The distribution of cells containing estrogen receptor-alpha (ER alpha) and ER beta messenger ribonucleic acid in the preoptic area and hypothalamus of the sheep: Comparison of males and females

We have used in situ hybridization to compare the distributions of estrogen receptor alpha (ER alpha) and ER beta messenger RNA (mRNA)-containing cell s in the preoptic area and hypothalamus of ewes and rams. Perfusion-fixed b rain tissue was collected from luteal phase ewes and intact rams (n = 4) du ring the breeding season. Matched pairs of sections were hybridized with sh eep-specific, S-35-labeled riboprobes, and semiquantitative image analysis was performed on emulsion-dipped slides. A number of sex differences were o bserved, with females having a greater density of labeled cells than males (P < 0.001) and a greater number of silver grains per cell (P < 0.01) in th e ventromedial nucleus for both ER subtypes. In addition, in the retrochias matic area, males had a greater (P < 0.05) cell density for ER alpha mRNA-c ontaining cells than females, whereas in the paraventricular nucleus, femal es had a greater density (P < 0.05) of ER alpha mRNA-containing cells than males. There was a trend (P = 0.068) in the arcuate nucleus for males to ha ve a greater number of silver grains per cell labeled for ER alpha mRNA. In both sexes, there was considerable overlap in the distributions of ER alph a and ER beta mRNA-containing cells, but the density of labeled cells withi n each nucleus differed in a number of instances. Nuclei that contained a h igher (P < 0.001) density of ER alpha than ER beta mRNA-containing cells in cluded the preoptic area, bed nucleus of the stria terminalis, and ventrome dial nucleus, whereas the subfornical organ (P < 0.001), paraventricular nu cleus (males only, P < 0.05), and retrochiasmatic nucleus (females only, P < 0.05) had a greater density of ER alpha than ER beta mRNA-containing cell s. The anterior hypothalamic area and supraoptic nucleus had similar densit ies of cells containing both ER subtypes. The lateral septum and arcuate nu cleus contained only ER alpha, whereas only ER beta mRNA-containing cells w ere seen in the zona incerta. The sex differences in the populations of ER mRNA-containing cells in the ventromedial and arcuate nuclei may explain in part the sex differences in the neuroendocrine and behavioral responses to localized estrogen treatment in these nuclei. Within sexes, the difference s between the distributions of ER alpha and ER beta mRNA-containing cells m ay reflect differential regulation of the actions of estrogen in the sheep hypothalamus. Low levels of ER beta mRNA in the preoptic area and ventromed ial and arcuate nuclei, regions known to be important for the regulation of reproduction, suggest that ER beta may not be involved in these functions.