Immunoreactive Gonadotropin-releasing Hormone Research Articles

The gonadotropin-releasing hormone neurosecretory system of the jerboa (Jaculus orientalis) and its seasonal variations.

The distribution of cells expressing gonadotropin-releasing hormone (GnRH) immunoreactivity was examined in the brain of adult jerboa during two distinct periods of the reproductive cycle. During spring-summer, when the jerboa is sexually active, a high density of cell bodies and fibres immunoreactive (IR) for GnRH was observed at the level of separation of the frontal lobes, in the medial septal nucleus (MS) and in the diagonal band of Broca (DBB), in the preoptic area (POA), in the organum vasculosum laminae terminalis (OVLT), in the retrochiasmatic area and hypothalamus. In autumn, when the jerboa is sexually inactive, GnRH-immunoreactivity was less intense than during spring-summer. In the POA, we noted a 55% decrease in the number of GnRH containing cells with no change in cell numbers in the MS-DBB. Furthermore, a lower density of GnRH immunopositive axon fibres is observed in all the previously mentioned structures and the immunoreaction intensity was very weak particularly within the median eminence and OVLT. Independently of the season, the GnRH immunoreactivity within neurones and fibres was similar in jerboas living in captivity and in jerboas living in their natural biotope. The effects of photoperiod on the density of POA-GnRH and arcuate nucleus beta-endorphin-containing cells were studied in jerboas maintained in long day [(LD) 16-h light, 8-h dark] and short day [(SD) 8-h light, 16-h dark] for 8 weeks. In the POA, the GnRH-IR cell number was not significantly altered by the photoperiod. Similarly, in the mediobasal hypothalamus, the number of beta-endorphin-IR neurones was not affected by such a parameter. Consequently, the GnRH seasonal variations cannot be correlated to changes in the photoperiod alone.

Evidence for Gonadotropin-Releasing Hormone-like Peptides in a Cnidarian Nervous System

There is increasing evidence that peptides of the gonadotropin-releasing hormone (GnRH) family, long considered a vertebrate preserve, are also present in invertebrate (molluscan) nervous systems. The possibility was examined that GnRHs are present and bioactive in cnidarians, considered to be representatives of the most primitive animals possessing a nervous system. Immunoreactive GnRH was detected in endodermal neurons of two anthozoans, the sea pansy Renilla koellikeri and the sea anemone Nematostella vectensis. In the sea pansy, immunoreactivity was detected throughout the autozooid polyps, including gamete-producing endoderm. High-performance liquid chromatography and radioimmunoassays of extracts from whole sea pansy colonies yielded two elution peaks exhibiting GnRH immunoreactivity with antisera raised against shark or mammalian GnRH. Vertebrate GnRHs as well as the two sea pansy GnRH-like factors inhibited the amplitude and frequency of peristaltic contractions in the sea pansy, and these actions were blocked by the LHRH analog [D-pGlu1,D-Phe2,D-Trp3,6]-LHRH. These results suggest that the GnRH family of neuropeptides is more widespread in metazoans than previously thought. Although our physiological data are preliminary, they point to a role for GnRHs as inhibitory modulators of neuromuscular transmission in the sea pansy.

Photostimulation affects gonadotropin-releasing hormone immunoreactivity and activates a distinct neuron population in the hypothalamus of the mallard

To reveal central mechanisms that transduce photic stimuli to sexually related neuroendocrine changes, Fra-2-ir, an inducible immediate-early gene marker of neuronal activation has been consecutively localized with that of GnRH-I in the brain of mallards that were triggered by artificial light at the photosensitive phase of the reproductive cycle. Strong neuronal activation was found in the POM and PVN in response to 1× or 4× 20 h light exposure that was accompanied with an increase of GnRH-ir in the hypothalamus and a dramatic depletion of GnRH-ir from terminals in the median eminence. The Fra-2 and GnRH-ir profiles, however, were not co-localized in any region at any phase of photostimulation. These results demonstrate profound changes of GnRH-ir in the hypothalamus and reveal a distinct, photoresponsive cell population in the anterior hypothalamic area of the mallard.

Gonadotropin-Releasing Hormone (GnRH) Variants in a Lizard Brain: Is Mammalian GnRH Being Expressed?

In reptiles as in other vertebrates, multiple forms of gonadotropin-releasing hormone (GnRH) within a single brain have been identified. In this group the following GnRH molecular variants have been characterized either by direct or indirect methods: chicken GnRH I (cGnRH-I), chicken GnRH II (cGnRH-II), salmon GnRH (sGnRH) and several unidentified GnRH-like forms. In the present study GnRH variants were investigated in brain extracts of the lizard Tupinambis teguixin (= T. merinae) by combining high-performance liquid chromatography (RP-HPLC) followed by radioimmunoassays (RIA). Two peaks showing GnRH immunoreactivity with the elution position of synthetic mammalian GnRH (mGnRH) and cGnRH-II were detected. Both peaks were further analyzed with different radioimmunoassay systems specific for mGnRH, cGnRH-I, and cGnRH-II. Pooled fractions corresponding to the first eluting peak showed no crossreactivity when analyzed with a cGnRH-I specific assay and logit-log displacement curves were not significantly different from those of synthetic mGnRH with homologous RIA systems. The second peak showed immunological characteristics of cGnRH-II when analyzed with a specific antiserum. The first ir-GnRH peak was selected for further RP-HPLC purification showing similar chromatographic behavior as mGnRH synthetic standard. We demonstrated the absence of cGnRH-I in this lizard using well-characterized antisera.

Biological and Immunological Characterization of Multiple GnRH in an Opisthobranch Mollusk, Aplysia californica

Gonadotropin-releasing hormone (GnRH) is a neurohormone central to the regulation of reproductive functions in vertebrates. Recently, several studies have reported the presence of GnRH immunoreactivity (IR) in a number of mollusks, suggesting that the distribution of GnRH may not be restricted to Phylum Chordata. In the present study, we extend our investigations to an opisthobranch mollusk, Aplysia californica, to characterize the source, chemical nature, and biological activity of molluscan GnRH-related molecules. Specific radioimmunoassays (RIAs) of various tissue extracts of Aplysia revealed that only ovotestis, hemocytes, and hemolymph contained significant amounts of GnRH that crossreacts with antisera raised against tunicate-I (tI) and mammalian (m) GnRH. Further RIAs and extractions revealed that the GnRH-IR in the hemolymph is biochemically and immunologically distinct from the GnRH-IR in the hemocytes and ovotestis. Using reverse-phase high-performance liquid chromatography coupled with RIAs, the GnRH-IR in the hemolymph was resolved into two major peaks. The first peak eluted earlier than most known forms of vertebrate GnRH, and the later peak coeluted with m, lamprey I, chicken II, and tI-GnRH. However, both peaks were broad and may contain a heterogeneous mixture of GnRH-IR. Immunocytochemical study showed that tI-GnRH-IR was present in the connective sheath surrounding the central nervous system, with a strong presence in what appeared to be vascular space, again suggesting the close association between Aplysia GnRH-IR and circulation. Finally, treatment of the neuroendocrine bag cells with chicken II GnRH significantly decreased the duration of the afterdischarge (AD, a characteristic pattern of electrical firing in bag cell neurons) and the number of action potentials fired during an AD, indicating the presence of a corresponding GnRH receptor in the Aplysia central nervous system. Overall, the results demonstrated the presence of multiple forms of GnRH-IR that crossreact with tI- and mGnRH antisera in A. californica and the ability of a vertebrate GnRH to alter Aplysia neural activity. Together, these data suggest that GnRH may be a factor released by the ovotestis and hemocytes into the circulation to alter neural functions. GnRH-IR produced by the latter may serve as a novel mediator of the neural and immune functions in Aplysia.

Gonadotropin-Releasing Hormones in the Brain and Pituitary of the Teleost, the White Sucker

The present study investigated GnRH forms within the brain of a representative of the order Cypriniformes, the white sucker, Catostomus commersoni, using HPLC, RIA, and immunocytochemistry. Several immunoreactive (ir) GnRH forms were identified in the brain of the white sucker by chromatography and radioimmunoassay, including ir-salmon GnRH, ir-lamprey GnRH-I and -III, and ir-chicken GnRH-II. Results from immunocytochemical studies were consistent with multiple GnRH forms distributed in different patterns, particularly for fibers. Neuronal perikarya containing ir-salmon GnRH and ir-lamprey-like GnRH were found laterally within the preoptic area and rostral hypothalamus. Cells containing exclusively ir-salmon GnRH appeared slightly more rostrally, but in the same region. Fibers containing ir-salmon GnRH and ir-lamprey-like GnRH were seen throughout the caudal telencephalon and extended into the diencephalon, toward the pituitary. Fibers containing ir-chicken-II-like GnRH were also seen in the caudal telencephalon, but were concentrated more dorsally in the diencephalon. Within the pituitary, fibers containing ir-salmon GnRH and ir-lamprey-like GnRH entered the neurohypophysis, but differed in their destinations. Fibers containing ir-salmon GnRH remained within the neurohypophysis, while fibers containing ir-lamprey-like GnRH targeted adenohypophyseal tissue. These findings are consistent with the hypothesis that multiple GnRH forms with multiple functions exist within the brain and pituitary of teleosts and provide further evidence of a lamprey-like GnRH within an early evolved teleost species.

Immunoreactivity for Gonadotropin-Releasing Hormone in Microdialyzed Perfusates of Bovine Mature Follicles In Vitro.

The presence of gonadotropin-releasing hormone (GnRH)-like protein has been previously demonstrated in the bovine follicle. This GnRH-like protein was purified and concluded to be histone H2A. However, neither GnRH peptide nor specific GnRH-immunoreactivity (GnRH-IR) has been demonstrated in the bovine follicle so far. Thus, this study focused on the detection of specific GnRH-IR using the second-antibody enzyme immunoassay in isolated bovine mature follicles, and on an examination of the direct effect of luteinizing hormone (LH), endothelin-1 (ET-1), and cytokines on the GnRH-IR using an in vitro microdialysis system (MDS). We further examined a cross-reactivity of the GnRH antibody with bovine histone H2A. GnRH-IR was detected in microdialyzed perfusate from isolated bovine mature follicles at 4.40 ± 0.35 pg/ml (mean ± SEM). Bovine histone H2A showed no GnRH-IR at all. Heat treatment of the extract (100 C for 10 min) did not affect the GnRH-IR. Single infusion of LH, ET-1, or cytokines into the MDS did not affect the GnRH-IR. However, infusion of ET-1 after LH exposure increased the GnRH-IR. These results demonstrate the presence of specific GnRH-IR, that is different from histone H2A, in microdialyzed perfusate of isolated bovine mature follicles in vitro, suggesting that the GnRH-IR may reflect a role of GnRH-like peptide or some peptide structurally similar to GnRH in the local regulation of mature follicles.

Determination of immunoreactive gonadotropin-releasing hormone in serum and urine by on-line immunoaffinity capillary electrophoresis coupled to mass spectrometry

The need for urgent diagnoses has propelled the development of automated analyses that can be performed in a short time at reasonable cost. One such method is immunoaffinity capillary electrophoresis. This emerging hybrid technology employs two powerful techniques coupled on-line for the direct and rapid determination of analytes present in biological fluids. The first technique, immunoaffinity, is used for the selective extraction of a molecule present in a complex matrix, utilizing a microscale-format chamber affinity device. An analyte (affinity target) present in serum or urine is captured by an immobilized molecular recognition antibody molecule (affinity ligand) bound to a solid support constituent (glass beads or an appropriate porous structure) of a microchamber affinity device. The second technique, capillary electrophoresis, is used for the high-resolution analytical separation of the purified and concentrated affinity target material after elution from the microchamber affinity device. In this work, immunoaffinity capillary electrophoresis was developed for the identification and characterization of a single constituent of a complex matrix. Immunoreactive gonadotropin-releasing hormone was determined in serum and urine specimens derived from a normal individual and from a patient suffering from benign prostatic hyperplasia. Furthermore, the on-line immuno-separation system was coupled in tandem to mass spectrometry to obtain molecular mass information of the affinity isolated and CE separated neuropeptide. This hybrid immuno-analytical technology is simple, rapid, selective and sensitive. In addition, an attempt was also made to characterize other urinary constituents by CE–MS that may lead to marker activity in the urine of the diseased subject. The hyphenation of analytical techniques has proved valuable in enhancing their individual features. The future of bioanalysis using miniaturized affinity systems is discussed in this paper.

Gonadotropin-releasing hormone (GnRH) neuronal systems in the pejerrey, Odontesthes bonariensis (Atheriniformes)

The brain of the pejerrey (Odontesthes bonariensis) has recently been shown to contain three forms of gonadotropin-releasing hormone (GnRH): salmon GnRH (sGnRH), chicken GnRH-II (cGnRH-II) and pejerrey GnRH (pjGnRH), nevertheless neuroanatomical studies on the distribution of these peptides are lacking. In this study we investigated the distribution of immunoreactive GnRH in the brain of adult pejerrey. Four different policlonal antisera and a monoclonal antibody against different GnRH variants were applied on cryosections and visualized using the ABC method. Three antisera (PBL#49, sGnRH#2 and cII741) revealed three different immunoreactive areas: the terminal nerve ganglion (at the junction between the olfactory bulbs and the anterior telencephalon), the preoptic area just anterior to the hypothalamus and the midbrain tegmentum. Fibers immunoreactive to GnRH were detected in different brain areas: the olfactory bulbs, the ventral thelencephalon, the hypothalamus, the mesencephalic area and an important innervation entering into the pituitary gland. Two other antibodies (LRH13 and s1668) labeled the two nuclei corresponding to the forebrain but not the midbrain tegmentum. As both antibodies have low crossreactivity to cGnRH-II, the data suggest that this group of cells express cGnRH-II. In summary, three different areas with immunoreactivity to GnRH were detected in the pejerrey brain. The distribution of sGnRH, pjGnRH and cGnRH-II expressing neurons, is discussed. Abbreviations: C‐ cerebelum ;C M ‐corpus mamilaris ;D cd ‐area dorsalis telencephali pars centralis ;D d ‐ area dorsalis telencephali pars dorsalis ;D l ‐area dorsalis telencephali pars lateralis ;D lv ‐area dorsalis telencephali pars lateralis ;D m ‐area dorsalis telencephali pars medialis ;M t ‐midbrain tegmentum; NDLl ‐ nucleus difusus lobi inferioris ;N G ‐nucleus glomerulosus ;N PGC ‐nucleus preglomerulosus pars medialis ;N PP ‐ nucleus preopticus periventricularis ;N R ‐nucleus rotundus ;N T ‐nucleus tenia; Ob ‐ olfactory bulbs; Oc ‐ optic chiasma; ON ‐ optic nerve; Otec ‐ optic tectum; Pit ‐ pituitary; Tel ‐ telencephalon; Tl ‐ torus longitudianalis; TNG ‐ terminal nerve ganglion; Vd ‐ area ventralis telencephali pars centreli ; area ventralis telencephali pars ventralis.

Lesions to the Medial Preoptic Area Affect Singing in the Male European Starling (Sturnus vulgaris)

The aromatization of testosterone (T) in the medial preoptic nucleus (POM) is known to regulate male courtship and sexual behaviors expressed prior to, and in anticipation of, copulation. Singing in male European starlings is used to attract mates prior to physical sexual contact, suggesting that the POM might be involved. The present study was performed to examine the effects of lesions targeting the POM on singing and courtship behavior in reproductively active male starlings. A significant decrease in song output and the gathering of green nest materials was observed in males with lesions to the POM compared to males with damage to brain areas outside of the POM. Lesions did not affect a male's tendency to remain near a female or to occupy a nestbox, suggesting that the effects of POM lesions were specific to courtship behaviors. Behavioral differences were not related to testis mass or volume, and GnRH immunoreactivity was observed within the hypothalamus and median eminence for each male, suggesting that the effects of POM lesions were related specifically to POM involvement in song expression rather than to a disruption of the GnRH axis. These results suggest a general role for the POM in the expression of behaviors related to sexual arousal or anticipation, including song.

Fos localization in cytosolic and nuclear compartments in neurones of the frog, Rana esculenta, brain: an analysis carried out in parallel with GnRH molecular forms.

C-fos activity was determined in the brain of the frog, Rana esculenta, during the annual sexual cycle. The localization of GnRH molecular forms (mammalian- and chicken-GnRHII) was also carried out to determine whether or not the proto-oncogene and the peptides showed a functional relationship. Northern blot analysis of total RNA revealed the presence of a single strong signal of c-fos like mRNA of 1.9 Kb during February and April. This was followed by expression of c-Fos protein (Fos) in several brain areas during March and July shown by immunocytochemistry. In particular, the olfactory region, the lateral and medial pallium, the nucleus lateralis septi, the ventral striatum, the caudal region of the anterior preoptic area, the suprachiasmatic nucleus, the ventral thalamus, tori semicircularis and ependymal layers of the tectum were immunostained. There was no overlap between Fos immunoreactive perikarya and GnRH immunoreactive perikarya (e.g. gonadotrophin-releasing hormone (GnRH) in the rostral part and Fos in the caudal region of the anterior preoptic area). Interestingly, a cytoplasmic localization of Fos was also observed by immunocytochemistry and gel retardation experiments supported this observation. Cytoplasmic extracts from September-October animals bound the AP1 oligonucleotide. The complex was not available in the nuclear extracts from the same preparation, suggesting that, besides Fos, Jun products were also present. Conversely, nuclear but not cytosolic binding was detected in the brain of animals collected in July. In conclusion, we show that Fos and GnRH activity does not correlate in the frog brain and, for the first time in a vertebrate species, we give evidence of a cytoplasmic AP1 complex in neuronal cells.

Development and Differentiation of Gonadotropin Hormone-Releasing Hormone Neuronal Systems and Testes in the Japanese Eel (Anguilla japonica)

In this study we investigated the relationship between the development of the olfactory, preoptic, and midbrain gonadotropin-releasing hormone (GnRH) neuronal systems and testicular differentiation in eels (Anguilla japonica) from embryonic stages through adulthood (5.4–50 cm body length). GnRH-synthesizing neuronal populations were first observed in the youngest fish (∼5.0 cm) at the rostrobasal and caudalmost olfactory bulbs immunoreactive to a “promiscuous” (nonspecific) GnRH antiserum (635.5), and in the preoptic area and midbrain tegmentum immunoreactive to chicken GnRH II antiserum. The eel brains lacked salmon and seabream GnRH immunoreactivity. The evidence from our study suggests that the olfactory, preoptic, and midbrain GnRH populations have origins independent from those of proliferative periventricular zones within the brain. However, the olfactory GnRH neurons could have migrated out of the olfactory placodes during ages earlier than those observed in this study. Although all three GnRH neuronal populations contribute to pituitary innervation to some degree, the preoptic GnRH innervation was pronounced in the pituitary when primordial germ cells (animals ∼5.0 cm) differentiated into male germ cells (animals 14–16 cm) and, therefore, an association can be assumed between preoptic GnRH expression and testicular differentiation in the Japanese eel.

Gonadotropin-releasing hormone immunoreactivity in the adult and fetal human olfactory system

Studies in fetal brain tissue of rodents, nonhuman primates and birds have demonstrated that cells containing gonadotropin-releasing hormone (GnRH) migrate from the olfactory placode across the nasal septum into the forebrain. The purpose of this study was to examine GnRH neurons in components of the adult and fetal human olfactory system. In the adult human brain ( n=4), immunoreactive GnRH was evident within diffusely scattered cell bodies and processes in the olfactory bulb, olfactory nerve, olfactory cortex, and nervus terminalis located on the anterior surface of the gyrus rectus. GnRH-immunoreactive structures showed a similar distribution in 20-week human fetal brains ( n=2), indicating that the migration of GnRH neurons is complete at this time. In 10–11-week fetal brains ( n=2), more cells were noted in the nasal cavity than in the brain. Our data are consistent with observations made in other species, confirming olfactory derivation and migration of GnRH neurons into the brain from the olfactory placode.

Gonadotropin-Releasing Hormone in Mulberry Cells ofSaccoglossusandPtychodera(Hemichordata: Enteropneusta)

Mulberry cells are epidermal gland cells bearing a long basal process resembling a neurite and are tentatively regarded as neurosecretory cells. They occur scattered through the ectoderm of the proboscis, collar, and anterior trunk regions of the acorn wormsSaccoglossus,usually in association with concentrations of nervous tissue. They contain secretion granules that appear from electron micrographs to be released to the exterior. The granules are immunoreactive with antisera raised against mammalian and salmon gonadotropin-releasing hormone (GnRH). Similar results were obtained with another enteropneust,Ptychodera bahamensis,using antisera raised against tunicate-1 and mammalian GnRH. Mulberry cells were not found in eitherCephalodiscusorRhabdopleura(Hemichordata: Pterobranchia). Extracts of tissues from 4200Saccoglossuscontain an area of immunoreactive GnRH that is detected by an antiserum raised against lamprey GnRH when characterized by high-performance liquid chromatography and radioimmunoassay. This is the first report of the occurrence of GnRH in hemichordates, probably the most primitive group clearly belonging to the chordate lineage. The physiological function of GnRH in enteropneusts is unknown, but an exocrine function appears more likely than an endocrine or neurotransmitter role.

GnRH mRNA and protein expression in human preimplantation embryos.

Gonadotrophin-releasing hormone (GnRH) regulates gonadotrophin biosynthesis and release in the anterior pituitary via specific receptors. Extrapituitary expression and action of GnRH have been demonstrated in several species. A possible role for GnRH in preimplantation embryonic development, endometrial preparation, and the implantation process has been previously suggested. Moreover, the presence of an immunoreactive GnRH in preimplantation embryos has been demonstrated in different species; however, there are no data for human embryos. We postulate that in humans GnRH may play a role in preimplantation embryonic development as well as in the implantation process. To examine this hypothesis, we assessed GnRH and GnRH-receptor mRNA and protein expression in human preimplantation embryos with three pronuclei. GnRH is expressed in peri-implantation human embryos at both the mRNA and protein level. GnRH-receptor mRNA is also present in the embryos studied. Immunohistochemical localization of GnRH showed intense staining in all the blastomeres at morula stage as well as in the trophectoderm and inner cell mass of the blastocysts. The results of the present study challenge the widely held view that GnRH has a predominantly central action, and suggests a pathway to describe a local role for the GnRH system in successful preimplantation embryonic development and implantation.

Regional changes in GnRH immunoreactivity with puberty in the male Syrian hamster

Gonadotropin-releasing-hormone immunopositive (GnRH+) neurons were identified in juvenile and adult male Syrian hamsters. There were significantly fewer GnRH+ cells in the diagonal band of Broca/organum vasculosum of the lamina terminalis (DBB/OVLT) and medial septum (MS) in adults as compared to juvenile males, while no cell number difference was found in the preoptic area (POA). The decrease in cell number likely reflects reduced somal stores of GnRH in DBB/OVLT and MS, suggesting that these subpopulations promote increased GnRH release during pubertal maturation in male hamsters.

Innervation and control of the adenohypophysis by hypothalamic peptidergic neurons in teleost fishes: EM immunohistochemical evidence.

Previous light microscopic studies have revealed neuropeptide-immunoreactive neurosecretory fibers in the teleostean neurohypophysis, and ultrastructural work has reported direct innervation of endocrine cells by the terminals of fibers penetrating the adenohypophysis. This paper reviews our recent data from ultrastructural, immunohistochemical, receptor localization, and superfusion studies, which suggest a role for neuropeptides in the control of teleost pituitary secretion. We have used a combination of pre- and post-embedding electron microscopic immunolabeling methods to determine which neuropeptides are present in fibers innervating the pituitaries of three species: Poecilia latipinna, Dicentrarchus labrax, and Clarias gariepinus. Numerous axon profiles with immunoreactivity for the neurosecretory peptides vasotocin and isotocin formed large Herring bodies and terminal-like boutons in contact with corticotropic, growth hormone, thyrotropic, and pars intermedia cells. Numerous melanin-concentrating hormone-immunoreactive fibers and scarcer neurotensin and corticotropin-releasing factor-immunoreactive fibers showed similar distributions, terminating close to pars intermedia and corticotropic cells. Somatostatin, cholecystokinin, galanin, substance P, neuropeptide Y, growth hormone-releasing factor, thyrotropin-releasing hormone, and gonadotropin-releasing hormone-immunoreactivities were found in small calibre fibers penetrating among growth hormone, thyrotropic, and gonadotropic cells. These morphological findings have been supplemented by autoradiographic studies, which showed the distribution of binding sites for vasotocin, isotocin, galanin, and neuropeptide Y ligands over specific groups of pituitary cells, and superfusion studies that showed growth hormone release was stimulated by growth hormone-releasing factor and thyrotropin-releasing hormone, but inhibited by somatostatin. The implications of these results for neuropeptidergic control of teleostean pituitary secretions are discussed.

Close association of gonadotropin-releasing hormone fibers and gonadotropin, growth hormone, somatolactin and prolactin expressing cells in pejerrey, Odontesthes bonariensis

The purpose of this study was to determine if there is any association between immunoreactive (ir) gonadotropin-releasing hormone (GnRH) fibers with different pituitary endocrine cell types in the pejerrey, Odontesthes bonariensis. Using a monoclonal antibody raised against mammalian GnRH (mGnRH) (LRH13), ir-GnRH fibers were observed passing through the pituitary stalk and reaching the three areas of the pituitary gland: rostral (RPD) and proximal pars distalis (PPD) and pars intermedia (PI). Double labeled immunocytochemistry showed ir-GnRH fibers in close association with prolactin (PRL)-producing cells in the RPD, growth hormone (GH)-producing cells in the PPD, gonadotropin (GtH)-producing cells in the PPD and the external border of the PI, and with somatolactin (SL)-producing cells in the PI. Our results show, direct morphological evidences of a close association of GnRH fibers with GH, PRL, GtH and SL-expressing cells. These results would suggest that GnRH has a broad role in the regulation of the secretion of different pituitary hormones.

Differential distribution of gonadotropin-releasing hormone variants in the brain of Hydrochaeris hydrochaeris (Mammalia, Rodentia).

1. In a previous paper we reported evidence for the presence of mGnRH- and sGnRH-like peptides in the preoptic-hypothalamic region of the capybara Hydrochaeris hydrochaeris (Montaner et al., 1998). In that study, the presence of a cGnRH-II like molecule in olfactory bulb extracts was suggested. 2. The capybara, the largest living rodent in the world, belongs to the order Hystricomorpha, which is considered to be one of the oldest groups of rodents. Some authors consider that this group is the ancestor of all remaining rodents. 3. In this study we have characterized GnRH molecular variants found in extracts from the olfactory bulbs and the mesencephalic region of capybara. These regions represent the two GnRH neuronal systems: the terminal nerve-septopreoptic and the midbrain systems. 4. An indirect method combining reverse-phase high-performance liquid chromatography (RP-HPLC) and radioimmunoassay (RIA) was used to characterize GnRH variants. The analysis of both extracts with two different RIA systems revealed three immunoreactive GnRH peaks, coeluting with mGnRH, cIIGnRH, and sGnRH synthetic standards. These results were additionally supported by serial dilution studies with specific antisera. 5. To our knowledge this the first report on the presence of three GnRH variants in the brain of an eutherian mammal. These results suggest that, similarly to other vertebrates, the expression of multiple GnRH variants may also be a common pattern in mammals.

Sex Differences in Mammalian and Chicken-II Gonadotropin-Releasing Hormone Immunoreactivity in Musk Shrew Brain

Many vertebrates have more than one molecular form of gonadotropin-releasing hormone (GnRH) present in brain. In all cases documented to date, GnRH neurons located in the forebrain are critical players in the brain–pituitary–gonadal feedback axis although the details of how steroids regulate GnRH remain elusive. The function of the second form, usually produced in cells in the midbrain, is not known. It has been hypothesized that this GnRH acts as a neurotransmitter. In the musk shrew (Suncus murinus), as in other mammals, the forebrain cells produce mammalian GnRH (mGnRH) and chicken-II GnRH (cGnRH-II) is present in midbrain neurons. Immunocytochemical analyses were performed to examine sex differences and determine whether the presence or absence of the gonads had any affect on cell number and/or fiber area in the major terminal fields of both forms of GnRH. We detected a significant sex difference in the numbers of immunoreactive (ir) neurons containing mGnRH and cGnRH-II. In both GnRH systems, males have significantly more GnRH-ir cells than females. Furthermore, ovariectomy significantly increased the number of mGnRH-ir and cGnRH-II-ir cell bodies in female brains. In females, changes in the size of the immunoreactive fiber area of the medial habenula were identical to those noted for cGnRH-II cells. In males, the major terminal field for the mGnRH fibers was significantly larger in gonad-intact than in castrated males. In sum, ovarian hormones regulate cGnRH-II production and release, as well as some aspects of mGnRH production in neurons. In males, mGnRH fiber area is sensitive to changes in testicular hormones. These data suggest that the phylogenetically conserved cGnRH-II form is regulated by ovarian hormones and, thus, may be involved in the brain–pituitary–gonadal feedback axis.