The effect of estrogen on the estrogen receptor-immunoreactive cells in the rat medial preoptic nucleus.

The localization of estrogen receptor-immunoreactive (ER-IR) cells in the medial preoptic nucleus (MPN) and the effect of estrogen upon these cells were quantitatively analyzed by immunohistochemistry using a monoclonal antibody to estrogen receptor (ER) protein in rat. ER was distributed in the nucleus of MPN neurons and was not detected in either cytoplasm or glial cells. There were more ER-IR cells with higher immunoreactivities in ovariectomized (OVX) rats than in estradiol (E2)-treated rats. The number of ER-IR cells in E2-treated compared with OVX rats was reduced by 43%. In particular, the number of ER-IR cells in the central part of the MPN was largely decreased. Our data indicate that the central part of the MPN is most sensitive to estrogen.