Hypothalamic Estrogen Receptor-lmmunoreactivity in Prepubertal vs Adult Female Guinea Pigs

Juvenile guinea pigs (18–20 days old) rarely display lordosis in response to estradiol and progesterone treatments that elicit sexual behavior in adult females. Nor do immature animals release a preovulatory-like surge of luteinizing hormone in response to estradiol. In vitro radioligand binding assays have revealed similar concentrations of estrogen receptors in thehypothalamus and preoptic area of prepubertal and adult guinea pigs. The aim of the present study was to compare estrogen receptor-immunoreactivity in a variety of forebrain regions of immature and adult guinea pigs, to determine whether age differences in estrogen receptor levels inmore discrete portions of the hypothalamus and preoptic area exist. Forebrain tissue from juvenile (17 days) and adult females (> 6 weeks), ovariectomized 6 days previously, was processed forestrogen receptor-immunoreactivity, using Abbott Laboratories' H222 anti-human estrogen receptor antibody. Juveniles had estrogen receptor-immunoreactive cells in all of the same regions as adults: medial preoptic area, medial preoptic nucleus, bed nucleus of the stria terminalis, periventricular, paraventricular, dorsomedial and arcuate nuclei, ventrolateral and anterior hypothalamic regions, and amygdala. Among the areas in which estrogen receptor-immunoreactivity was quantified (medial preoptic area, medial preoptic nucleus, anterior periventricular nucleus, arcuate nucleus and ventrolateral hypothalamus), the only region in which an age difference in estrogen receptor-immunostaining was observed was the rostral portion of the ventrolateral hypothalamus. Juvenile females had, on average, 30% fewer estrogen receptor-immunoreactive cells in asample of this region than adults (440 ± 25 vs 626 ± 25, P = 0.001). These data are consistent with the hypothesis that insufficient estrogen receptors in the rostral ventrolateral hypothalamus may underlie, in part, the markedly deficient responses of juvenile female guinea pigs to estradiol.