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A J Silverman

Publications and source records attributed to A J Silverman.

At least 37 records · Page 2Linked to original sources
PubMed1996

Joint migration of gonadotropin-releasing hormone (GnRH) and neuropeptide Y (NPY) neurons from olfactory placode to central nervous system.

The olfactory epithelium in vertebrates generates the olfactory sensory neurons and several migratory cell types. Prominent among the latter are the gonadotropin-releasing hormone (GnRH) neurons that differentiate within the olfactory epithelium during embryogenesis and migrate along the olfactory nerve to the central nervous system. We initiated studies to characterize additional neuronal phenotypes of olfactory epithelial derivation. Neuropeptide Y (NPY) neurons are functionally related to the reproductive axis, modulating the release of GnRH and directly enhancing GnRH-induced luteinizing hormone (LH) secretion from gonadotrophs. We demonstrate that a population of migratory NPY neurons originates within the olfactory epithelium of the chick. At stage 25, NPY-positive fibers, but not cells, were detected in the epithelium and the nerve. By stages 28-34, NPY neurons and processes were present in the olfactory epithelium, olfactory nerve, and at the junction of the olfactory nerve and forebrain. In these regions the number of NPY neurons increased until stage 30 and then declined as development progressed. Electron microscopic immunocytochemistry confirmed the neuronal phenotype of the NPY-positive cells. The origin and migratory nature of some of these NPY cells was confirmed by double-label immunocytochemical detection of NPY and GnRH. A large percentage of the NPY-cells coexpressed the GnRH peptide. Between stages 28 and 34 single- and double-labeled NPY and GnRH neurons were found side by side along the GnRH migratory route emanating from the nasal epithelium, along the olfactory nerve, and into the ventral forebrain. These data suggest that an NPY population originates in the olfactory epithelium and migrates into the central nervous system during embryogenesis. By stage 42, no NPY/GnRH double-labeled cells were detected.

Animals↗
PubMed1996

Mast cells in the brain: evidence and functional significance.

For the past two decades the brain has been considered to be an immune-privileged site that excludes circulating cells from the parenchyma. New evidence indicates that some hematocytes reside in the brain, while others traffic through it. Mast cells belong to both of these functional types. Moreover, the appearance of mast cells in the CNS can be triggered behaviorally. After a brief period of courtship, for example, there is a marked increase in mast cells in the medial habenula of sexually active doves compared with controls. Exposure to gonadal steroids that occur endogenously or that are administered exogenously increases both the number of mast cells and their state of activation in the brain. These results show that hematopoietic cells can provide targeted delivery of neuromodulators to specific regions of the brain, thereby influencing neural-endocrine interactions.

Brain↗
PubMed1995

Gonadotropin-releasing hormone neurons in the rhesus macaque are not immunoreactive for the estrogen receptor.

The issue of whether gonadotropin-releasing hormone (GnRH) neurons in the primate contain the estrogen receptor was examined by immunocytochemistry using prepubertal and adult (intact and ovariectomized) female rhesus macaques. No GnRH neurons were found to contain nuclei that were immunoreactive for the estrogen receptor. These results confirm in primates what has been reported in other species and leave open the question of how the effects of gonadal steroids on GnRH neurons are mediated.

Animals↗
PubMed1995

Cellular localization of corticotrophin releasing hormone in the human placenta, fetal membranes and decidua.

Corticotrophin releasing hormone (CRH), is produced by the human placenta, fetal membranes and decidua and has been detected in maternal and fetal plasma and amniotic fluid during human pregnancy. Previous studies of the cellular localization of CRH in the placenta and fetal membranes have yielded conflicting results. In this study, placentae were obtained from uncomplicated pregnancies immediately after elective termination or after normal delivery at term. Zamboni's fixed sections of villi and membrane-decidua, were cut at 10 microns by cryostat and immunocytochemistry was performed using an anti-rat/human CRH antiserum. In first and second trimester placentae, the amount of CRH reaction product present was variable. CRH was localized in both the syncytiotrophoblast and cytotrophoblast in first and second trimester tissue. In term placentae, CRH was identified consistently in the syncytiotrophoblast. In addition, strong CRH reaction was localized to the amnion epithelium of the fetal membranes. Positive immunoreactivity was also detected in the chorion and decidua although at a lower level of intensity. In trophoblast cells and in the amnion epithelium, CRH reaction product was contained in distinct granules. The regulation of CRH and its physiological role may differ in these diverse cell types. Possible effects of CRH include autocrine or paracrine actions within the amnion, chorion and decidua while CRH derived from syncytiotrophoblast may have endocrine effects through access to the maternal and fetal circulations.

Antibody Specificity↗
PubMed1995

Neuromodulation of transplanted gonadotropin-releasing hormone neurons in male and female hypogonadal mice with preoptic area brain grafts.

Implantation of normal preoptic area (POA) tissue into the third ventricle of adult hypogonadal (HPG) mice provides a source of GnRH neurons that innervate the host median eminence and stimulate reproductive development in the sterile mutants. To further evaluate graft-host integration, the effects of N-methyl-D,L-aspartic acid (NMA) and opiate antagonists on LH secretion in HPG mice with POA transplants (HPG/POA) were tested. NMA challenges significantly stimulated LH secretion in 10 of 11 HPG/POA females. Only 5 of 12 HPG/POA males responded to the same treatment. Administration of the opiate antagonists naloxone or naloxone methiodide was ineffective in stimulating LH release in any mice, but opiate antagonist pretreatment significantly potentiated the LH secretory response to NMA in female, but not male, HPG/POA mice. A potential anatomical substrate for this facilitation may be the beta-endorphin-immunoreactive innervation of the POA grafts in all HPG/POA brains examined. beta-Endorphin fibers were also present in the median eminence in the vicinity of GnRH outgrowth from the grafts. However, similar innervation patterns in HPG/POA males that did not respond to opioid antagonism suggests that this is not sufficient. We tested whether the sex difference in HPG/POA responsivity to neuromodulation is related to the steroid milieu in the hosts. 17 beta-Estradiol (E2) treatment facilitated the LH secretory response of male HPG/POA to NMA challenges whether animals were castrated and given an E2 capsule prior to graft implantation or one week before testing two months after graft surgery. Intact or vehicle (sesame oil)-treated, castrated HPG/POA males rarely responded to NMA challenges, yet graft-derived GnRH innervation of the hosts' median eminence was comparable in all treatment groups. GnRH challenge testing indicated that pituitary sensitivity of the HPG/POA males was not significantly altered by E2 treatment, suggesting that estrogen acted centrally. These results indicate that the activity of grafted GnRH neurons may be modulated by endogenous opioids of host origin as well as by the hormonal milieu.

Animals↗
PubMed1995

Gonadotropin-releasing hormone (GnRH) neurons of the developing tectum of the mouse.

Using a modified immunocytochemistry protocol with enhanced sensitivity, we were able to visualize a population of neurons in the tectum of the developing mouse that contained GnRH-like immunoreactivity. In microscopic studies conducted using 100 microns sections cut in sagittal or horizontal planes, 10-20 lightly-stained neurons were first detected in the tectum at E13.75 (morning of plug = E0.5). The number of immunostained cells increased exponentially reaching a peak at E15.75 before decreasing in number. No positive neurons were seen in the tectum at PN20 or later. The GnRH cells were located medially along the dorso-ventral axis of the tectum in a region of the brain distinct from that containing GnRH neurons that migrate into the CNS from the olfactory placode. To determine the nature of the immunoreactivity, two approaches were used. Analysis of tissue from an hpg mutant strongly supports the hypothesis that these cells make mammalian GnRH. Immunocytochemical data suggest that although the precursor protein is synthesized, the cleaved and amidated decapeptide may be absent or be present at an undetectable level. Our results demonstrate that in addition to the GnRH neurons from the placade, a population of GnRH neurons exists in the mouse tectum. This population is developmentally regulated, appearing only during embryonic and early postnatal ages but not in the adult.

Aging↗
PubMed1995

Novel associations among gonadotropin-releasing hormone neurons.

GnRH is secreted in bursts into the hypophyseal portal vasculature by a small dispersed population of neurons. The means by which the activity of these intrinsically pulsatile cells is coordinated are unknown. This study was initiated as a continuation of our examination of the synaptic input to these cells and their anatomical relationships. Brain tissue from female rhesus monkeys and male and female rats was prepared for the immunocytochemical demonstration of GnRH. At the light microscopic level, GnRH neurons were occasionally found to be in close apposition. Such pairs (or small groups) were randomly distributed throughout the population of GnRH neurons from the diagonal band of Broca through the anterior hypothalamic area in rats and monkeys and in the medial basal hypothalamus in monkeys. The percentage of neurons found in such associations was small (2-7% in rats and 3-15% in monkeys) and was independent of the hormonal condition of the animal. GnRH neurons, either singly or in pairs, were serially sectioned for electron microscopic examination. The sparsity of synaptic input to the cell body that we had reported earlier on the basis of random sampling was confirmed. No soma had more than a dozen synapses, but none totally lacked innervation. The most significant result of serial reconstruction was the discovery of intercellular bridges or passageways between contiguous pairs of GnRH neurons. These were formed by the fusion of processes extending from the two cells or by fusion and opening of passageways in the membranes along regions of contiguity between the two cells. They were found in four of seven pairs of neurons examined in the rat and in four of eight pairs in the monkey. This syncytial arrangement along with GnRH-GnRH synaptic interactions could contribute to the coordination of dispersed influences on these neurons and the propagation of coordinated pulsatile release of GnRH.

Animals↗
PubMed1995

Acute myocarditis presenting as acute myocardial infarction.

Myocarditis, often caused by an infectious agent, may have a presentation mimicking that of acute myocardial infarction. The authors describe a young man who, when first seen in the emergency department, appeared to have an acute myocardial infarction with normal coronary arteries. At autopsy, the histologic findings were diagnostic of active myocarditis, mixed-cell type. Neutrophilic infiltration with microabscess suggested an infectious cause, although the etiology was uncertain. The patient's clinical course, pathologic findings, and several treatment modalities are discussed. The differentiation between acute myocardial infarction and acute myocarditis can be difficult. Electrocardiographic changes and enzyme elevations are common in both. Therefore, clinicians should consider myocarditis in all patients--particularly young patients--with normal coronary arteries and suspected myocardial infarction.

Acute Disease↗
PubMed1994

Mast cells with gonadotropin-releasing hormone-like immunoreactivity in the brain of doves.

Using an antiserum (LR-1) raised against mammalian gonadotropin-releasing hormone (GnRH), we previously identified a nonneuronal cell that was more numerous in the medial habenula (MH) of courting ring doves than in individuals housed in visual isolation. The current studies suggest that they are mast cells. Both acidic toluidine blue and toluidine blue dissolved in water/butanediol revealed metachromatic cells with a distribution and morphology similar to that obtained by immunostaining with the GnRH antiserum in the MH. Some cells had granules reactive to safranin in the presence of alcian blue, indicative of a highly sulfated proteoglycan of the heparin family. Immunocytochemical studies demonstrated that all MH cells containing GnRH-like immunoreactivity contained histamine, another mast cell marker. The GnRH-immunoreactive cells had a unilobular, ovoid nucleus. Secretory granules within the cells were electron dense and displayed a variety of internal structures. Fine filamentous processes appeared evenly distributed on the cell surface whether cells were located on the pial surface or within the brain parenchyma. All of these features are characteristic of mast cells. To test whether the epitope recognized by the GnRH antiserum was produced by the mast cells or endocytosed from the cerebrospinal fluid, an iodinated GnRH analog was injected intracerebroventricularly at the initiation of courtship. Radioautography revealed no radioactive cells in the brain, indicating that the GnRH antibody recognized a molecule synthesized by the nonneuronal cells rather than internalized by a receptor-mediated mechanism. These observations suggest an interaction between a component of the immune network and specific regions of the central nervous system.

Animals↗
PubMed1994

Ultrastructural changes in gonadotropin-releasing hormone neurons as a function of age and ovariectomy in rats.

In this study we examined the effects of aging on various aspects of the ultrastructure of gonadotropin-releasing hormone neurons in female rats, including the density of synaptic input and the volume fraction of various subcellular organelles. In addition, we explored the possibility that removal of estrogen might provide a protective effect on the aging of the gonadotropin-releasing hormone neuron as exposure to gonadal steroids alters the time course of reproductive aging. Our experimental groups included four- and 18-20-month-old virgin female rats divided as follows: young intact, young short-term ovariectomized, old intact, old short-term ovariectomized and old long-term ovariectomized. Brain tissue was processed for immunocytochemical detection of gonadotropin-releasing hormone neurons and selected cells from the preoptic area were chosen for electron microscopic examination. The percentage of plasma membrane containing synaptic modification was quantified using a morphometrics program, and the volume fraction of lysosomes/lipofuscin, rough endoplasmic reticulum and Golgi apparatus were estimated using point count stereology. Whereas we had previously found a significant increase in the density of synaptic input to gonadotropin-releasing hormone neurons in aged virgin male rats, the density of synaptic input to gonadotropin-releasing hormone cells in the virgin female was not affected by age. The volume fraction of lysosomes/lipofuscin was increased in all age groups. Aging produced a dramatic decrease in the volume fraction of rough endoplasmic reticulum as well as a decrease in Golgi, suggesting a general decrease in biosynthetic activity of the cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1994

Biosynthesis of gonadotropin-releasing hormone during the rat estrous cycle: a cellular analysis.

In an attempt to understand the regulatory events that control the synthesis of gonadotropin-releasing hormone (GnRH) during the estrous cycle of the rat, we undertook a cellular analysis of time of translation of GnRH mRNA into protein. A specific antiserum, Rb 1076, which recognizes both the extended proGnRH as well as the processed form of the decapeptide was used for immunocytochemical staining. A cell was considered to be actively translating the pro-GnRH mRNA if elements of the rough endoplasmic reticulum (RER), including the outer nuclear envelope, were filled with reaction product. A synthetically quiescent cell contained only immunopositive neurosecretory granules. Cycling rats were killed at various times and all GnRH cells scored as being RER positive (+) or negative (-). On the morning of estrus almost all GnRH neurons in 5 out of 6 of the animals studied were synthesizing their unique peptide. The immunostaining in many of the cells at this time was very pale, suggesting a prior depletion. This was the only time point examined where near uniformity among individuals in a group was observed. At all other times considerable heterogeneity was observed among animals within a group. For example, at 17.30 h on the afternoon of proestrus 50% or more of the GnRH neurons were RER+ in half of the animals; the other half had values of 16-45% RER+. Synthetically active and inactive cells were found in close proximity in all animals. No regional differences were observed; all GnRH cell subpopulations from the level of the diagonal band of Broca through the hypothalamus reflected the population as a whole.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

FOS expression in the gonadotropin-releasing hormone (GnRH) neuron does not increase during the ovarian steroid-induced GnRH surge in the rhesus monkey.

The purpose of this study was to investigate the expression of the immediate early gene, c-fos, in GnRH neurons in female rhesus monkeys as a function of generation of the LH surge. Adult monkeys were either intact (n = 6) or ovariectomized (n = 10). Intact animals received estradiol benzoate (EB; 330 micrograms in oil, sc; n = 5) or oil (n = 1). Ovariectomized animals received either EB (n = 5) or EB, followed by progesterone (P; 2.5 ml in oil, im; n = 4), or oil (n = 1). Animals were killed from 31-75 h after EB treatment. Blood samples were collected to document LH release in response to steroid treatment. A surge of LH was initiated in most animals that received EB alone or EB plus P about 30 h after steroid treatment. Animals were perfused with 4% paraformaldehyde, and brain blocks encompassing the region known to contain the majority of GnRH neurons (septum through the medial basal hypothalamus) were cut on the vibratome. Sites of FOS and GnRH immunoreactivities were demonstrated using double labels with a variety of chromogens. Regardless of the time in the surge, there were very few GnRH neurons with FOS immunoreactivity in their nuclei (0-9%). FOS-positive nuclei were seen in many other neurons in various brain regions, including the suprachiasmatic and supraoptic nuclei. There were no differences in FOS expression in GnRH neurons in intact and ovariectomized animals or in steroid- or oil-treated animals. These results suggest that FOS activation in GnRH neurons is not associated with the initiation of the secretory GnRH stimulus to the LH surge in the rhesus monkey. If confirmed, these data suggest that the GnRH nerve terminal may be the primary site for the control of the GnRH surge.

Animals↗
PubMed1993

Gonadotropin-releasing hormone (GnRH) neurons in the hypogonadal mouse elaborate normal projections despite their biosynthetic deficiency.

This study was undertaken to determine whether gonadotropin-releasing hormone (GnRH) neurons in the mutant hypogonadal (hpg) mouse can establish axonal connections with their target despite their failure to synthesize and secrete the GnRH neuropeptide. Normal and hpg males received intraperitoneal injections of the retrograde tracer Fluoro-Gold. This tracer does not cross the blood-brain-barrier and hence is taken up only by neurons in the central nervous system whose axons terminate on fenestrated capillaries, such as the capillaries of the median eminence. The brains of the injected animals were processed for in situ hybridization to visualize GnRH transcribing cells. In 3 hpg males 64.1 +/- 5.6% of GnRH transcribing cells contained Fluoro-Gold, while 55.8 +/- 6.4% of the cells in 3 normal males had Fluoro-Gold. Thus, we have demonstrated that secretory-deficient GnRH neurons can establish axonal connections with their primary secretory target, the median eminence. We conclude that the capability of GnRH neurons to recognize and interact with their target is not dependent upon their neurosecretory function.

Animals↗
PubMed1993

Biochemical differentiation and intercellular interactions of migratory gonadotropin-releasing hormone (GnRH) cells in the mouse.

GnRH cells are first detected in the olfactory placode of the mouse on Gestational Day 11.5 (E11.5). Between E12.5 and E15.5 they migrate across the nasal septum and by E16.5 attain their adult distribution within the forebrain. In the present study, we used immunocytochemistry at the light and electron microscopic level to study the biochemical and morphological differentiation of gonadotropin-releasing hormone (GnRH) neurons and the cellular associations that they make during this migratory process. On E12.5, when the majority of GnRH cells are still in the nasal septum, only 15% of the population can process the pro-GnRH precursor to the amidated decapeptide. Two days later (E14.5), when most of the cells have advanced into the forebrain, 79% contain mature GnRH. In keeping with these light microscopic observations, ultrastructural analysis reveals that on E12.5 GnRH immunologic reaction product is confined to the outer nuclear envelope and rough endoplasmic reticulum. By E14.5 these migratory cells in the nasal septum have more reaction product in the rough endoplasmic reticulum and some of the Golgi cisternae are also immunopositive. Neurosecretory granules, some of which are immunoreactive, also appear at this stage. We had anticipated that the expression of GAP-43 would coincide with axonal elongation and pathfinding in GnRH neurons. Instead, GAP-43 was expressed at the early migratory stage of GnRH cells and its expression declined rapidly after these neurons had entered the forebrain and commenced axonal outgrowth. Hence, on E12.5, 62.3% of GnRH cells in the nasal septum are immunopositive for GAP-43, while only 12.6% of the forebrain population at the same embryonic stages express the protein. Similarly, on E14.5 GAP-43 is expressed in 50.7% of the nasal septum GnRH cells but only 11.6% of cells in the E14.5 forebrain express this protein. While in the nasal septum, GnRH neurons migrate only within the confines of the olfactory and vomeronasal axonal fascicles. During this part of the migratory route, the cells maintain close membrane apposition with each other and with the axons and ensheathing glia of the nerve fascicles. Once in the forebrain, GnRH neurons no longer maintain these associations, nor do they follow any defined anatomical structure. These findings indicate that although GnRH cells express their unique neuropeptide early in their ontogeny, their differentiation continues and is coordinated with their migration.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

Reproductive behavior, endocrine state, and the distribution of GnRH-like immunoreactive mast cells in dove brain.

Previous studies indicate that there is an increase in the number of detectable mast cells expressing gonadotropin-releasing hormone-like immunoreactivity (GnRH-ir) in the medial habenular region of the brain in ring doves after a period of 2 hr of courtship. In the present experiment the overall distribution of GnRH-ir mast cells in the brain is described, and the influence of behavioral and endocrine state on brain mast cell distribution and detectable mast cell number is explored. Four groups of male birds were studied: (1) paired with a female and displaying courtship behavior, (2) paired with a squab and displaying aggressive behavior, (3) visually isolated from other doves, and (4) long-term castrates housed communally. In all four groups, GnRH-ir mast cells were observed in the following areas: the medial habenula, circumventricular organs, organum vasculosum lamina terminalis and organum subseptale, the pia mater, and blood vessels. Cell counting revealed differences among groups in numbers of habenular mast cells. Courted doves had the most habenular mast cells, followed by doves paired with squabs, and then visually isolated doves, while castrates had the fewest. One-way ANOVA indicates significant differences among groups. All pairwise comparisons show that the courting animals had significantly more detectable mast cells in the habenular area than did visually isolated and castrated groups. These results suggest that the appearance and/or detectability of GnRH-ir mast cells in the habenula is related to the behavioral state and possibly to the endocrine state of the animal and suggest a novel mechanism for interactions among the nervous, endocrine, and immune systems.

Aggression↗
PubMed1993

Characterization of pituitary mediation of stress-induced antinociception in rats.

Antinociception, induced by continuous cold-water swims (CCWS) and certain parameters of inescapable foot shock, is reduced in hypophysectomized rats receiving supplements of corticosterone and l-thyroxine. To assess which lobe of the pituitary gland is involved in this effect, the first experiment compared the effects of total hypophysectomy and posterior lobectomy in supplemented rats upon CCWS antinociception on the tail-flick and jump tests and upon continuous inescapable foot shock antinociception on the tail-flick test. Total hypophysectomy, but not posterior lobectomy, significantly reduced CCWS antinociception on both tests in supplemented rats relative to sham surgery. Both total and posterior hypophysectomy either reduced or potentiated foot shock antinociception as functions of shock intensity or duration of exposure in supplemented rats. To assess whether hormonal supplementation is necessary for the observed effects, the second experiment examined CCWS antinociception in sham-operated and hypophysectomized rats that received either no hormonal supplements or corticosterone and/or l-thyroxine. These regimens failed to alter CCWS antinociception in sham-operated rats. Treatment of hypophysectomized rats with corticosterone and l-thyroxine either separately or together significantly reduced CCWS antinociception. In contrast, if hypophysectomized rats did not receive supplements, CCWS antinociception was significantly potentiated relative to sham-operated controls. These effects could not be attributed to treatment-induced changes in either body weight or CCWS hypothermia. These data suggest that the anterior lobe of the pituitary gland and adrenal cortex are involved in the mediation and/or maintenance of CCWS antinociception.

Adrenal Cortex↗
PubMed1993

The ontogeny of gonadotropin-releasing hormone neurons in the chick.

The origin of gonadotropin-releasing hormone (GnRH) neurons in the olfactory placode and their subsequent migration into the central nervous system (CNS) has been described in several species. The current study was undertaken to delineate the time course and route of GnRH neuronal migration in the chick using antisera generated against both the mammalian form of GnRH (LR1) and a specific chicken GnRH (cGnRH I). Chicks aged E4.5 through day of hatching were processed for GnRH immunocytochemistry. Under the incubation conditions employed in this study, GnRH neurons first appeared on E4.5 in the olfactory epithelium. GnRH neurons exit from the olfactory epithelium and follow the extracranial course of the olfactory nerve to the anterior pole of the developing forebrain. Within the nerve, cells are in close apposition to each other. By E5, cells had reached the surface of the telencephalon. Upon entering the CNS, the GnRH neurons dispersed within the neuropil and continued their migration as individuals. As development progressed, GnRH neurons migrated dorsally and caudally within the brain and reached their adult positions by E12. GnRH axons were detected in the vicinity of GnRH cell bodies with the cGnRH I antiserum as early as E4.5; however, GnRH axons did not reach the median eminence until E14. These results extend earlier reports in mammal and chick on the extracranial origin of GnRH neurons and their path of entry into and dispersion within the CNS.

Animals↗