Immunocytochemical detection of estrogen receptor-alpha in the female rabbit forebrain: topography and regulation by estradiol.

Two antibodies (H222 and Zymed) directed towards different sites of the estrogen receptor-alpha (ERalpha) were used for the following objectives: (1). to map the ERalpha in the forebrain of ovariectomized (ovx) rabbits by immunocytochemistry and (2). to determine the effect of endogenous (intact non-pregnant animals) and exogenous (ovx, estrogen-treated animals) estradiol (E2) on the population of ERalpha in the forebrain. Similar results were obtained with both antibodies used: dense aggregations of ERalpha-immunoreactive (IR) neurons were found in the infundibular nucleus (IN), the medial preoptic area (POA), the bed nucleus of the stria terminalis (BNST), and some nuclei of the amygdala. By contrast, no ERalpha-IR neurons were present in the ventromedial hypothalamic nucleus (VMN), but a dense aggregation of ERalpha-IR neurons occurred lateral to it in nucleus X. Numerous ERalpha-IR neurons were observed in the paraventricular hypothalamic nucleus, but not in the supraoptic or suprachiasmatic nuclei. The hippocampus proper lacked ERalpha-IR neurons, but the ventral subiculum in the hippocampal formation had a dense group of such cells. Intact non-pregnant rabbits showed less ERalpha-IR neurons in all regions tested than ovx animals. This difference was particularly clear in the medial POA, amygdala and BNST, while the IN showed only a marginal decrease. The dorsal, but much less the ventral, part of nucleus X also showed a decrease in the number of ERalpha-IR neurons compared with ovx animals. E2 benzoate (5 microg/day for 5 days) reduced even further the number of ERalpha-IR neurons in all regions except in a circumscribed area of the IN and the ventral part of nucleus X. These results show the existence of both sensitive and insensitive neurons to the down-regulatory effect of E2 on the presence of ERalpha. Sensitive neurons are located in the telencephalon, POA and several hypothalamic nuclei (PVN), while insensitive neurons are mainly restricted to the IN and the ventral part of nucleus X in the basal hypothalamus. Copyright 2003 S. Karger AG, Basel