Gonadotropin-releasing Hormone Variants Research Articles

Characterization and localization of two forms of gonadotropin-releasing hormone (GnRH) in the spinal cord of the frog Rana ridibunda.

Two molecular variants of gonadotropin-releasing hormone (GnRH) have been previously characterized in the brain of amphibians, i.e., mammalian GnRH (mGnRH) and chicken GnRH-II (cGnRH-II). The aim of the present study was to identify the molecular forms of gonadotropin-releasing hormone and to localize gonadotropin-releasing hormone-containing elements in the spinal cord of the frog Rana ridibunda using highly specific antisera against mGnRH and cGnRH-II. High-performance liquid chromatography (HPLC) analysis combined with radioimmunoassay (RIA) detection revealed that frog spinal cord extracts contained both mGnRH and cGnRH-II. Immunohistochemical labeling revealed that the frog spinal cord was devoid of GnRH-containing cell bodies. In contrast, numerous GnRH-immunoreactive fibers were observed throughout the entire length of the cord. mGnRH immunoreactivity was only detected in the rostral region of the cord and consisted of varicose processes located in the vicinity of the central canal. cGnRH-II-positive fibers were found throughout the spinal cord, the density of immunoreactive processes decreasing gradually toward the caudal region. Two main cGnRH-II-positive fiber tracts with a rostrocaudal orientation were observed: a relatively dense fiber bundle surrounding the central canal, and a more diffuse plexus in the white matter. In addition, short, varicose cGnRH-II-positive processes with a radial orientation were present throughout the gray matter. These fibers were particularly abundant ventromedially and formed a diffuse network that ramified laterally to end in the vicinity of motoneurons. Taken together, these data indicate that the frog spinal cord, like the frog brain, contains two forms of GnRH. The presence of numerous cGnRH-II-immunoreactive fibers in the ventral horn suggests that cGnRH-II may influence the activity of a subpopulation of motoneurons.

Chromatographic and immunological identification of GnRH (Gonadotropin-releasing hormone) variants. Occurrence of mammalian and a salmon-like GnRH in the forebrain of an eutherian mammal: Hydrochaeris hydrochaeris (Mammalia, Rodentia).

The molecular variants of Gonadotropin releasing hormone (GnRH) in brain extracts of the eutherian mammal Hydrochaeris hydrochaeris (Mammalia, Rodentia) were characterized. An indirect method combining reverse-phase high-performance liquid chromatography (RP-HPLC) and radioimmunoassay (RIA) with different antisera was used. Two different forebrain regions (olfactory bulbs and preoptic–hypothalamic region) were analyzed. Characterization of RP-HPLC fractions from preoptic–hypothalamic extracts with three different RIA systems revealed two immunoreactive GnRH (ir-GnRH) peaks coeluting with mammalian GnRH (mGnRH) and salmon GnRH (sGnRH) synthetic standards. These results were additionally supported by serial dilution studies with specific antisera. Similar results were obtained from olfactory bulb extracts with the same methodology. However, a third ir-GnRH peak in a similar position to that of chicken GnRH II (cIIGnRH) synthetic standard was revealed. As far as we know, this is the first report showing chromatographic and immunological evidences for the presence of a second GnRH variant in the forebrain of an eutherian mammal.

Characterization of molecular variants of GnRH, induction of spermiation and sex reversal using salmon GnRH-A and domperidone in the protogynous diandric fish, Synbranchus marmoratus Bloch, (Teleostei, Synbranchidae)

This paper studies the molecular variants of gonadotropin-releasing hormone (GnRH) present in the brain of the protogynous swamp eel, Synbranchus marmoratus, and the effects of the administration of salmon GnRH analogue (sGnRH-A) and the dopamine receptor antagonist, domperidone (DOM) on final maturation and gamete release in this species. Evidence for the presence of two GnRH variants, sGnRH and cIIGnRH were obtained by reverse phase high-pressure liquid chromatography (RP-HPLC) and radioimmunoassay with different antisera. The effects of treatment with sGnRH-A+DOM were checked by three ways: oocyte and milt release by stripping, histological analysis of the gonadal tissue, and androgen serum levels at different times throughout the experiment. In males, spermiation was induced after three weeks of treatment. In the female group, sGnRH-A+DOM did not induce ovulation at the end of the experiment. Histological analysis of the gonads from the female group showed evidence of sex reversal. All the treated fish had elevated androgen serum levels from the third week, with respect to control fish. In all cases, serum estradiol levels were undetectable. These results suggest that treatment with sGnRH analog and DOM induce sex reversal in female and spermiation in males.

Identification of immunoreactive mammalian gonadotropin-releasing hormone in the brain of metamorphic larvae of Bufo arenarum hensel (Amphibia: Anura)

Gonadotropin-releasing hormone (GnRH) immunoreactivity in brain extracts of Bufo arenarum tadpoles were investigated by high-performance liquid chromatography, followed by radioimmunoassay analysis using two different antisera raised against different GnRH variants. Only one immunoreactive peak was identified, eluting in the same position as synthetic mammalian GnRH. This result was further confirmed by serial dilution studies using more specific mammalian GnRH antisera. Our results suggest that mammalian GnRH is most likely an endogenous peptide in the brain of the developing larvae and froglets of Bufo arenarum and quite likely it is the only GnRH variant present during those development stages. The distribution and density of cell bodies and fibers were analysed by immunocytochemical procedures. Immunoreactive cell bodies appeared in the olfactory epithelium and across the olfactory nerve at late prometamorphic larval stages. Near the metamorphic climax and in froglets, perikarya and fibers were detected in basal forebrain, preoptic and hypothalamic areas. No immunoreaction was observed at midbrain, hindbrain and spinal cord levels. This study suggests that mammalian GnRH is most likely an endogenous peptide and is probably the only GnRH variant in the brain of the developing larvae and froglets of Bufo arenarum.

Evolutionary aspects of gonadotropin-releasing hormone and its receptor.

1. Gonadotropin-releasing hormone (GnRH) was originally isolated as a hypothalamic peptide hormone that regulates the reproductive system by stimulating the release of gonadotropins from the anterior pituitary. However, during evolution the peptide was subject to gene duplication and structural changes, and multiple molecular forms have evolved. 2. Eight variants of GnRH are known, and at least two different forms are expressed in species from all vertebrate classes: chicken GnRH II and a second, unique, GnRH isoform. 3. The peptide has been recruited during evolution for diverse regulatory functions: as a neurotransmitter in the central and sympathetic nervous systems, as a paracrine regulator in the gonads and placenta, and as an autocrine regulator in tumor cells. 4. Evidence suggests that in most species the early-evolved and highly conserved chicken GnRH II has a neurotransmitter function, while the second form, which varies across classes, has a physiologic role in regulating gonadotropin release. 5. We review here evolutionary aspects of the family of GnRH peptides and their receptors.

Immunoreactive GnRH Suggesting a Third Form of GnRH in Addition to cIIGnRH and sGnRH in the Brain and Pituitary Gland of Prochilodus lineatus (Characiformes)

Molecular variants of GnRH (gonadotropin-releasing hormone) in brain and pituitary extracts of the South American characiforme Prochilodus lineatus were studied using a combination of reverse-phase high-performance liquid chromatography and radioimmunoassay with different antisera. In brain extracts our study revealed that this fish has at least two different types of GnRH: cIIGnRH (chicken II) and sGnRH (salmon), and possibly a third variant of this molecule. In pituitary extracts we could find only two immunoreactive peaks corresponding to sGnRH and the possible third form.

The Salmon GnRH Encoding Gene in Teleost Fish

Publisher Summary This chapter describes the salmon gonadotropin-releasing hormone (GnRH) encoding gene in teleost fish. Following the identification of the mammalian GnRH variant, designated “mGnRH,” two GnRH forms have been isolated from chicken hypothalamus—cGnRH-I and cGnRH-II. Sherwood et al. characterized two novel GnRH variants from salmon and lamprey, designated “sGnRH” and “lGnRH,” respectively. The GnRH variants are distributed in the different vertebrate groups. Mammalian studies have demonstrated that the GnRH neurons originate outside the brain in the olfactory placode. During embryogenesis, these neurons migrate into the forebrain along with the terminal nerve. The spatial and temporal appearance of GnRH neurons in the brain of chicken and the newt Cynops pyrrhogaster during embryogenesis indicates a similar migration route in these vertebrate groups. sGnRH neurons are widely distributed in the teleost brain. Immunoreactive sGnRH cell bodies have been localized in the olfactory nerve and the bulbs along the ventral part of telencephalon and the preoptic area and in the lateral-basal hypothalamus of several species. The amount and distribution of sGnRH and cGnRH-II are the two most common GnRH variants in teleosts, which have been studied in the brain of several species using specific antisera. sGnRH fibers innervate the pituitary directly, whereas cGnRH-II fibers are absent from the pituitary.

Effects of gonadotropin‐releasing hormone variants on plasma and testicular androgen levels in intact and hypophysectomized male frogs, Rana esculenta

The effects of vertebrate gonadotropin-releasing hormone (GnRH) variants on plasma and testicular androgen level in intact and hypophysectomized (PDX) male frogs, Rana esculenta, have been investigated. In intact animals, mammalian (m)-GnRH, m-GnRH analog (buserelin), salmon (s)-GnRH, chicken (c) I-GnRH, cII-GnRH, D-Arg6-cII-GnRH (cII-GnRHA), and lamprey (l)-GnRH (1.5 micrograms and 6 micrograms, total dose given on alternate days for 5 days) were able to enhance androgen production showing that specificity of pituitary responsiveness to GnRH variants appears to be low. Chicken II-GnRH was more effective than s-GnRH in eliciting testicular and circulatory androgen level increase. Moreover, in animals treated with 6 micrograms of cII-GnRH and s-GnRH in combination, androgens decreased as compared with animal treated with cII-GnRH only, suggesting that GnRH receptors bind preferentially the s-GnRH form. In PDX animals, buserelin (1.5 and 6 micrograms), cII-GnRH, and its analog (6 micrograms) were able to increase plasma androgen levels whereas testis androgen concentrations were increased by cII-GnRH (1.5 and 6 micrograms), D-Arg6-cII-GnRHA, and buserelin (6 micrograms). Since androgen production in PDX animals is influenced especially by peptides sharing cII-GnRH structure, it is suggested that a testicular cII-GnRH-like material play a role as local modulator of the gonadal activity in Rana esculenta.

Immunohistochemical Localization of Multiple Forms of Gonadotropin-Releasing Hormone in the Brain of the Adult Frog

Abstract Immunohistochemical mapping with antibodies against four different types of gonadotropin-releasing hormone (GnRH)-like neuro-peptides has been studied in the brain of adult Rana esculenta. This study confirms the earlier described distribution pattern of the immunoreactive mammaiian GnRH system in the frog brain, as well as revealing that this system of neuronal cell bodies and fibres is immunopositive to antisera for mammalian, chicken-I, chicken-II and salmon GnRH-like molecules. The results also indicate coexistence of the four GnRH variants in the same anatomical areas. The presence of immunoreactive fibre endings in the cerebellum is also described, perhaps for the first time in the vertebrate brain. In addition, it was found that many immunoreactive GnRH fibres arising in the anterior preoptic area and thalamus-periventricular area project posteriorly to reach the interpeduncular nucleus-tegmentum area, thus connecting the diencephalon with the rhombencephalon. These data provide further information on the complex GnRH system in the frog brain. What role(s) in vivo the non-mammalian forms of GnRH-like peptides may play in amphibian reproduction is briefly discussed, and in the light of paucity of data it is here stressed that more amphibian species should be studied.

Gonadotropin‐releasing hormone (GnRH) immunoreactive system in the brain of the dwarf gourami (Colisa lalia) as revealed by light microscopic immunocytochemistry using a monoclonal antibody to common amino acid sequence of GnRH

The present paper aims to give a morphological basis for the study of the terminal nerve system and its relation to the whole gonadotropin-releasing hormone (GnRH) immunoreactive (ir) neuronal system. We examined the GnRH-ir neuronal system of a tropical fish, the dwarf gourami, by using a recently developed monoclonal antibody against GnRH (LRH13) which recognizes the amino acid sequence common to all known variants of GnRH (Park and Wakabayashi, Endocrinol. Jpn. 33:257-272, '86). The ganglion cells of the terminal nerve (TN-ggl cells) in the transitional area between the olfactory bulb and the telencephalon reacted strongly with the LRH13. A distinct bundle of axons emanating from the TN-ggl cells ran caudally through the ventral telencephalon and the preoptic area. Some of these axons entered the optic nerve and innervated the retina. The remaining axons continued caudally to enter the hypothalamus and the midbrain. A second group of GnRH-ir cell bodies was found in the preoptic area. A distinct bundle of GnRH-ir fibers originating from these cell bodies innervated the pituitary. This pathway is equivalent to the preoptico-infundibular pathway of other vertebrates, and the GnRH in this pathway is presumed to function as hypophysiotrophic hormone to facilitate the release of gonadotropins from the pituitary. The distribution of GnRH-ir fibers in the brain was extensive. Most fibers apparently originated from the TN-ggl cells and covered various brain regions from the olfactory bulb to the spinal cord. They were especially abundant in the olfactory bulb, ventral telencephalon, preoptic area, optic tectum, and some hypothalamic areas. Thus, GnRH might function as a neuromodulator and/or neurotransmitter in these areas. The abundant GnRH-ir fibers in the ventral telencephalon and the preoptic area might affect some aspects of sexual behavior, since these areas have been suggested to be involved in the control of sexual behavior in teleosts.