Ontogeny of sex differences in the mammalian hypothalamus and preoptic area

1. There are numerous sites in the nervous system where steroid hormones dramatically influence development. Increasing interest in mechanisms in neural development is providing avenues for understanding how gonadal steroids alter the ontogeny of these regions during sexual differentiation. 2. An increasing number of researchers are examining effects of gonadal steroids on neurite outgrowth, cell differentiation, cell death, cell migration, and synaptogenesis. The interrelated timing of these events may be a key aspect influenced by gonadal steroids throughout development. 3. The preoptic area and hypothalamus are characteristically heterogeneous in terms of cell type (e.g., different neuropeptides) and cell derivation. Perhaps a major reason for the ontogeny of sexual differences in the preoptic area and hypothalamus lies in the convergence of many different cell types from diverse sources (i.e., proliferative zones surrounding the lateral and third ventricles, and the olfactory placodes) that can be influenced in an interactive manner by gonadal steroid mechanisms. 4. The characterization of multiple mechanisms (e.g., trophic, migratory, apoptotic, fate, etc.,) that contribute to permanent changes in brain structure and ultimately function is essential for unraveling the process of sexual differentiation.

Gonadotropin-releasing hormone containing neurons and olfactory fibers during development: from lamprey to mammals

Gonadotropin releasing-hormone (GnRH) regulates the hypothalamo-pituitary-gonadal axis in all vertebrates. The vast majority of GnRH neurons are thought to be derived from progenitor cells in medial olfactory placodes. Several antibodies and lectins that recognize cell surface carbohydrates have been useful for delineating the migratory pathway from the olfactory placodes and vomeronasal organ, through the nasal compartment, and across the cribriform plate into the brain. In rats, alpha-galactosyl-linked glycoconjugates (immunoreactive with the CC2 monoclonal antibody) are expressed on fibers along the GnRH migration pathway and approximately 10% of the GnRH neuronal population. In lamprey, the alpha-galactosyl binding lectin, Grifonia simplicifolia-I (GS-1), identifies cells and fibers of the developing olfactory system. In contrast to the CC2 immunoreactive GnRH neurons in rats, the GS-1 does not label a subpopulation of presumptive GnRH neurons in lamprey. Results from these and other experiments suggest that GnRH neurons in developing lamprey do not originate within the olfactory placode, but rather within proliferative zones of the diencephalon. However, the overlap of olfactory- and GnRH-containing fibers from prolarval stages to metamorphosis, suggest that olfactory stimuli may play a major role in the regulation of GnRH secretion in lamprey throughout life. By contrast, olfactory fibers are directly relevant to the migration of GnRH neurons from the olfactory placodes in mammalian species. Primary interactions between olfactory fibers and GnRH neurons are likely transient in mammals, and so in later life olfactory modulation of GnRH secretion is likely to be indirect.

Migration of neurons containing gonadotropin releasing hormone (GnRH) in slices from embryonic nasal compartment and forebrain

During development, neurons containing gonadotropin-releasing hormone traverse fiber bundles in the nose, cross into the brain, and move through a maze of glial and axonal fibers. To test whether GnRH neurons utilize cues intrinsic to their migration route to traverse the nasal/brain boundary, tissue slices that maintain connections between the forebrain and nasal compartment were prepared from mouse embryos. Cell migration between the nasal and brain compartments was evident based on changes in cell positions after successive days in vitro.

Relationship of gonadotropin-releasing hormone (GnRH) neurons to the olfactory system in developing lamprey (Petromyzon marinus)

Gonadotropin releasing-hormone (GnRH) regulates the hypothalamo-pituitary-gonadal axis in vertebrates. The regulation of GnRH is intimately related to information from the olfactory system. Additionally, GnRH neurons are thought to be derived from progenitor cells in medial olfactory placodes. The present experiments were conducted to characterize the earliest development of GnRH neurons in lamprey and to determine their relationship to cells and fibers derived from the olfactory system. Eggs from fertile adult sea lamprey were fertilized in the laboratory, and larvae were maintained for up to 100 days. GnRH neurons were visualized within the lamprey preoptic area and hypothalamus as soon as GnRH was detectable (22 days after fertilization). The number of neurons increased with age through day 100. GnRH neurons were never seen within the olfactory system. The cells and fibers of the olfactory system were identified using the lectin, Grifonia Simplicifolia-1 (GS-1). Overlap between the olfactory and GnRH systems were at the level of fiber projections. GS-1 reactive cells of apparent placodal origin did not enter the region of the preoptic area or hypothalamus that contained GnRH neurons. Recently divided cells were labeled with the thymidine analog, bromodeoxyuridine (BrdU). The positions of BrdU-labeled cells after different survival times suggest a predominant medial-lateral radial neuron migration with a small number in positions suggestive of migration between the olfactory epithelium and the telencephalic lobes. Regardless of survival time, these cells were always found close to their entry point into the brain, suggesting minimal rostral-caudal migration. Based on these results, we hypothesize that GnRH neurons in developing lamprey originate within proliferative zones of the diencephalon and not in the olfactory system. Based on the overlap of olfactory- and GnRH-containing fibers from prolarval stages to metamorphosis, olfactory stimuli may play a major role in the regulation of GnRH secretion in lamprey.

Expression of gamma-aminobutyric acid and gonadotropin-releasing hormone during neuronal migration through the olfactory system

Neurons containing the decapeptide GnRH originate in the olfactory placodes and migrate into the central nervous system during fetal development. The neurotransmitter gamma-aminobutyric acid (GABA) has been proposed as a trophic factor and may also influence neuronal migration. Immunocytochemical analyses were conducted in fetal rats, mice, and humans to identify potential developmental relationships between cells containing GABA, and GnRH neurons. Cells containing GABA were found along the nasal portion of the GnRH migration pathway in rats, mice, and humans during development. A peak number of cells containing immunoreactive GABA was observed in the nasal compartment of rats at embryonic day 15. At this time (E15), a majority of GnRH neurons were clustered in the region of the cribriform plate. By postnatal day 1, all GnRH neurons had migrated into the CNS and GABA cells were virtually absent from the nasal compartment. Double-label and confocal analyses of GABA and GnRH in mice and rats demonstrated that some olfactory GABAergic neurons coexpress GnRH. This implies that neurons that transiently express GABA originate in olfactory placodes and migrate into the forebrain. Based on the transient dual-label and adjacent relationships between GABA and GnRH containing cells in the nasal compartment, and other data showing migrational and trophic roles for GABA in development, we suggest that GABA may directly influence GnRH neuronal migration and development.

Neurogenesis and cell migration into the sexually dimorphic preoptic area/anterior hypothalamus of the fetal ferret

A sexually dimorphic male nucleus (MN) of the preoptic area/anterior hypothalamus (POA/AH), comprising large, estradiol-receptor containing neurons, is formed in male ferrets due to the action of estradiol, derived from the neural aromatization of circulating testosterone, during the last quarter of a 41-day gestation. Two experiments were conducted to compare the birthdates and the migration pattern of cells into the sexually dimorphic portion of the dorsomedial POA/AH as well as the nondimorphic ventral nucleus (VN) of the POA/AH of males and females. In experiment 1 the thymidine analog, bromodeoxyuridine (BrdU), was injected into the amniotic sacs of fetuses of different mothers between embryonic (E) days 18 and 30. Kits from all mothers were sacrificed on E38, and brains were processed to localize BrdU immunoreactivity (IR) for determining the birthdates of neurons in the POA/AH. Cells in the MN-POA/AH of males and in a comparable region of females were born between E22 and E28; cells in the nondimorphic VN-POA/AH of both sexes were born between these same ages. These results suggest that cells in the sexually dimorphic as well as the nondimorphic subdivision of the ferret POA/AH are born during the same embryonic period. This is well before the ages (E30-E41) when administering testosterone to females can stimulate, and blocking androgen aromatization in males can inhibit, MN-POA/AH differentiation. In experiment 2 BrdU was injected on E24, and kits from different litters were perfused on E30, E34, or E38. Brains were processed for BrdU-IR as well as glial fibrillary acidic protein (GFAP), which served as a marker for radial glial processes. The orientation of radial glial processes in fetal brains of both sexes suggested that cells migrate into the dorsomedial POA/AH from proliferative zones lining the lateral as well as the third ventricles. Quantitative, computer-assisted image analysis of BrdU-IR in groups of male and female brains supported this hypothesis. There were no significant sex differences in the distribution of BrdU-IR over the three ages studied, suggesting that formation of the MN-POA/AH in males cannot be attributed to an effect of estradiol on the migration of those cells born on E24 into this sexually dimorphic structure. Finally, total BrdU-IR did not change significantly in the POA/AH of male and female kits killed at E30, E34, or E38 while the area of the POA/AH increased more than 2.5-fold over this period, suggesting that few of the POA/AH cells born on E24 die during this period in either sex. In the absence of evidence that formation of the male ferret's MN-POA/AH depends on steroid-induced changes in neurogenesis, cell migration, or death, we suggest that the specification of a particular neuronal phenotype (e.g., large somal size; capacity to produce some undetermined neurotransmitter or neuropeptide) may be responsible.

Estrogenic control of preoptic area development in a carnivore, the ferret

1. Evidence is reviewed which shows that a sexually dimorphic nucleus located in the dorsomedial portion of the male ferret's preoptic area/anterior hypothalamus (POA/AH), called the male nucleus of the POA/AH (Mn-POA/AH), develops during fetal life in response to the action of estradiol, which is formed directly in the nervous system from circulating testosterone over the final quarter of a 41-day gestation. 2. Results are summarized which establish that neurons which make up the Mn-POA/AH are born prior to the critical period of estradiol's action in the male brain. Other data show that some radial glial processes, visualized immunocytochemically using antibodies against GFAP, emanate from proliferative zones at the base of the lateral ventricles in a dorsal-ventral orientation, whereas other glial processes emanate laterally from proliferative zones lining the third ventricle. 3. We suggest that at least some neurons which constitute the dorsomedial POA/AH are born in proliferative zones surrounding the lateral ventricles, raising the question of whether estradiol acts in developing males to influence the migration of these neurons along radial glial guides into the Mn-POA/AH. 4. Finally, evidence is summarized showing that excitotoxic lesions of the dorsomedial POA/AH enhance males' preference to approach and interact with another sexually active male, as opposed to an estrous female, when adult subjects are castrated and treated with estradiol benzoate. These data suggest that the sexually dimorphic Mn-POA/AH is an essential part of a CNS circuit which determines heterosexual partner preference in the male ferret.

The migration of luteinizing hormone-releasing hormone neurons in the developing rat is associated with a transient, caudal projection of the vomeronasal nerve

Luteinizing hormone-releasing hormone (LHRH) neurons originate in the olfactory placode and vomeronasal organ and migrate to the brain from embryonic day 14 (E14) in the rat. We investigated the development of the vomeronasal nerve and its role as a guide for migrating LHRH neurons. Using fluorescent, lipophilic dye tracing methods, we observed axons that emerge from the vomeronasal organ and cross the nasal septum as several large fascicles. At E14-15, these fascicles converge as they enter the region of the cribriform plate and subsequently disperse, projecting dorsally and caudally across the olfactory bulb and rostral forebrain. At E16, the dorsal branch of the vomeronasal nerve forms a more tightly fasciculated projection; the caudal fibers remain dispersed, extending along the medial forebrain. The number of caudally directed axons decreases during development, leaving four or five present at postnatal day 4 (P4). Immunohistochemical studies indicate that the vomeronasal nerve can be divided into four spatially distinct subpopulations of fibers. One subset, composed of caudal fibers that terminate in the lamina terminalis, selectively expresses TAG-1, a transient axonal surface glycoprotein and PSA-N-CAM, a highly polysialated form of neural cell adhesion molecule. The extension and subsequent retraction of this branch of the vomeronasal nerve corresponds spatially and temporally with the migration of LHRH neurons from the nasal cavity to the brain. Our studies show that between E14 and E18, LHRH neurons migrate in contact with the TAG-1+, PSA-N-CAM+ caudal branch of the vomeronasal nerve.

Telencephalic and diencephalic origin of radial glial processes in the developing preoptic area/anterior hypothalamus

Neuronal birth-dating studies using [3H] thymidine have indicated that neurons in the preoptic area/anterior hypothalamus (POA/AH) are derived primarily from progenitors in proliferative zones surrounding the third ventricle. Radial glial processes are potential guides for neuronal migration, and their presence and orientation during development may provide further information about the origin of cells in the POA/AH. In addition to determining the orientation of radial glial fibers, we examined the relationship of neurons with identified birth dates to radial glial processes in the developing POA/AH of ferrets. Neuronal birth dates were determined by injecting ferret fetuses with bromodeoxyuridine (BrdU) at several different gestational ages; brains were taken from ferret kits at subsequent prenatal ages. Sections were processed for immunocytochemistry to reveal vimentin or glial fibrillary acidic protein in radial glial, or BrdU-labeled cell nuclei. Numerous radial glial processes extended from the lateral ventricles through ventral portions of the septal region to the pial surface of the POA/AH. These fibers both encapsulated and coursed ventrally through and around the anterior commissure of ferret, rat, and mouse fetuses. These ventrally directed fibers were less evident at older ages. In double-labeled sections from ferrets, BrdU-labeled cells in the dorsal POA/AH were often aligned in the same dorsal-ventral orientation as adjacent radial glial fibers. We suggest that a subset of neurons, originating in telencephalic proliferative zones, migrates ventrally along radial glial guides into the dorsal POA/AH.

Can gonadal steroids influence cell position in the developing brain?

The preoptic area/anterior hypothalamus (POA/AH) is a site where hormones dramatically influence development. The POA/AH is comprised of multiple subgroups, but little is known about the derivation of these subgroups during development. Results from several laboratories suggest that some cells in the POA/AH originate from progenitor cells in other regions of the developing nervous system. We are exploring pathways for migration in the developing POA/AH in two ways. First, we are examining the distribution of radial glial processes as potential migratory guides using immunocytochemistry. We have identified a transient pattern of radial glial processes from the lateral ventricles to the pial surface at the base of the POA/AH. Additionally, the expression of a molecule in radial glial processes originating in the third ventricle was decreased by prenatal treatment with testosterone. Second, we are utilizing time-lapse video microscopy in vitro to assess the extent and direction of movements of fluorescent dye-labeled cells at different ages in brain slice preparations from the POA/AH of developing rats. Data from these studies indicate that cell migration in the POA/AH includes movements along dorsal-ventral routes and from lateral to medial positions, in addition to the predicted medial to lateral pathway away from the third ventricle. Several researchers have examined effects of gonadal steroids on neurite outgrowth, cell differentiation, cell death, and synaptogenesis. The determination of cell position, however, may be a key event influenced by gonadal steroids earlier in development. The characterization of migratory pathways that contribute to permanent changes in brain structure and ultimately function is essential for unraveling the process of sexual differentiation.

Sex and regional differences in intracellular localization of estrogen receptor immunoreactivity in adult ferret forebrain

Estrogen receptors were visualized in adult ferret brains using the H222 estrogen receptor antibody and immunocytochemical techniques. H222 immunoreactive (H222ir) cell nuclei were present in many forebrain regions in gonadectomized ferrets of both sexes. In many instances, H222ir cells also had immunoreaction product in their processes. All cells with H222ir processes also contained H222ir nuclei. More H222ir processes were observed in females in the medial and lateral preoptic area/anterior hypothalamus, and at the level of the descending fornix and caudal anterior commissure. Quantitative image analysis confirmed that females had significantly more (approximately 50%) extranuclear H222 immunoreaction product than males in cells in the magnocellular or preoptic subnuclei of the bed nucleus of the stria terminalis. Cells in the principal subnucleus of the bed nucleus of the stria terminalis and ventrolateral septum were notable for the relative paucity of H222ir processes. Sex differences in the intracellular extranuclear distribution of estrogen receptor protein in particular brain regions might contribute to the differential regulation of estrogen-dependent functions in the two sexes.

Rostrocaudal expression of antibody HNK-1-reactive glycolipids in mouse cerebellum: relationship to developmental compartments and leaner mutation

Sulfoglucuronylglycolipids (SGGLs) and glycoproteins, reacting with monoclonal antibody HNK-1, are developmentally and spatially regulated in the mammalian cortex and cerebellum. It has been proposed that the HNK-1 carbohydrate epitope is involved in intercellular adhesion and cell-cell interactions. Biochemical analysis and immunocytochemical localization of SGGLs and other neolacto series glycolipids were studied in the leaner mutant mouse cerebellum, where a slow and progressive rostral to caudal degeneration occurs with a gradual loss of both granule cells and Purkinje cells. Biochemical analyses showed that SGGLs and other neolacto series of glycolipids were significantly decreased in the adult leaner cerebellum; however, HNK-1-reactive glycoproteins were not affected. By an immunocytochemical method which selectively localizes the lipid antigens, it is shown that SGGLs are primarily associated with Purkinje cell bodies and their dendrites in the molecular layer and in cerebellar nuclei where Purkinje cell axons terminate. At postnatal day 30 (P30), SGGL immunoreactivity (SGGL-ir) in the leaner cerebellum was reduced moderately compared to normal littermates, which correlated with the minimal degree of Purkinje cell degeneration at this age in leaner and with the biochemical data. At P67 and P90, the SGGL-ir was significantly more reduced in the leaner as Purkinje cell degeneration proceeded. There was a direct correlation between loss of Purkinje cells and SGGL-ir in the cerebellar molecular layer. In both normal and young leaner cerebella, the SGGL-ir in different lobules was not uniform; there were distinct rostrocaudal and mediolateral differences. SGGL-ir was markedly more intense in rostral than in caudal lobules in the vermis, the dividing line being the region immediately caudal to the primary fissure and rostral to the declival sulcus. In the lateral cerebellum, the SGGL-ir was less intense than in the vermis and the rostrocaudal difference was not as pronounced. There was also nonuniformity in the intensity of staining in different folia. The rostrocaudal as well as mediolateral differences in the intensity of SGGL-ir were confirmed independently by biochemical analysis. The differential phenotypic expression of SGGLs and the selective susceptibility to Purkinje cell death in leaner mutant are discussed in relation to the known embryologic and ontogenetic compartmentation of cerebellum.

Ontogeny of Leu-enkephalin and beta-endorphin innervation of the preoptic area in male and female rats

The distribution of endogenous opioid peptide-containing fibers in the medial preoptic area of developing male and female rats was examined using immunohistochemical methods. In particular, the ontogeny of leucine-enkephalin (leu-enk) and beta-endorphin (beta-endo) innervation was studied using antisera directed against these compounds. The distribution of Leu-enk and beta-endo differed at each age examined from birth to postnatal day 12 (P12). Furthermore, the patterns of fiber innervation differed across development. Leu-enk-like immunoreactivity was initially densest in the lateral preoptic region of both sexes, ultimately expanding into the medial preoptic region to become densest in the lateral portion of the medial preoptic nucleus by P12. This latter pattern was observed only in males, however, as females continued to exhibit diffuse medial preoptic Leu-enk-like immunoreactivity at P12. In contrast, the distribution and developmental pattern of beta-endo-like immunoreactivity was similar in both sexes; diffuse staining was observed in the medial preoptic region at birth, later becoming dense only in the periventricular and parastrial nuclei. The time course of development of Leu-enk and beta-endo innervation of the medial preoptic area suggests that the sexually dimorphic expression of opioid immunoreactivity occurs after preoptic neurons appear in their sexually dimorphic configuration. Therefore, although the development of opioid-containing pathways could be influenced by the perinatal gonadal steroid hormone environment, medial preoptic Leu-enk and beta-endo innervation might not contribute directly to the sexually dimorphic neuronal organization of the preoptic area.

Cellular organization in rat somatosensory cortex: effects of sex and laterality

Layer IV of rodent somatosensory cortex contains distinct arrangements of cells characterized as barrels. When barrels first form in rats, each barrel consists of a cell-dense "wall" and a cell-sparse "hollow." With age, the distinction of the boundary between barrel walls and hollows diminishes. Cellular arrangements within barrels were quantified to test whether the barrels are influenced by sex and laterality during cortical development. A computer-assisted method was developed to measure cell densities in relation to barrel boundaries. The boundaries between barrel walls and hollows were determined in tissue double-stained for Nissl substance and cytochrome oxidase histochemistry. The distinction between barrel walls and hollows revealed by Nissl stains differed significantly between anterior and posterior barrels. This distinction declined significantly in anterior barrels from Postnatal Day 10 (P10) to P30. The area of cortex containing barrels was estimated from composites of Nissl-stained sections. At P20 the detectable barrel cortex area was larger on the right in females and on the left in males resulting in a significant sex difference in barrel cortex asymmetry. This sex difference in barrel cortex laterality was detected only in Nissl-stained tissue; there were no differences attributable to sex or side in barrel cortex area analyzed for cytochrome oxidase reactivity. We hypothesize that sex-dependent differences in barrel cortex structure result from lateralized differences in cellular organization.

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.

Relationship of migrating luteinizing hormone-releasing hormone neurons to unique olfactory system glycoconjugates in embryonic rats

Following their birth in olfactory placode, luteinizing hormone-releasing hormone (LHRH)-containing neurons migrate across the developing cribriform plate and form a dispersed population in the mammalian basal forebrain. The present study reveals the colocalization of unique glycoconjugate antigens (detected with monoclonal antibody CC2) on a subset of LHRH-immunoreactive (LHRHir) cell bodies and growth cones in the rostral forebrain during embryonic development in rats. In addition, LHRHir neurons were found along CC2-immunoreactive (CC2ir) fibers in the nasal cavity, across the cribriform plate, and in the rostral forebrain. At embryonic Day 16 (E16) approximately 20% of the LHRHir neuronal population in the forebrain had the CC2 epitope on surfaces of cell bodies. This percentage fell as the number of LHRHir neurons in the forebrain increased. Prior to the detection of LHRH-containing neurons, beginning on E14, CC2ir glycoconjugates were observed on vomeronasal cells and axons and also on a dorsomedial subset of olfactory neurons and axons. As early as E14 CC2ir fibers extended into the rostral forebrain. LHRHir neurons were seen in close apposition to CC2ir fibers in both the nasal cavity and rostral forebrain. These studies raise the possibility that CC2ir glycoconjugates provide a specific chemical guide for a subset of LHRH neurons along a part of their migratory pathways. The small percentage of LHRHir neurons which have CC2ir on their surfaces prenatally may constitute a selective homogenous functional subgroup within the population of LHRH neurons.

A sex comparison of serotonin immunoreactivity and content in the ferret preoptic area/anterior hypothalamus

Previous studies with rats raised the possibility that sexually dimorphic features of the medial preoptic area/anterior hypothalamus (POA/AH) may result, in part, from a sex difference in the serotonergic innervation of this region. We asked whether a similar phenomenon may occur in a carnivore, the ferret. A sexually dimorphic male nucleus of the dorsal POA/AH (Mn-POA/AH) has previously been characterized in Nissl-stained sections of the male ferret forebrain; this nucleus is absent in females. A nondimorphic ventral nucleus of the POA/AH is found in both sexes. In the present study numerous serotonin (5-HT) immunoreactive (ir) fibers were observed in the dorsal POA/AH of gonadectomized adult ferrets of both sexes. By contrast, in both sexes the ventral nucleus of the POA/AH had many fewer 5-HTir fibers. A similar difference in the distribution of immunoreactivity between dorsal and ventral POA/AH was observed for tyrosine hydroxylase (TH) localized in cell bodies and in nerve fibers and for H222ir estrogen receptors localized in cell nuclei. Likewise, in both sexes the content of 5-HT and dopamine (DA), measured by high pressure liquid chromatography with electrochemical detection, were significantly higher in the dorsal than the ventral POA/AH, thereby corroborating observed regional differences in 5-HTir and THir fibers, respectively. The present findings provide no support for the notion that sexually dimorphic cytoarchitectonic features of the dorsal POA/AH in ferrets are associated with a sex difference in the serotonergic innervation of this region.

Effects of sex and androgen treatment on dendritic dimensions of neurons in the sexually dimorphic preoptic/anterior hypothalamic area of male and female ferrets

A sexually dimorphic group of cells at the dorsal border of the preoptic/anterior hypothalamic area (POA/AH) of ferrets has been previously identified in Nissl-stained tissue. In this study, Golgi-stained tissue was examined in order 1) to determine whether sex differences exist in dendritic dimensions of neurons from this region, and 2) to assess the effects of adult androgen treatment on dendritic morphology in ferrets of both sexes. Brains from adult ferrets given daily injections of testosterone propionate (5 mg/kg body weight) or oil vehicle for 5 weeks after gonadectomy were impregnated by Golgi-Cox procedures. After sectioning at 120 microns, 78 multipolar neurons were selected from the sexually dimorphic POA/AH of 12 ferrets and reconstructed in three dimensions with the aid of a computer-assisted neuron tracing system. Large sex differences were observed in somal area and most aspects of dendritic morphology, including total length, number of branches, and total dendritic surface area. Androgen also appeared to accentuate dendritic arborization in both sexes, but this effect was weaker than the sex effect, more apparent in males than females, and restricted to fewer variables. The most statistically significant effects of adult androgen treatment in males were found for total dendritic surface area and percentage of fourth order dendrites, and in females, average dendritic thickness. These data show that strong sex differences exist in dendritic structure of neurons in the POA/AH, and suggest that alterations in levels of gonadal steroids in adulthood may promote synaptic remodeling in a region of the brain involved in the control of sexually dimorphic behaviors.

Expression of the Raf-1 protein in rat brain during development and its hormonal regulation in hypothalamus

To study mechanisms involved in the sexual differentiation of the rat brain, the expression of the protein product of the proto-oncogene c-raf-1 (Raf-1) was examined. Biochemical and immunocytochemical analyses localized Raf-1 in embryonic rat brain regions and demonstrated hormonally induced changes in Raf-1 expression. For this study an affinity-purified anti-peptide antiserum specific for Raf-1 (NH-44) was used. Western blots revealed an approximately 77 kD polypeptide isolated in the cytosol of developing rat brains. Raf-1 levels were highest in the embryonic (E) day 22 female hypothalamus (HYP), and approximately twofold higher than levels detected in male HYP at E22 as determined by quantitative protein dot blot and semiquantitative Western blot analyses. Raf-1 levels in HYP were greater than those in either brain stem (BS) or cortex. Immunocytochemical analysis revealed high levels of Raf-1 in selective brain regions (e.g., the ventromedial nucleus in the HYP, the mitral cell layers in the main and accessory olfactory bulbs (OB), and the locus coeruleus) at E22 and postnatal (P) day 1. Lower levels of immunoreactivity were observed in many areas of the perinatal neuraxis. To test hormonal regulation of Raf-1, testosterone propionate (TP) was administered to pregnant rats on E17; male and female fetuses were examined on E22. This treatment significantly decreased Raf-1 levels in female HYP, but not in male HYP, as determined by Western blot analysis. No significant sex difference or response to prenatal hormone treatments were observed in either brain stem or cortex. No significant sex difference was noted postnatally, and administration of TP 3 h after birth did not change Raf-1 levels examined 24 h later. In summary, Raf-1 was localized within selective regions of the rat brain, and its expression was altered by exogenous prenatal hormonal stimulation. One role for Raf-1 in signal transduction may be to delimit hormonal critical periods in sexual differentiation of the brain.

Differential hormonal modulation of brain antigens recognized by the AB-2 monoclonal antibody

The expression of monoclonal antibody AB-2 immunoreactivity is age- and sex-dependent in radial glia of developing rat hypothalamus and is regulated by prenatal exposure to gonadal steroids. In the present study, several proteins were recognized by AB-2 and were distributed selectively in subcellular fractions from neonatal hypothalamus (HYP), remaining forebrain (FB), and brainstem regions. Immunoblots revealed polypeptide bands in 3 major molecular weight classes: one at approximately 195 kDa in the cytosolic compartment; and two doublets at 220 kDa and 340 kDa in both microsomal and crude mitochondrial membrane fractions. The 220 kDa and 340 kDa doublets were also Triton-insoluble, suggesting a cytoskeletal association. The 195 kDa-AB-2-immunoreactive band was present in both Triton-soluble and insoluble fractions. AB-2 also recognized several acidic glycolipids extracted from postnatal rat brain regions on immunoblots following high performance thin layer chromatography. One of the bands from postnatal rat brain extracts migrated similarly to purified bovine brain sulfatide, which was also immunoreactive with AB-2. AB-2 immunoreactivity with proteins, polar lipids, and sulfatide suggests that the epitope is a carbohydrate present in multiple cellular compartments. AB-2 recognized the same molecular bands in males and females. Testosterone treatment selectively decreased the level of the 195 kDa AB-2-immunoreactive polypeptide. The 195 kDa AB-2-immunoreactive polypeptide possibly acts in radial glia in the determination of sexually dimorphic neurons in the preoptic area/hypothalamus.

Estradiol binding in the sexually dimorphic nucleus of the preoptic/anterior hypothalamic area of adult male ferrets and in the equivalent region of females

A large number of estradiol-concentrating cells were visualized by autoradiography in a subpopulation of large neurons located in and around the sexually dimorphic male nucleus of the preoptic/anterior hypothalamic area (MN-POA/AH) of castrated male ferrets and in a comparable dorsal portion of the POA/AH of ovariectomized females. Considerably fewer estradiol-labelled cells were seen in the non-dimorphic ventral POA/AH nucleus of both sexes. Estrogen binding in cells in or around the MN-POA/AH may contribute to the formation of this sexually dimorphic nucleus in fetal males and may mediate specific estrogen-dependent behavioral functions in adulthood.

Vaginocervical stimulation of ferrets induces release of luteinizing hormone-releasing hormone

Abstract Vaginocervical stimulation of ovariectomized estradiol-primed ferrets (which are reflex ovulators) with a glass rod in the presence of a neck-gripping male induced an increase in plasma luteinizing hormone (LH) from undetectable levels (</=0.50 ng/ml) before stimulation, to 2.4 +/- 0.43 ng/ml 75 min after stimulation (stimulated females). Forty-eight h after stimulation plasma LH returned to baseline levels (post-stimulated females). A significant decrease in the number of perikarya containing LH-releasing hormone (LHRH), detected by immunocytochemistry, was associated with the increase in plasma LH following stimulation. Approximately one half of the number of immunoreactive LHRH neurons (243+/-27) were detected in the forebrain of stimulated females, compared to those detected in the forebrain of post-stimulated animals (436 +/- 88) using antiserum AR 744. Equivalent results were obtained with a different antiserum (RM 1076) capable of detecting the extended decapeptide, or precursor, as well as partially or fully processed decapeptide. We conclude that controlled Vaginocervical stimulation of female ferrets evokes the release of LHRH as well as LH, depleting approximately 50% of the LHRH perikarya of detectable LHRH. Additionally, electron microscopy of LHRH perikarya of stimulated females revealed more Golgi complexes/cell compared to baseline females. We propose that Vaginocervical stimulation also augments the processing of extended precursor forms of LHRH to generate the decapeptide.

Developmental expression of HNK-1-reactive antigens in the rat cerebellum and localization of sulfoglucuronyl glycolipids in molecular layer and deep cerebellar nuclei

Monoclonal antibody HNK-1-reactive carbohydrate epitope is expressed on proteins, proteoglycans, and sulfoglucuronyl glycolipids (SGGLs). The developmental expression of these HNK-1-reactive antigens was studied in rat cerebellum. The expression of sulfoglucuronyl lacto-N-neotetraosylceramide (SGGL-1) was biphasic with an initial maximum at postnatal day one (PD 1), followed by a second rise in the level at PD 20. The level of sulfoglucuronyl lacto-N-norhexaosyl ceramide (SGGL-2) in cerebellum was low until PD 15 and then increased to a plateau at PD 20. The levels of SGGLs increased during postnatal development of the cerebellum, contrary to their diminishing expression in the cerebral cortex. The expression of HNK-1-reactive glycoproteins decreased with development of the rat cerebellum from PD 1. Several HNK-1-reactive glycoproteins with apparent molecular masses between 150 and 325 kDa were visualized between PD 1 and PD 10. However, beyond PD 10, only two HNK-1-reactive bands at 160 and 180 kDa remained. The latter appeared to be neural cell adhesion molecule, N-CAM-180. A diffuse HNK-1-reactive band seen at the top of polyacrylamide electrophoretic gels was due mostly to proteoglycans. This band increased in its reactivity to HNK-1 between PD 15 and PD 25 and then decreased in the adult cerebellum. The lipid antigens were shown by two complementary methodologies to be localized primarily in the molecular layer and deep cerebellar nuclei as opposed to the granular layer and white matter. A fixation procedure which eliminates HNK-1-reactive epitope on glycoproteins and proteoglycans, but does not affect glycolipids, allowed selective immunoreactivity in the molecular layer and deep cerebellar nuclei.(ABSTRACT TRUNCATED AT 250 WORDS)