Gonadotropin-inhibitory hormone (GnIH) is a hypothalamic neuropeptide that inhibits gonadotropin secretion and socio-sexual behaviours. Oestrogen (neuroestrogen) synthesized in the brain from androgen by aromatase regulates male socio-sexual behaviours. Here we show that GnIH directly activates aromatase and increases neuroestrogen synthesis in the preoptic area (POA) and inhibits socio-sexual behaviours of male quail. Aromatase activity and neuroestrogen concentration in the POA are low in the morning when the birds are active, but neuroestrogen synthesis gradually increases until the evening when the birds become inactive. Centrally administered GnIH in the morning increases neuroestrogen synthesis in the POA and decreases socio-sexual behaviours. Centrally administered 17β-oestradiol at higher doses also inhibits socio-sexual behaviours in the morning. These results suggest that GnIH inhibits male socio-sexual behaviours by increasing neuroestrogen synthesis beyond its optimum concentration for the expression of socio-sexual behaviours. This is the first demonstration of any hypothalamic neuropeptide that directly regulates neuroestrogen synthesis.

Several neuropeptides with the C-terminal RFamide sequence have been identified in the hypothalamus of a variety of vertebrates. Among the RFamide peptide groups, however, only LPXRFamide peptides, including gonadotropin-inhibitory hormone, have been characterized in the avian brain. In the present study, we sought for the presence of other RFamide peptides in the avian hypothalamus. We identified a cDNA encoding an RFamide peptide orthologous to 26RFa (also referred to as QRFP) in the hypothalamus of the Japanese quail. The deduced quail 26RFa precursor consisted of 120-amino-acid residues, encoding one RFamide peptide with 27 amino acids. This RFamide peptide was flanked at the N terminus by a dibasic amino acid cleavage site and at the C terminus by a glycine amidation signal. Quantitative RT-PCR analysis demonstrated specific expression of quail 26RFa mRNA in the diencephalon including the hypothalamus. Furthermore, mass spectrometry analysis revealed the presence of a peptide exhibiting the mass of mature 26RFa, indicating that the peptide is actually produced from the precursor in the diencephalon. 26RFa-producing cell bodies were localized in the anterior hypothalamic nucleus in the brain. Synthetic 26RFa increased intracellular Ca2+ concentration in HEK293T cells transfected with the chicken G protein-coupled receptor GPR103. Intracerebroventricular injection of 26RFa in broiler chicks stimulated feeding behavior. These data provide the first evidence for the occurrence of the peptide 26RFa in the avian hypothalamus and indicate that this peptide exerts orexigenic activity.

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.

Gonadotropin-inhibitory hormone (GnIH) was first identified in Japanese quail to be an inhibitor of gonadotropin synthesis and release. GnIH peptides have since been identified in all vertebrates, and all share an LPXRFamide (X = L or Q) motif at their C-termini. The receptor for GnIH is the G protein-coupled receptor 147 (GPR147), which inhibits cAMP signaling. Cell bodies of GnIH neurons are located in the paraventricular nucleus (PVN) in birds and the dorsomedial hypothalamic area (DMH) in most mammals. GnIH neurons in the PVN or DMH project to the median eminence to control anterior pituitary function via GPR147 expressed in gonadotropes. Further, GnIH inhibits gonadotropin-releasing hormone (GnRH) -induced gonadotropin subunit gene transcription by inhibiting the adenylate cyclase/cAMP/PKA -dependent ERK pathway in an immortalized mouse gonadotrope cell line (LT2 cells). GnIH neurons also project to GnRH neurons that express GPR147 in the preoptic area (POA) in birds and mammals. Accordingly, GnIH can inhibit gonadotropin synthesis and release by decreasing the activity of GnRH neurons as well as by directly inhibiting pituitary gonadotrope activity. GnIH and GPR147 can thus centrally suppress testosterone secretion and spermatogenesis by acting in the hypothalamic-pituitary-gonadal axis. GnIH and GPR147 are also expressed in the testis of birds and mammals, possibly acting in an autocrine/paracrine manner to suppress testosterone secretion and spermatogenesis. GnIH expression is also regulated by melatonin, stress and social environment in birds and mammals. Accordingly, the GnIH-GPR147 system may play a role in transducing physical and social environmental information to regulate optimal testicular activity in birds and mammals. This review discusses central and direct inhibitory effects of GnIH and GPR147 on testosterone secretion and spermatogenesis in birds and mammals.

Gonadotropin-inhibitory hormone (GnIH) was first identified in the Japanese quail as a hypothalamic neuropeptide inhibitor of gonadotropin secretion. Subsequent studies have shown that GnIH is present in the brains of birds including songbirds, and mammals including humans. The identified avian and mammalian GnIH peptides universally possess an LPXRFamide (X = L or Q) motif at their C-termini. Mammalian GnIH peptides are also designated as RFamide-related peptides from their structures. The receptor for GnIH is the G protein-coupled receptor 147 (GPR147), which is thought to be coupled to G_αi protein. Cell bodies of GnIH neurons are located in the paraventricular nucleus (PVN) in birds and the dorsomedial hypothalamic area (DMH) in mammals. GnIH neurons in the PVN or DMH project to the median eminence to control anterior pituitary function. GPR147 is expressed in the gonadotropes and GnIH suppresses synthesis and release of gonadotropins. It was further shown in immortalized mouse gonadotrope cell line (LβT2 cells) that GnIH inhibits gonadotropin-releasing hormone (GnRH) induced gonadotropin subunit gene transcriptions by inhibiting adenylate cyclase/cAMP/PKA-dependent ERK pathway. GnIH neurons also project to GnRH neurons in the preoptic area, and GnRH neurons express GPR147 in birds and mammals. Accordingly, GnIH may inhibit gonadotropin synthesis and release by decreasing the activity of GnRH neurons as well as directly acting on the gonadotropes. GnIH also inhibits reproductive behavior possibly by acting within the brain. GnIH expression is regulated by a nocturnal hormone melatonin and stress in birds and mammals. Accordingly, GnIH may play a role in translating environmental information to inhibit reproductive physiology and behavior of birds and mammals. Finally, GnIH has therapeutic potential in the treatment of reproductive cycle and hormone-dependent diseases, such as precocious puberty, endometriosis, uterine fibroids, and prostatic and breast cancers.