Immunocytochemical Detection of Estrogen Receptor-α in the Female Rabbit Forebrain: Topography and Regulation by Estradiol

Abstract

Two antibodies (H222 and Zymed) directed towards different sites of the estrogen receptor-α (ERα) were used for the following objectives: (1) to map the ERα 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 ERα in the forebrain. Similar results were obtained with both antibodies used: dense aggregations of ERα-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 ERα-IR neurons were present in the ventromedial hypothalamic nucleus (VMN), but a dense aggregation of ERα-IR neurons occurred lateral to it in nucleus X. Numerous ERα-IR neurons were observed in the paraventricular hypothalamic nucleus, but not in the supraoptic or suprachiasmatic nuclei. The hippocampus proper lacked ERα-IR neurons, but the ventral subiculum in the hippocampal formation had a dense group of such cells. Intact non-pregnant rabbits showed less ERα-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 ERα-IR neurons compared with ovx animals. E2 benzoate (5 µg/day for 5 days) reduced even further the number of ERα-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 ERα. 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.

Estrogen and Ovariectomy Regulate mRNA and Protein of Glutamic Acid Decarboxylases and Cation-Chloride Cotransporters in the Adult Rat Hippocampus

“…The effect of prolonged OVX on estrogen-induced luteinizing hormone surges was interpreted as a supersensitization phenomenon of neurotransmitter or steroid receptors by deafferentation or receptor blockade. Indeed, estradiol treatment after OVX suppresses, and OVX alone increases, levels of nuclear ERs, especially ERα, in the hypothalamus [86, 87, 88]and the CA1 region of the hippocampus [9, 89]. We suggest that basal levels of estrogen normally maintain GAD levels in intact females and that the positive estrogenic effect unmasks the maintenance effect as the GAD levels decline after long-term OVX.…”

Disruption of sexual function, FSH secretion, and spermiogenesis in rabbits following developmental exposure to vinclozolin, a fungicide

“…Across a large number of vertebrate species, one particularly important region is the preoptic area and anterior hypothalamus (POA/AH) -a region well-known for sex differences in brain structure and function (reviewed by Tobet & Fox 1992). While estrogens are known to bind to receptors in this region of the rabbit brain (Caba et al 2003), male/female differences and their dependence on developmental exposure to estrogens or androgens have not been examined. Emerging data from our laboratory reveal that the rabbit POA/AH is sexually dimorphic, and that vinclozolin seems to disrupt organization of a specific, sexually dimorphic region that is known to be critical in male sexual behavior.…”

Immunolocalisation of α and β Oestrogen Receptors in Basolateral Amygdala of Rabbit Males

“…In the same examinations, the comparison of α-oestrogen receptor expression in ovariectomised and intact females revealed that the higher percentage of neurons in which IHC reaction was observed occurred in ovariectomised females. Oestradiol administration caused in most of the examined structures, except infundibulum nucleus and ventral part of nucleus X, a decrease in the percentage of neurons in which the reaction was observed (2). In immunoreactive neurons, the product of immunohistochemical reaction was observed in both cell nucleus and cytoplasm, but the nuclei of neurons were the main place of reaction.…”

“…In the amygdale, reaction of strong density was observed in the medial amygdaloid nucleus, basal nuclei, and cortical nuclei. Weak reaction was also observed in the central amydgaloid nucleus (2). There are no data on the expression of the examined receptors in other regions of the amygdala.…”