Comparative distribution of estrogen receptor α and β immunoreactivities in the forebrain and the midbrain of the female guinea pig

Abstract

Estrogen plays an important role in regulating gonadotropin secretion and reproductive behavior. The estrogen receptor α (ERα) was believed to be the only receptor which mediated the actions of the hormone until the identification of a novel ER called ERβ. In the present study, the map of ERα immunoreactive (IR) neurons was compared with the distribution pattern of ERβ-IR neurons in the forebrain and midbrain of ovariectomized guinea pigs using immunocytochemistry. The immunoreactivities appeared to be mainly nuclear in their subcellular distribution. Both ERα- and ERβ-like immunoreactivities were highly expressed in the bed nucleus of the stria terminalis and the ventrolateral hypothalamic nucleus but were found to be differentially expressed in discrete subregions of the amygdaloid complex. A large number of intensely labeled ERα cells were observed throughout the rostrocaudal extent of the preoptic region, whereas only a few ERβ-IR neurons were found in the periventricular preoptic nucleus bordering the third ventricle or scattered in the medial preoptic area. In contrast, only ERα-immunoreactivity was seen in the septum, and in the magnocellular supraoptic, paraventricular, arcuate, and premammillary nuclei. In the midbrain, neurons containing ERα were observed throughout the rostrocaudal extent of the gray matter, whereas ERβ was only detected within the dorsal raphe nucleus. These observations provide evidence of a distinct neuroanatomical pattern for the two subtypes of the ER which may have different roles in regulating behavior and the neuroendocrine mechanisms of reproduction. Species similarities and differences in the distributions of ERα and ERβ immunoreactivities are discussed.