Autoradiographic localization of 3H-estradiol or its metabolites in the central nervous system of the developing rat

Membrane estradiol signaling in the brain

While the physiology of membrane-initiated estradiol signaling in the nervous system has remained elusive, a great deal of progress has been made toward understanding the activation of cell signaling. Membrane-initiated estradiol signaling activates G proteins and their downstream cascades, but the identity of membrane receptors and the proximal signaling mechanism(s) have been more difficult to elucidate. Mounting evidence suggests that classical intracellular estrogen receptor-alpha (ERalpha) and ERbeta are trafficked to the membrane to mediate estradiol cell signaling. Moreover, an interaction of membrane ERalpha and ERbeta with metabotropic glutamate receptors has been identified that explains the pleomorphic actions of membrane-initiated estradiol signaling. This review focuses on the mechanism of actions initiated by membrane estradiol receptors and discusses the role of scaffold proteins and signaling cascades involved in the regulation of nociception, sexual receptivity and the synthesis of neuroprogesterone, an important component in the central nervous system signaling.

Estrogen and environmental estrogenic chemicals exert developmental effects on rat hypothalamic neurons and glias

We investigated effects of 17beta-estradiol (E(2)) and endocrine disrupters, nonylphenol (NP) and bisphenol-A (BPA), focusing on the neuronal development in cultures of fetal rat hypothalamic cells. We applied different concentrations of E(2), NP or BPA to the cultured hypothalamic cells and observed their effects on dendritic and synaptic development by immunocytochemistry using anti-microtubule associated protein-2 (MAP2) and anti-synapsin I antibodies, respectively. Administration of E(2) for 7 days affected MAP2-positive area as well as synapsin I-positive area. NP and BPA also influenced neuronal developments. The significant increase both in MAP2- and synapsin I-positive areas was observed at 10 and/or 100 nM of them, while 1 microM of them reduced the positive areas. Synaptic densities calculated from synapsin I-positive area/MAP2-positive area were not constant among different doses of three chemicals, but increased at 10 and/or 100 nM and decreased at 1 microM. Furthermore, immunostaining of NP-treated cells with the antibody against glial fibrillary acidic protein (GFAP) revealed that glial development was similarly influenced by NP. Therefore, the present results demonstrated that not only E(2) but also the environmental estrogenic chemicals, NP and BPA, affect development of fetal rat hypothalamic cells in vitro.

Histochemistry and cytochemistry of nuclear receptors

Receptors of steroid hormones, thyroid hormones and several kinds of vitamins have been shown to act as nuclear transcription factors and to form a nuclear receptor (NR) family. Histochemical techniques including autoradiography using radio-labeled ligands, immunohistochemistry and in situ hybridization histochemistry, have displayed that target cells of these receptors are distributed not only in the classical target organs but also widely in a variety of tissues; these techniques can demonstrate the presence of receptor proteins and mRNAs, even though they are expressed in a small cell population of tissues. On the other hand, many studies have been performed to demonstrate the interaction between NRs and nuclear and cytoplasmic proteins, and to clarify the mechanism of transcriptional regulation through NRs in artificial conditions which are created in gene transfer experiments or under cell-free conditions. Some data coincide with those obtained from histochemical techniques, however, some histochemical data do not support the results of studies in vitro. This review focuses on the following topics: histochemical methodologies to detect NRs, the distribution and function of NRs in the tissues, the intracellular and intranuclear localization of NRs, roles of gonadal steroid receptors and their ligands on developing tissues including cell communications such as mesenchymal-stromal interaction, and the interaction between other cellular components and NRs. In addition, the agreement and disagreement between the results of histochemical studies and those from the experiments in the model systems or in vitro are discussed.

Estrogen modulates spontaneous alternation and the cholinergic phenotype in the basal forebrain

We report that a small population of neurons expresses both choline acetyltransferase and classical estrogen receptor immunoreactivity and they are found primarily in the bed nucleus of the stria terminalis. In short-term ovariectomized ageing mice (24 months, n = 5) there were 41.0 +/- 4.1% fewer of these double-labeled cells than in young (five months, n = 5) short-term ovariectomized C57BL/6J mice. To study cholinergic neuron estrogen responsiveness, young mice (n = 8) were ovariectomized at puberty (five weeks). After three months half of the mice (n = 4) were given physiological levels of 17beta estradiol for 10 days. Bed nucleus double-labeled neurons increased by 32.9% (P < or = 0.003) in the young mice given estrogen. In a gel shift assay, double-stranded oligonucleotides with putative estrogen response elements from the choline acetyltransferase gene were used as competitors against estrogen receptor binding to consensus estrogen response elements. A sequence with 60% homology to the vitellogenin estrogen response element was found to compete at 500- and 1000-fold excess. Young mice (five months) with ovaries demonstrated significantly (P < or = 0.04) better performance in the spontaneous alternation T-maze test than did old (19 month) mice with ovaries (young = 66.3 +/- 3.3% correct choices; vs old = 55.0 +/- 4.0% in old mice with ovaries). Young mice (five months old), ovariectomized for one month and treated with estrogen, showed significantly more spontaneous alternation than ovariectomized controls (69.1 +/- 2.8% vs 58.3 +/- 3.9%; P < or = 0.04). Estrogen also increased spontaneous alternation in old, short-term ovariectomized mice (61.5 +/- 2.7% vs 48 +/- 3.3%; P < or = 0.005). In either young or old ovariectomized mice, estrogen increased spontaneous alternation to levels seen in young animals with ovaries. Estrogen increases the number of choline acetyltransferase-immunoreactive and choline acetyltransferase/estrogen receptor-immunoreactive cells in old or young mice lacking estrogen, and enhances working memory in old or young mice lacking estrogen. Our data suggest that estrogen may act at the level of the choline acetyltransferase gene, but in view of the limited distribution of cholinergic cells expressing the classical estrogen receptor, it is unlikely that these cells can account for a memory enhancing effect of estrogen replacement.

Postnatal development and sex difference in neurons containing estrogen receptor-alpha immunoreactivity in the preoptic brain, the diencephalon, and the amygdala in the rat

Estrogen has been considered as a key substance that induces sexual differentiation of the brain during fetal and neonatal life in the rat. Thus, to define the brain regions involved in the brain sexual differentiation, we examined the regions where the estrogen receptor (ER) is located in the developing rat brain. We examined immunohistochemical distribution of the cells containing estrogen receptor-alpha (ER-alpha) in the preoptic region, the diencephalon, and the amygdala in male and female rats on postnatal days 1-35 (PD1-PD35). The antibody used recognizes ER-alpha equally well for both occupied and unoccupied forms. ER-alpha immunostaining was restricted to the cell nuclei of specific cell groups. In PD1 rats, ER-alpha-immunoreactive (ER-IR) signals were detected in the lateral septum, the organum vasculosum lamina terminalis, the medial preoptic nucleus (MPN), the median preoptic nucleus, the bed nucleus of the stria terminalis, the hypothalamic periventricular nucleus, the lateral habenula, the posterodorsal part of the medial amygdala nucleus, the posterior part of the cortical amygdala nucleus, the hypothalamic ventromedial nucleus (VMH), the hypothalamic arcuate nucleus, and the posterior hypothalamic periventricular nucleus. The distribution pattern of ER-IR cells in the newborn rat was much the same as that in the adult in the preoptic-hypothalamic and amygdala regions. Moreover, the signals in the MPN and the VMH were stronger in the female than in the male, perhaps reflecting the ability ofestrogen generated by aromatization of testosterone in the male to down-regulate the ER signal. Thus, the brain regions showing sex differences may be sites of sexual differentiation of the brain by aromatizable androgen during the neonatal period.

Hormonally induced neuronal plasticity in the adult motoneurons

Sex steroids are known to play a crucial role in reproductive neuroendocrine functions in adulthood. A number of neurons in the neuroendocrine brain contain sex steroid receptors, and are thought to be a key element of functional neural circuits that are regulated by sex steroids. Motoneurons in the spinal nucleus of the bulbocavernosus in adult male rodents are one of the androgen-sensitive neural substrates. In the spinal nucleus of the bulbocavernosus, castration of adult male rats results in a significant decrease in the somatic size and dendritic length of the motoneurons, and in the number and size of chemical and electrical (gap junction) synapses onto these motoneurons. Androgen treatment of castrates reverses these changes. Furthermore, androgen has been reported to be involved in regulation of androgen receptor expression and gene expression of structural proteins such as beta-actin, beta-tubulin and gap junction channels in these motoneurons. The findings suggest that androgen induces morphological and molecular changes in the motoneurons that reflect their neural functions, and may provide evidence for the mechanisms of hormonally induced neuronal plasticity in the motoneurons in adulthood.

Roles of steroid hormones and their receptors in structural organization in the nervous system

Due to their chemical properties, steroid hormones cross the blood-brain barrier where they have profound effects on neuronal development and reorganization both in invertebrates and vertebrates, including humans mediated through their receptors. Steroids play a crucial role in the organizational actions of cellular differentiation representing sexual dimorphism and apoptosis, and in the activational effects of phenotypic changes in association with structural plasticity. Their sites of action are primarily the genes themselves but some are coupled with membrane-bound receptor/ion channels. The effects of steroid hormones on gene transcription are not direct, and other cellular components interfere with their receptors through cross-talk and convergence of the signaling pathways in neurons. These genomic and non-genomic actions account for the divergent effects of steroid hormones on brain function as well as on their structure. This review looks again at and updates the tremendous advances made in recent decades on the study of the role of steroid (gonadal and adrenal) hormones and their receptors on developmental processes and plastic changes in the nervous system.

Estrogen receptor mRNA levels in the preoptic area of neonatal rats are responsive to hormone manipulation

Testosterone, after conversion to estrogen, masculinizes the developing preoptic area (POA) of rats, via binding to intracellular estrogen receptors located within the POA. Our previous studies have shown what seems to be a paradox, in that the levels of estrogen receptor mRNA are lower in males than in females. In the present study, we examined the effects of hormone manipulations on estrogen receptor (ER) mRNA levels in the preoptic area of neonatal male and female rats to test the hypothesis that gonadal steroid hormones regulate ER mRNA during the perinatal period. The relative amount of steady state ER mRNA was assessed in the preoptic area of postnatal day 4 animals using in situ hybridization and film autoradiography. Hybridization density was approximately 2-fold higher in females compared with hybridization density in males. Depletion of testosterone by bilateral removal of the testes on the day of birth increased the level of ER mRNA in males to that observed in females. Treatment of females with the synthetic estrogen, diethylstilbestrol (1 microgram per day, in pellet form), reduced ER mRNA levels to a level comparable to that in intact males. The non-aromatizable androgen, dihydrotestosterone (50 micrograms per day, in pellet form), had no effect on ER mRNA in females. These results suggest that estrogen, derived from the local aromatization of circulating testosterone, down-regulates ER mRNA in the neonatal male preoptic area. Down-regulation of ER mRNA may be an important estrogen-regulated event in the process of sexual differentiation of the preoptic area.

Transient expression of estrogen receptor-immunoreactivity (ER-IR) in the layer V of the developing rat cerebral cortex

Occurrence of estrogen receptor-immunoreactivity (ER-IR) in the cerebral cortex was examined in neonatal and adult rats. In newborn rats of postnatal day 1 (= day of birth) and postnatal day 5 (PD1 and PD5, respectively), ER-IR was not evident in the neocortex. On postnatal days 7, 10 and 13 (PD7, PD10 and PD13 respectively), a group of cells with distinct ER-IR appeared in the layer V of the auditory cortex. At the PD10, weak but specific ER-IR were also appeared in the somatosensory and the visual cortices. Among these areas, the ER-IR positive neurons occurred most frequently in the auditory cortex at PD10 rats. By examination of adjacent sections, one stained with Cresyl violet and the another stained with acethylcholinesterase (AChE) histochemistry, it was revealed that the region with ER-IR at PD7 to PD13 was limited to layer V of the neocortex. These signals, however, disappeared at PD15. In layer II of the neocortex, on the other hand, weak ER-IR signals were detected throughout the area sporadically at PD21 and in adults. The ER-IR detected transiently in the auditory cortex by the antiserum might contribute to maturation and establishment of the neurons of the rat auditory circuit.

Estrogen receptor found in the facial nucleus of the newborn rat is suppressed by exogenous estrogen: immuno- and in situ hybridization histochemical studies

Expression of the messenger RNA coding estrogen receptor (ER-mRNA) was detected in the ventromedial subnucleus of the facial nucleus of the newborn rat by in situ hybridization histochemistry (ISHH). The hybridization signal in this subnucleus increased from 1 to 6 days of age, then decreased at 11 days. By immunohistochemistry (IHC) using an antiserum which detects estrogen receptor (ER) specifically, immunopositive signals were also detected in the same subnucleus of the adjacent sections. On the other hand, neither of these signals were encountered in the same subnucleus of the adult rat. Thus, the present result extend our previous work (Yokosuka and Hayashi, 1992) showing that the expression of the ER in the facial nucleus is transient. A sex difference in the expression of ER molecules was not apparent by ISHH and IHC. Moreover, daily injections of estradiol from the day of birth suppressed the expression of ER in the subnucleus at 6 and 11 days of age. Thus, as has been detected in the mediobasal hypothalamus, ER-mRNA was revealed to be down-regulated by estrogen.

Developmental profile of estrogen receptor mRNA in the preoptic area of male and female neonatal rats

Exposure to estrogen or estrogenic metabolites of testosterone during the early postnatal period has permanent effects on rodent brain development. Differential sensitivity to estrogen, as reflected by transcription of the estrogen receptor gene, might determine the period of maximal sensitivity to the masculinizing effects of estrogen. We used an 35S-labeled riboprobe and in situ hybridization to chart the development of estrogen receptor (ER) mRNA expression in the rat preoptic area, a brain region for which sexual dimorphisms and the effects of estrogen on development are particularly well documented. Neonatal male and female rats were sacrificed by perfusion fixation on postnatal days 0, 2, 4, 7 or 10 (PND; day of birth is PND 0). Many ER mRNA-containing cells were detected in the periventricular preoptic area and medical preoptic nucleus and the distribution of ER-synthesizing cells was similar in both sexes. Analysis of film autoradiograms showed that the relative steady state level of ER mRNA was significantly higher in females than in males at all ages except PND 0 and 10. The temporal profile of ER mRNA expression was different in males and females. ER mRNA did not change with age in males, whereas in females, ER mRNA was significantly higher on PND 2 compared with PND 0 and 10. These results demonstrate that the pattern of ER mRNA expression is quantitatively and qualitatively different between the sexes during the neonatal period. The pattern of ER mRNA expression contrasts markedly with previous reports of estrogen binding based on biochemical and autoradiographic steroid binding assays.(ABSTRACT TRUNCATED AT 250 WORDS)

The ontogeny of GAP-43 (neuromodulin) mRNA in postnatal rat brain: evidence for a sex dimorphism

GAP-43 is a membrane-bound protein selectively concentrated in axonal growth cones during brain development and implicated in axonal outgrowth and elongation. A sex dimorphism in the number of synapses in certain regions of the adult rat brain has been attributed to differences in gonadal steroid hormone action during early postnatal life. The results of recent studies have demonstrated that gonadal steroids modulate GAP-43 mRNA in regions of the postnatal and adult brain where steroid hormone receptors are concentrated. Since gonadal steroids influence the development of the sexually undifferentiated brain during the first few weeks of postnatal life, the present study investigated the ontogeny of GAP-43 mRNA in the male and female rat brain between postnatal days 1 and 25. On postnatal days 1, 3, 6, 12, 18, and 25, brains were collected from male and female postnates and frozen, and 16 microns cryostat sections were processed and hybridized with a 35S-labeled antisense riboprobe complementary to GAP-43 mRNA. Evaluation of film autoradiograms demonstrated a widespread distribution of GAP-43 mRNA in postnatal brain regions, including the cerebral cortex; bed nucleus of the stria terminalis; and medial preoptic area, ventromedial nucleus, and arcuate nucleus of the hypothalamus. Densitometric measurements revealed that GAP-43 mRNA was transiently elevated during early postnatal life, with a subsequent decrease during brain maturation, although the pattern of change varied among the brain regions investigated. In addition, the level of GAP-43 hybridization signal was significantly higher in the male cortex, bed nucleus, and medial preoptic nucleus, but not the ventromedial and arcuate nuclei, than in postnatal females. Analysis of slide autoradiograms demonstrated that the change in GAP-43 mRNA during postnatal development was due to changes at the cellular level. The present results indicate that expression of GAP-43 mRNA is transiently elevated and sexually dimorphic in certain regions of the early postnatal rat brain. The results further suggest that the differential expression of GAP-43 in the male and female postnatal brain may be related to sex differences in neuronal outgrowth and connectivity resulting in a dimorphism in the pattern of adult neuronal circuitry.

Androgenic regulation of expression of beta-tubulin messenger ribonucleic acid in motoneurons of the spinal nucleus of the bulbocavernosus

Expression of beta-tubulin mRNA was examined in androgen-sensitive motoneurons of the spinal nucleus of the bulbocavernosus (SNB) in adult male rats by in situ hybridization histochemistry using cDNA encoding mouse beta-tubulin. Hybridizable beta-tubulin mRNA was localized in the somata and proximal dendrites of SNB motoneurons. Removal of androgen by castration significantly reduced the expression level of beta-tubulin mRNA in the SNB motoneurons, whereas the change was prevented by testosterone treatment. On the contrary, castration or testosterone treatment did not induce any changes in the expression level of beta-tubulin mRNA in the androgen-insensitive motoneurons of the retrodorsolateral nucleus. These results suggest that androgen regulates the expression of beta-tubulin gene in the SNB motoneurons and may provide evidence for the molecular mechanisms of hormonally-induced neuronal plasticity in the SNB motoneurons.

Gonadal steroids modulate the growth-associated protein GAP-43 (neuromodulin) mRNA in postnatal rat brain

Gonadal steroid hormone action during early postnatal life determines the growth and connectivity of certain neuronal populations in the hypothalamus. The results of recent studies indicate that steroid hormones modulate the growth-associated protein GAP-43 mRNA in the adult rodent hypothalamus. Since GAP-43 is concentrated in axonal growth cones and has been implicated in axonal elongation and synaptogenesis, the present study investigated the effect of various gonadal hormonal conditions on GAP-43 mRNA levels in postnatal rat brain. On postnatal day 1, male rats were castrated or sham-operated and injected with sesame oil. Additional intact female rats were also injected with oil, while a group of female pups were injected with testosterone propionate. On postnatal day 6, brains were frozen and 16-microns cryostat sections processed and hybridized with a 35S-labeled antisense riboprobe complimentary to GAP-43 mRNA. Slide-mounted sections were stringently washed, apposed to X-ray film and then dipped in liquid emulsion. Evaluation of slide and film autoradiograms revealed an extensive presence of GAP-43 mRNA in the medial preoptic nucleus, bed nucleus of the stria terminalis and cerebral cortex, while the intensity of hybridization signal in other brain regions including the striatum was low. Quantitative assessment of GAP-43 mRNA in the medial preoptic area revealed that the level of GAP-43 mRNA was highest in the sham-operated male, attenuated after male castration, low in the intact female and markedly augmented in the testosterone-treated female. The pattern of change in the bed nucleus of the stria terminalis and laminae II and III of the frontal cortex was similar to that observed in the preoptic area. The changes in hybridization signal were positively correlated with changes in serum testosterone levels as determined by RIA. The results of these studies indicate that GAP-43 mRNA levels in the medial preoptic area, bed nucleus of the stria terminalis and cerebral cortex are sexually dimorphic and modulated by changes in gonadal steroid hormone levels. The results further suggest that the differential regulation of GAP-43 mRNA by sex steroids in the male and female postnatal brain may influence the phenotype of forebrain neuronal circuitry and thereby determine the phenotype of adult neuronal function.

Estrogen receptor immunoreactive neurons in the fetal ferret forebrain

The development of estrogen receptors was studied in the preoptic area/anterior hypothalamus (POA/AH) of fetal male and female ferrets. In males this region includes a nucleus (MN-POA/AH), delineated by Nissl stains, which is not discernible in females. The results reveal the distribution of estrogen receptor containing cells during the period when estrogen is known to induce the differentiation of the male ferret's MN-POA/AH. Brains were taken from ferret kits on days 30, 34, 37 and 40 of a 41-42 day gestation, and were processed utilizing the H222 monoclonal antibody to reveal estrogen receptors. At E30 there were numerous H222 immunoreactive (ir) cells in central regions of the POA/AH. From E30 to E40 there was a striking increase in the number of H222ir cells in the POA/AH. A broad sweep of H222ir cells extended from the ventral POA dorsally and laterally into the caudal POA and AH of both males and females. H222ir cells were not restricted to the region of the MN-POA/AH at any fetal age. H222 immunoreaction product at E30 was restricted to nuclear compartments. By E40, H222ir processes extended from some cells with H222ir nuclei in the medial and lateral POA/AH in both males and females. At the older fetal ages immunopositive cell numbers increased in lateral positions. At E34 and E37 (but not E30) selective ventricular zones, and regions between the hypothalamus and amygdala contained H222ir cells, suggesting the presence of estrogen receptors in cells during migration. Although the amygdala contained a few H222ir cells as early as E34, the cortex lacked H222ir cells even as late as E40. The appearance of H222ir cells in positions suggestive of migration is consistent with the hypothesis that estrogen receptors play some role in determining cell positions in certain regions of the developing nervous system.

Transient expression of estrogen-receptor-like immunoreactivity (ER-LI) in the facial nucleus of the neonatal rat

Estrogen receptor-like immunoreactivity (ER-LI) was detected in the medial subnucleus of the facial nucleus by immunocytochemistry in both male and female neonatal rats, but not in the adult rat. Identity of the motoneurons in this subnucleus projecting to the corresponding facial muscles and the cells with ER-LI positive signals was examined by retrograde tracing. The majority of the cells marked with the tracer did not carry ER-LI signals.

Effect of androgen on the expression of gap junction and beta-actin mRNAs in adult rat motoneurons

Expression of gap junction and beta-actin mRNAs was examined in androgen-sensitive motoneurons of the spinal nucleus of the bulbocavernosus (SNB) in adult male rats by in situ hybridization histochemistry using complementary DNAs encoding rat liver gap junction protein (connexin 32) and chick beta-actin. Hybridizable gap junction and beta-actin mRNAs were localised on the somata and proximal dendrites of SNB motoneurons. Removal of androgen by castration significantly reduced the expression levels of both gap junction and beta-actin mRNAs in the SNB motoneurons, whereas these changes were prevented by testosterone treatment. On the contrary, castration or testosterone treatment did not induce any changes in the expression levels of gap junction and beta-actin mRNAs in the motoneurons of the retrodorsolateral nucleus (RDLN), which accumulate androgen less frequently and sparsely than those in the SNB. These results suggest that androgen regulates the expression of both gap junction and beta-actin genes in the SNB motoneurons and may provide evidence for the molecular mechanisms of hormonally induced neuronal plasticity in the SNB motoneurons.

Distribution of estrogen target sites in the 2-day-old mouse forebrain and pituitary gland during the 'critical period' of sexual differentiation

The present study provides a detailed anatomical description of estrogen target cells in the mouse forebrain and pituitary gland during the sexual imprinting stage of the brain. Six 2-day-old mice (3 males and 3 females) were s.c. injected with 16 alpha-[125I]iodo-11 beta-methoxy-17 beta-estradiol ([125I]MIE2) and two additional mice (one male and one female) were s.c. injected with 1000x unlabeled 17 beta-estradiol 1 h before [125I]MIE2 to check the specificity of estradiol binding. Two hours after injection the mice were decapitated, the brains dissected, frozen sectioned, and processed for thaw mount autoradiography. The highest intensity of nuclear labeling was observed in the preoptic-anterior hypothalamic area, amygdala and cortex entorhinalis. Strong labeling was present in the cerebral cortex and moderate to strong labeling in the lateral septum, bed nucleus of stria terminalis and pituitary gland. Weak to moderate labeling was observed in the bulbus olfactorius, circumventricular organs, basal ganglia, ventral striatum, thalamus, hippocampus and pineal gland. No sex differences were observed in the intensity of labeling and distribution of the estrogen target sites. The topographic distributions of estrogen-concentrating cells in the hypothalamus of the 2-day-old mouse forebrain was similar to the adult pattern but differed prominently in the cerebral cortex, entorhinal cortex and thalamus: the cerebral cortex showed an extensive and intensive labeling, the intensity of labeling in the entorhinal cortex greatly exceeded that observed in the adult and the nucleus anterior medialis thalami was distinctly labeled.

Progestin receptor cells in mouse cerebral cortex during early postnatal development: a comparison with preoptic area and central hypothalamus using autoradiography with [125I]progestin

The distribution of progestin target cells in the cerebral cortex and the effect of estrogen treatment was assessed during the critical period of brain development and compared with the preoptic/central hypothalamic regions. [125I]progestin was injected into 0, 2, 8, and 12 day postnatal mice pretreated for 3 days with oil, 5 micrograms/100 g b, wt., or 100 micrograms/100 g b. wt. of estradiol dissolved in oil. Two hours after injection of radiolabeled ligand, brains were frozen and processed for thaw-mount autoradiography. At birth, labeled cells were detected in the deep (lamina VI) and intermediate (lamina V) layers of the lateral cortical regions, increased in laminae V-VI of the lateral cortex and laminae II-VI of the cingulate/paracingulate cortex at days 2 and 8, and decreased throughout the cortex by day 12. Pretreatment of animals with estradiol had no noticeable effect on the nuclear concentration of [125I]progestin in cortical cells, while estrogen weakly enhanced labeling in preoptic/central hypothalamic regions at day 2 and markedly augmented labeling in the 8 and 12 day brain. The results demonstrated that progestin receptor cells are present in the postnatal dorsal cortex, preoptic area, and hypothalamus and that the topography of cortical progestin target cells differs in part from that of estrogen target cells reported earlier.

Can a single androgen receptor fill the bill?

If the above two hypotheses are correct, they would require at least one more specific nuclear receptor for T, and at least one membrane receptor to account for the very rapid effects induced by androgens on certain target tissues. If this is the case, clearly a single androgen receptor will not fill the bill.

Synaptogenic action of sex steroids in developing and adult neuroendocrine brain

Sex steroids exert potent influences on modulating neural development and neural circuit formation in both developing and adult sex steroid-sensitive neuroendocrine brain. During development, estrogen or aromatizable androgen can act as a neurotropic factor on neural tissues, stimulating axonal and dendritic growth and synapse formation. The development of sexual dimorphic synaptic organization may reflect sex steroid-modulating synaptogenesis in the hypothalamus and limbic system during the perinatal period. The onset of puberty also may be due, at least in part, to stimulation of synapse formation by estrogen in the hypothalamus. In adulthood, estrogen has a facilitatory effect on synapse formation in neural structures such as septum, hypothalamus and midbrain with or without brain lesions, and androgen plays a significant role in regulating synaptic remodeling in the androgen-sensitive spinal motoneuron pools. Thus, sex steroids seems to be critical from the developmental period to adulthood for organizing and reorganizing the neuronal circuitry driving neuroendocrine and behavioral functions.

Obese (ob/ob) and diabetes (db/db) mutations: two factors modulating brain and peripheral tissue accumulation of estradiol in C57BL/KsJ mice

The effect of two mutant genes for obesity (ob/ob) and diabetes (db/db) on the accumulation rate of radiolabeled estradiol was examined in female C57BL/KsJ mice. Mutant mice were match-paired with normal (+/?) animals at 16 weeks of age. All ob/ob and db/db mice exhibited overt obesity and hyperglycemia relative to normals. The distribution and uptake of the radiolabeled estradiol was subsequently examined in specified CNS and peripheral tissues. In all cases, the db/db and ob/ob mutant conditions resulted in a depressed cellular accumulation of radiolabeled estradiol in both CNS and peripheral tissues relative to normal mice. The ob/ob mutation resulted in a more severe depression of tissue estradiol uptake than did the db/db mutation. These studies indicate that the abnormal metabolic and hormonal states induced by the mutations, and not the mere presence of the genomic mutation itself, probably accounts for the depressed cellular affinity for gonadal steroids in these murine models.

Steroid autoradiography of the sexually dimorphic nucleus of the preoptic area

Autoradiography was performed to determine if the neurons of the sexually dimorphic nucleus of the preoptic area (SDN-POA) in the adult rat accumulate estradiol (E2), testosterone (T), and/or dihydrotestosterone (DHT). Three days prior to steroid administration, adult male and female Sprague-Dawley rats were gonadectomized and adrenalectomized. Animals were then given either [3H]T, [3H]E2, or [3H]DHT through an indwelling jugular cannula. One hour later, animals were decapitated and brain sections processed for thaw mount autoradiography. The autoradiograms which contained the SDN-POA and an adjacent area of the medial preoptic area (MPOA) were quantitatively analyzed using the 3 times background, 5 times background, and Poisson criteria for labeled cells. In general, cells in the SDN-POA and the MPOA accumulate T, E2, or DHT. For both sexes, there is a greater percentage of labeled cells in the SDN-POA than in the MPOA, and a greater percentage of labeled cells following E2 exposure than following T or DHT exposure. In addition, there is a sex difference (male greater than female) in the percentage of labeled cells following T exposure. In summary, these data indicate that adult SDN-POA neurons do accumulate gonadal steroids.

Sites of aromatization of [3H]testosterone in forebrain of male, female and androgen receptor-deficient Tfm mice: an autoradiographic study

The distribution of radioactivity after injection of [3H]testosterone was studied in the forebrain of adult mice by thaw-mount autoradiography. Nuclear labeling was high in neurons in the dorsal part of the medial nucleus of the amygdala and in the dorsocaudal part of the bed nucleus of the stria terminalis. Low nuclear uptake occurred in the medial preoptic nucleus, in mediobasal hypothalamic nuclei and in the ventromedial amygdala. Nuclear concentration of radioactivity was not influenced by competition with dihydrotestosterone and was present in androgen receptor deficient Tfm mice. It was totally abolished by competition with estradiol. This indicates that in the brain [3H]testosterone is converted to estrogenic metabolites which bind to estrogen receptors. Nuclear labeling after [3H]testosterone was restricted to a few of the brain nuclei, known to contain estrogen receptors indicating that aromatization occurs only in select regions. The results suggest that testosterone acts on the brain via estrogen receptors.

Development of sexual dimorphism in synaptic organization in the ventromedial nucleus of the hypothalamus in rats

The ventromedial nuclei of the hypothalamus (VMN) were examined ultrastructurally in both male and female rats at 5, 20, 45 and 100 days of age. Synaptic number in the VMN was increased to 70-80% of that at 45 days of age during the first 20 days. At 5 days of age, sexual difference in the numerical density of dendritic shaft and spine synapses was not detected. Synaptic sexual difference developed by 20 days of age in the ventrolateral VMN where receptors for sex steroid were abundant. This tendency persisted until adulthood. However, no sexual difference in synaptic pattern was recognized in the dorsomedial VMN. From these results, it is suggested that sexual dimorphism in synaptic organization in the VMN develops from the early prepubertal period.

The ontogeny of androgen receptors in the CNS of Xenopus laevis frogs

Androgenic steroids have been implicated in the development of sex differences in Xenopus laevis frogs. In order to determine when neurons first acquire the ability to concentrate androgen, we prepared autoradiograms of CNS in developing frogs following injection of tritiated dihydrotestosterone (DHT). X. laevis tadpoles and juveniles from stage 60 to 2 months post-metamorphosis (PM) were injected with [3H]DHT. Brain and spinal cord autoradiograms from these animals were examined for the presence of labelled cells. The pattern of [3H]DHT labelling in stage-64 tadpoles and in PM juveniles was similar but not identical to that seen in adults. Heavily labelled cells were seen in the motor nucleus of cranial nerves IX and X, medullary reticular formation, a presumed sensory nucleus of cranial nerve V, pretrigeminal nucleus of the dorsal tegmental area of the medulla, laminar nucleus of the torus semicircularis, anterior pituitary, ventral thalamus and anterior spinal cord. The vestibular sensory nucleus of cranial nerve VIII was the only area that concentrates DHT in adults but did not contain labelled cells in young animals. No [3H]DHT-labelled cells were found in stage-60 tadpoles. The onset of androgen concentrating capability in X. laevis CNS thus probably occurs between stages 60 and 64.

Estrogen treatment enhances survival of cultured fetal rat amygdala neurons in a defined medium

Effects of estradiol on the survival of cultured fetal rat amygdala neurons were estimated to assess a possible organizational action of the sex steroid on the developing amygdala tissue. Dissociated 17-day fetal amygdala cells were cultivated initially in a serum-containing and then in a serum-free defined medium. The survival of the cells in the serum-free medium was highly enhanced when supplemented with estradiol at the concentration of 10 ng/ml. Predominant cell populations of the culture were identified as neuronal cells by the tetanus toxin labeling method. The results support the idea that sex steroids play a role in the brain sexual differentiation by enhancing the neuronal survival in the developing amygdala tissue.

Estrogens before birth and development of sex-related reproductive traits in the female guinea pig

Influences of estrogens on the differentiation of psychosexual traits in the female guinea pig were studied. Pregnant animals were injected intramuscularly with either 1, 2, or 3.3 micrograms estradiol benzoate (EB) or with 1 or 3 micrograms diethylstilbestrol dipropionate (DESDP). Injections were started on the 29th day of pregnancy, given daily for 6 days, and continued every other day until parturition. Female offspring were evaluated for onset of puberty, ovarian function, and lordosis and mounting behavior in adulthood. Prenatal treatment with 3 micrograms DESDP caused delayed puberty, impaired ovarian function, reduced responsiveness of lordosis to EB and P in adulthood (defeminization), augmented mounting in the absence of hormones (masculinization), and reduced responsiveness of mounting to exogenous EB and P in adulthood (defeminization). Prenatal treatment with 1 microgram DESDP produced similar but less pronounced effects. Prenatal treatment with 3.3 micrograms EB also caused a delay in puberty. However, responsiveness of lordosis to EB and P in adulthood was enhanced by treatment with either 1 or 3.3 micrograms EB prenatally. Further, neither mounting in the absence of hormones nor mounting in response to EB and P in adulthood were affected in any measurable way by any prenatal treatment with EB. These results show that estrogens can have masculinizing and defeminizing effects on sexually dimorphic reproductive traits in guinea pigs. The failure of EB to duplicate or parallel the effects of DESDP is not completely understood at this time, but it may indicate that less of the active substance reaches the target tissues following maternal and placental metabolism of EB than of DESDP.

The ontogeny of estrogen receptors: brain and pituitary

This study examines the prenatal and neonatal development of estrogen receptors in the central nervous system of the mouse. [3H]Diethylstilbestrol (DES) was injected into pregnant mice on days 4, 7, 10, 13, 14, 15 and 17 of gestation or into neonates. DES is an estrogen agonist that circumvents the alpha-fetoprotein barrier, thereby gaining access to intracellular estrogen receptors. Sixty minutes after injection whole embryos, fetuses or neonates were rapidly frozen and processed for autoradiography. Although the transplacental movement of the isotope was confirmed in all age groups evidence for nuclear estrogen receptors was not seen in the brain until day E14. On this day a few labeled cells first appeared in the basal hypothalamus, preoptic area, amygdala, midbrain and spinal cord. The number and the labeling intensity of target cells increased in each of these areas on days E15, E17 and P0. The first appearance of estrogen receptors closely follows the reported birthdates of neurons in these regions.

Anatomy and physiology of the neuroendocrine arcuate nucleus

The arcuate nucleus surrounds the ventral part of the third ventricle and contains densely packed small neurons with 1-3 dendrites. At least fifteen transmitters and neuropeptides have been found in perikarya of arcuate neurons. Each transmitter and neuropeptide have a characteristic distribution. In many cases distributions overlap (for example, dopamine and somatostatin, dopamine and neurotensin, neuropeptide Y and somatostatin) and alpha-MSH and beta-endorphin seem to have identical distributions but there are also distinctive neuronal populations containing only one of the described transmitters or neuropeptides (neuropeptide Y and alpha-MSH). Studies show extensive colocalization of dopamine and neurotensin and sparse colocalization of dopamine and GABA, neuropeptide Y and FMRF-NH2 and neuropeptide Y and somatostatin. Colocalization does not seem to be the rule in the arcuate, however, it is possible that colocalization may vary with the physiological state or sex of the animal. It also should be noted that our techniques may not be sensitive enough. To study efferent projections as a possible organizing principle within the arcuate, retrograde fluorescent tracing was combined with transmitter and neuropeptide immunohistochemistry. Mainly NPY and alpha-MSH neurons were studied and both peptides are present in projections to the preoptic area as well as to the midbrain periaqueductal gray. Some arcuate neurons were found to have collateral axons to both these areas. The arcuate communicates primarily with the pituitary gland, hypothalamus, limbic system, midbrain periaqueductal gray and autonomic nuclei of the brain stem. In this way, the arcuate may be involved in integrating emotional, sensory, vegetative homeostatic and autonomic functions with endocrine functions.

Diabetes-associated changes in estradiol accumulation in the aging C57BL/KsJ mouse brain

The effects of aging and diabetes on the uptake and incorporation of [3H]estradiol (E) in various brain areas was analyzed in C57BL/KsJ mice. Control (C; +/?) and diabetic (D; db/db) mice were pulse treated (30 min) with 10 muCi of [3H]E at 1, 2 and 4 months of age and the brains were subsequently microdissected, digested and the amount of incorporated [3H]E assessed. The pituitary and amygdala exhibited the highest levels of [3H]E incorporation of all brain areas, with the hypothalamus, septal nuclei, midbrain, hippocampus, medulla and parietal cortex exhibiting moderate retention levels at one month of age in C animals. All brain areas in D mice had significantly lower incorporation rates than in matchpaired, C animals. An age-related decrease in [3H]E accumulation was observed in all brain regions in both C and D groups, with a significant depression in [3H]E incorporation occurring between 1 and 4 months of age. These data demonstrate that an age-related decrease in [3H]E uptake occurs in most brain areas in the C57BL/KsJ mouse, and that the diabetic condition exacerbates this phenomenon.

Estrogen target neurons in the forebrain of the cat during postnatal development

The postnatal ontogeny of estrogen binding neurons in the forebrain of the kitten was studied quantitatively by counting 14,000 neurons in thaw-mount autoradiograms. One hour after the i.v. injection of [3H]estradiol into male and female kittens at 3, 10 and 22 days of age, concentrations of radioactivity were observed in the nuclei of neurons in the septal-bed nucleus-preoptic area, hypothalamus, and amygdala; these are the same regions that have been shown to contain estrogen target neurons in adult female cats. In addition, however, estrogen target neurons were present in the lateral third of the caudate nucleus (n.) and in the putamen in 3-day-old kittens; regions that are devoid of any estrogen target cells in the adult. Between 3 and 10 days of age, the numbers of labeled neostriatal neurons decreased markedly, and they were down to about 15% of 3-day values in kittens 22 days of age. The transient presence of estrogen target neurons during the phase of rapid dendritic development and synaptogenesis in the caudate n. immediately after birth raises the question of whether gonadal hormones may influence sexual differentiation in the neostriatum. In the medial preoptic n., a greater percentage of neurons were labeled in males than in females. There were no consistent sex differences in labeling in six other regions examined: ventromedial n., arcuate n., medial amygdaloid n., septofimbrial n., caudate n. and putamen.

Perinatal development of estrogen receptors in mouse brain assessed by radioautography, nuclear isolation and receptor assay

The development of estrogen receptors was investigated in vivo in the brains of fetal and neonatal mice 2 h after administering [3H]moxestrol to the pregnant mothers or neonates. Moxestrol bypasses the alpha-fetoprotein 'protective barrier' and gains access to estrogen receptors. Analysis of [3H]moxestrol uptake by radioautography and by cell nuclear isolation and counting of radioactivity revealed a marked increase in the number of estrogen receptors and estrophilic cells in the brain during late fetal and early postnatal development. Assays of cytosol estrogen receptors were conducted in parallel and revealed a comparable pattern of development. The increase in estrogen receptors and labeling was especially great from embryonic day (E) 15 to E18. Cytosol assays revealed a low level of receptors in the whole brain on E13. Radioautography revealed that clearly labeled cells in the hypothalamus and preoptic area were virtually absent on E13 but were evident on E15, with marked increases occurring between E15 and E18, both in number of labeled cells and in intensity of labeling per cell. Within the cerebral cortex the dorsal cingulate cortex was the most extensively labeled area; however, clearcut labeling was not evident on E13 or E15. Thus, the development of cortical estrogen receptors occurs somewhat later than that in the hypothalamus and preoptic area. The perinatal increase in estrogen receptors usually begins several days after the birthdates of neurons in these estrophilic regions of the brain, and corresponds to the early responsiveness of these neurons to the organizational and activational influences of estrogen.

Short- and long-term influences of neonatal sex steroids on alpha-bungarotoxin binding capacity in the mouse amygdala

Short- and long-term influences of various neonatal hormonal manipulations were assessed in the mouse amygdala with respect to alpha-bungarotoxin binding capacity, a possible parameter for cholinergic receptor integrity and function. To estimate the short-term effects, [125I]alpha-bungarotoxin binding to the tissue homogenate obtained from the posterior corticomedial amygdala was determined by a filtration assay using mice killed at 14 days post partum. The amygdaloid tissue from the normal male had a greater binding capacity for [125I]alpha-bungarotoxin than that from the normal female. However, castration of the male on the day of birth decreased the binding down to the female's level. A treatment of the female with either 250 micrograms testosterone propionate or 10 micrograms estradiol benzoate on days 1, 3, 5 and 7 increased the binding up to the male's level, although similar neonatal administration of 250 micrograms 5 alpha-dihydrotestosterone was ineffective. The long-term effects of neonatal hormonal manipulations were examined with 77-day-old mice which had been gonadectomized for 49 days. A quantitative light-microscopic autoradiography for [125I]alpha-bungarotoxin binding showed that specific grain density over the nucleus amygdaloideus medialis posterior of the androgenized female exceeded that of the female without neonatal hormone treatment. These observations provide further evidence that neonatal sex steroids play a determinate role in the sexual differentiation of the brain by exerting an organizational influence on developing cholinergic binding sites in the amygdala.

Regional differences in intraneuronal localization of alpha-fetoprotein in developing mouse brain

Estrogen receptor-containing regions of limbic, hypothalamic and amygdaloid areas of the developing mouse brain exhibited little or no intraneuronal immunofluorescence reactivity for AFP in comparison with the bright fluorescence of adjacent regions. These regional differences in the topographic distribution of intraneuronal AFP may represent intrinsic differences in the uptake, turnover or immunoreactivity of the internalized protein, perhaps related to estrogen metabolism by such neurons.

Androgen-concentrating cells in the periventricular brain of the female rhesus monkey

Although androgens act on the primate central nervous system to modulate both endocrine functions and a number of limbic-related behaviors, little is known about the anatomical location of the neurons which sequester these steroids in primates. To determine the prime location of these androgen-concentrating neurons in the forebrain of the primate, we injected three castrated female rhesus monkeys in the femoral vein with 1 microgram of 5 alpha-dihydro (1,2,4,5,6,7-3H) testosterone (3H-DHT, 107 Ci/mmole) per kg of body weight. One of these animals also received an IV injection of 100 micrograms/kg body weight of unlabeled dihydrotestosterone (DHT) to serve as a control. One hour after the injection of 3H-DHT we rapidly exsanguinated each animal. The forebrain was sliced and blocks containing the amygdala, diencephalon, frontal pole, and hippocampus were frozen and stored in liquid nitrogen until processing. The tissue was then processed for autoradiography. A specific topographic pattern of nuclear concentration of DHT or one of its metabolites was obtained in neurons of the basal hypothalamus, preoptic region, amygdala, and hippocampus. This pattern was similar to that found in rodent species.

Ontogeny of sexual difference in alpha-bungarotoxin binding capacity in the mouse amygdala

We have shown a sex difference in the nucleus amygdaloideus medialis posterior (NAMP) of the mouse with respect to the binding capacity for alpha-bungarotoxin (alpha-BGT) under various steroid-hormonal environments. The present study describes histochemically the postnatal development of alpha-BGT binding capacity in the NAMP of the intact male and female mouse, and characterizes biochemically the toxin binding component at different developmental stages. Light microscopic autoradiography using radio-iodinated alpha-BGT revealed characteristic patterns of development of alpha-BGT binding capacity in the NAMP of both sexes. On the day of birth, the autoradiographic grain density for [125]alpha-BGT binding sites was low in the NAMP and no sex difference was detected. During the next 4 days the grain density increased in each sex, but the density in the female increased to a lesser extent than in the male, resulting in a marked sex difference at 4 days after birth. The grain density in each sex was maximal at 7-10 days and then declined toward the adult level by 28 days of age. The density in the male exceeded that in the female throughout postnatal life except for the day of birth. The biochemical filtration assay on the tissue homogenates provided evidence suggesting that alpha-BGT binding sites in the posterior corticomedial amygdaloid region including the NAMP are sexually different in number, but not in the binding affinity, at an early postnatal age as well as in adulthood. These results indicate the importance of the early postnatal days for the sexual differentiation of alpha-BGT binding sites in the NAMP.

Prepubertal ontogeny of responsiveness to estradiol in female rat central nervous system

The physiological response to systemic estrogens changes dramatically during the period from birth to puberty. With the onset of puberty, the rat reaches a critical developmental plateau with regard to endocrinological responsiveness to estradiol. Since the appearance of the pubertal response pattern appears to be less a consequence of some intrinsic "trigger' than the natural continuation of a developmental sequence that begins prenatally, its ontogeny should be examined in a broad context that will take account of the impact of each of the dynamic components influencing the interactions between estradiol and the central nervous system on the functional development of the organism as a whole. The prepubertal ontogeny of endocrinological responsiveness to estradiol in the central nervous system of the female rat is examined in the context of several of the important factors that are known to influence the functional development of the hypothalamo-pituitary-gonadal circuit:the rapidly changing hormonal environment of the morphologically and physiologically immature juvenile rat, the shifting predominance of alphafetoprotein and "adult" estradiol-binding protein, sexual differentiation of the neural substrate, and the development of mature pituitary-gonadal feedback mechanisms. The availability of ever more sensitive techniques for the measurement of the actions of estradiol in the central nervous system of the immature organism has necessitated a re-evaluation of existing data. This, in turn, suggests that new approaches should be applied to the examination of problems related to the development of reproductive maturity of the central nervous system.