HYPOTHALAMIC ESTROGEN RECEPTOR-IMMUNOREACTIVITY IN PREPUBERTAL VS ADULT FEMALE GUINEA-PIGS

Juvenile guinea pigs (18-20 days old) rarely display lordosis in respo nse to estradiol and progesterone treatments that elicit sexual behavi or in adult females. Nor do immature animals release a preovulatory-li ke surge of luteinizing hormone in response to estradiol. In vitro rad ioligand binding assays have revealed similar concentrations of estrog en receptors in the hypothalamus and preoptic area of prepubertal and adult guinea pigs. The aim of the present study was to compare estroge n receptor-immunoreactivity in a variety of forebrain regions of immat ure and adult guinea pigs, to determine whether age differences in est rogen receptor levels in more discrete portions of the hypothalamus an d preoptic area exist. Forebrain tissue from juvenile (17 days) and ad ult females (> 6 weeks), ovariectomized 6 days previously, was process ed for estrogen receptor-immunoreactivity, using Abbott Laboratories' H222 anti-human estrogen receptor antibody. Juveniles had estrogen rec eptor-immunoreactive cells in all of the same regions as adults: media l preoptic area, medial preoptic nucleus, bed nucleus of the stria ter minalis, periventricular, paraventricular, dorsomedial and arcuate nuc lei, ventrolateral and anterior hypothalamic regions, and amygdala. Am ong the areas in which estrogen receptor-immunoreactivity was quantifi ed (medial preoptic area, medial preoptic nucleus, anterior periventri cular nucleus, arcuate nucleus and ventrolateral hypothalamus), the on ly region in which an age difference in estrogen receptor-immunostaini ng was observed was the rostral portion of the ventrolateral hypothala mus. Juvenile females had, on average, 30% fewer estrogen receptor-imm unoreactive cells in a sample of this region than adults (440 +/- 25 v s 626 +/- 25, P=0.001). These data are consistent with the hypothesis that insufficient estrogen receptors in the rostral ventrolateral hypo thalamus may underlie, in part, the markedly deficient responses of ju venile female guinea pigs to estradiol.