Neuropeptidergic control of neurosteroids biosynthesis.

Neurosteroids are steroids synthesized within the central nervous system either from cholesterol or by metabolic reactions of circulating steroid hormone precursors. It has been suggested that neurosteroids exert pleiotropic activities within the central nervous system, such as organization and activation of the central nervous system and behavioral regulation. It is also increasingly becoming clear that neuropeptides exert pleiotropic activities within the central nervous system, such as modulation of neuronal functions and regulation of behavior, besides traditional neuroendocrinological functions. It was hypothesized that some of the physiological functions of neuropeptides acting within the central nervous system may be through the regulation of neurosteroids biosynthesis. Various neuropeptides reviewed in this study possibly regulate neurosteroids biosynthesis by controlling the activities of enzymes that catalyze the production of neurosteroids. It is now required to thoroughly investigate the neuropeptidergic control mechanisms of neurosteroids biosynthesis to characterize the physiological significance of this new neuroendocrinological phenomenon.

Advancing reproductive neuroendocrinology through research on the regulation of GnIH and on its diverse actions on reproductive physiology and behavior.

The discovery of gonadotropin-inhibitory hormone (GnIH) in 2000 has led to a new research era of reproductive neuroendocrinology because, for a long time, researchers believed that only gonadotropin-releasing hormone (GnRH) regulated reproduction as a neurohormone. Later studies on GnIH demonstrated that it acts as a new key neurohormone inhibiting reproduction in vertebrates. GnIH reduces gonadotropin release andsynthesis via the GnIH receptor GPR147 on gonadotropes and GnRH neurons. Furthermore, GnIH inhibits reproductive behavior, in addition to reproductive neuroendocrine function. The modification of the synthesis of GnIH and its release by the neuroendocrine integration of environmental and internal factors has also been demonstrated. Thus, the discovery of GnIH has facilitated advances in reproductive neuroendocrinology. Here, we describe the advances in reproductive neuroendocrinology driven by the discovery of GnIH, research on the effects of GnIH on reproductive physiology and behavior, and the regulatory mechanisms underlying GnIH synthesis and release.

Regulation of stress response on the hypothalamic-pituitary-gonadal axis via gonadotropin-inhibitory hormone.

Under stressful condition, reproductive function is impaired due to the activation of various components of the hypothalamic-pituitaryadrenal (HPA) axis, which can suppress the activity of the hypothalamic-pituitary-gonadal (HPG) axis at multiple levels. A hypothalamic neuropeptide, gonadotropin-inhibitory hormone (GnIH) is a key negative regulator of reproduction that governs the HPG axis. Converging lines of evidence have suggested that different stress types and their duration, such as physical or psychological, and acute or chronic, can modulate the GnIH system. To clarify the sensitivity and reactivity of the GnIH system in response to stress, we summarize and critically review the available studies that investigated the effects of various stressors, such as restraint, nutritional/metabolic and social stress, on GnIH expression and/or its neuronal activity leading to altered HPG action. In this review, we focus on GnIH as the potential novel mediator responsible for stress-induced reproductive dysfunction.

A mammalian gonadotropin-inhibitory hormone homolog RFamide-related peptide 3 regulates pain and anxiety in mice.

RFamide-related peptide (RFRP) is a homologous neuropeptide to gonadotropin-inhibitory hormone (GnIH), which is a hypothalamic neuropeptide that negatively regulates the hypothalamic-pituitary-gonadal axis. RFRP/GnIH is thought to be the mediator of stress because various stressors increase RFRP/GnIH mRNA expression and/or RFRP/GnIH neuronal activities. RFRP/GnIH may also directly regulate behavior, because RFRP/GnIH neuronal fibers and RFRP/GnIH receptor are widely expressed in the brain. Here, we create a RFRP/GnIH knockout (GnIH-KO) mice and conduct various behavioral tests. Dense RFRP/GnIH neuronal fibers are located in the limbic system and broad areas in the thalamus, hypothalamus, and midbrain in wild-type mice but not in RFRP/GnIH-KO mice. Spatial working memory is not improved in GnIH-KO mice as shown by Y-maze test. GnIH-KO mice perform intensive wheel running exercise for several hours after light-off. Hot plate test shows that GnIH-KO mice have decreased sensitivity to pain and central administration of RFRP3 to GnIH-KO mice recovers pain sensitivity. Elevated plus maze test shows that GnIH-KO mice have decreased level of anxiety and central administration of RFRP3 to GnIH-KO mice recovers anxiety level. These results indicate that RFRP3 regulates pain and anxiety in mice. RFRP3 may be involved in the negative regulation of spontaneous activity in addition to negatively regulating the reproductive neuroendocrine axis in stressful conditions.

Gonadotropin-inhibitory hormone (GnIH): A new key neurohormone controlling reproductive physiology and behavior.

The discovery of novel neurohormones is important for the advancement of neuroendocrinology. In early 1970s, gonadotropin-releasing hormone (GnRH), a hypothalamic neuropeptide that promotes gonadotropin release, was identified to be an endogenous neurohormone in mammals. In 2000, thirty years later, another hypothalamic neuropeptide, gonadotropin-inhibitory hormone (GnIH), that inhibits gonadotropin release, was found in quail. GnIH acts via GPR147 and inhibits gonadotropin release and synthesis and reproductive function in birds through actions on GnRH neurons in the hypothalamus and pituitary gonadotrophs. Later, GnIH was found in other vertebrates including humans. GnIH studies have advanced the progress of reproductive neuroendocrinology. Furthermore, recent GnIH studies have indicated that abnormal changes in GnIH expression may cause pubertal disorder and reproductive dysfunction. Here, we describe GnIH discovery and its impact on the progress of reproductive neuroendocrinology. This review also highlights advancement and perspective of GnIH studies on drug development for pubertal disorder and reproductive dysfunction. (149/150).

Reproductive neuroendocrinology of mammalian gonadotropin-inhibitory hormone.

BACKGROUND: Gonadotropin-inhibitory hormone (GnIH) was discovered in the Japanese quail brain in 2000 as a hypothalamic neuropeptide that suppresses luteinizing hormone release from cultured quail anterior pituitary. METHODS: The authors investigated the existence of mammalian orthologous peptides to GnIH and their physiological functions in the following 19 years of research. MAIN FINDINGS: Mammals have orthologous peptide to GnIH, often described RFamide-related peptide, expressed in the hypothalamus and gonads. Mammalian GnIH may also suppress gonadotropin synthesis and release by suppressing gonadotropin-releasing hormone (GnRH) synthesis and release in addition to directly suppressing gonadotropin synthesis and release from the pituitary. Mammalian GnIH may also suppress kisspeptin, a stimulator of GnRH, release. Mammalian GnIH is also expressed in the testis and ovary and suppresses gametogenesis and sex steroid production acting in an autocrine/paracrine manner. Thus, mammalian GnIH may act at all levels of the hypothalamic-pituitary-gonadal axis to suppress reproduction. GnIH may be involved in the regulation of puberty, estrous or menstrual cycle, seasonal reproduction, and stress responses. CONCLUSION: Studies suggest that mammalian GnIH is an important neuroendocrine suppressor of reproduction in mammals.

Gonadotropin-inhibitory hormone mediates behavioral stress responses.

Gonadotropin-inhibitory hormone (GnIH) is an inhibitor of the hypothalamic-pituitary-gonadal (HPG) axis. GnIH is also called RFamide-related peptide (RFRP) as GnIH peptides have a characteristic C-terminal LPXRFiamide (X = L or Q) sequence. GnIH is thought to be the mediator of stress by negatively regulating the HPG axis as various stressors increase GnIH mRNA, GnIH peptide or GnIH neuronal activity. On the other hand, GnIH may also mediate behavioral stress responses as GnIH neuronal fibers and GnIH receptors are widely located in the limbic system of telencephalon, diencephalon and midbrain area. Previous studies have shown that intracerebroventricular (i.c.v.) administration of GnIH (RFRP) blocks morphine-induced analgesia in hot plate and formalin injection tests in rats suggesting that GnIH increases sensitivity to pain. GnIH (RFRP) also increases anxiety-like behavior in rats. RNA interference of GnIH gene (GnIH RNAi) increases locomotor activity of white-crowned sparrow and Japanese quail and i.c.v. administration of GnIH decreases GnIH RNAi induced locomotor activity. It was further shown that i.c.v. administration of GnIH (RFRP) decreases aggressive behavior in male quail and sexual behavior in male rats, female white-crowned sparrow and female hamsters. These results suggest that GnIH decreases threat to homeostasis of the organism by increasing pain sensitivity, anxiety and decreasing locomotor activity, aggressive behavior and sexual behavior. GnIH may also mediate the effect of stress on behavior.

Review: Structure, function and evolution of GnIH.

Neuropeptides that possess the Arg-Phe-NH2 motif at their C-termini (i.e., RFamide peptides) have been characterized in the nervous system of both invertebrates and vertebrates. In vertebrates, RFamide peptides make a family and consist of the groups of gonadotropin-inhibitory hormone (GnIH), neuropeptide FF (NPFF), prolactin-releasing peptide (PrRP), kisspeptin (kiss1 and kiss2), and pyroglutamylated RFamide peptide/26RFamide peptide (QRFP/26RFa). It now appears that these vertebrate RFamide peptides exert important neuroendocrine, behavioral, sensory, and autonomic functions. In 2000, GnIH was discovered as a novel hypothalamic RFamide peptide inhibiting gonadotropin release in quail. Subsequent studies have demonstrated that GnIH acts on the brain and pituitary to modulate reproductive physiology and behavior across vertebrates. To clarify the origin and evolution of GnIH, the existence of GnIH was investigated in agnathans, the most ancient lineage of vertebrates, and basal chordates, such as tunicates and cephalochordates (represented by amphioxus). This review first summarizes the structure and function of GnIH and other RFamide peptides, in particular NPFF having a similar C-terminal structure of GnIH, in vertebrates. Then, this review describes the evolutionary origin of GnIH based on the studies in agnathans and basal chordates.

Strain differences in intermale aggression and possible factors regulating increased aggression in Japanese quail.

The National Institute for Environmental Studies (NIES) of Japan established a strain of Japanese quail (Coturnix japonica) known as NIES-L by rotation breeding in a closed colony for over 35years; accordingly, the strain has highly inbred-like characteristics. Another strain called NIES-Brn has been maintained by randomized breeding in a closed colony to produce outbred-like characteristics. The current study aimed to characterize intermale aggressive behaviors in both strains and to identify possible factors regulating higher aggression in the hypothalamus, such as sex hormone and neuropeptide expression. Both strains displayed a common set of intermale aggressive behaviors that included pecking, grabbing, mounting, and cloacal contact behavior, although NIES-Brn quail showed significantly more grabbing, mounting, and cloacal contact behavior than did NIES-L quail. We examined sex hormone levels in the blood and diencephalon in both strains. Testosterone concentrations were significantly higher in the blood and diencephalon of NIES-Brn quail compared to NIES-L quail. We next examined gene expression in the hypothalamus of both strains using an Agilent gene expression microarray and real-time RT-PCR and found that gene expression of mesotocin (an oxytocin homologue) was significantly higher in the hypothalamus of NIES-Brn quail compared to NIES-L quail. Immunohistochemistry of the hypothalamus revealed that numbers of large cells (cell area>500µm2) expressing mesotocin were significantly higher in the NIES-Brn strain compared to the NIES-L strain. Taken together, our findings suggest that higher testosterone and mesotocin levels in the hypothalamus may be responsible for higher aggression in the NIES-Brn quail strain.

Inhibitory action of gonadotropin-inhibitory hormone on the signaling pathways induced by kisspeptin and vasoactive intestinal polypeptide in GnRH neuronal cell line, GT1-7.

Gonadotropin-inhibitory hormone (GnIH) acts as a negative regulator of reproduction by acting on gonadotropes and gonadotropin-releasing hormone (GnRH) neurons. Despite its functional significance, the molecular mechanism of GnIH action in the target cells has not been fully elucidated. To expand our previous study on GnIH actions in gonadotropes, we investigated the potential signal transduction pathway that conveys the inhibitory action of GnIH in GnRH neurons by using the GnRH neuronal cell line, GT1-7. We examined whether GnIH inhibits the action of kisspeptin and vasoactive intestinal polypeptide (VIP), positive regulators of GnRH neurons. Although GnIH significantly suppressed the stimulatory effect of kisspeptin on GnRH release in hypothalamic culture, GnIH had no inhibitory effect on kisspeptin stimulation of serum response element and nuclear factor of activated T-cell response element activities and ERK phosphorylation, indicating that GnIH may not directly inhibit kisspeptin signaling in GnRH neurons. On the contrary, GnIH effectively eliminated the stimulatory effect of VIP on p38 and ERK phosphorylation, c-Fos mRNA expression, and GnRH release. The use of pharmacological modulators strongly demonstrated the specific inhibitory action of GnIH on the adenylate cyclase/cAMP/protein kinase A pathway, suggesting a common inhibitory mechanism of GnIH action in GnRH neurons and gonadotropes.-Son, Y. L., Ubuka, T., Soga, T., Yamamoto, K., Bentley, G. E., Tsutsui, K. Inhibitory action of gonadotropin-inhibitory hormone on the signaling pathways induced by kisspeptin and vasoactive intestinal polypeptide in GnRH neuronal cell line, GT1-7.

Seasonal control of gonadotropin-inhibitory hormone (GnIH) in birds and mammals.

Animals inhabiting temperate and boreal latitudes experience marked seasonal changes in the quality of their environments and maximize reproductive success by phasing breeding activities with the most favorable time of year. Whereas the specific mechanisms driving seasonal changes in reproductive function vary across species, converging lines of evidence suggest gonadotropin-inhibitory hormone (GnIH) serves as a key component of the neuroendocrine circuitry driving seasonal changes in reproduction and sexual motivation in some species. In addition to anticipating environmental change through transduction of photoperiodic information and modifying reproductive state accordingly, GnIH is also positioned to regulate acute changes in reproductive status should unpredictable conditions manifest throughout the year. The present overview summarizes the role of GnIH in avian and mammalian seasonal breeding while considering the similarities and disparities that have emerged from broad investigations across reproductively photoperiodic species.

Molecular, cellular, morphological, physiological and behavioral aspects of gonadotropin-inhibitory hormone.

Gonadotropin-inhibitory hormone (GnIH) is a hypothalamic neuropeptide that was isolated from the brains of Japanese quail in 2000, which inhibited luteinizing hormone release from the anterior pituitary gland. Here, we summarize the following fifteen years of researches that investigated on the mechanism of GnIH actions at molecular, cellular, morphological, physiological, and behavioral levels. The unique molecular structure of GnIH peptide is in its LPXRFamide (X=L or Q) motif at its C-terminal. The primary receptor for GnIH is GPR147. The cell signaling pathway triggered by GnIH is initiated by inhibiting adenylate cyclase and decreasing cAMP production in the target cell. GnIH neurons regulate not only gonadotropin synthesis and release in the pituitary, but also regulate various neurons in the brain, such as GnRH1, GnRH2, dopamine, POMC, NPY, orexin, MCH, CRH, oxytocin, and kisspeptin neurons. GnIH and GPR147 are also expressed in gonads and they may regulate steroidogenesis and germ cell maturation in an autocrine/paracrine manner. GnIH regulates reproductive development and activity. In female mammals, GnIH may regulate estrous or menstrual cycle. GnIH is also involved in the regulation of seasonal reproduction, but GnIH may finely tune reproductive activities in the breeding seasons. It is involved in stress responses not only in the brain but also in gonads. GnIH may inhibit male socio-sexual behavior by stimulating the activity of cytochrome P450 aromatase in the brain and stimulates feeding behavior by modulating the activities of hypothalamic and central amygdala neurons.

RFamide peptides in agnathans and basal chordates.

Since a peptide with a C-terminal Arg-Phe-NH2 (RFamide peptide) was first identified in the ganglia of the venus clam in 1977, RFamide peptides have been found in the nervous system of both invertebrates and vertebrates. In vertebrates, the RFamide peptide family includes gonadotropin-inhibitory hormone (GnIH), neuropeptide FF (NPFF), prolactin-releasing peptide (PrRP), pyroglutamylated RFamide peptide/26RFamide peptide (QRFP/26RFa), and kisspeptins (kiss1 and kiss2). They are involved in important functions such as the release of hormones, regulation of sexual or social behavior, pain transmission, reproduction, and feeding. In contrast to tetrapods and jawed fish, the information available on RFamide peptides in agnathans and basal chordates is limited, thus preventing further insights into the evolution of RFamide peptides in vertebrates. In this review, we focus on the previous research and recent advances in the studies on RFamide peptides in agnathans and basal chordates. In agnathans, the genes encoding GnIH, NPFF, and PrRP precursors and the mature peptides have been identified in lamprey (Petromyzon marinus) and hagfish (Paramyxine atami). Putative kiss1 and kiss2 genes have also been found in the genome database of lamprey. In basal chordates, namely, in amphioxus (Branchiostoma japonicum), a common ancestral form of GnIH and NPFF genes and their mature peptides, as well as the ortholog of the QRFP gene have been identified. The studies revealed that the number of orthologs of vertebrate RFamide peptides present in agnathans and basal chordates is greater than expected, suggesting that the vertebrate RFamide peptides might have emerged and expanded at an early stage of chordate evolution.

A new pathway mediating social effects on the endocrine system: female presence acting via norepinephrine release stimulates gonadotropin-inhibitory hormone in the paraventricular nucleus and suppresses luteinizing hormone in quail.

Rapid effects of social interactions on transient changes in hormonal levels are known in a wide variety of vertebrate taxa, ranging from fish to humans. Although these responses are mediated by the brain, neurochemical pathways that translate social signals into reproductive physiological changes are unclear. In this study, we analyzed how a female presence modifies synthesis and/or release of various neurochemicals, such as monoamines and neuropeptides, in the brain and downstream reproductive hormones in sexually active male Japanese quail. By viewing a female bird, sexually active males rapidly increased norepinephrine (NE) release in the paraventricular nucleus (PVN) of the hypothalamus, in which gonadotropin-inhibitory hormone (GnIH) neuronal cell bodies exist, increased GnIH precursor mRNA expression in the PVN, and decreased luteinizing hormone (LH) concentration in the plasma. GnIH is a hypothalamic neuropeptide that inhibits gonadotropin secretion from the pituitary. It was further shown that GnIH can rapidly suppress LH release after intravenous administration in this study. Centrally administered NE decreased plasma LH concentration in vivo. It was also shown that NE stimulated the release of GnIH from diencephalic tissue blocks in vitro. Fluorescence double-label immunohistochemistry indicated that GnIH neurons received noradrenergic innervations, and immunohistochemistry combined with in situ hybridization have further shown that GnIH neurons expressed α2A-adrenergic receptor mRNA. These results indicate that a female presence increases NE release in the PVN and stimulates GnIH release, resulting in the suppression of LH release in sexually active male quail.

Possible role of pineal allopregnanolone in Purkinje cell survival.

It is believed that neurosteroids are produced in the brain and other nervous systems. Here, we show that allopregnanolone (ALLO), a neurosteroid, is exceedingly produced in the pineal gland compared with the brain and that pineal ALLO acts on the Purkinje cell, a principal cerebellar neuron, to prevent apoptosis in the juvenile quail. We first demonstrated that the pineal gland is a major organ of neurosteroidogenesis. A series of experiments using molecular and biochemical techniques has further demonstrated that the pineal gland produces a variety of neurosteroids de novo from cholesterol in the juvenile quail. Importantly, ALLO was far more actively produced in the pineal gland than in the brain. Pinealectomy (Px) decreased ALLO concentration in the cerebellum and induced apoptosis of Purkinje cells, whereas administration of ALLO to Px quail chicks prevented apoptosis of Purkinje cells. We further found that Px significantly increased the number of Purkinje cells that expressed active caspase-3, a key protease in apoptotic pathway, and daily injection of ALLO to Px quail chicks decreased the number of Purkinje cells expressing active caspase-3. These results indicate that the neuroprotective effect of pineal ALLO is associated with the decrease in caspase-3 activity during the early stage of neuronal development. We thus provide evidence that the pineal gland is an important neurosteroidogenic organ and that pineal ALLO may be involved in Purkinje cell survival during development. This is an important function of the pineal gland in the formation of neuronal circuits in the developing cerebellum.

Evolution of gonadotropin-inhibitory hormone receptor and its ligand.

Gonadotropin-inhibitory hormone (GnIH) is a neuropeptide inhibitor of gonadotropin secretion, which was first identified in the Japanese quail hypothalamus. GnIH peptides share a C-terminal LPXRFamide (X=L or Q) motif in most vertebrates. The receptor for GnIH (GnIHR) is the seven-transmembrane G protein-coupled receptor 147 (GPR147) that inhibits cAMP production. GPR147 is also named neuropeptide FF (NPFF) receptor 1 (NPFFR1), because it also binds NPFF that has a C-terminal PQRFamide motif. To understand the evolutionary history of the GnIH system in the animal kingdom, we searched for receptors structurally similar to GnIHR in the genome of six mammals (human, mouse, rat, cattle, cat, and rabbit), five birds (pigeon, chicken, turkey, budgerigar, and zebra finch), one reptile (green anole), one amphibian (Western clawed flog), six fishes (zebrafish, Nile tilapia, Fugu, coelacanth, spotted gar, and lamprey), one hemichordate (acorn worm), one echinoderm (purple sea urchin), one mollusk (California sea hare), seven insects (pea aphid, African malaria mosquito, honey bee, buff-tailed bumblebee, fruit fly, jewel wasp, and red flour beetle), one cnidarian (hydra), and constructed phylogenetic trees by neighbor joining (NJ) and maximum likelihood (ML) methods. A multiple sequence alignment of the receptors showed highly conserved seven-transmembrane domains as well as disulfide bridge sites between the first and second extracellular loops, including the receptor of hydra. Both NJ and ML analyses grouped the receptors of vertebrates into NPFFR1 and NPFFR2 (GPR74), and the receptors of insects into the receptor for SIFamide peptides that share a C-terminal YRKPPFNGSIFamide motif. Although human, quail and zebrafish GnIHR (NPFFR1) were most structurally similar to SIFamide receptor of fruit fly in the Famide peptide (FMRFamide, neuropeptide F, short neuropeptide F, drosulfakinin, myosuppressin, SIFamide) receptor families, the amino acid sequences and the peptide coding regions of GnIH precursors were most similar to FMRFamide precursor of fruit fly in the precursors of Famide peptide families. Chromosome synteny analysis of the precursor genes of human, quail and zebrafish GnIH and fruit fly Famide peptides further identified conserved synteny in vertebrate GnIH and fruit fly FMRFa precursor genes as well as other Famide peptide precursor genes. These results suggest that GnIH and its receptor pair and SIFamide and its receptor pair may have diverged and co-evolved independently in vertebrates and insects, respectively, from their ancestral Famide peptide and its receptor pair, during diversification and evolution of deuterostomian and protostomian species.

Breakthrough in neuroendocrinology by discovering novel neuropeptides and neurosteroids: 1. Discovery of gonadotropin-inhibitory hormone (GnIH) across vertebrates.

Bargmann-Scharrer's discovery of "neurosecretion" in the first half of the 20th century has since matured into the scientific discipline of neuroendocrinology. Identification of novel neurohormones, such as neuropeptides and neurosteroids, is essential for the progress of neuroendocrinology. Our studies over the past two decades have significantly broadened the horizons of this field of research by identifying novel neuropeptides and neurosteroids in vertebrates that have opened new lines of scientific investigation in neuroendocrinology. Since the discovery of gonadotropin-releasing hormone (GnRH) in mammals at the beginning of 1970s, it was generally believed that GnRH is the only hypothalamic neuropeptide regulating gonadotropin release in vertebrates. In 2000, however, we discovered a novel hypothalamic neuropeptide that actively inhibits gonadotropin release in quail and termed it gonadotropin-inhibitory hormone (GnIH). It now appears that GnIH is highly conserved across vertebrates, including humans, and serves a number of behavioral and physiological functions other than regulation of reproduction, providing enormous opportunity for investigators from a wide array of disciplines to study this neuropeptide. This review summarizes the discovery of GnIH and its contribution to the progress of neuroendocrinology.

Gonadotropin-inhibitory hormone inhibits aggressive behavior of male quail by increasing neuroestrogen synthesis in the brain beyond its optimum concentration.

The action of testosterone on male socio-sexual behaviors, such as aggressive and sexual behaviors, requires its aromatization into estrogen (neuroestrogen) in the brain. Gonadotropin-inhibitory hormone (GnIH) is a hypothalamic neuropeptide that inhibits gonadotropin secretion from the pituitary. On the other hand, wide distribution of GnIH-immunoreactive (ir) neuronal fibers in the brain suggested their roles in the regulation of behavior. Our recent studies have shown that GnIH indeed inhibits aggressive and sexual behaviors. Accordingly, we further investigated the effect of GnIH on aromatase activity and estrogen synthesis in the brain. Abundant GnIH-ir neuronal fibers were observed in the vicinity of aromatase-ir cells in the brain, such as in the preoptic area (POA) that is thought to be the most critical site of aromatization and neuroestrogen action for the regulation of socio-sexual behavior. GnIH receptor (GPR147) mRNA was also expressed in aromatase-ir cells in the POA. GnIH stimulated the activity of aromatase and increased neuroestrogen synthesis in the POA through GPR147. The increase in neuroestrogen concentration in the POA was associated with a significant decrease in aggressive behavior. Finally, centrally administered 17ß-estradiol at higher doses inhibited aggressive behavior. These findings indicated that GnIH inhibits aggressive behavior by directly activating aromatase and increasing neuroestrogen synthesis in the brain beyond its optimum concentration for the expression of aggressive behavior. This review highlights recent findings of the role of GnIH in the regulation of neuroestrogen synthesis and its possible function in the regulation of socio-sexual behaviors.

Review: Melatonin stimulates the synthesis and release of gonadotropin-inhibitory hormone in birds.

Gonadotropin-inhibitory hormone (GnIH), a neuropeptide that inhibits gonadotropin synthesis and release, was first identified in the quail hypothalamus. To understand the physiological role of GnIH, this review will demonstrate the mechanisms that regulate GnIH synthesis and release. Pinealectomy (Px) combined with orbital enucleation (Ex) decreased the synthesis of GnIH precursor mRNA and content of mature GnIH peptide in the diencephalon. Melatonin administration to Px plus Ex birds caused a dose-dependent increase in the synthesis of GnIH precursor mRNA and production of mature peptide. A melatonin receptor subtype, Mel(1c,) was expressed in GnIH-immunoreactive neurons, suggesting direct action of melatonin on GnIH neurons. Melatonin administration further increased GnIH release in a dose-dependent manner from hypothalamic explants in vitro. GnIH mRNA expression and GnIH release during the dark period were greater than those during the light period in explants from quail exposed to long-day photoperiods. Conversely, plasma luteinizing hormone (LH) concentration decreased during the dark period. This review summarizes that melatonin appears to act on GnIH neurons in stimulating not only GnIH synthesis but also its release, thus inhibiting plasma LH concentration in birds.

RNA interference of gonadotropin-inhibitory hormone gene induces aggressive and sexual behaviors in birds.

Gonadotropin-inhibitory hormone (GnIH) was originally identified in the Japanese quail as a hypothalamic neuropeptide inhibitor of pituitary gonadotropin synthesis and release. GnIH neuronal fibers not only terminate in the median eminence to control anterior pituitary function but also extend widely in the brain, suggesting multiple roles in the regulation of behavior. To identify the role of GnIH neurons in the regulation of behavior, we tested the effect of RNA interference (RNAi) of the GnIH gene on aggressive and sexual behaviors of white-crowned sparrows and Japanese quail. Administration of small interfering RNA against GnIH precursor mRNA (GnIH siRNA) into the third ventricle of white-crowned sparrows reduced resting time, spontaneous production of complex vocalizations, and stimulated brief agonistic vocalizations. These behaviors resembled those of breeding birds during territorial defense. Central administration of GnIH siRNA induced aggressive and sexual behaviors and GnIH administration suppressed GnIH RNAi induced aggressive and sexual behaviors in the male quail. In summary, GnIH may function as a central nervous system suppressor of social interaction, thus playing an important role in the control of reproductive behavior, general aggression and territorial defense.