics of the SGN implicate the nucleus in sex-biased brain functions and behaviors. In this study, we examined involvement of the SGN in sexual arousal in female rats. Immunohistochemical staining of c-Fos, a marker of neuronal activity was performed after administration of an estrus-inducing dose of estrogen and progesterone in ovariectomized female rats. Analysis of microscopic images showed a significant increase in the number of c-Fos-expressing neurons in the SGN following hormonal manipulation. Moreover, neuronal activity in the region exhibited a further increase after each animal was coupled with a male and allowed to mate. These results suggest that the SGN plays an important role in sexual activity in female rat.