Responses in the brain of estrogen receptor alpha-disrupted mice

These studies sought to determine if neurons in the estrogen receptor-alpha knockout (ERalphaKO) mouse brain concentrated 16alpha-[125I]iodo-11beta-methoxy-17beta-estradiol (125I-estrogen), and if so, whether estrogen binding augmented the expression of progesterone receptor (PR) mRNA. Mice were injected with 125I-estrogen and cryostat sections thaw mounted onto emulsion-coated slides. After 30-90 days of exposure, cells with a nuclear uptake and retention of 125I-estrogen were observed in a number of ERalphaKO mouse brain regions including the preoptic nucleus and arcuate nucleus of the hypothalamus, bed nucleus of the stria terminalis, and amygdala, although the number of labeled cells and intensity of nuclear concentration was markedly attenuated when compared with wild-type littermates. Competition studies with excess 17beta-estradiol, diethylstilbestrol, or moxestrol, but not with R5020 or dihydrotestosterone, prevented the nuclear concentration of 125I-estrogen. To determine if the low level of estrogen binding was capable of regulating gene expression, in situ hybridization was used to evaluate PR mRNA in the brain. ERalphaKO and wild-type mice were ovariectomized and treated with vehicle or 17beta-estradiol, and brains were sectioned and hybridized with a PR cRNA probe. Analysis of hybridization signal revealed a similar, low level of PR mRNA in ovariectomized wild-type and homozygous mice, and a marked increase in expression after treatment of ovariectomized animals with 17beta-estradiol, with the level of hybridization signal being significantly higher in wild-type animals when compared with ERalphaKO mice. The results demonstrate that estrogen binds in the ERalphaKO brain and is capable of modulating PR gene expression, thus supporting the presence and functionality of a nonclassical estrogen receptor.