Estrogen receptor β messenger ribonucleic acid expression in the forebrain of proestrous, pregnant, and lactating female rats

Estrogen receptor (ER) beta is present in hypothalamic and limbic neurons of female rat brains, but little is known about its regulation under physiological conditions. To determine whether ERbeta expression varies during physiological conditions in which sex steroid hormone profiles are significantly different, we used in situ hybridization to assess ERbeta mRNA expression in the periventricular preoptic area, bed nucleus of stria terminalis, paraventricular nucleus, supraoptic nucleus, and the posterodorsal medial amygdala of female rats on proestrus, on d 22 of pregnancy, or on d 10 of lactation (L10). In the periventricular preoptic area, d-22 pregnant females had fewer ERbeta-mRNA-expressing cells than did females at proestrus, but the level of ERbeta mRNA expression per cell in pregnant females was higher than in the two other groups. In the paraventricular nucleus, no changes in ERbeta mRNA expression were observed; whereas in the supraoptic nucleus, proestrous females had fewer ERbeta-mRNA-expressing cells than L10 females. In the posterodorsal medial amygdala, proestrous females had a greater number of ERbeta-mRNA-expressing cells than did L10 females. These results demonstrate that ERbeta mRNA expression is differentially regulated in a brain-region-specific and temporal manner under physiological conditions and suggest that ERbeta may participate in the regulation of estrogen-sensitive reproductive functions in female rats.