Estradiol target sites immunoreactive for beta-endorphin in the arcuate nucleus of rat and mouse hypothalamus.

Combined autoradiography and immunocytochemistry was performed to examine estradiol-concentrating neurons of the arcuate nucleus in the hypothalamus of ovariectomized rats and mice for beta-endorphin-like immunoreactivity. A high number of [3H]estradiol-labeled cells occurred in the arcuate nucleus of both species. Neurons immunoreactive for beta-endorphin could be visualized throughout the arcuate nucleus as well as ventrolaterally outside of this nucleus. Colocalization of [3H] estradiol nuclear labeling and beta-endorphin-like cytoplasmic immunoreactivity could be found scattered throughout the arcuate nucleus, most frequently in the ventromedial part, although most of the [3H]estradiol target neurons did not react with the antibodies. The results suggest that a subpopulation of beta-endorphin neurons is directly addressed by estradiol and that the arcuate nucleus contains different groups of estradiol receptive neurosecretory cells.