The Effects of GABA on embryonic gonadotropin-releasing hormone neurons in rat hypothalamic primary culture.

Gonadotropin-releasing hormone (GnRH) neurons arise in the olfactory placode, migrate into the preoptic area (POA), and then extend axons to the median eminence during embryogenesis. Little information is available concerning the properties of GnRH neurons during the late gestational period when GnRH neurons reach the POA and form neuronal networks, although many studies have examined such properties during earlier developmental stages or the postnatal period. The present study was performed to elucidate the involvement of gamma-aminobutyric acid (GABA), one of the major neurotransmitters modifying GnRH neural activity, in regulation of GnRH gene expression on embryonic day 18.5 (E18.5) using transgenic rats expressing enhanced green fluorescence protein (EGFP) under the control of GnRH promoter. First, using RT-PCR, the mRNA of two isoforms of the GABA-synthesizing enzyme glutamic acid decarboxylase (GAD), GAD65 and GAD67 was detected in E18.5 embryonic POA-containing tissues. GAD67-positive cells were also demonstrated in close vicinity to GnRH-positive cells by immunohistochemistry, and immunoreactivity for both the GABA-A and GABA-B receptor subunits was detected in GnRH neurons. Next, primary cultures derived from anterior hypothalamic tissue of E18.5 embryos were prepared, and the effects of GABA and its agonists on GnRH promoter activity were evaluated using EGFP expression as a marker. GABA and the GABA-A receptor agonist muscimol, but not the GABA-B receptor agonist baclofen, significantly increased the EGFP-positive/GnRH-positive cell ratio. These results suggest that GABA plays a role in stimulating GnRH gene expression through GABA-A receptors in embryonic GnRH neurons in late gestational stages.

Hypothalamic imprinting by gonadal steroid hormones.

The results of more than four decades of research on different mammalian species have established that the brain, like the rest of the reproductive system, is esentially basically female. For the male to develop structural and functional characteristics typical of his species, his brain must be exposed to testicular hormones during a critical period, or critical periods, of development. As mammals, human beings are most likely subject to this process of the hormone-dependent sexual differentiation of the brain, but proving it will be difficult. Common sense ethics preclude experimental procedures such as castration of neonatal infants or exposing the female fetus to testosterone perinatally. Thus, scientists are restricted to the retrospective study of "Experiments of Nature." The results of such studies support to a degree a meaningful role of hormones in the development of the human brain. The concept of the sexual differentiation of brain structure and function has a potentially profound influence on clinical decisions with respect to sex assignment and clinical management of infants with ambiguous or poorly developed external genitalia. Because of the importance of a baby's sex in our culture, parents of such infants must be given consideration, but so should the infant whose hormonal environment prenatally may well have produced permanent changes in the structure and functional potential of his/her brain.

Sexual differentiation of the human hypothalamus.

Functional sex differences in reproduction, gender and sexual orientation and in the incidence of neurological and psychiatric diseases are presumed to be based on structural and functional differences in the hypothalamus and other limbic structures. Factors influencing gender, i.e., the feeling to be male or female, are prenatal hormones and compounds that change the levels of these hormones, such as anticonvulsants, while the influence of postnatal social factors is controversial. Genetic factors and prenatal hormone levels are factors in the determination of sexual orientation, i.e. heterosexuality, bisexuality or homosexuality. There is no convincing evidence for postnatal social factors involved in the determination of sexual orientation. The period of overt sexual differentiation of the human hypothalamus occurs between approximately four years of age and adulthood, thus much later than is generally presumed, although the late sexual differentiation may of course be based upon processes that have already been programmed in mid-pregnancy or during the neonatal period. The recently reported differences in a number of structures in the human hypothalamus and adjacent structures depend strongly on age. Replication of these data is certainly necessary. Since the size of brain structures may be influenced by premortem factors (e.g. agonal state) and postmortem factors (e.g. fixation time), one should not only perform volume measurements, but also estimate a parameter that is not dependent on such factors as, i.e., total cell number of the brain structure in question. In addition, functional differences that depend on the levels of circulating hormones in adulthood have been observed in several hypothalamic and other brain structures. The mechanisms causing sexual differentiation of hypothalamic nuclei, the pre- and postnatal factors influencing this process, and the exact functional consequences of the morphological and functional hypothalamic differences await further elucidation.

Intact osmoregulatory centers in the preterm ovine fetus: Fos induction after an osmotic challenge.

We previously demonstrated a functional systemic dipsogenic response in the near-term fetal sheep (128-130 days; 145 days = full-term) with swallowing activity stimulated in response to central and systemic hypertonic saline. Preterm fetal sheep (110-115 days) do not consistently demonstrate swallowing in response to hypertonic stimuli, and it is unclear whether this is due to immaturity of osmoreceptor mechanisms or neuronal pathways activating swallowing motor neurons. To determine whether osmoreceptive regions in the preterm fetus are activated by changes in plasma tonicity, we examined Fos expression with immunostaining in these neurons in response to an osmotic challenge. Nine preterm fetal sheep [five hypertonic saline-treated fetuses (Hyp) and four isotonic saline-treated fetuses (Iso)] were prepared with vascular and intraperitoneal catheters. Seventy-five minutes before tissue collection, hypertonic (1.5 M) or isotonic saline was infused (12 ml/kg) via an intraperitoneal catheter to fetuses. Brains were examined for patterns of neuronal activation (demonstrated by Fos protein expression). Hyp demonstrated increases in plasma osmolality (~10 mosmol/kg H(2)O) and Na concentrations (5 meq/l). Increased Fos expression was detected in Hyp in the organum vasculosum of the lamina terminalis (OVLT), subfornical organ (SFO), median preoptic nucleus (MnPO), supraoptic (SON), and paraventricular nuclei (PVN) compared with Iso animals. Neuronal activation within the OVLT, SFO, and MnPO indicates intact osmoregulatory mechanisms, whereas activation of the SON and PVN suggests intact fetal neural pathways to arginine vasopressin neurons. These results suggest that preterm fetal swallowing insensitivity to osmotic stimuli may be due to immaturity of integrated motor neuron pathways.

Target-dependent sexual differentiation of a limbic-hypothalamic neural pathway.

Neural pathways between sexually dimorphic forebrain regions develop under the influence of sex steroid hormones during the perinatal period, but how these hormones specify precise sex-specific patterns of connectivity is unknown. A heterochronic coculture system was used to demonstrate that sex steroid hormones direct development of a sexually dimorphic limbic-hypothalamic neural pathway through a target-dependent mechanism. Explants of the principal nucleus of the bed nuclei of the stria terminalis (BSTp) extend neurites toward explants of the anteroventral periventricular nucleus (AVPV) derived from male but not female rats. Coculture of BSTp explants from male rats with AVPV explants derived from females treated in vivo with testosterone for 9 d resulted in a high density of neurites extending from the BSTp to the AVPV explant, as was the case when the BSTp explants were derived from females and the AVPV explants were derived from males or androgen-treated females. These in vitro findings suggest that during the postnatal period testosterone induces a target-derived, diffusible chemotropic activity that results in a sexually dimorphic pattern of connectivity.

Maternal and perinatal brain aromatase: effects of dietary soy phytoestrogens.

Phytoestrogens are extensively investigated for their potential to prevent many hormone-dependent cancers and age-related diseases, however little is known about their effects in brain. Brain aromatase and plasma phytoestrogen levels were determined in Sprague-Dawley rats fed a phytoestrogen-rich diet during pregnancy/lactation. Ingested phytoestrogens cross the placenta and become concentrated in maternal milk as evident from high infantile plasma concentrations. Dietary phytoestrogens, however, do not alter brain aromatase during pregnancy/lactation or perinatal development.

Phytoestrogens alter hypothalamic calbindin-D28k levels during prenatal development.

Calbindin-D28K (CALB) in the medial basal hypothalamic (MBH) and preoptic area (POA) of male and female fetuses from pregnant rats fed different phytoestrogens diets during gestation was examined by Western analysis. In animals fed a phytoestrogen containing diet (Phyto-200), males displayed significantly higher CALB levels compared to females. Whereas, in animals fed a phytoestrogen-free diet (Phyto-free), females exhibited significantly higher CALB levels compared to Phyto-200 female values. The present data have far reaching implications where phytoestrogen content in diets apparently influence MBH-POA CALB levels prenatally. The altered CALB levels may in turn modify sexually dimorphic brain structures during neuronal development by buffering Ca2+ that is associated with programmed cell death.

Developmental sex differences in estrogen receptor-beta mRNA expression in the mouse hypothalamus/preoptic region.

Estrogens play a significant role during mammalian brain development and are required for the masculinization of neuronal circuits involved in sex-specific behaviors and neuroendocrine functions. Cellular estrogen signalling is transmitted through nuclear estrogen receptors (ER) which are divided into two subforms: the ER-alpha as well as the recently cloned ER-beta have been demonstrated in the hypothalamus. In the present study, we have analyzed the sex-specific expression of ER-beta mRNA in the pre- and postnatal mouse hypothalamus/preoptic region (Hyp/POA) by semiquantitative RT-PCR. The ER-beta mRNA was detectable as early as embryonic day (E) 15 in the diencephalon of both sexes. In males, levels of mRNA expression in the Hyp/POA increased until birth and remained high throughout postnatal (P) development, whereas in females, such an increase was not observed. Significantly higher mRNA levels were detected in the male Hyp/POA from E17 until P15. Perinatal sex differences in ER-beta mRNA expression coincide with higher estrogen-forming rates in the male Hyp/POA. At present, no direct evidence is available which demonstrates that estrogen signalling through ER-beta is involved in brain development. However, data from our and other studies suggest a potential role for this signal transduction pathway for brain differentiation.

Ontogeny of region-specific sex differences in androgen receptor messenger ribonucleic acid expression in the rat forebrain.

Testosterone and its metabolites are the principal gonadal hormones responsible for sexual differentiation of the brain. However, the relative roles of the androgen receptor (AR) vs. the estrogen receptor in specific aspects of this process remain unclear due to the intracellular metabolism of testosterone to active androgenic and estrogenic compounds. In this study, we used an 35S-labeled riboprobe and in situ hybridization to analyze steady state, relative levels of AR messenger RNA (mRNA) expression in the developing bed nucleus of the stria terminalis, medial preoptic area, and lateral septum, as well as the ventromedial and arcuate nuclei of the hypothalamus. Each area was examined on embryonic day 20 and postnatal days 0, 4, 10, and 20 to produce a developmental profile of AR mRNA expression. AR mRNA hybridization was present on embryonic day 20 in all areas analyzed. In addition, AR mRNA expression increased throughout the perinatal period in all areas examined in both males and females. However, between postnatal days 4 and 10, sharp increases in AR mRNA expression in the principal portion of the bed nucleus of the stria terminalis and the medial preoptic area occurred in the male that were not paralleled in the female. Subsequently, males exhibited higher levels of AR mRNA than females in these areas by postnatal day 10. There was no sex difference in AR mRNA content in the lateral septum, ventromedial nucleus, or arcuate nucleus at any age. These results suggest that sex differences in AR mRNA expression during development may lead to an early sex difference in sensitivity to the potential masculinizing effects of androgen.

Development of the human hypothalamus.

The hypothalamus has been claimed to be involved in a great number of physiological functions in development, such as sexual differentiation (gender, sexual orientation) and birth, as well as in various developmental disorders including mental retardation, sudden infant death syndrome (SIDS), Kallman's syndrome and Prader-Willi syndrome. In this review a number of hypothalamic nuclei have therefore been discussed with respect to their development in health and disease. The suprachiasmatic nucleus (SCN) is the clock of the brain and shows circadian and seasonal fluctuations in vasopressin-expressing cell numbers. The SCN also seems to be involved in reproduction, adding interest to the sex differences in shape of the vasopressin-containing SCN subnucleus and in its VIP cell number. In addition, differences in relation to sexual orientation can be seen in this perspective. The vasopressin and VIP neurons of the SCN develop mainly postnatally, but as premature children may have circadian temperature rhythms, a different SCN cell type is probably more mature at birth. The sexually dimorphic nucleus (SDN, intermediate nucleus, INAH-1) is twice as large in young male adults as in young females. At the moment of birth only 20% of the SDN cell number is present. From birth until two to four years of age cell numbers increase equally rapidly in both sexes. After this age cell numbers start to decrease in girls, creating the sex difference. The size of the SDN does not show any relationship to sexual orientation in men. The large neurosecretory cells of the supraoptic (SON) and paraventricular nucleus (PVN) project to the neurohypophysis, where they release vasopressin and oxytocin into the blood circulation. In the fetus these hormones play an active role in the birth process. Fetal oxytocin may initiate or accelerate the course of labor. Fetal vasopressin plays a role in the adaptation to stress--caused by the birth process--by redistribution of the fetal blood flow. Corticotropin-releasing hormone (CRH) neurons of the PVN play a central role in stress response. Thus fetal CRH neurons may play a role in the timing of the moment of birth. Recently, alterations have been described in peptidergic, aminergic and cholinergic transmitters in the hypothalamus in SIDS. Future research will have to establish whether these changes are part of the course of SIDS. A large proportion of the SON and PVN neurons also produce tyrosine hydroxylase (TH). In neonates the majority of TH-immunoreactive neurons colocalizes vasopressin, while in the adult the majority of TH-positive neurons colocalizes oxytocin.(ABSTRACT TRUNCATED AT 400 WORDS)

Ontogeny of immunocytochemically demonstrable androgen- and androgen receptor-containing cells in the hypothalamus and adenohypophysis of the chick embryo.

Brain sections of male chick embryos, 6.5-18.5 days of age, were examined immunocytochemically for the presence of androgen- and androgen receptor-containing cells in the hypothalamus and adenohypophyseal pars distalis. Using antibodies (Ab) against both androgens (T-Ab) and the androgen receptor (AR-Ab), single- and double-immunostained cells were located in a total of five nuclei of the anterior-, mid-, and posterior-hypothalamus, as well as in the rostral and caudal lobes of the adenohypophyseal pars distalis. From Days 9.5-12.5, the mean number of androgen-immunostained cells within the hypothalamus and pars distalis increased significantly (P < 0.01), while from Days 12.5-18.5 there was no further statistically significant increase. The results of the present investigation support previous findings which suggest that in the chick embryo the negative feedback loop of the hypothalamo-adenohypophyseal-testicular (HATest) axis is functional by the 13th day of development (Woods et al., 1989a,b). They also agree with the observations of Wilson and Glick (1970) that in the male chick embryo testosterone organizes masculine mating behavior prior to Day 13.0.

The ontogeny of gene expression of progestin receptors in the female rat brain.

The postnatal development of the progestin receptor (PR) system in the rat brain is a region-specific and stage-related process. In an attempt to analyze the molecular mechanism by which the dramatic change of gene expression of the PR occurs we have examined the level of PR mRNAs in the hypothalamus-preoptic area (HPOA) and cerebral cortex in development from fetal to postnatal stages of female rats. We used polymerase chain reaction to clone, from uterine cDNA, the cDNA corresponding to the steroid-binding domain of the PR forms 'A' and 'B' mRNA as well as the region around the translation-initiation site (ATG1) of the putative PR form 'B' mRNA. A quantitative reverse transcription-polymerase chain reaction assay was used to measure the level of mRNAs for PR forms 'A' and 'B' (total PR mRNAs) and PR form 'B'. There was a regional difference in the intracerebral distribution between the total and form 'B' mRNAs, indicating possible distinct mechanisms responsible for regulating the expression of the PR mRNAs. The PR mRNAs in the brain, already detectable 2 days before birth, increased at early neonatal stages. The total PR mRNAs in the cortex developed in a manner essentially similar to the PR protein at the early stages, but, surprisingly, unlike the receptor, the messages remained high at the later stages from day 18 to 8 weeks of life. On the other hand, the ontogeny of the cortical mRNA for form 'B', which predominantly existed in the region, resembled that of the cortical PR protein. In the HPOA the postnatal development of the form 'B' mRNAs was also roughly similar to the PR. These results suggest region-specific and stage-related gene expression of the PR isoform system in the developing brain: gene expression of form 'B' seems to be predominantly, first, "turned on" around birth, followed by form 'A' mRNA expression around days 8-12. Moreover, lowered levels of the cortical PR mRNAs in the propylthiouracil-induced hypothyroid rat, together with suppressed PR level, indicate a possible regulatory role of thyroid hormone on gene expression of the cortical receptor.

Application of a fluorescent dye to study connectivity between third ventricular preoptic area grafts and host hypothalamus.

The mutant hypogonadal (hpg) mouse lacks a functioning gene for the neurohormone gonadotropin releasing hormone (GnRH). Previous studies from our laboratory had indicated that the initiation and maintenance of reproductive function in these mice could be brought about by the implantation of normal fetal grafts into adult hosts. Testicular or ovarian growth and other indicators of normal neurosecretory output were always accompanied by survival of GnRH neurons and growth of GnRH axons into the host median eminence where such axons terminate on the hypophysial portal capillaries. To determine if other connections exist between graft and the host hypothalamus, small crystals of the carbocyanine dye, 1,1'-dioctadecyl-3,3,3',3'-tetramethyl-indocarbocyanine perchlorate (DiI) were applied to either graft or host after fixation of the brain. Tissue sections were analyzed for retrograde and and anterograde movement of the dye. When crystals were placed on the graft, labeled axons were found in the host median eminence or in the host hypothalamus taking an arching trajectory toward the median eminence. Retrogradely labeled neurons in the host were few in number and largely confined to the host arcuate nucleus. With DiI crystals applied to the basal hypothalamus, labeled axons were distributed widely in the host but much sparser in the graft. Axons appeared to enter primarily at sites where the graft and host interface lacked an ependymal lining. Small numbers of retrogradely labeled neurons were also seen in the graft. Most were cells of very simple morphology and were distributed randomly in the graft. When double label experiments were carried out most DiI positive cells in the graft contained GnRH. These results indicate the connectivity between host hypothalamus and the third ventricular preoptic area grafts exists but is limited in nature.

Gender and sexual orientation in relation to hypothalamic structures.

Animal experiments have provided evidence for the presence of sex differences from the synaptic level up to behaviour. Although sex differences in the human brain may have been presumed implicitly since the days of Aristotle, research on the presence of functional and structural sex differences of the human brain started only relatively recently. The most conspicuous sex difference in the mammalian brain was described by Gorski et al. [1978] in the preoptic area (POA) of the rat hypothalamus. We found that the volume of a putative homologue of this sexually dimorphic nucleus (SDN) in the adult human hypothalamus was more than twice as large in men as in women and contained about twice as many cells. Recently a similar sex difference and volume has been described for the human bed nucleus of the stria terminalis and 'interstitial nuclei of the hypothalamus' (INAH). Sexual differentiation of the hypothalamus was generally believed to take place between 4 and 7 months of gestation. A life span study on the SDN of more than 100 subjects revealed, however, that only after the age of 2-4 years postnatally sexual differentiation becomes manifest by a decrease in volume and cell number in the female SDN. If sexual differentiation of the brain indeed takes place postnatally, not only chemical and hormonal factors may influence this process but also social factors. A prominent theory on the development of sexual orientation is that it develops as a result of an interaction between the developing brain and sex hormones. According to Dörner's hypothesis, male homosexuals have a female differentiation of the hypothalamus. This hypothesis was not supported by our observations on the SDN. Neither the SDN volume nor the cell number in the hypothalamus of homosexual men differed from that of heterosexual men. However, a difference in SCN cell number was observed in relation to sexual orientation. The volume and cell number of the SCN of homosexual men was twice as large as that of a reference group. During development, the SCN volume and cell counts reach peak values around 13-16 months after birth. At this age the SCN contains about the same number of cells as the SCN of adult male homosexuals, whereas in the reference group the cell numbers subsequently decline to the adult value, which is about 35% of the peak value.(ABSTRACT TRUNCATED AT 400 WORDS)

Progestin receptors in brain and pituitary of 20-day-old fetal mice: an autoradiographic study using [125I]progestin.

The distribution of progestin target sites in the brain and pituitary of estrogen-primed 20-day-old fetal mice was investigated by thaw-mount autoradiography. Three pregnant mice were each implanted sc with a Silastic tube containing estrogen on day 17 and ovariectomized on day 19 of gestation. Twenty-four hours after ovariectomy 10 fetuses (5 males and 5 females) were collected and each injected sc with 0.33 microgram/100 g BW [125I]progestin (SA, 2200 Ci/mM). For competition, two additional fetuses were injected with 20 micrograms R5020 1 h before (Z)-17 beta-hydroxy-17 alpha-(2[125I]iodovinyl)4-estren-3-one [( 125I]Progestin) to demonstrate that nuclear uptake and retention of radioactivity were specific for progestin. Two hours after injection of [125I]Progestin all fetuses were mounted, frozen, and sectioned in a cryostat. After 1-37 days of exposure, sections were developed and scanned for labeled cells. Cells with nuclear concentration were found in the male and female preoptic area, within certain nuclear groups in the basal hypothalamus, in the central gray of the midbrain, and in the pituitary. No labeling was detected in the cortex or amygdala. The results indicate that cells in certain regions of the brain and pituitary express progestin receptors at the end of gestation and suggest that progesterone is important for the normal development of these cells.

Sex- and hormone-dependent antigen immunoreactivity in developing rat hypothalamus.

Morphological sex differences in adults can result from differential gonadal steroid exposure during critical perinatal periods. This study describes the use of a monoclonal antibody we have developed to study mechanisms of sexual differentiation of brain structure and function. Used as a marker in immunocytochemistry, antibody AB-2 revealed subsets of cells, including radial glia, transiently during the perinatal period. Peak reactivity in radial glia was on embryonic day 19 in males and on postnatal day 1 in females. On postnatal day 1, AB-2 immunoreactivity in radial glia was 2-fold greater in females than in males. Greater activity was detected in males on one side of the brain than the other (2- to 4-fold, depending on the region). To test the hormone dependence of this sex difference, pregnant rats were injected with testosterone propionate to expose fetal females to androgen on embryonic day 18. This resulted in lower levels of AB-2 immunoreactivity in radial glia of the treated female offspring on postnatal day 1 relative to control females, and the pattern was bilaterally asymmetric, approaching that of males. Thus the difference between sexes in immunoreactivity with AB-2 as a marker was hormone dependent in a predictable manner. Whether this marker is revealing a sex difference in accessibility of antigen by immunocytochemistry or a sex difference in intrinsic antigen levels is not yet resolved. In either case these results support the hypothesis that certain hormone-dependent molecular events occur transiently during development.

Modulation of aromatase activity by testosterone in transplants of fetal rat hypothalamus-preoptic area.

Conversion of androgens to estrogens by neural aromatase appears to be a prerequisite for a variety of effects of androgens on brain function, including sexual differentiation. Activity of aromatase is modulated by its substrate testosterone (T) in adult hypothalamus-preoptic area (HPOA), resulting in significantly higher levels in the male. Perinatal sex differences in activity have also been observed in hypothalamus, POA and/or amygdala. However, it is not known if higher levels in the perinatal male occur in response to circulating androgens, nor whether early exposure to gonadal steroids is necessary to establish either basal levels or the androgen sensitivity of aromatase activity in the adult brain. In order to investigate the influence of early steroid exposure on the development of neural aromatase activity, embryonic day (E)17 fetal HPOA was transplanted onto the choroidal pia overlying the superior colliculus of adult ovariectomized-adrenalectomized (OVX-ADX) Holtzman female hosts. In the first experiment, the effect of androgen exposure on aromatase activity in mature HPOA transplants was determined. Hosts received T-filled silastic capsules or underwent sham surgery 7 weeks after transplantation and were sacrificed 7 days later. Aromatase activity was determined in vitro using the stereospecific production of 3H2O from [1 beta-3H]androstenedione as an index of estrogen formation. Aromatase activity was significantly greater in T-treated HPOA versus controls (P less than 0.005). Activity was not affected by the sex of the donor fetus. In the second experiment, the effect of androgen exposure during the first 6 days following transplantation of E17 HPOA (corresponding to the last gestational week) was determined.(ABSTRACT TRUNCATED AT 250 WORDS)

Estrogen and progestin receptors appear in transplanted fetal hypothalamus-preoptic area independently of the steroid environment.

Sexual maturation and differentiation of the rat brain are believed to result from the interaction of gonadal steroids with specific neural receptors during late fetal and early postnatal life. A variety of evidence indicates that the first appearance of estrogen receptors in the hypothalamus-preoptic area (HPOA) during the perinatal period is a crucial evident underlying these processes. However, it is unknown to what extent the ontogeny of estrogen receptors is itself influenced by gonadal steroids present in the fetal environment. In order to address this question, estrogen receptors were assayed in HPOA 8 weeks after transplantation of the tissue from embryonic day 15 to 18 fetuses to either the choroidal pia overlying the superior colliculus or to the anterior chamber of the eye of adult female hosts. Host animals were either intact or ovariectomized and adrenalectomized, with or without estrogen replacement. The saturable binding of estradiol to cytosol of HPOA transplants exhibited the steroid specificity and high affinity characteristic of authentic estrogen receptors. No differences in the level of cytosol estrogen receptors in transplanted HPOA grown in the presence or absence of gonadal steroids were found. Receptor concentrations were also similar in HPOA taken from male or female fetuses. Autoradiography with [3H]estradiol revealed clusters of estrophilic cells in the transplants similar to those of the adult host hypothalamus, again regardless of whether the transplant developed in the presence of gonadal steroids. Estrogen receptors from both groups were also found to be biochemically functional as indicated by the ability of acute estrogen treatment to induce progestin receptors in the transplants.(ABSTRACT TRUNCATED AT 250 WORDS)

Ontogeny of neuropeptidergic systems: luteinizing hormone releasing hormone (LHRH); somatostatin (SRIF) and neurophysin (NF) in the hypothalamus of the domestic pig by immunocytochemistry.

The ontogenic development of some hypothalamic neuropeptides: luteinizing hormone releasing hormone (LHRH); somatostatin (SRIF) and neurophysin (NF) and their localization in the hypothalamus of fetuses in different stages of the fetal life were studied by immunoperoxidase method. It was found that differentiation of the neurons which produce the examined hormones begins in the midstage of pregnancy. LHRH is stored in the nerve terminals of the median eminence (ME) and organum vasculosum of the lamina terminalis (OVLT) since 72 day of gestation and its amount gradually increases with the development of the embryo. In this stage a few immunoreactive (ir) LHRH perikarya appear but they are most numerous in the last days of pregnancy (110 day). They are localized in the most anterior periventricular parts of the hypothalamus, area preoptica, diagonal band of Broca and very rare in the medial-basal hypothalamus. Somatostatin is produced in the separate neuronal system and appears in the last days of fetal life. Neurophysin is present in both magnocellular nuclei in 72 day-old fetuses, but at the end of gestation it is seen also in some preoptico-septal region.