G protein-coupled estrogen receptor immunoreactivity in the rat hypothalamus is widely distributed in neurons, astrocytes and oligodendrocytes, fluctuates during the estrous cycle and is sexually dimorphic.

Introduction The membrane-associated G protein-coupled estrogen receptor 1 (GPER) mediates the regulation by estradiol on arginine-vasopressin immunoreactivity in the supraoptic and paraventricular hypothalamic nuclei of female rats and is involved in the estrogenic control of hypothalamic regulated functions, such as food intake, sexual receptivity and lordosis behavior. Objective To assess GPER distribution in the rat hypothalamus. Methods GPER immunoreactivity was assessed in different anatomical subdivisions of five selected hypothalamic regions of young adult male and cycling female rats: the arcuate nucleus, the lateral hypothalamus, the paraventricular nucleus, the supraoptic nucleus and the ventromedial hypothalamic nucleus. GPER immunoreactivity was colocalized with NeuN as a marker of mature neurons, GFAP as a marker of astrocytes and CC1 as a marker of mature oligodendrocytes. Results GPER immunoreactivity was detected in hypothalamic neurons, astrocytes and oligodendrocytes. Sex and regional differences and changes during the estrous cycle were detected in the total number of GPER immunoreactive cells and in the proportion of neurons, astrocytes and oligodendrocytes that were GPER immunoreactive. Conclusions These findings suggest that estrogenic regulation of hypothalamic function through GPER may be different in males and in females and may fluctuate during the estrous cycle in females.