Distribution of estrogen receptor beta immunoreactivity in the rat central nervous system

Abstract

The discovery of estrogen receptor beta (ER beta) and subsequent localization of its mRNA in the rat central nervous system (CNS) has provided new insights about estrogen action in brain. A critical step in understanding the role of ER beta is demonstrating that the mRNA is translated into functional protein. The present study used a new ER beta-specific polyclonal antiserum (Z8P) and immunocytochemistry (ICC) to investigate the distribution of ER beta in the rat CNS. Ovariectomized female rats were perfusion fixed, and free-floating sections were incubated with Z8P. After visualization with a standard ABC method, nuclear immunoreactivity was seen in neurons throughout the brain, including the olfactory nuclei, laminae IV-VI of the cerebral cortex, medial septum, preoptic area, bed nucleus of the stria terminalis, supraoptic nucleus, paraventricular nucleus, zona incerta, medial and cortical amygdaloid nuclei, cerebellum, nucleus of the solitary tract, ventral tegmental area, and spinal trigeminal nucleus. Moreover, the results of a double-label ICC/ in situ hybridization study revealed that ER beta mRNA and immunoreactivity were colocalized in neurons of the brain, thus confirming the specificity of the antiserum. Through the use of Western blot analysis, Z8P was shown to recognize in vitro translated ER beta, but not ER alpha, as well as a 60-kDa protein from rat granulosa cells and ovary extracts. The results of these studies have demonstrated that (1) ER beta mRNA is translated into immunoreactive protein throughout the rat brain, and (2) ER beta resides in the cell nucleus. Together, these data provide an anatomic foundation for future studies and advance our understanding of estrogen action in hypothalamic and extrahypothalamic brain regions.