Regulation of estrogen receptor beta mRNA in the brain: opposite effects of 17beta-estradiol and the phytoestrogen, coumestrol

Estrogen receptor alpha (ERalpha) and estrogen receptor beta (ERbeta) are differentially distributed in the brain and likely mediate different estrogen-dependent processes. ERbeta is abundant in the bed nucleus of the stria terminalis, medial preoptic nucleus, paraventricular nucleus of the hypothalamus and the amygdala of the rat. In the paraventricular nucleus, which is devoid of ERalpha, ERbeta is colocalized with the neuropeptides, oxytocin and vasopressin, suggesting a potential functional role for ERbeta in the regulation of these peptides. We examined the regulation of ERbeta mRNA expression in the rat brain by 17beta-estradiol and the phytoestrogen, coumestrol. 17beta-Estradiol treatment decreased ERbeta mRNA in situ hybridization signal by 44.5% in the paraventricular nucleus of the hypothalamus (PVN), but had no effect in the bed nucleus of the stria terminalis (BnST) or the medial preoptic nucleus (MPA). In contrast, dietary exposure to coumestrol increased ERbeta mRNA signal by 47.5% in the PVN but had no effect in the BnST or the MPA. These data demonstrate that like ERalpha, ERbeta is down regulated by estrogen in a region specific manner in the rat brain. Furthermore, exposure to coumestrol may modulate ERbeta-dependent processes by acting as an anti-estrogen at ERbeta. This data contradicts results from cell transfection assays which suggest an estrogenic activity of coumestrol on ERbeta, indicating that the mode of action may be tissue specific, or that metabolism of dietary coumestrol may alter its effects. Because the highest concentrations of phytoestrogens are found in legumes, vegetables and grains, they are most prevalent in vegetarian and traditional Asian diets. Understanding the neuroendocrine effects of phytoestrogens is particularly important now that they are being marketed as a natural alternative to estrogen replacement therapy and sold in highly concentrated pills and powders.     

Progestin receptor expression in the developing rat brain depends upon activation of estrogen receptor alpha and not estrogen receptor beta

Perinatal 17beta-estradiol (E2) rapidly and markedly affects the morphological and neurochemical organization of the vertebrate brain. For instance, the sex difference in perinatal progestin receptor (PR) immunoreactivity in the medial preoptic nucleus (MPN) of the rat brain is due to the intracellular conversion of testosterone into E2 in males. Neonatal alpha-fetoprotein prevents circulating estrogens from accessing the brain, therefore, to overcome alpha-fetoprotein sequestration of E2, estrogen replacement studies during development have used natural and synthetic estrogen dosages in the milligram to microgram range. These levels could be considered as supraphysiological. Moreover, it is not clear through which ER subtype E2 acts to induce PR expression in the neonatal rat MPN because E2 binds similarly to estrogen receptor (ER)alpha and ERbeta. Consequently, we investigated whether nanogram levels of E2 affected PR protein and mRNA levels in the neonatal MPN. Furthermore, propylpyrazole-triol (PPT), a highly selective agonist for ERalpha, and diarylpropionitrile (DPN), a highly selective agonist for ERbeta, were used to determine if E2-dependent PR expression in the neonatal rat is mediated through ERalpha and/or ERbeta. Immunocytochemistry and quantitative real-time RT-PCR determined that as little as 100 ng E2 significantly induced PR protein and mRNA in the female and neonatally castrated male MPN on PN 4, indicating that the neonatal rat brain is highly sensitive to circulating estrogens. PPT, but not DPN, induced PR expression in the neonatal MPN and arcuate nucleus (Arc), demonstrating that PR expression in the neonatal rat brain depends solely on E2 activated ERalpha. In the lateral bed nucleus of the stria terminalis (BSTL), neither PPT nor DPN affected PR expression, suggesting the presence of a gonadal hormone-independent PR regulatory mechanism.     

Testosterone regulates substance P within neurons of the medial nucleus of the amygdala, the bed nucleus of the stria terminalis and the medial preoptic area of the male golden hamster

The medial nucleus of the amygdala, bed nucleus of the stria terminalis, and medial preoptic area appear to mediate steroidal regulation of mating behavior in male rodents. The mechanism of action has not been determined. One way testosterone could enhance neuronal function is by increasing neurotransmitter levels, thus altering neuronal transmission. To assess this hypothesis, we examined the effect of castration and testosterone treatment on substance P levels in the neurons of these three brain regions. Brains from male Syrian hamsters that were (1) gonadally intact, (2) castrated for 13 weeks, or (3) castrated for 9 weeks and treated with testosterone for 4 weeks, were processed for substance P, and the numbers of substance P immunoreactive neurons in the medial nucleus of the amygdala, bed nucleus of the stria terminalis, and medial preoptic area were determined. Castration reduced the number of substance P neurons in the bed nucleus of the stria terminalis and medial preoptic area relative to those in intact hamsters: the number of substance P neurons in these regions was restored by testosterone treatment. Castration did not reduce the number of substance P neurons in the medial nucleus of the amygdala; however, testosterone treatment increased the numbers of these neurons when compared to intacts. Thus, testosterone regulates substance P levels in areas that regulate mating behavior. As substance P enhances male copulatory behavior our results suggest that testosterone may regulate copulatory behavior by enhancing substance P levels in medial nucleus of the amygdala, bed nucleus of the stria terminalis and medial preoptic area.     

The development of the septal region in the rat. I. Neurogenesis examined with 3H-thymidine autoradiography

Neurogenesis in the rat septal region was examined with³H-thymidine autoradiography. The rats in the prenatal groups were the offspring of pregnant females given two injections of ³H-thymidine on consecutive days in an overlapping series: embryonic day (E) 13 + E14, E14 + E15, … E21 + E22. The rats in the postnatal groups were injected in a nonoverlapping series: the day of birth and postnatal day (P) 1, P2 + P3, P3 + P4. On 60 days of age, the percentage of labelled cells and the proportion of cells added during each day of formation were determined at several anatomical levels within the midline nuclear group (nucleus of the diagonal band, medial and triangular septal nuclei), the lateral septal nucleus, and the ventrolateral nuclear group (nucleus accumbens, bed nuclei of the stria terminalis and the anterior commissure). The neurons within each nuclear group form in significantly different waves, those of the midline group forming between E13-E17, the lateral septal nucleus between E15-E19, the bed nuclei of the stria terminalis and anterior commissure between E14-E18, the nucleus accumbens between E17-P2. All nuclei and nuclear groups show characteristic gradients of formation. Both the midline nuclear group and the bed nucleus of the stria terminalis (including the commissural bed nucleus) have their earliest forming neurons lying near the crossing of the anterior commissure; younger neurons are located both rostrally and caudally with the youngest neurons lying in the most rostral extension of the diagonal band nucleus and the strial bed nucleus. The lateral septal nucleus forms along a strong mediolateral gradient throughout its length after neurogenesis is almost complete in the midline nuclear group. Throughout the length of the nucleus accumbens, the oldest neurons are located ventrally while progressively younger cells are found dorsally beneath the inferior horn of the lateral ventricle.     

Distribution and steroid hormone regulation of aromatase mRNA expression in the forebrain of adult male and female rats: A cellular-level analysis using in situ hybridization

Many of the effects of gonadal steroid hormones in the male brain are due to the actions of the testosterone metabolite estradiol, which is synthesized by the actions of the P450 enzyme aromatase. Aromatase activity is present in regions of the preoptic area, hypothalamus, and limbic system. Levels of aromatase activity in the brain are highly dependent on gonadal steroid hormones in many brain regions, but not all. We examined the distribution of aromatase mRNA in adult male and female rat brains as well as the regulation of the levels of aromatase mRNA in the brains of males by gonadal steroid hormones using in situ hybridization. This method was performed using a ³⁵S-labelled cRNA probe, transcribed in vitro from the rat ovarian aromatase cDNA. In the adult male, many heavily labelled cells were found in the encapsulated bed nucleus of the stria terminalis (BNST), the medial preoptic nucleus (MPN), the ventromedial nucleus (VMN), the medial amygdala (mAMY), and the cortical amygdala (CoAMY). The regional distribution of aromatase mRNA was similar in females, but females tended to have a lower number of aromatase mRNA expressing cells in each region compared to males. Aromatase mRNA levels in the BNST, MPN, VMN, and mAMY tended to be lower in castrated males than in intact males, whereas aromatase mRNA levels were unaltered by castration in the CoAMY. The degree of reduction in mean levels of aromatase mRNA following castration does not simply account for the large changes measured in activity following castration. Examination of the entire population of individual cells expressing aromatase mRNA in castrated males suggests that aromatase mRNA may be regulated by steroid hormones differentially in specific populations of neurons within regions where activity is known to decrease following castration. © 1996 Wiley-Liss, Inc.     

Sex and age differences of neurons expressing gaba-immunoreactivity in the rat bed nucleus of the stria terminalis

Neurons, containing GABA were visualised immunohistochemically in the bed nucleus of the stria terminalis. Young prepubertal (20 days of age) and postpubertal (3 months and 1 year of age) Sprague-Dawley rats were used. Quantitative studies revealed greater density of GABA-immunoreactive perikarya in female than in male bed nucleus of the stria terminalis. This difference was not due to distribution in different volumes, since the volumes of the bed nucleus of the stria terminalis in the three ages studied did not differ by gender. Castration of new-born male rats caused elevation of the density of GABA-immunoreactive neurons in the bed nucleus of the stria terminalis to female levels on the third month of life. The percentage of nerve cells, expressing detectable amounts of GABA increased with age in the rat bed nucleus of the stria terminalis. The sexual dimorphism of GABA-immunoreactive neurons in the bed nucleus of the stria terminalis may contribute to the formation of reproductive behavior. The elevation of GABA expression with age might reflect change of the cellular activity in this part of the limbic circuitry.     

Distribution of immunoreactive atrial natriuretic peptides in the central nervous system of the rat

The distribution of immunoreactive (ir) atrial natriuretic peptides (ANPs) in 47 microdissected brain and spinal cord regions of the rat was determined by radioimmunoassay. The highest concentrations of ir-ANPs exist in the paraventricular nucleus and median preoptic nucleus (580.9 and 558.0 fmol/mg protein, respectively). High concentrations of ir-ANP (greater than 300 fmol/mg protein) are present in the interpeduncular nucleus, preoptic and hypothalamic periventricular nuclei, median eminence and organum vasculosum of the lamina terminalis. Moderate concentrations of ir-ANPs (between 100 and 300 fmol/mg protein) are found in 16 brain regions such as the bed nucleus of the stria terminalis, nucleus of the diagonal band, most of the hypothalamic nuclei, central gray, locus coeruleus and parabrachial nuclei. Low levels of ir-ANPs (less than 100 fmol/mg protein) exist in 22 brain regions including cortical areas, amygdala, caudate nucleus, nucleus accumbens, hippocampus, supraoptic nucleus, subfornical organ, medial mammillary nucleus, substantia nigra, dorsal raphe nucleus, cerebellum, nucleus of the solitary tract and others. Cervical spinal cord and neurointermediate lobe of pituitary gland contain low levels of ir-ANPs.     

Distribution of estrogen receptor beta immunoreactivity in the rat central nervous system.

The discovery of estrogen receptor beta (ER beta) and subsequent localization of its mRNA in the rat central nervous system (CNS) has provided new insights about estrogen action in brain. A critical step in understanding the role of ER beta is demonstrating that the mRNA is translated into functional protein. The present study used a new ER beta-specific polyclonal antiserum (Z8P) and immunocytochemistry (ICC) to investigate the distribution of ER beta in the rat CNS. Ovariectomized female rats were perfusion fixed, and free-floating sections were incubated with Z8P. After visualization with a standard ABC method, nuclear immunoreactivity was seen in neurons throughout the brain, including the olfactory nuclei, laminae IV-VI of the cerebral cortex, medial septum, preoptic area, bed nucleus of the stria terminalis, supraoptic nucleus, paraventricular nucleus, zona incerta, medial and cortical amygdaloid nuclei, cerebellum, nucleus of the solitary tract, ventral tegmental area, and spinal trigeminal nucleus. Moreover, the results of a double-label ICC/ in situ hybridization study revealed that ER beta mRNA and immunoreactivity were colocalized in neurons of the brain, thus confirming the specificity of the antiserum. Through the use of Western blot analysis, Z8P was shown to recognize in vitro translated ER beta, but not ER alpha, as well as a 60-kDa protein from rat granulosa cells and ovary extracts. The results of these studies have demonstrated that (1) ER beta mRNA is translated into immunoreactive protein throughout the rat brain, and (2) ER beta resides in the cell nucleus. Together, these data provide an anatomic foundation for future studies and advance our understanding of estrogen action in hypothalamic and extrahypothalamic brain regions.     

Distribution of estrogen receptor alpha and beta immunoreactive profiles in the postnatal rat brain

The present study was conducted to identify the localization and possible contribution of the two estrogen receptor (ER) subtypes in the rat brain at postnatal (P) days 3, 7 and 14. Evaluation of the distribution of ERalpha and ERbeta immunoreactive (ir) nuclei did not reveal gender differences at the developmental point times examined. With the exception of the cerebral cortex, the pattern of staining for these ERs was unchanged across the postnatal ages examined. The distribution of ERalpha-ir nuclei was wider than ERbeta-ir during brain development. From P3, ERbeta and ERalpha-ir nuclei were found in different regions of the cerebral cortex, basal forebrain, amygdala, thalamus, hypothalamus, mesencephalon, pons, cerebellum and medulla oblongata. In addition, ERalpha-ir nuclei were exclusively detected in the hippocampal subfields, epithalamus and in several circumventricular organs. ERalpha and ERbeta dual immunofluorescence revealed positive nuclei in the medial part of the bed nucleus of the stria terminalis, periventricular preoptic nucleus and in caudal aspects of the ventrolateral part of the ventromedial hypothalamic nucleus. Although the functional significance of the dual expression of both ERs within the same nuclei remains unknown, it is possible that ERs play different roles in gene regulation within the same cell. The presence of ERs in diverse brain regions through early postnatal periods supports a potential role for estrogens in neural differentiation.     

Sex difference in the bed nucleus of the stria terminalis of the human brain.

A quantitative analysis of the volume of the darkly staining region of the posteromedial bed nucleus of the stria terminalis was performed on the brains of 26 age-matched male and female human subjects. We suggest the term "darkly staining posteromedial" component of the bed nucleus of the stria terminalis (BNST-dspm) to describe this sexually dimorphic region of the human brain. The volume of the BNST-dspm was 2.47 times greater in males than in females. This region in humans appears to correspond to an area of the bed nucleus of the stria terminalis in laboratory animals that exhibits volumetric and neurochemical sexual dimorphisms, concentrates gonadal steroids, and is anatomically connected to several other sexually dimorphic nuclei. Furthermore, the bed nucleus of the stria terminalis is involved in sexually dimorphic functions, including aggressive behavior, sexual behavior, and gonadotropin secretion, which are also influenced by gonadal steroids. Therefore, it is possible that in human beings as well, gonadal hormones influence the sexual dimorphism in the BNST-dspm and that this morphological difference, in part, underlies sexually dimorphic function.     

The expression of Huntingtin‐associated protein (HAP1) mRNA in developing, adult and ageing rat CNS: implications for Huntington's disease neuropathology

Using radioactive in situ hybridization, we have mapped the expression of Huntingtin-associated protein (HAP1) mRNA in rat brain at developmental stages (E12–E19, P0–P21), in adult rats (3 months) and in ‘aged’ (19–21 months) rats. Using two pairs of 45mer oligonucleotide probes specific for HAP1A and a probe which recognizes regions of both the HAP1A and HAP1B mRNA sequences (panHAP1), we find that the expression of HAP1 mRNA is specific to the CNS and restricted predominantly to anatomically connected limbic structures, particularly the amygdala (medial and corticomedial nuclei), the hypothalamus (arcuate, preoptic, paraventricular and lateral hypothalamic area), bed nucleus of the stria terminalis (BNST) and the lateral septal nuclei. HAP1 mRNA was detected in embryos at E12 and displayed a prevalent distribution in the developing limbic structures by E15. In aged, 19–21-months-old, rats there is a downregulation of HAP1 mRNA expression across all CNS loci where HAP1 was previously abundant. The lowest levels of HAP1 mRNA expression corresponded with the areas of greatest pathological cell loss in Huntington's disease (HD); the caudate putamen, globus pallidus and neocortex. These observations support the suggestion that HAP1 plays an important role in the neuropathology of HD.     

Sex differences in the distribution and abundance of androgen receptor mRNA-containing cells in the preoptic area and hypothalamus of the ram and ewe

Rams and ewes show a negative-feedback response to peripheral treatment with testosterone, with both sexes having a similar degree of suppression in luteinizing hormone (LH) secretion during the breeding season. At least part of the action of testosterone to suppress gonadotropin-releasing hormone/LH secretion is exerted via interaction with an androgen receptor. The distribution of androgen receptor-containing cells in the hypothalamus has been described for the ram, but similar studies have not been performed in the ewe. In the present study, we tested the hypothesis that levels of androgen receptor mRNA expression in the preoptic area and hypothalamus would be similar in rams and ewes. Perfusion-fixed brain tissue was obtained from adult Romney Marsh ewes (luteal phase) and rams during the breeding season (n = 4/sex). Androgen receptor mRNA expression was quantified in hypothalamic sections by in situ hybridization using an (35)S-labelled riboprobe and image analysis. Hybridizing cells were found in the medial preoptic area, bed nucleus of the stria terminalis, anterior hypothalamic area, ventromedial nucleus, arcuate nucleus and premamillary nucleus. The level of androgen receptor mRNA expression was higher in rams than ewes in the rostral preoptic area, caudal preoptic area and rostral portion of the bed nucleus of the stria terminalis, with no sex difference in other regions. The preoptic area and bed nucleus of the stria terminalis are important for reproductive behaviour and the sex differences in androgen receptor mRNA expression at these levels may relate to this. The high level of androgen receptor mRNA expression in the basal hypothalamus, with no sex difference, is consistent with the role of this region in the regulation of gonadotropin secretion.     

Regional distribution of DARPP-32 (dopamine- and adenosine 3',5'-monophosphate-regulated phosphoprotein of Mr = 32,000) mRNA in mouse brain.

DARPP-32 (dopamine- and adenosine 3',5'-monophosphate-regulated phosphoprotein of Mr = 32,000) mRNA distribution was examined in adult mouse central nervous system by in situ hybridization. In general, DARPP-32 mRNA was found in regions of brain where cells express the dopamine D1 subtype receptor. Cells of the olfactory tubercle, caudate-putamen, and nucleus accumbens had the highest levels of DARPP-32 mRNA, as did choroid plexus and Purkinje cells. Relatively high levels were found in medial habenula and lateral piriform cortex. Moderate levels were seen in cerebral cortex layer VI, medial piriform cortex, lateral entorhinal cortex, tenia tecta, anterior olfactory nucleus, and lateral bed nucleus of the stria terminalis. Low levels were observed in hippocampus, cerebral cortex layers II and III, olfactory bulb, and the nucleus of the lateral olfactory tract. DARPP-32 mRNA levels in the amygdaloid nuclei varied greatly.     

Mu,delta, and kappa opioid receptor mRNA expression in the rat CNS: An in situ hybridization study

The μ, δ, and κ opioid receptors are the three main types of opioid receptors round in the central nervous system (CNS) and periphery. These receptors and the peptides with which they interact are important in a number of physiological functions, including analgesia, respiration, and hormonal regulation. This study examines the expression of μ, δ, and κ receptor mRNAs in the rat brain and spinal cord using in situ hybridization techniques. Tissue sections were hybridized with ³⁵S-labeled cRNA probes to the rat μ (744–1, 064 b), δ (304–1,287 b), and κ (1,351–2,124 b) receptors. Each mRNA demonstrates a distinct anatomical distribution that corresponds well to known receptor binding distributions. Cells expressing μ receptor mRNA are localized in such regions as the olfactory bulb, caudate-putamen, nucleus accumbens, lateral and medial septum, diagonal band of Broca, bed nucleus of the stria terminalis, most thalamic nuclei, hippocampus, amygdala, medial preoptic area, superior and inferior colliculi, central gray, dorsal and median raphe, raphe magnus, locus coeruleus, parabrachial nucleus, pontine and medullary reticular nuclei, nucleus ambiguus, nucleus of the solitary tract, nucleus gracilis and cuneatus, dorsal motor nucleus of vagus, spinal cord, and dorsal root ganglia. Cellular localization of δ receptor mRNA varied from μ or κ, with expression in such regions as the olfactory bulb, allo- and neocortex, caudate-putamen, nucleus accumbens, olfactory tubercle, ventromedial hypothalamus, hippocampus, amygdala, red nucleus, pontine nuclei, reticulotegmental nucleus, motor and spinal trigeminal, linear nucleus of the medulla, lateral reticular nucleus, spinal cord, and dorsal root ganglia. Cells expressing, κ receptor mRNA demonstrate a third pattern of expression, with cells localized in regions such as the claustrum, endopiriform nucleus, nucleus accumbens, olfactory tubercle, medial preoptic area, bed nucleus of the stria terminalis, amygdala, most hypothalamic nuclei, median eminence, infundibulum, substantia nigra, ventral tegmental area, raphe nuclei, paratrigeminal and spinal trigeminal, nucleus of the solitary tract, spinal cord, and dorsal root ganglia. These findings are discussed in relation to the physiologica functions associated with the opioid receptors.     

Sex differences in subregions of the medial nucleus of the amygdala and the bed nucleus of the stria terminalis of the rat

Sex differences are described in subregions of two nuclei of the rat brain: the medical nucleus of the amygdala (MA) and the bed nucleus of the stria terminalis (BNST). The volume of the posterodorsal region of the medial nucleus of the amygdala (MApd) is approximately 85% greater and the volume of the encapsulated region of the bed nucleus of the stria terminalis (BNSTenc) is approximately 97% greater in males than in females. The MApd and BNSTenc are distinct subregions of the MA and BNST. They exhibit intense uptake of gonadal hormones and are anatomically connected to each other and to other sexually dimorphic nuclei. The MA and BNST in general are involved in regulation of several sexually dimorphic functions, including aggression, sexual behavior, gonadotropin secretion and integration of olfactory information. Precise localization of sex differences in subregions of the MA and BNST, such as the MApd and BNSTenc, may facilitate understanding of the neural basis of such functions.     

Postnatal development and sex difference in neurons containing estrogen receptor-α 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-α (ER-α) 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-α equally well for both occupied and unoccupied forms. ER-α immunostaining was restricted to the cell nuclei of specific cell groups. In PD1 rats, ER-α-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 of estrogen 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. J. Comp. Neurol. 389:81–93, 1997. © 1997 Wiley-Liss, Inc.     

Vasopressin and oxytocin immunoreactive neurons and fibers in the forebrain of male and female common marmosets (Callithrix jacchus)

Vasopressin (AVP) and oxytocin (OT) immunoreactive (ir) neurons and fibers were examined in the forebrain of male and female common marmosets (Callithrix jacchus). As expected from previous studies of cell distribution in the rodent and primate brain, AVP-ir cells were most evident in the paraventricularis, supraopticus, and suprachiasmaticus of the hypothalamus. AVP-ir cells were also widely distributed in the lateral hypothalamus and the bed nucleus of the stria terminalis. A sexually dimorphic pattern of AVP-ir cells was found in the bed nucleus of the stria terminalis, in which males had more AVP-ir cells than females. OT-ir cells were found in the paraventricularis and supraopticus of the hypothalamus as well as in the bed nucleus of the stria terminalis and the medial amygdala. Male and female marmosets did not differ in the distribution of OT-ir cells. Fibers for both AVP and OT were evident outside of the hypothalamic-neurohypophyseal tract, but a plexus of AVP-ir fibers in the lateral septum or lateral habenular nucleus, as seen in the rat brain, could not be detected for either peptide. Synapse 27:14–25, 1997. © 1997 Wiley-Liss, Inc.     

Steroid sensitive sites in the avian brain: does the distribution of the estrogen receptor alpha and beta types provide insight into their function?

Studies in avian species have often been useful in elucidating basic concepts relevant to the regulation of reproductive behaviors by sex steroid hormones. Once a link between a steroid hormone and a behavioral response has been established, one can use the localization of steroid hormone receptors in the brain to facilitate the identification of neural circuits that control behavior. The recent identification of a second type of estrogen receptor called estrogen receptor beta or ERbeta has raised new issues about the action of steroid hormones in the brain. A hypothesis has been proposed by Kuiper et al. [1998] based on studies in mammalian species suggesting that ERalpha (the name given to the ER that was previously described) is important for reproduction while ERbeta is more important for non-reproductive functions. In this paper we apply this hypothesis more generally by examining possible functions of ERbeta in avian species. We have initiated studies of the ERbeta in the brain of two avian species, the Japanese quail (Coturnix japonica) and the European starling (Sturnus vulgaris). ERbeta was cloned in both species and the mRNA for this receptor type was localized in the brain employing in situ hybridization histochemistry methods. In both species ERbeta was found to be diffusely present in telencephalic areas consistent with a role for this receptor subtype in cognitive functions. However, ERbeta mRNA was also found in many brain areas that are traditionally thought to be important in the regulation of reproductive functions such as the preoptic region, the bed nucleus of the stria terminalis and the nucleus taeniae. Of the two receptor types, only mRNA for ERalpha was observed in the telencephalic vocal control nucleus HVc of male starlings. Steroid receptors in this nucleus are thought to be an example of an evolutionary specialization that has evolved to coordinate the production of courtship vocalizations with other aspects of reproduction. The lack of ERbeta mRNA expression in HVc is consistent with the hypothesis that ERalpha is preferentially involved in reproductive behaviors while ERbeta is involved in the steroid regulation of other neural functions. However, the widespread occurrence of ERbeta in other nuclei involved in reproductive function suggests that one must be cautious about the general applicability of the above hypothesis until more is known about ERbeta function in these other nuclei.     

Distribution of progesterone receptor immunoreactivity in the fetal and neonatal rat forebrain

Steroid hormones play an influential role in neural development. In addition to androgens and estrogens of fetal and neonatal origin, the developing brain may also be exposed to progesterone. In this regard, identifying forebrain nuclei that are sensitive to progesterone during neural development may elucidate the impact of progesterone on the developing brain. Using immunocytochemistry, the present study documented the distribution of progesterone receptor (PR) expression in the rat forebrain from embryonic day (E) 17 through postnatal day (P) 28. The results indicate that PR expression in the developing brain is extensive, present in numerous forebrain nuclei, but transient, in that PR expression was absent in most nuclei by P28. Regions displaying the highest levels of PR-immunoreactivity (PRir) were found in preoptic and hypothalamic nuclei including the medial preoptic, anteroventral periventricular, arcuate, and ventromedial nuclei. PRir was moderately abundant in the limbic region, particularly in subdivisions of the amygdala, the bed nucleus of the stria terminalis, and hippocampus. The choroid plexus and neocortex were additional structures that demonstrated relatively abundant levels of PRir. The presence PR expression in the developing forebrain implicates the involvement of progesterone and PR in fundamental mechanisms of neural development.