Evidence that chicken hypothalamic luteinizing hormone-releasing hormone is [Gln8]-LH-RH

The gonadotropin-releasing hormones: Lessons from fish

Fish have been of paramount importance to our understanding of vertebrate comparative neuroendocrinology and the mechanisms underlying the physiology and evolution of gonadotropin-releasing hormones (GnRH) and their genes. This review integrates past and recent knowledge on the Gnrh system in the fish model. Multiple Gnrh isoforms (two or three forms) are present in all teleosts, as well as multiple Gnrh receptors (up to five types), which differ in neuroanatomical localization, pattern of projections, ontogeny and functions. The role of the different Gnrh forms in reproduction seems to also differ in teleost models possessing two versus three Gnrh forms, Gnrh3 being the main hypophysiotropic hormone in the former and Gnrh1 in the latter. Functions of the non-hypothalamic Gnrh isoforms are still unclear, although under suboptimal physiological conditions (e.g. fasting), Gnrh2 may increase in the pituitary to ensure the integrity of reproduction under these conditions. Recent developments in transgenesis and mutagenesis in fish models have permitted the generation of fish lines expressing fluorophores in Gnrh neurons and to elucidate the dynamics of the elaborate innervations of the different neuronal populations, thus enabling a more accurate delineation of their reproductive roles and regulations. Moreover, in combination with neuronal electrophysiology, these lines have clarified the Gnrh mode of actions in modulating Lh and Fsh activities. While loss of function and genome editing studies had the premise to elucidate the exact roles of the multiple Gnrhs in reproduction and other processes, they have instead evoked an ongoing debate about these roles and opened new avenues of research that will no doubt lead to new discoveries regarding the not-yet-fully-understood Gnrh system.

Post-photostimulation energy intake accelerated pubertal development in broiler breeder pullets

The effect of ME intake (MEI) on the reproductive system was evaluated. Ross 308 broiler breeder pullets (n = 140) were assigned to 2 treatments from 22 to 26 wk of age: (1) Low-energy diet fed restricted (2,807 kcal/kg, low MEI) and (2) high-energy diet fed unrestricted (3,109 kcal/kg, high MEI). Daylength was increased from 8 to 14 h at 22 wk of age with a light intensity of 30 lux. Daily palpation was used to detect sexual maturity via the presence of a hard-shelled egg in the shell gland. Expression of gonadotropin releasing hormone-I (GnRH) and gonadotropin inhibitory hormone (GnIH) genes in the hypothalamus and GnRH receptor (GnRH-RI) and GnIH receptor (GnIH-R) genes in the anterior pituitary gland of each pullet was evaluated from 22 to 26 wk of age using quantitative real time-PCR. Blood samples were taken weekly and luteinizing hormone (LH), follicle stimulating-hormone (FSH), and 17-beta-estradiol (E2) determined using commercial ELISA kits. Carcass samples were used for determination of CP and fat content. Data were analyzed using the MIXED procedure in SAS, and differences were reported where P ≤ 0.05. High MEI treatment pullets had 2.3-fold higher GnRH and 1.8-fold higher GnRH-RI mRNA levels than low MEI pullets. MEI affected neither expression of GnIH and GnIH-R nor carcass protein content. For high MEI (489 kcal/D) and low MEI treatments (258 kcal/D), respectively, from 22 to 26 wk of age (P ≤ 0.05), LH concentration was 3.05 and 1.60 ng/mL; FSH concentration was 145 and 89.3 pg/mL; E2 concentration was 429 and 266 pg/mL, and carcass lipid was 13.9 and 10.3%. The onset of lay for pullets in the high MEI treatment advanced such that 100% had laid by 26 wk of age compared with 30% in the low MEI treatment. We concluded that higher MEI advanced the activation of the hypothalamic–pituitary–gonadal axis and also increased body lipid deposition, and moreover, stimulated reproductive hormone levels which overall accelerated puberty in broiler breeder pullets.

Origin and Evolution of the Neuroendocrine Control of Reproduction in Vertebrates, With Special Focus on Genome and Gene Duplications

In humans, as in the other mammals, the neuroendocrine control of reproduction is ensured by the brain-pituitary gonadotropic axis. Multiple internal and environmental cues are integrated via brain neuronal networks, ultimately leading to the modulation of the activity of gonadotropin-releasing hormone (GnRH) neurons. The decapeptide GnRH is released into the hypothalamic-hypophysial portal blood system and stimulates the production of pituitary glycoprotein hormones, the two gonadotropins luteinizing hormone and follicle-stimulating hormone. A novel actor, the neuropeptide kisspeptin, acting upstream of GnRH, has attracted increasing attention in recent years. Other neuropeptides, such as gonadotropin-inhibiting hormone/RF-amide related peptide, and other members of the RF-amide peptide superfamily, as well as various nonpeptidic neuromediators such as dopamine and serotonin also provide a large panel of stimulatory or inhibitory regulators. This paper addresses the origin and evolution of the vertebrate gonadotropic axis. Brain-pituitary neuroendocrine axes are typical of vertebrates, the pituitary gland, mediator and amplifier of brain control on peripheral organs, being a vertebrate innovation. The paper reviews, from molecular and functional perspectives, the evolution across vertebrate radiation of some key actors of the vertebrate neuroendocrine control of reproduction and traces back their origin along the vertebrate lineage and in other metazoa before the emergence of vertebrates. A focus is given on how gene duplications, resulting from either local events or from whole genome duplication events, and followed by paralogous gene loss or conservation, might have shaped the evolutionary scenarios of current families of key actors of the gonadotropic axis.

Neuroendocrinology of reproduction: Is gonadotropin-releasing hormone (GnRH) dispensable?

Gonadotropin releasing hormone (GnRH) is a highly conserved neuroendocrine decapeptide that is essential for the onset of puberty and the maintenance of the reproductive state. First identified in mammals, the GnRH signaling pathway is found in all classes of vertebrates; homologues of GnRH have also been identified in invertebrates. In addition to its role as a hypothalamic releasing hormone, GnRH has multiple functions including modulating neural activity within specific regions of the brain. These various functions are mediated by multiple isoforms, which are expressed at diverse locations within the central nervous system. Here we discuss the GnRH signaling pathways in light of new reports that reveal that some vertebrate genomes lack GnRH1. Not only do other isoforms of GnRH not compensate for this gene loss, but elements upstream of GnRH1, including kisspeptins, appear to also be dispensable. We discuss routes that may compensate for the loss of the GnRH1 pathway.

An updated model to describe the neuroendocrine control of reproduction in chickens

Since its first identification in quail 15 years ago, gonadotropin inhibitory hormone (GnIH) has become a central regulator of reproduction in avian species. In this review, we have revisited our original model published in 2009 to incorporate recent experimental evidence suggesting that GnIH acts as a molecular switch during the integration of multiple external and internal cues that allow sexual maturation to proceed in chickens. Furthermore, we discuss the regulation of a dual inhibitory/stimulatory control of the hypothalamo-pituitary-gonadal axis involving the interaction between GnIH and gonadotropin releasing hormone (GnRH). Finally, beyond seasonality, we also propose that GnIH along with this dual control may be responsible for the circadian control of ovulation in chickens, allowing eggs to be laid in a synchronized manner.

Reproductive neuropeptides: prevalence of GnRH and KNDy neural signalling components in a model avian, gallus gallus

Diverse external and internal environmental factors are integrated in the hypothalamus to regulate the reproductive system. This is mediated through the pulsatile secretion of GnRH into the portal system to stimulate pituitary gonadotrophin secretion, which in turn regulates gonadal function. A single subpopulation of neurones termed 'KNDy neurones' located in the hypothalamic arcuate nucleus co-localise kisspeptin (Kiss), neurokinin B (NKB) and dynorphin (Dyn) and are responsive to negative feedback effects of sex steroids. The co-ordinated secretion from KNDy neurones appears to modulate the pulsatile release of GnRH, acting as a proximate pacemaker. This review briefly describes the neuropeptidergic control of reproduction in the avian class, highlighting the status of reproductive neuropeptide signalling systems homologous to those found in mammalian genomes. Genes encoding the GnRH system are complete in the chicken with similar roles to the mammalian counterparts, whereas genes encoding Kiss signalling components appear missing in the avian lineage, indicating a differing set of hypothalamic signals controlling avian reproduction. Gene sequences encoding both NKB and Dyn signalling components are present in the chicken genome, but expression analysis and functional studies remain to be completed. The focus of this article is to describe the avian complement of neuropeptidergic reproductive hormones and provide insights into the putative mechanisms that regulate reproduction in birds. These postulations highlight differences in reproductive strategies of birds in terms of gonadal steroid feedback systems, integration of metabolic signals and seasonality. Also included are propositions of KNDy neuropeptide gene silencing and plasticity in utilisation of these neuropeptides during avian evolution.

Gonadotrophin-releasing hormone in winter flounder (Pseudopleuronectes americanus): molecular characterization, distribution and effects of fasting

Gonadotrophin-releasing hormone (GnRH) is primarily related to reproductive processes in vertebrates. However other physiological roles, including functions in food intake regulation and energy status, have been demonstrated for GnRH in animals. The ten amino acid active peptide is relatively conserved throughout chordates, more specifically in fish species. Teleosts generally have at least two variants of GnRH present in their genomes. GnRH2 (commonly termed chicken-GnRH) is common to all fish, whereas other prevalent forms include GnRH1 and/or GnRH3 (also known as salmon-GnRH). The mRNAs of all three forms were identified in winter flounder (Pseudopleuronectes americanus). Winter flounder GnRH1 appears to be ubiquitously and strongly expressed throughout the brain. GnRH2 mRNA is highly expressed in the optic tectum/thalamus. Finally, GnRH3 mRNA is expressed throughout the brain, but not in the pituitary, with apparent highest expression in the telencephalon/preoptic area. Flounder GnRH1 mRNA is found in most peripheral tissues examined, including the foregut, midgut and gonads. GnRH2 mRNA appears to be expressed throughout the periphery, with apparent highest transcript expression in male gonads. Finally, winter flounder GnRH3 transcript is found at low levels in the skin, heart, and gonads. The effect of fasting on the expression of each of the three isoforms was assessed. Fasting reduces GnRH2 and GnRH3 mRNA expression in the optic tectum/thalamus and hypothalamus, and telencephalon/preoptic area, respectively, compared with fed fish. GnRH1 mRNA expression does not appear to be altered by feeding status. GnRH mRNAs do not seem to regulate food intake peripherally through the gut based on our preliminary findings. Our preliminary results suggest that the GnRH system could play a central role in food intake regulation of winter flounder.

Structural and functional evolution of gonadotropin-releasing hormone in vertebrates

The neuropeptide gonadotropin-releasing hormone (GnRH) has a central role in the neural control of vertebrate reproduction. This review describes an overview of what is currently known about GnRH in vertebrates in the context of its structural and functional evolution. A large body of evidence has demonstrated the existence of three paralogous genes for GnRH (GnRH1, GnRH2 and GnRH3) in the vertebrate lineage. They are most probably the products of whole-genome duplications that occurred early in vertebrate evolution. Although GnRH3 has been identified only in teleosts, comparative genomic analyses indicated that GnRH3 has not arisen from a teleost-specific genome duplication, but has been derived from an earlier genome duplication in an ancestral vertebrate, followed by its loss in the tetrapod lineage. A loss of other paralogous genes has also occurred independently in different vertebrate lineages, leading to species-specific differences in the organization of the GnRH system. In addition to the GnRH3 gene, the GnRH2 gene has been deleted or silenced in certain mammalian species, while some teleosts seem to have lost the GnRH1 or GnRH3 gene. The duplicated GnRH genes have undergone subfunctionalization during the evolution of vertebrates; GnRH1 has become the major stimulator of gonadotropins and probably other pituitary hormones as well, whereas GnRH2 and GnRH3 would have functioned as neuromodulators, affecting reproductive behaviour. Conversely, in cases where a paralogous gene for GnRH has been lost, one of the remaining paralogues appears to have adopted its role.

Influence of a new slow-release GnRH analogue implant on reproduction in the Budgerigar (Melopsittacus undulatus, Shaw 1805)

The neuroendocrine conditioning of reproduction in birds could perform a very important role in captive breeding, especially in endangered species. Whereas in domestic and wild mammals pharmacological reproductive conditioning is well developed, in birds an effective method is not available. The aim of this study was to test the influence of a new slow-release GnRH analogue (buserelin acetate) implant on the reproductive activity of the Budgerigar (Melopsittacus undulatus), used as model species for captive-bred endangered birds. The effects were assessed by looking at reproductive parameters (egg-laying rate, egg fertility rate) and measuring excreted sex steroid metabolite concentrations in male and female birds. Modification of reproductive parameters and steroid metabolites excretion patterns were observed among birds administered with a GnRH analogue implant and maintained under artificial photoperiod (group I; 16L:8D). Implanted birds showed higher rates of egg-laying, potentially a higher proportion of fertile eggs and higher excreted steroid metabolite concentrations than birds maintained under natural photoperiod (group II; 10L:14D) and birds maintained under artificial photoperiod (group III; 16L:8D). Thus, it is concluded that the new slow-release GnRH analogue implant may represent an innovative and practicable treatment to rapidly induce reproductive activity in the Budgerigar, and that excreted sex hormone metabolites detection permits to monitor male and female gonadal activity.

Evolution of GnRH ligands and receptors in gnathostomata

Gonadotropin-releasing hormone (GnRH) is the final common signaling molecule used by the brain to regulate reproduction in all vertebrates. Until now, a total of 24 GnRH structural variants have been characterized from vertebrate, protochordate and invertebrate nervous tissue. Almost all vertebrates already investigated have at least two GnRH forms coexisting in the central nervous system. Furthermore, it is now well accepted that three GnRH forms are present both in early and late evolved teleostean fishes. The number and taxonomic distribution of the different GnRH variants also raise questions about the phylogenetic relationships between them. Most of the GnRH phylogenetic analyses are in agreement with the widely accepted idea that the GnRH family can be divided into three main groups. However, the examination of the gnathostome GnRH phylogenetic relationships clearly shows the existence of two main paralogous GnRH lineages: the ''midbrain GnRH" group and the "forebrain GnRH" group. The first one, represented by chicken GnRH-II forms, and the second one composed of two paralogous lineages, the salmon GnRH cluster (only represented in teleostean fish species) and the hypophysotropic GnRH cluster, also present in tetrapods. This analysis suggests that the two forebrain clades share a common precursor and reinforces the idea that the salmon GnRH branch has originated from a duplication of the hypophysotropic lineage. GnRH ligands exert their activity through G protein-coupled receptors of the rhodopsin-like family. As with the ligands, multiple GnRHRs are expressed in individual vertebrate species and phylogenetic analyses have revealed that all vertebrate GnRHRs cluster into three main receptor types. However, new data and a new phylogenetic analysis propose a two GnRHR type model, in which different rounds of gene duplications may have occurred in different groups within each lineage.

Expression and distribution of octopus gonadotropin-releasing hormone in the central nervous system and peripheral organs of the octopus (Octopus vulgaris) by in situ hybridization and immunohistochemistry

We recently purified a peptide with structural features similar to vertebrate gonadotropin-releasing hormone (GnRH) from the brain of Octopus vulgaris, cloned a cDNA encoding the precursor protein, and named it oct-GnRH. In the current study, we investigated the expression and distribution of oct-GnRH throughout the central nervous system (CNS) and peripheral organs of Octopus by in situ hybridization on the basis of the cDNA sequence and by immunohistochemistry using a specific antiserum against oct-GnRH. Oct-GnRH mRNA-expressing cell bodies were located in 10 of 19 lobes in the supraesophageal and subesophageal parts of the CNS. Several oct-GnRH-like immunoreactive fibers were seen in all the neuropils of the CNS lobes. The sites of oct-GnRH mRNA expression and the mature peptide distribution were consistent with each other as judged by in situ hybridization and immunohistochemistry. In addition, many immunoreactive fibers were distributed in peripheral organs such as the heart, the oviduct, and the oviducal gland. Modulatory effects of oct-GnRH on the contractions of the heart and the oviduct were demonstrated. The results suggested that, in the context of reproduction, oct-GnRH is a key peptide in the subpedunculate lobe and/or posterior olfactory lobe-optic gland-gonadal axis, an octopus analogue of the hypothalamo-hypophysial-gonadal axis. It may also act as a modulatory factor in controlling higher brain functions such as feeding, memory, movement, maturation, and autonomic functions

Evolutionary aspects of cellular communication in the vertebrate hypothalamo-hypophysio-gonadal axis

This review emphasizes the comparative approach for developing insight into knowledge related to cellular communications occurring in the hypothalamus-pituitary-gonadal axis. Indeed, research on adaptive phenomena leads to evolutionary tracks. Thus, going through recent results, we suggest that pheromonal communication precedes local communication which, in turn, precedes communication via the blood stream. Furthermore, the use of different routes of communication by a certain mediator leads to a conceptual change related to what hormones are. Nevertheless, endocrine communication should leave out of consideration the source (glandular or not) of mediator. Finally, we point out that the use of lower vertebrate animal models is fundamental to understanding general physiological mechanisms. In fact, different anatomical organization permits access to tissues not readily approachable in mammals.

Gonadotropin-releasing hormone (GnRH): from fish to mammalian brains

This work deals with a family of neuropeptides, gonadotropin-releasing hormone (GnRH), that play a key role in the development and maintenance of reproductive function in vertebrates. 2. Until now, a total of 16 GnRH structural variants have been isolated and characterized from vertebrate and protochordate nervous tissue. All vertebrate species already investigated have at least two GnRH forms coexisting in the central nervous system. However, it is now well accepted that three forms of GnRH in early and late evolved bony fishes are present. 3. In these cases, cGnRH-II is expressed by midbrain neurons, a species-specific GnRH is present mainly in the preoptic area and the hypothalamus, and sGnRH is localized in the terminal nerve ganglion (TNG). In this context it is possible to think that three GnRH forms and three GnRH receptor (GnRH-R) subtypes are expressed in the central nervous system of a given species. 4. Then it is possible to propose three different GnRH lineages expressed by distinct brain areas in vertebrates: (1) the conserved cGnRH-II or mesencephalic lineage; or (2) the hypothalamic or "releasing" lineage whose primary structure has diverged by point mutations (mGnRH and its orthologous forms: hrGnRH, wfGnRH, cfGnRH, sbGnRH, and pjGnRH); and (3) the telencephalic sGnRH form. Also different GnRH nomenclatures are discussed.

Three forms of gonadotropin-releasing hormone, including a novel form, in a basal salmonid, Coregonus clupeaformis

Multiple forms of GnRH within individual brains may have different functions. However, some vertebrates such as salmonids continue to reproduce even though they have lost or do not express 1 of the 3 forms of GnRH found in most other teleosts. We examined a basal salmonid, lake whitefish, to determine the mechanism by which a reduction in the number of GnRH forms occurs. We identified for the first time 3 distinct GnRHs in a salmonid. One form is novel and is designated whitefish GnRH. The primary structure is pGlu-His-Trp-Ser-Tyr-Gly-Met-Asn-Pro-Gly-NH(2). HPLC and RIA were used for purification followed by Edman degradation for sequence determination. Mass spectroscopy was used to confirm the sequence and amidation of the peptide. The other 2 forms, salmon GnRH and chicken GnRH-II, are identical to the 2 forms found in salmon, which evolved later than whitefish. Synthetic whitefish GnRH is biologically active, as it increased mRNA expression of growth hormone and the alpha-subunit for LH and thyroid-stimulating hormone in dispersed fish pituitary cells. Our data support the hypothesis that the ancestral salmonid had a third GnRH form when the genome doubled (tetraploidization), but the third form was lost later in some salmonids due to chromosomal rearrangements. We suggest that the salmon GnRH form compensated for the loss of the third form.

Ontogenic origin of salmon GnRH neurons in the ventral telencephalon and the preoptic area in masu salmon

During the ontogeny of masu salmon Oncorhynchus masou, neurons producing the salmon type of gonadotropin-releasing hormone (sGnRH) were first detected in the olfactory epithelium of the eyed egg and, subsequently, in the brain, suggesting a migration of these cells. Among sGnRH neurons distributed from the olfactory nerve (ON) through the preoptic area (POA), those in the ventral telencephalon (VT) and the POA are indicated to regulate gonadotropin secretion. Thus, it is of interest to know whether all the sGnRH neurons originate from the olfactory epithelium. In the present study, we examined by in situ hybridization whether sGnRH neurons are present in the VT-POA of fish, whose olfactory epithelia including sGnRH clusters were cauterized just after hatching (44 days after fertilization). Fish were sampled in June (212 days after the operation). Neurons expressing sGnRH mRNA were detected in the VT-POA as well as in the ON, ventral olfactory bulb, and transitional area between the olfactory bulb and telencephalon (which is considered to correspond to the terminal nerve ganglion) in the control group. In contrast, neurons expressing sGnRH mRNA were not detected in the VT-POA in the olfactory epithelium lesioned (OEL) group. Furthermore, pituitary sGnRH content in the OEL group was just above the detectable limit and was significantly lower than that in the corresponding control group in both sexes. These results indicate that sGnRH neurons in the VT-POA are derived from the olfactory epithelium in masu salmon, although the possibility cannot be ruled out that sGnRH neurons in the VT-POA arise from the VT-POA, but were delayed in expressing sGnRH because of the trauma of cauterization.

Guinea pig gonadotropin-releasing hormone: expression pattern, characterization and biological activity in rodents

Gonadotropin-releasing hormone (GnRH) is a decapeptide widely known for its role in regulating vertebrate reproduction by serving as a signal from the hypothalamus to pituitary gonadotropes. The first form of GnRH to be identified was isolated from mammals (mGnRH) and the same form has been reported for all mammals studied, which includes marsupials and placental mammals. Later, another variant, chicken GnRH-II (cGnRH-II) was shown to be expressed together with mGnRH in the brains of all jawed vertebrates, including mammals such as rats, monkeys and humans. Our objective was to characterize a third form of GnRH that was isolated previously as mRNA from guinea pigs (gpGnRH), but has not been reported for any other mammal to date. Furthermore, the gonadotropic activity of gpGnRH has not been fully characterized. Our results, using chromatographical and immunological methods, show for the first time that gpGnRH is expressed together with mGnRH in some rodents (wild guinea pig and capybara), but not in others (mouse and hamster). Also, the gonadotropic activity of gpGnRH and mGnRH was tested in two different rat cell culture systems. Although there have been reports that the salmon(s) form of GnRH is present in mammals, we did not detect sGnRH in capybara, wild guinea pigs, hamsters, rats or mice. Taken together with previous reports, the present results support the idea that the expression of multiple GnRH variants in a single species is a common pattern in most vertebrate groups.

Primary structure of a novel gonadotropin-releasing hormone in the brain of a teleost, Pejerrey

The neuropeptide GnRH is the major regulator of reproduction in vertebrates acting as a first signal from the hypothalamus to pituitary gonadotropes. Three GnRH molecular variants were detected in the brain of a fish, pejerrey (Odontesthes bonariensis), using chromatographic and immunological methods. The present study shows that one form is identical to chicken GnRH-II (sequence analysis and mass spectrometry) and the second one is immunologically and chromatographically similar to salmon GnRH. The third form was proven to be a novel form of GnRH by isolating the peptide from the brain and determining its primary structure by chemical sequencing and mass spectrometry. The sequence of the novel pejerrey GnRH is pGlu-His-Trp-Ser-Phe-Gly-Leu-Ser-Pro-Gly-NH(2), which is different from the known forms of the vertebrate and protochordate GnRH family. The new form of GnRH is biologically active in releasing gonadotropin and GH from pituitary cells in an in vitro assay.

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.

Differential distribution of gonadotropin-releasing hormone-immunoreactive neurons in the stingray brain: functional and evolutionary considerations

Gonadotropin-releasing hormone (GnRH) is a neuropeptide that occurs in multiple structural forms among vertebrate species. Bony fishes, amphibians, reptiles, birds, and mammals express different forms of GnRH in the forebrain and endocrine regions of the hypothalamus which regulate the release of reproductive gonadotropins from the pituitary. In contrast, previous studies on bony fishes and tetrapods have localized the chicken GnRH-II (cGnRH-II) nucleus in the midbrain tegmentum and, combined with cladistic analyses, indicate that cGnRH-II is the most conserved form throughout vertebrate evolution. However, in elasmobranch fishes, the neuroanatomical distribution of cGnRH-II and dogfish GnRH (dfGnRH) cells and their relative projections in the brain are unknown. We used high-performance liquid chromatography and radioimmunoassay to test for differential distributions of various GnRH forms in tissues from the terminal nerve (TN) ganglia, preoptic area, and midbrain of the Atlantic stingray, Dasyatis sabina. These experiments identified major peaks that coelute with cGnRH-II and dfGnRH, minor peaks that coelute with lamprey GnRH-III (lGnRH-III), and unknown forms. Immunocytochemistry experiments on brain sections show that dfGnRH-immunoreactive (-ir) cell bodies are localized in the TN ganglia, the caudal ventral telencephalon, and the preoptic area. Axons of these cells project to regions of the hypothalamus and pituitary, diencephalic centers of sensory and behavioral integration, and the midbrain. A large, discrete, bilateral column of cGnRH-II-ir neurons in the midbrain tegmentum has sparse axonal projections to the hypothalamus and regions of the pituitary but numerous projections to sensory processing centers in the, midbrain and hindbrain. Immunocytochemical and chromatographic data are consistent with the presence of lGnRH-III and other GnRH forms in the TN that differ from dfGnRH and cGnRH-II. This is the first study that shows differential distribution of cGnRH-II and dfGnRH in the elasmobranch brain and supports the hypothesis of divergent function of GnRH variants related to gonadotropin control and neuromodulation of sensory function.

GnRH molecular variants in the brain and pituitary gland of pejerrey, Odontesthes bonariensis (Atheriniformes). Immunological and chromatographic evidence for the presence of a novel molecular variant

Gonadotropin-releasing hormone (GnRH) molecular variants in the brain and pituitary gland of pejerrey, Odontesthes bonariensis (Atheriniformes), were characterized by gradient reverse phase high performance liquid chromatography (RP-HPLC). Eluted fractions were tested in radioimmunoassays with different antisera. The results show that the brain extract contains three forms of GnRH: one is immunologically and chromatographically similar to cIIGnRH (chicken II), and another is similar to sGnRH (salmon). A third GnRH appears to be chromatographic and immunologically different from the nine other known forms of the vertebrate hormone. This is the only variant present in the pituitary gland.

Structural requirements for alpha-mating factor activity

The sexual hormone of S. cerevisiae, alpha-mating factor (alpha-MF, WHWLQLKPGQPMY) has structural homology with mammalian luteinizing hormone releasing hormone (LHRH, pEHWSYGLRPG-NH2) and has been shown to exhibit LHRH activity [Loumaye et al. (1982) Science 218, 1323-1325]. We have tested whether LHRH has alpha-MF activity in yeast and found that it does not. We therefore synthesized a series of hybrid peptides of alpha-MF and LHRH to study the structural features which determine alpha-MF and LHRH activities. A hybrid peptide consisting of the LHRH sequence with the C-terminal tetrapeptide (QPMY) of alpha-MF did not exhibit alpha-MF activity. Thus, the lack of alpha-MF activity of LHRH is not due solely to the absence of the C-terminal residues. Substitution of Lys7 in alpha-MF with Arg, as is found in LHRH, did not affect the alpha-MF activity, nor did an additional substitution of Trp1 with pGlu. However, the C-terminal four amino acids of alpha-MF were necessary for alpha-MF activity. Our results indicate that insertion of a Ser residue in position 4 as found in LHRH abolishes alpha-MF activity. These results suggest that, in addition to an intact C-terminus, correct spacing of the N-terminal His2 and the C-terminus is required for alpha-MF activity. The hybrid peptides all exhibited less LHRH activity than either LHRH or alpha-MF. These structure-function studies indicate that the structural homology between these two reproductive hormones may not reflect an evolutionary relationship between them.

Rapid separation of gonadotropin-releasing hormone molecular forms by isocratic high-performance liquid chromatography on an ion-exchange column

The purpose of the present work was to develop a chromatographic system for the separation of five molecular forms of the gonadotropin-releasing hormone (GnRH); mammalian GnRH (mGnRH) (LHRH), salmon GnRH (sGnRH), chicken I GnRH (cIGnRH), chicken II GnRH (cIIGnRH) and lamprey GnRH I (IGnRH-I). By using an ion-exchange HPLC column and isocratic elution, it was possible to separate properly the five peptides in approximately 20 min. The utility of the system in determining the GnRHs forms present in the brain of two species of vertebrates was examined.

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.

Identification of chicken GnRH II in brains of metatherian and early-evolved eutherian species of mammals

Two molecular forms of GnRH (chicken GnRH II and a second variant) are present in the brains of species from all the major vertebrate groups. In mammals, two forms are present in metatherian species and early-evolved eutherian species, but chicken GnRH II has not been identified in more advanced eutherian species. We investigated the nature of GnRH molecular forms in several early-evolved mammalian species, using high performance liquid chromatography and radioimmunoassay with specific GnRH antisera. These chromatographic and immunological data indicate that in the brains of a metatherian species (possum, Trichosurus vulpecula) and in two early-evolved eutherian species (order Insectivora: musk shrew, Suncus murinus and mole, Chrysochloris asiatica), both mammalian and chicken II GnRHs are present, while in another relatively early-evolved eutherian species (order Chiroptera: bat, Miniopterus schreibersii) only mammalian GnRH is present. In the adult possum and mole brains the proportion of chicken GnRH II was lower than that of mammalian GnRH, while in the musk shrew brain chicken GnRH II predominated. A peptide likely to be mammalian proGnRH was detected in the brains of the three eutherian species (musk shrew, mole, and bat). These findings suggest that metatherian and primitive eutherian species of mammals continue to express chicken GnRH II as in the vast majority of nonmammalian vertebrates, while the peptide is apparently not expressed in modern placental mammalian species. The functional significance of chicken GnRH II is not yet clear, but there are indications that it has a neurotransmitter or neuromodulator role in addition to that of regulating pituitary hormone release in certain vertebrate species.

A second gene for gonadotropin-releasing hormone: cDNA and expression pattern in the brain

In vertebrates, the gonadotropin-releasing hormone (GnRH) decapeptide is secreted from hypothalamic nerve terminals to regulate reproduction via control of synthesis and release of pituitary gonadotropins. Only one GnRH peptide has been found in mammals, with one exception, although numerous other vertebrate species express more than one of the eight known decapeptide forms as shown by immunocytochemical labeling of distinct cell groups in the brain. However, neither the functional nor the evolutionary relationships among these GnRH forms are clear, because only one preprohormone gene sequence from any species has been reported. The most ubiquitous alternative form of GnRH is [His5,Trp7,Tyr8]GnRH (also referred to as chicken-II), which differs from the mammalian sequence at amino acids 5, 7, and 8. This peptide has been shown to have the most potent releasing-hormone activity, although immunocytochemical staining has suggested it is synthesized only in the mesencephalon. Here we report the cloning and expression pattern of the gene for the precursor of this form from the teleost fish Haplochromis burtoni. This is the second GnRH-encoding gene to be characterized in this species. The newly discovered preprohormone gene differs from that previously reported in two ways. First, whereas the original gene predicts only a single associated peptide, this one predicts two associated peptides, both of which appear to be unique. Second, the gene for [His5,Trp7,Tyr8]GnRH is expressed in only one cell group in the mesencephalon. In contrast, the previously reported gene is expressed only in the terminal nerve. The striking differences between the preprohormone structure and localization suggest that the genes coding for the two known GnRH forms in H. burtoni did not arise from a recent duplication event. Interestingly, neither of the two genes found to date in this species is expressed in cells which project from the hypothalamus to the pituitary, suggesting that yet a third gene coding for GnRH may exist.

Chromatographic and immunological identification of gonadotropin-releasing hormone in five marine teleosts

Brain extracts from bluefin tuna, Thunnus thynnus, red seabream, Pagrus major, black seabream, Acanthopagrus schlegeli, red spotted grouper, Epinephelus akaara and Japanese flounder, Paralichthys olivaceus, were analyzed by high performance liquid chromatography (HPLC) and specific radioimmunoassays. Immunoreactive material co-eluting from HPLC with salmon gonadotropin-releasing hormone (GnRH) and chicken GnRH-II, respectively, was found in all five species. In addition, a GnRH immunoreactive fraction showing the same HPLC retention time as lamprey GnRH-I was detected in the brain extracts of all species examined when using an unspecific radioimmunoassay which detects several GnRH forms, including lamprey GnRH-I. In the Japanese flounder brain extract, a fourth GnRH immunoreactive fraction was detected with the unspecific radioimmunoassay which did not co-elute with any of the six synthetic GnRH standards used in the present study.

Chicken gonadotropin-releasing hormones enhance soluble and insoluble fibronectin production by granulosa cells of the domestic fowl in vitro

Experiments were conducted in vitro to examine the effect of two chicken gonadotropin-releasing hormones, cGnRH-I ([Gln8]-GnRH) and cGnRH-II ([His5,Trp7,Tyr8]-GnRH), on fibronectin (soluble and insoluble) production by chicken granulosa cells isolated from the largest (F1; about 35 mm in diameter), and third largest (F3; 15 to 20 mm in diameter) preovulatory follicles as well as from a pool of immature small yellow follicles (SYF; 6 to 8 mm in diameter). The amounts of soluble fibronectin (fibronectin secreted into the incubation medium) and insoluble fibronectin (fibronectin associated with cells plus fibronectin attached to culture substratum) were quantified with a specific ELISA. Fibronectin secreted into the incubation medium (soluble fibronectin) by unstimulated cells increased with advanced stages of follicular maturation. Addition of both cGnRH-I and -II increased the amount of fibronectin secreted into the incubation medium by all follicular cell types. The amount of insoluble fibronectin in culture wells that contained unstimulated cells also increased with advanced stages of follicle development. Both cGnRH-I and -II increased the quantity of insoluble fibronectin by granulosa cells from all follicle types. Total (soluble plus insoluble) fibronectin production was elevated when cGnRH-I or -II was added to F1, F3, and SYF granulosa cells. The magnitude of cGnRH-I or -II stimulation (percentage increase) of soluble, insoluble, or total fibronectin production was calculated as a multiple of the unstimulated (control) value for each follicle type, and they were greatest in cells derived from developing and immature follicles. These results indicate that homologous cGnRH-I and -II are capable of directly modulating the physiology of the avian ovary.

Distribution of luteinizing hormone-releasing hormones I and II (LHRH-I and -II) in the quail and chicken brain as demonstrated with antibodies directed against synthetic peptides

Polyclonal antibodies were raised in rabbits against polypeptides corresponding to the N-terminal part (heptapeptides) of the two avian gonadotropin-releasing hormones, chicken (c) LHRH-I and -II. These peptides, which were synthesized by the continuous-flow technique, were selected because they contained the smallest number of common amino acid residues. The pGlu-His-Trp-Ser sequence at the C-terminal was suppressed to avoid possible cross-reactions between the antisera. The antisera generated in this way were tested for specificity by solid and liquid phase absorption as well as by antigen spot tests. The antiserum raised against cLHRH-I recognized this peptide preferentially though not exclusively. Some cross-reaction with cLHRH-II was observed in the absorption test, although spotting tests suggested a total specificity. The anti cLHRH-II appeared to be completely specific in all tests. These two antibodies were then used to study the distribution of cLHRH-I and -II immunoreactive structures in the quail and chicken brain. cLHRH-I immunoreactive perikarya were observed in a fairly wide area covering the preoptic-anterior hypothalamic and septal region. By contrast, cLHRH-II cells were confined to a single group located in the dorsal aspects of the occulomotor nuclei, at the junction of the di- and mesencephalon. A sex difference in the number of cLHRH-I cells was detected in the anterior lateral preoptic region of the quail. Fibers immunoreactive for either cLHRH-I or cLHRH-II were widely distributed in the telencephalon, diencephalon, and mesencephalon but showed a specific pattern of anatomical localization. In particular, a high density of cLHRH-I fibers were seen in the external layer of the median eminence, while cLHRH-II fibers were less prominent at this level. Contrary to previous reports, a significant amount of cLHRH-II fibers were however seen throughout the median eminence (mostly external layer). The extensive distribution of both cLHRH-I and -II fibers in the quail and chicken brain is consistent with the potential role played by these peptides in the gonadotropin secretion and in the control of reproductive behavior. The specific role of cLHRH-II remains however elusive at present.

Multiple molecular forms of gonadotropin-releasing hormone in the brain of an elasmobranch: evidence for IR-lamprey GnRH

These studies investigated brains of skate, Raja erinacea (order Rajiformes, class Chondrichthyes), for gonadotropin-releasing hormone (GnRH) peptides by chromatograph and immunoreactivity with region-specific antisera raised against mammalian GnRH and lamprey GnRH. The region-specific antibody to lamprey GnRH-I was produced following conjugation to bovine serum albumin using the bis-diazotized benzidine method. This antibody was characterized by assaying a range of increasing dilutions of the known vertebrate GnRHs, as well as analogs to lamprey GnRH-I. Two analogs, lamprey [Phe2]GnRH-I and lamprey [Leu7]GnRH-I, were synthesized by solid phase peptide synthesis using a benzhydrylamine resin as the supporting medium and purified by chromatography. This antibody demonstrated less than 0.01% cross-reactivity with all GnRH peptides tested, suggesting a highly specific antibody with a region of amino acids 2-8 that appears essential for binding. In the skate brain, five immunoreactive (IR) GnRH forms were detected, four of which eluted in the same positions as synthetic mammal and chicken GnRH-I (which coelute): lamprey GnRH-I, salmon and chicken GnRH-II, and one that was an unidentified form. A minor peak coeluted with lamprey GnRH-III. The major form in the skate brain is considered to have eluted with synthetic mammalian GnRH. These studies confirm an earlier report of an IR-mammalian GnRH peptide and provide new evidence for IR-lamprey GnRH in the brain of an elasmobranch.

Evolution of gonadotropin-releasing hormones

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, multiple molecular forms of the peptide have evolved, which have been coopted for a variety of 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. We review here the evolution of these variant forms of GnRH and their functions.

The Atlantic salmon prepro-gonadotropin releasing hormone gene and mRNA

Screening for the gene encoding salmon gonadotropin releasing hormone (sGnRH) in an Atlantic salmon (Salmo salar) genomic library resulted in isolation of a positive clone designated lambda sGnRH-1. An anchor polymerase chain reaction (PCR) technique was used to amplify GnRH cDNA derived from salmon hypothalamic mRNA. The cDNA sequence was aligned to the 7607 base pair genomic sequence which was shown to encode the entire prepro-GnRH gene. The cDNA proved that the cloned gene is expressed in the hypothalamus of mature salmon. The coding domain of sGnRH differs from the mammalian GnRH by six nucleotide changes which allow the two amino acid differences between the two GnRH variants. Salmon GnRH associated peptide (GAP) differs extensively in sequence and size from the mammalian counterpart. Compared to the GnRH cDNA of a cichlid species the similarity is 69.3% in the protein coding sequence.

Gonadotropin-releasing hormone in elasmobranch (electric ray, Torpedo marmorata) brain and plasma: chromatographic and immunological evidence for chicken GnRH II and novel molecular forms

Gonadotropin-releasing hormone (GnRH) peptides in the brain, testis and plasma of an electric ray (Torpedo marmorata) were investigated by gel filtration chromatography, reverse phase high performance liquid chromatography and radioimmunoassay with region-specific antisera. In the brain, two major forms of GnRH were demonstrated. One form had identical chromatographic and immunological properties to chicken GnRH II, and the second, novel, molecular form had structural features in common with mammalian, chicken II and salmon GnRHs. A minor, early-eluting immunoreactive peak, possibly also a novel GnRH, was also evident. Immunoreactive GnRH was not detected in the testis. In the plasma, a single major early-eluting immunoreactive peak was demonstrated. This peak, identical to the minor peak observed in the brain, is likely to represent a novel form of GnRH which has immunological properties in common with mammalian, chicken II and salmon GnRHs. Immunoreactive GnRH was not detected in the plasma of species from other vertebrate classes, including rabbit, chicken, monitor lizard, clawed toad, frog, cichlid fish and lamprey. The finding of chicken GnRH II in a species of Chondrichthyes adds further support to our hypothesis that this widespread structural variant may represent an early-evolved and conserved form of GnRH. The presence of a GnRH molecular form in the plasma of the electric ray suggests that GnRH may reach target organs (pituitary and gonads) via the general circulation in some species of Chondrichthyes.

Gonadotropin-releasing hormone (GnRH) in bony fish that are phylogenetically ancient: reedfish (Calamoichthys calabaricus), sturgeon (Acipenser transmontanus), and alligator gar (Lepisosteus spatula)

Three species of fish that are phylogenetically older than other members of the bony fish lineage were selected to determine if gonadotropin-releasing hormone (GnRH) is present in their brains. Brain extracts were prepared from each species and found to contain immunoreactive (ir) GnRH. To further characterize the molecular forms of GnRH in each species, the extracts were injected into a high pressure liquid chromatograph (HPLC). The elution time of each GnRH-like form was compared to those of the synthetic forms of the five known GnRHs. Several antisera were used to detect both the synthetic and unknown GnRHs in the HPLC fractions. All three species of fish had two forms of GnRH: a dominant form that is mammalian GnRH-like (mGnRH), and a minor form of irGnRH material that is similar to chicken GnRH-II (cGnRH-II). The other known forms of GnRH (salmon, lamprey, and chicken-I) were not detected. The appearance in these ancient bony fish of a mammalian-like form of GnRH, which has not been found in the jawless or cartilaginous fish studied to date, suggests that mGnRH arose in a common phylogenetic ancestor of the bony fish and tetrapods. This mGnRH-like molecule is known to have been conserved in the amphibian and mammalian lineage, but not in the reptilian or avian line. In addition, the presence of a cGnRH-II-like molecule in the bony fish examined here, and in the cartilaginous fish studied earlier, implies that this form of GnRH may have been present in an ancestor common to both of these classes of fish.

Ontogeny of immunoreactive gonadotropin-releasing hormone neuronal systems in amphibians

The ontogeny of gonadotropin-releasing hormone (GnRH) systems was investigated in 3 anuran amphibians (genus Rana) by means of immunocytochemical (ICC) techniques and antibodies generated against 3 different forms of GnRH. Antisera that recognize primarily chicken II and mammalian GnRHs revealed two anatomically and developmentally distinct GnRH systems. One system, referred to here as the forebrain-spinal cord system, contained GnRH immunoreactive (ir) fibers extending from the rostral diencephalon through the ventromedial brainstem to the spinal cord. Intensity of labeling was robust in the youngest, premetamorphic tadpoles, but decreased with age. GnRH immunolabeling in the hypothalamic-pituitary tract was not detected until late prometamorphosis and increased with age. Development of GnRHir in the hypothalamic-pituitary tract coincided with first appearance of GnRHir in the terminal nerve in R. catesbeiana, but not in R. cascadae or R. aurora, suggesting species differences. Comparisons of results obtained with antisera to different forms of GnRH support the interpretation that the forebrain-spinal cord system, hitherto undescribed in amphibians, develops first and synthesizes a non-mammalian, chicken II-like GnRH, and that the hypothalamic-pituitary system develops later and synthesizes primarily mammalian GnRH. We speculate that the forebrain-spinal cord system may represent a GnRH innervation of frog sympathetic ganglia, and that the two GnRH systems are chemically and embryonically distinct.

Differences in salmon GnRH and chicken GnRH-II contents in discrete brain areas of male and female rainbow trout according to age and stage of maturity

We have developed sensitive and specific radioimmunoassays (RIA) for salmon gonadotropin-releasing hormone (sGnRH) and chicken GnRH-II (cGnRH-II). Synthetic sGnRH and cGnRH-II(2-10) were conjugated to bovine serum albumin and injected into rabbits to raise specific antisera. The antiserum against sGnRH showed cross-reactivities of 1.58 and 0.08% for cGnRH-II and lamprey GnRH, respectively. The antiserum against cGnRH-II showed cross-reactivities of 0.05 and 0.01% for sGnRH and lamprey GnRH, respectively. Both antisera were observed not to cross-react with mammalian GnRH and cGnRH-I or other peptide hormones. Synthetic sGnRH and cGnRH-II were iodinated using the chloramine-T method. The iodinated GnRH was purified by HPLC using a reverse-phase C18 column. The RIA system was developed as a double antibody method. Brain extracts of rainbow trout showed displacement curves which were parallel to the sGnRH and cGnRH-II standards in each RIA. HPLC analysis followed by RIA has revealed that rainbow trout brain contains two types of GnRH: sGnRH and cGnRH-II. Total sGnRH content in the brain was about three-fold higher than that of cGnRH-II. In the olfactory bulbs, telencephalon, optic tectum-thalamus, hypothalamus, and pituitary, sGnRH content (per region) was higher than cGnRH-II content, whereas cerebellum and medulla oblongata contained much more cGnRH-II than sGnRH. sGnRH content in the optic tectum-thalamus and pituitary was the highest in 1-year-old immature fish and 3-year-old mature fish, respectively. Medulla oblongata showed the highest cGnRH-II content in all groups. sGnRH concentrations (per milligram of protein) were high in the pituitary and intermediate in the olfactory bulbs, hypothalamus, and telencephalon. In all groups, the cGnRH-II concentration was high in the medulla oblongata, whereas the concentration in the olfactory bulbs and pituitary gland was below the detectable limit in most individuals.

Neuroendocrine control of reproduction in lampreys

In most vertebrate classes, the hypothalamus and pituitary have well-defined roles in the control of reproduction. Until recently, there was little evidence for neuroendocrine control of reproduction in lampreys, one of the only two living representative groups of the oldest lineage of vertebrates, the Agnathans. The question whether there is hypothalamic control over reproduction has special significance since these fishes, with the hagfishes, are modern descendants of the most primitive vertebrates available for study. This paper summarizes the studies on the structure and function of lamprey GnRH which provide evidence for the regulatory influence of the hypothalamus on the pituitary-gonadal axis. These data imply that evolution of this mechanism most likely antedated the origin of all known vertebrates.

Chromatographic and immunological evidence for mammalian GnRH and chicken GnRH II in eel (Anguilla anguilla) brain and pituitary

Gonadotropin-releasing hormone (GnRH) peptides in the brain and pituitary of the European eel (Anguilla anguilla) were investigated by reverse phase high performance liquid chromatography (HPLC) and radioimmunoassay with region-specific antisera. Two GnRH molecular forms were demonstrated in brain and pituitary extracts. One form eluted in the same position as synthetic mammalian GnRH on HPLC and was recognized by antibodies directed against the NH2 and COOH termini of mammalian GnRH as well as by antibodies to the middle region. The second form eluted in the same position as synthetic chicken GnRH II and was recognized by specific antibodies to this molecule. Salmon GnRH and chicken GnRH I were not detected. The occurrence of mammalian GnRH in teleost fish suggests that this molecular form is more ancient than was previously suspected and arose earlier than in primitive tetrapods, or that it has arisen in the eel through random mutation of salmon GnRH. The lack of salmon GnRH in the eel brain indicates that this molecular form is not common to all teleost species. The finding in eel brain of chicken GnRH II, which has previously been described in species of Mammalia, Aves, Reptilia, Amphibia, Osteichthyes, and Chondrichthyes, supports our hypothesis that this widespread structural variant may represent an early evolved and conserved form of GnRH.

Production of monoclonal antibodies against avian LHRH-I

Production of antibodies against peptides or poorly antigenic proteins by conventional methods often requires either large quantities of the native immunogen or some chemical modification to increase their antigenicity. In this study an in vivo and in vitro immunization protocol has been used to generate monoclonal antibodies against the decapeptide luteinizing hormone-releasing hormone (LHRH). Two injections of 100 micrograms of avian LHRH-I into BALB/c mice were given 7 d apart. Dissociated splenocytes were collected under sterile conditions. They were incubated with 100 micrograms of the immunogen in 75-cm2 tissue culture flasks in thymocyte-conditioned media. After 5 to 8 d exposure to the antigen, splenocytes were fused with SP2/O myeloma cells by polyethylene glycol. The cells were plated into 24 wells and then incubated in hypoxanthine aminopterin and thymidine selective media. After 14 d an initial screening was done by enzyme immunoassay. The positive wells (6/24) were expanded into 96-well plates and rescreened. Selected lines were cloned out 3 times by limiting dilution and the most positive expanded for ascites production. The antibody was affinity purified in a protein A column. The antibody cross-reacted with LHRH-I and II but preferentially to LHRH-I, as shown by competitive assay. A hypothalamic extract from a mature chick showed a higher response than preparations from whole brain explants of 1- to 3-d posthatched chicks, mature quail, and mature mouse.

Existence of a GnRH immunoreactive nucleus in the dorsal midbrain tegmentum of the chameleon

The GnRH system of the chameleon brain was studied at light microscopic and ultrastructural levels by use of an immunohistochemical technique with antibodies directed against salmon gonadotrophin-releasing hormone. Immunoreactive (IR) perikarya were found in the anterior midbrain tegmentum. At this level numerous IR cell bodies were detected around the fasciculus longitudinalis medialis (FLM). The more rostral neurons were observed dorsal to the FLM and progressively tended to be lateral to it along the midline. More caudally, they were found ventral to the FLM. At the electron microscope level, these cells were seen to contain large granular vesicles and to receive numerous synaptic inputs. A prominent pathway was traced from these cell bodies along the medulla oblongata to the spinal cord. A second IR pathway ascended rostrally to the habenular complex. No IR perikarya were located in the anterior brain including the olfactory bulbs.

Polygenic expression of gonadotropin-releasing hormone (GnRH) in human?

A non-mammalian lamprey-like gonadotropin-releasing hormone (lGnRH) has been detected in human hypothalami using a combination of immunocytochemistry, high performance liquid chromatography and radioimmunoassay. The hypothalamic distribution of immunopositive lGnRH neurons is similar to that observed for those containing the mammalian gonadotropin-releasing hormone (mGnRH), indicating a possible role for this newly identified peptide in the regulation of pituitary function. Our data suggest the existence of a separate gene for lamprey-like GnRH in humans. Confirmation of the exact nature and role of this newly detected form of GnRH will require future isolation and sequence analysis. The possibility that polygenic expression of a given peptide may be a common phenomenon even in higher mammals is discussed.

Identity of gonadotropin-releasing hormone in passerine birds: comparison of GnRH in song sparrow (Melospiza melodia) and starling (Sturnus vulgaris) with five vertebrate GnRHs

Gonadotropin-releasing hormone (GnRH) was detected in the brains of passerine birds, a recently evolved and diverse avian group. The molecular forms of GnRH in two species of birds under breeding conditions were deduced using methods of HPLC and immunology. The brain extracts of song sparrows (Melospiza melodia) contained a form of GnRH identified as chicken I GnRH-like peptide by its HPLC elution pattern and cross-reactivity with four antisera. In contrast, starling (Sturnus vulgaris) brain extracts showed molecular heterogeneity of GnRH forms; equal amounts of chicken I and chicken II GnRH-like peptides were present. Neither bird contained GnRH that could be identified as mammalian, salmon, or lamprey GnRH. Chicken II GnRH-like peptide may not have evolved after the separation of the song sparrow and starling as both peptides are found in chicken, a more primitive bird. The possibility remains that different stages of the life cycle are associated with the expression of these GnRH-like peptides or their ratio. Only determination of the primary structure will establish whether our chromatographic and immunological evidence is correct that chicken I and II GnRH are present in passerine birds and have been conserved in representatives throughout the reptiles and birds. Starlings can be added now to the growing list of submammalian species that express multiple forms of GnRH in their brains.

Localization of avian LHRH-immunoreactive neurons in the hypothalamus of the domestic fowl, Gallus domesticus, and the Japanese quail, Coturnix coturnix

The localization of LHRH-containing perikarya and nerve fibers in the hypothalami of the domestic fowl and Japanese quail was investigated by means of the specific immunoperoxidase ABC method, using antisera against chicken LHRH-I ([Gln8]-LHRH), chicken GnRH-II ([His5-Trp7-Tyr8]-LHRH[2-10]) and mammalian LHRH ([Arg8]-LHRH). Chicken LHRH-I-immunoreactive perikarya were sparsely scattered in the nucleus preopticus periventricularis (POP), nucleus filiformis (FIL) and nucleus septalis medialis (SM), and in bilateral bands extending from these nuclei into the septal area in both species. A few reactive perikarya were also observed in the nucleus accumbens (Ac) and lobus parolfactorius (LPO). Numerous cLHRH-I-immunoreactive fibers were widely scattered in the preoptic, septal and tuberal areas, and were densely concentrated in the external layer of the median eminence and in organum vasculosum of the lamina terminalis (OVLT) in both species. Anti-mammalian LHRH serum cross-reacted weakly with perikarya and fibers immunoreactive to anti-cLHRH-I serum in normal chicken and quail. Anti-cGnRH-II[2-10] serum immunoreacted with magnocellular neurons distributed in the rostral end of the mesencephalon along the midline close to the nervus oculomotorius (N III). These perikarya were apparently different from cLHRH-I immunoreactive neurons. No immunoreactive cells and fibers against anti-cGnRH-II[2-10] were observed in the hypothalamus and median eminence of the chicken or quail. Anti-cGnRH-II[2-10] bound specifically with cGnRH-II.(ABSTRACT TRUNCATED AT 250 WORDS)