Evidence that RF-amide related peptides are inhibitors of reproduction in mammals

Brain RFamide Neuropeptides in Stress-Related Psychopathologies

The RFamide peptide family is a group of proteins that share a common C-terminal arginine-phenylalanine-amide motif. To date, the family comprises five groups in mammals: neuropeptide FF, LPXRFamides/RFamide-related peptides, prolactin releasing peptide, QRFP, and kisspeptins. Different RFamide peptides have their own cognate receptors and are produced by different cell populations, although they all can also bind to neuropeptide FF receptors with different affinities. RFamide peptides function in the brain as neuropeptides regulating key aspects of homeostasis such as energy balance, reproduction, and cardiovascular function. Furthermore, they are involved in the organization of the stress response including modulation of pain. Considering the interaction between stress and various parameters of homeostasis, the role of RFamide peptides may be critical in the development of stress-related neuropathologies. This review will therefore focus on the role of RFamide peptides as possible key hubs in stress and stress-related psychopathologies. The neurotransmitter coexpression profile of RFamide-producing cells is also discussed, highlighting its potential functional significance. The development of novel pharmaceutical agents for the treatment of stress-related disorders is an ongoing need. Thus, the importance of RFamide research is underlined by the emergence of peptidergic and G-protein coupled receptor-based therapeutic targets in the pharmaceutical industry.

Structural basis for recognition of 26RFa by the pyroglutamylated RFamide peptide receptor

The neuropeptide 26RFa, a member of the RF-amide peptide family, activates the pyroglutamylated RF-amide peptide receptor (QRFPR), a class A GPCR. The 26RFa/QRFPR system plays critical roles in energy homeostasis, making QRFPR an attractive drug target for treating obesity, diabetes, and eating disorders. However, the lack of structural information has hindered our understanding of the peptide recognition and regulatory mechanism of QRFPR, impeding drug design efforts. In this study, we determined the cryo-EM structure of the Gq-coupled QRFPR bound to 26RFa. The structure reveals a unique assembly mode of the extracellular region of the receptor and the N-terminus of the peptide, and elucidates the recognition mechanism of the C-terminal heptapeptide of 26RFa by the transmembrane binding pocket of QRFPR. The study also clarifies the similarities and distinctions in the binding pattern of the RF-amide moiety in five RF-amide peptides and the RY-amide segment in neuropeptide Y. These findings deepen our understanding of the RF-amide peptide recognition, aiding in the rational design of drugs targeting QRFPR and other RF-amide peptide receptors.

The effect of gonadotropin-inhibitory hormone on steroidogenesis and spermatogenesis by acting through the hypothalamic-pituitary-testis axis in mice

Gonadotropin inhibitory hormone (GnIH) is essential for regulating the reproduction of mammals and inhibiting testicular activities in mice. This study aimed to explore the mechanism of GnIH on spermatogenesis and steroidogenesis by acting through the hypothalamus-pituitary-testis axis of mice. Mice were subcutaneously injected with different doses of GnIH (1 μg/150 μL, 3 μg/150 μL, 6 μg/150 μL, 150 μL saline, twice daily) for 11 days. Subsequently, luteinizing hormone (LH), testosterone (T), and inhibin B (INH B) levels of peripheral blood were determined, and the expression of GnRH synthesis-related genes (GnRH-1, Kiss-1, NPY) and gonadotropin synthesis-related genes (FSH β, LH β, GnRH receptor) in the hypothalamus and pituitary gland were respectively detected. Additionally, the expression of steroidogenesis-related genes/proteins (P450scc, StAR and 3β-HSD) and spermatogenesis-related proteins/genes including LH receptor (LHR), androgen receptor (AR), heat shock factor-2 (HSF-2) and INH B were analyzed using western blot and q-PCR. Results showed that GnIH treatment significantly reduced the concentration of LH in the peripheral blood. Further analysis revealed that GnIH treatment markedly reduced the expression of GnRHImRNA and Kiss-1 mRNA in the hypothalamus, and mRNA levels of FSH β, LH β, and GnRHR genes in the pituitary. We also observed that GnIH treatment significantly decreased T levels and expression of the P450scc, StAR, and 3β-HSD proteins in the testis. Furthermore, GnIH treatment down-regulated LHR, AR proteins, and HSF-2 gene in the testis. Importantly, the INH B concentration of and INH βb mRNA levels significantly declined following GnIH treatment. Additionally, GnIH treatment may induce germ cell apoptosis in the testis of mice. In conclusion, GnIH may suppress spermatogenesis and steroidogenesis by acting through the hypothalamus-pituitary-testis axis in mice.

Review: Early and late determinants of puberty in ruminants and the role of nutrition

This article reviews the scientific literature on puberty with a focus on ruminants and draws inference, where appropriate, from recent findings in transgenic mouse models and human pathology. Early genetic determinants of puberty have been discovered in humans suffering from hypogonadotropic hypogonadism or central precocious puberty. Transgenic mouse models selected on the basis of the causative defective genes helped in discovering the cellular and molecular mechanisms involved. Most of the genes found are involved in the development of neuroendocrine networks during embryo development and early postnatal life. Notwithstanding that the development of neuroendocrine networks takes place early in puberty, a delay or acceleration in the development of Gonadotropin Releasing Hormone (GnRH) neurons has an impact on puberty onset inducing a delay or an advance, respectively. Among the genes discovered in humans and laboratory models, only a few of them displayed polymorphisms associated with advanced sexual maturity, but also marbling, growth traits and callipygian conformation. This could be related to the fact that rather than puberty onset, most research monitored sexual maturity. Sexual maturity occurs after puberty onset and involves factors regulating the maturation of gonads and in the expression of sexual behaviour. The association with growth and metabolic traits is not surprising since nutrition is the major environmental factor that will act on late genetic determinants of puberty onset. However, a recent hypothesis emerged suggesting that it is the postnatal activation of the GnRH neuronal network that induces the acceleration of growth and weight gain. Hence, nutritional factors need the activation of GnRH neurons first before acting on late genetic determinants. Moreover, nutritional factors can also affect the epigenetic landscape of parental gamete's genome with the consequence of specific methylation of genes involved in GnRH neuron development in the embryo. Season is another important regulator of puberty onset in seasonal small ruminants and appears to involve the same mechanisms that are involved in seasonal transition in adults. The social environment is also an underestimated factor affecting puberty onset in domestic ruminants, most research studies focused on olfactory cues, but the genetic basis has not heretofore been adequately tackled by the scientific community. Additionally, there is some evidence to suggest transgenerational effects exist, in that nutritional and social cues to which parents were exposed, could affect the epigenetic landscape of parental gametes resulting in the epigenetic regulation of early genetic determinants of puberty onset in their offspring.

Photoperiod-induced changes in hypothalamic de novo DNA methyltransferase expression are independent of triiodothyronine in female Siberian hamsters (Phodopus sungorus)

Many temperate zone animals engage in seasonal reproductive physiology and behavior as a strategy to maximise the propagation of the species. The hypothalamus integrates environmental cues and hormonal signalling to optimize the timing of reproduction. Recent work has revealed that epigenetic modifications, such as DNA methylation, vary across seasonal reproductive states. Multiple hormones act in the hypothalamus to permit or inhibit reproductive physiology, and the increase in thyroid hormone triiodothyronine (T₃) has been implicated in the initiation of breeding in many species. The objective of this study was to examine the effect of T₃ on the photoperiod-dependent regulation of reproductive physiology and hypothalamic DNA methyltransferase enzyme expression in female Siberian hamsters (Phodopus sungorus). We tested the hypothesis that T₃ in short days (SD) would stimulate hypothalamic Rfrp3 and de novo DNA methyltransferase (Dnmt) expression in female Siberian hamsters. 10 weeks of SD lengths induced a decrease in body and uterine mass. Hamsters maintained in SD were found to express lower levels of GnRH, Rfrp3, Dnmt3a and Dnmt3b. Two weeks of daily T₃ injections did not affect body mass, uterine mass, Gnrh, Rfrp3, Dnmt3a or Dnmt3b expression in neuroendocrine tissues. SD significantly lowered Tshβ mRNA expression and T3 reduced Tshβ in LD hamsters. Our data indicate sex-dependent effects of T₃ for the neuroendocrine regulation of seasonal reproduction in hamsters.

Effects of Chronic Intracerebroventricular Infusion of RFamide-Related Peptide-3 on Energy Metabolism in Male Mice

RFamide-related peptide-3 (RFRP-3), the mammalian ortholog of avian gonadotropin-inhibitory hormone (GnIH), plays a crucial role in reproduction. In the present study, we explored the other functions of RFRP-3 by investigating the effects of chronic intracerebroventricular infusion of RFRP-3 (6 nmol/day) for 13 days on energy homeostasis in lean male C57BL/6J mice. The infusion of RFRP-3 increased cumulative food intake and body mass. In addition, the masses of brown adipose tissue (BAT) and the liver were increased by the administration of RFRP-3, although the mass of white adipose tissue was unchanged. On the other hand, RFRP-3 decreased O₂ consumption, CO₂ production, energy expenditure, and core body temperature during a short time period in the dark phase. These results suggest that the increase in food intake and the decrease in energy expenditure contributed to the gain of body mass, including the masses of BAT and the liver. The present study shows that RFRP-3 regulates not only reproductive function, but also energy metabolism, in mice.

Lipopolysaccharide reduces gonadotrophin-releasing hormone (GnRH) gene expression: role of RFamide-related peptide-3 and kisspeptin

RFamide-related peptide (RFRP)-3 reduces luteinising hormone (LH) secretion in rodents. Stress has been shown to upregulate the expression of the RFRP gene (Rfrp) with a concomitant reduction in LH secretion, but an effect on expression of the gonadotrophin-releasing hormone (GnRH) gene (Gnrh1) has not been shown. We hypothesised that lipopolysaccharide (LPS)-induced stress affects expression of Rfrp, the gene for kisspeptin (Kiss1) and/or Gnrh1, leading to suppression of LH levels in rats. Intracerebroventricular injections of RFRP-3 (0.1, 1, 5 nmol) or i.v. LPS (15μgkg-1) reduced LH levels. Doses of 1 and 5 nmol RFRP-3 were then administered to analyse gene expression by in situ hybridisation. RFRP-3 (5 nmol) had no effect on Gnrh1 or Kiss1 expression. LPS stress reduced GnRH and Kiss1 expression, without affecting Rfrp1 expression. These data indicate that LPS stress directly or indirectly reduces Gnrh1 expression, but this is unlikely to be due to a change in Rfrp1 expression.

Annual patterns of ocular melatonin level in the female grass puffer, Takifugu alboplumbeus: possible involvement in seasonal reproductive response

The aim of this study was to investigate the expression patterns of ocular melatonin in the annual reproductive cycle of the female grass puffer. Spawning season of the female grass puffer is from June to July in Jeju, South Korea. Time-resolved fluoroimmunoassay revealed that levels of ocular melatonin, which show an annual change, peaked in May (spawning season). Additionally, expression of reproductive-related genes also showed annual patterns: GnRH1 peaked in August, GnRH2 peaked in February, GnRH3, Kiss2, and LPXRFa peaked in November. These results suggest that ocular melatonin may be related to the annual reproductive cycle in the grass puffer. To better understand the photic regulation of AANAT1a mRNA in the retina, we observed the nocturnal pattern of ocular melatonin levels daily, which shows a nocturnal pattern in both short photoperiod (SD) and long photoperiod (LD) conditions. In the brain, AANAT2 mRNA also shows a nocturnal pattern in both SD and LD; however, the time of peak expression of AANAT2 mRNA was unchanged in both conditions. Following intraperitoneal injection of melatonin for 2 weeks, expression of GnRH2 and LPXRFa mRNA in the brain significantly increased, while that of Kiss2 mRNA was decreased, suggesting that melatonin has a reproduction-related effect. Furthermore, under SD and LD conditions for 14 weeks, the gonadosomatic index more increased and the maturity of the ovary progressed under LD compared with those under SD, suggesting that the SD photoperiodic signal inactivated ovarian development. These results indicate that the ocular melatonin may have a possible role in the reproductive endocrinology of the grass puffer.

Hyperactive LH Pulses and Elevated Kisspeptin and NKB Gene Expression in the Arcuate Nucleus of a PCOS Mouse Model

Polycystic ovary syndrome (PCOS), a common reproductive disorder in women, is characterized by hyperandrogenemia, chronic anovulation, cystic ovarian follicles, and luteinizing hormone (LH) hyper-pulsatility, but the pathophysiology isn't completely understood. We recently reported a novel mouse model of PCOS using chronic letrozole (LET; aromatase inhibitor). Letrozole-treated females demonstrate multiple PCOS-like phenotypes, including polycystic ovaries, anovulation, and elevated circulating testosterone and LH, assayed in "one-off" measures. However, due to technical limitations, in vivo LH pulsatile secretion, which is elevated in PCOS women, was not previously studied, nor were the possible changes in reproductive neurons. Here, we used recent technical advances to examine in vivo LH pulse dynamics of freely moving LET female mice versus control and ovariectomized (OVX) mice. We also determined whether neural gene expression of important reproductive regulators such as kisspeptin, neurokinin B (NKB), and dynorphin, is altered in LET females. Compared to controls, LET females exhibited very rapid, elevated in vivo LH pulsatility, with increased pulse frequency, amplitude, and basal levels, similar to PCOS women. Letrozole-treated mice also had markedly elevated Kiss1, Tac2, and Pdyn expression and increased Kiss1 neuronal activation in the hypothalamic arcuate nucleus. Notably, the hyperactive LH pulses and increased kisspeptin neuron measures of LET mice were not as elevated as OVX females. Our findings indicate that LET mice, like PCOS women, have markedly elevated LH pulsatility, which likely drives increased androgen secretion. Increased hypothalamic kisspeptin and NKB levels may be fundamental contributors to the hyperactive LH pulse secretion in the LET PCOS-like condition and, perhaps, in PCOS women.

Dynamic Changes of RFRP3/GPR147 in the Precocious Puberty Model Female Rats

BACKGROUND

Pubertal development is a complex physiological process regulated by the neuroendocrine system and hypothalamic-pituitary-gonadal axis. Sexual precocity is a common childhood endocrine disease.The pathogenesis of sexual precocity has not been fully elucidated. RFRP3/GPRl47 signal pathway is able to inhibit the reproductive capability in avians and mammals, probably by acting on the GnRH neuron and pituitary to regulate gonadotrophin synthesis and release. However, little is known about the role of RFRP3 in puberty development and sexual precocity.

OBJECTIVE

To observe the dynamic changes of RFamide related peptide 3/G proteincoupled receptor 147 (RFRP3/GPR147) in hypothalamic during puberty development and explore their role in precocious puberty based on a female rat model.

METHODS

The Sprague-Dawley female rats were randomly divided into three groups, normal, vehicle, and precocious puberty model. At 5 days old, the rat model with precocious puberty was prepared by subcutaneously injecting a mixture of danazoldissolved ethanol and glycol. At different day-age (15, 25, 30, 35, and 40 days), the levels of estradiol(E2), follicle-stimulating hormone(FSH), and luteinizing hormone (LH) in the peripheral blood were detected by the enzyme-linked immunosorbent assay, the messenger ribonucleic acid (mRNA) expressions of RFRP3, gonadotropin releasing hormone and GPR147 were examined by real-time polymerase chain reaction(R-T PCR). RFRP3 positive cells were observed using Immunofluorescence confocal microscopy.

RESULTS

At 25 and 30 days, the levels of sex hormones and the uterus coefficients were significantly higher in the precocious puberty model group than those in the normal and vehicle groups. The ovarian morphological development in the precocious puberty model rats was significantly earlier than those in the normal and vehicle groups. The mRNA expressions of RFRP3/GPR147 and GnRH in the precocious puberty model group gradually increased and peaked at 25 days. The different day-age and the interaction have significant statistical significance on the expression of RFRP3 mRNA, while the levels of RFRP3 mRNA in the model group and vehicle groups have no significant statistical significance. There was statistical significance between the model group and vehicle groups in different day-age on the expression of GPR147 mRNA.The expression of hypothalamic RFRP3/GPR147 mRNA and RFRP3 positive cells gradually decreased with puberty onset. At 35 days, the levels of RFRP3 mRNA and GPR147 mRNA were significantly lower in the precocious puberty model group than those in the vehicle groups. Meanwhile, the levels of LH in the precocious puberty model rats reached its peak at this age. In the vehicle group, the levels of RFRP3 mRNA and serum LH were gradually increased and LH nearly peaked at 35 day-age. Subsequently, it gradually decreased and reached the lowest level at 35 day-age. The expression of RFRP3 mRNA and LH were positively correlated.

CONCLUSION

The findings suggested that RFRP3/GPR147 signaling pathway may be involved in the pathogenesis of sexual precocity by regulating puberty development and sexual maturity in rats.

The role of kisspeptin system in cancer biology

Kisspeptins are a family of neuropeptides that are known to be critical in puberty initiation and ovulation. Apart from that kisspeptin derived peptides (KPs) are also known for their antimetastatic activities in several malignancies. Herein we report recent evidence of the role of kisspeptins in cancer biology and we examine the prospective of targeting the kisspeptin pathways leading to a better prognosis in patients with malignant diseases.

Isolation and identification of endogenous RFamide-related peptides 1 and 3 in the mouse hypothalamus

Although the RFamide-related peptide (RFRP) preproprotein sequence is known in mice, until now, the molecular structure of the mature, functional peptides processed from the target precursor molecule has not been determined. In the present study, we purified endogenous RFRP1 and RFRP3 peptides from mouse hypothalamic tissue extracts using an immunoaffinity column conjugated with specific antibodies against the mouse C-terminus of RFRP-1 and RFRP-3. Employing liquid chromatography coupled with mass spectrometry, we demonstrated that RFRP1 consists of 15 amino acid residues and RFRP3 consists of 10 amino acid residues (ANKVPHSAANLPLRF-NH2 and SHFPSLPQRF-NH2, respectively). To investigate the distribution of RFRPs in the mouse central nervous system, we performed immunohistochemical staining of the brain sections collected from wild-type and Rfrp knockout animals. These data, together with gene expression in multiple tissues, provide strong confidence that RFRP-immunoreactive neuronal cells are localised in the dorsomedial hypothalamic nucleus (DMH) and between the DMH and the ventromedial hypothalamic nuclei. The identification of RFRP1 and RFRP3 peptides and immunohistochemical visualisation of targeting RFRPs neurones in the mice brain provide the basis for further investigations of the functional biology of RFRPs.

The roles of RFamide-related peptides (RFRPs), mammalian gonadotropin-inhibitory hormone (GnIH) orthologues in female reproduction

OBJECTIVES

To benefit from reproduction and deal with challenges in the environmental conditions, animals must adapt internal physiology to maximize the reproduction rate. Maladaptive variations in the neurochemical systems and reproductive system can lead to manifestation of several significant mammalian reprocesses, including mammalian ovarian lifespan. RFamide-related peptide (RFRP, Rfrp), mammalian orthologues of gonadotropin-inhibitory hormone (GnIH), which is a regulator to prevent the gonadotropin-releasing hormone (GnRH) neural activity, is known to be related to reproductive traits. This review aimed to summarize recent five-year observations to outline historic insights and novel perspectives into the functions of RFRPs in coding the mammalian reproductive physiology, especially highlight recent advances in the impact on RFRPs in regulating mammalian ovary lifespan.

MATERIALS AND METHODS

We reviewed the recent five-year important findings of RFRP system involved in mammalian ovary development. Data for this review were collected from Google Scholar and PubMed using the RFRP keyword combined with the keywords related to physiological or pathological reproductive functions.

RESULTS

Recent discoveries are focused on three major fronts in research on RFRP role in female reproduction including reproductive functions, energy balance, and stress regulation. The roles of RFRPs in various development phases of mammal reproduction including prepuberty, puberty, estrous cycle, pregnancy, milking, menopause, and/or ovarian diseases have been shown.

CONCLUSION

Overall, these recent advances demonstrate that RFRPs serve as critical mediators in mammalian ovarian development.

Hindbrain dorsal vagal complex AMPK controls hypothalamic gluco-regulatory transmitter and counter-regulatory hormone responses to hypoglycemia

Pharmacologic activation of the hindbrain dorsal vagal complex energy sensor 5'-adenosine monophosphate-activated protein kinase (AMPK) causes site-specific adjustments in hypothalamic AMPK activity. DVC A2 noradrenergic neurons are a likely source of metabolo-sensory cues to downstream network components as they express substrate fuel-sensitive AMPK. This study investigated the hypothesis that DVC AMPK controls hypothalamic sensor, metabolic effector transmitter, and counter-regulatory hormone responses to insulin-induced hypoglycemia. Male rats were injected into the caudal fourth ventricle with the AMPK inhibitor compound C (Ccor vehicle before hypoglycemia. Arcuate (ARH), ventromedial (VMN), and dorsomedial (DMN) nuclei and lateral hypothalamic area (LHA) were micropunch-dissected for norepinephrine ELISA and Western blot analyses. Hypoglycemic stimulation of norepinephrine activity in each site was impeded by compound C. Hypoglycemia caused drug-revocable (ARH) or -refractory (VMN, DMN) reductions in AMPK, alongside hindbrain AMPK-dependent augmentation of phospho-AMPK expression in each location. Compound C prevented hypoglycemic augmentation of gluco-stimulatory ARH neuropeptide Y, VMN neuronal nitric oxide synthase, and LHA orexin-A expression, while hypoglycemic suppression of the catabolic neuron protein markers ARH pro-opiomelanocortin and VMN glutamate decarboxylase_65/67 was respectively averted or unaffected by drug treatment. DMN RFamide-related peptide-1 and -3 profiles were correspondingly amplified or suppressed hindbrain AMPK-reliant mechanisms during hypoglycemia. Results show that DVC AMPK is required for hypoglycemic intensification of norepinephrine activity in characterized hypothalamic gluco-regulatory structures, and that this sensor regulates AMPK activation and metabolic effector transmission in those sites.

Gonadotrophin-inhibitory hormone and its mammalian orthologue RFamide-related peptide-3: Discovery and functional implications for reproduction and stress

At the turn of the millennium, a neuropeptide with pronounced inhibitory actions on avian pituitary gonadotrophin secretion was identified and named gonadotrophin-inhibitory hormone (GnIH). Across bird species, GnIH acts at the level of the pituitary and the gonadotrophin-releasing hormone (GnRH) neuronal system to inhibit reproduction. Subsequent to this initial discovery, orthologues of GnIH have been identified and characterised across a broad range of species. In many vertebrates, the actions of GnIH and its orthologues serve functional roles analogous to those seen in birds. In other cases, GnIH and its orthologues exhibit more diverse actions dependent on sex, species, season and reproductive condition. The present review highlights the discovery and functional implications of GnIH across species, focusing on research domains in which the significance of this neuropeptide has been explored most.

Effect of RFRP-3, the mammalian ortholog of GnIH, on the epididymis of male rats

RFamide-related peptide-3 (RFRP-3) and its receptor (GPR147) play an important role in reproduction regulation in mammals. To understand the role of RFRP-3 in male reproductive function of epididymis, we first investigated the expression changes in RFRP-3 and its receptor at different stages of development, that is, postnatal day 20 (P20), 40 (P40), 60 (P60) and 80 (P80). Our results showed that fluctuations in the expression of GnIH and GPR147 during postnatal development occurred, and the highest epididymal GnIH and GPR147 expression were both detected in P60. Subsequently, we further investigated the effect of RFRP-3 on the histology, apoptosis and autophagy of the epididymis in vivo. For in vivo study, male rats were treated intratesticularly with different doses of RFRP-3 (control, 0.1 μg, 1 μg, and 10 μg per day) for 7 days. Our results show that RFRP-3 caused dose-dependent histological changes in the epididymal duct, such as a decline in the number of spermatozoa and an increase in degenerated and vacuolated epididymal epithelial cells. Rats treated intratesticularly with RFRP-3 also showed dose-dependent effects on caspase-3 activation and the expression of apoptotic markers (whole caspase-3, cleaved caspase-3 and Bcl-2). However, the expression of autophagy markers (Beclin-1 and Atg5) exhibited a bidirectional, dose-dependent effect. It is concluded that RFRP-3 plays a regulatory role in male rat reproduction, possibly because RFRP-3 mediates the apoptosis and autophagy of the epididymis.

Is precocious puberty linked to hypothalamic expression of arginine-phenylalanine-amide-related peptide?

The up-regulation and down-regulation of gonadotropin-releasing hormone (GnRH) in central precocious puberty is not yet known. However, recent advances in neuroendocrinology have shown the controlling role of arginine-phenylalanine RF-amide-related peptides (RFRPs) on GnRH secretion in different phenomenon of reproduction such as estrus cycle and pregnancy, but the exact role of RFRPs in puberty and its related pathologic condition, precocious puberty, is not clear yet. This paper hypothesizes that RFRP is a regulatory peptide of puberty and might prevent the precocious puberty. On the basis of previous studies on hormonal fluctuations at the time of puberty, RFRP might have a role on controlling of premature secretion of GnRH and avoiding central precocious puberty.

Central RFRP-3 Stimulates LH Secretion in Male Mice and Has Cycle Stage-Dependent Inhibitory Effects in Females

RFamide-related peptide (RFRP)-3 is a neuropeptide thought to play an inhibitory role in the regulation of reproduction in various mammalian species, although some stimulatory effects have been reported. To date, the effects of RFRP-3 on gonadotropin secretion have been scarcely studied in mice. The aim of the current study was to characterize the effect of RFRP-3 administration on gonadotropin secretion in male and female mice. Adult intact and castrated male mice received acute central injections of 0.5 to 5 nmol of RFRP-3, and luteinizing hormone (LH) concentration was assayed in tail-tip blood samples. RFRP-3 had a dose-dependent stimulatory effect on LH secretion when administered centrally to both intact and castrated mice, and this effect was diminished when RFRP-3 was administered to kisspeptin receptor knockout mice. In female mice, central RFRP-3 had an inhibitory effect on LH secretion when administered at the time of the preovulatory LH surge in intact mice, or of an estradiol-induced LH surge in ovariectomized mice. Conversely, central RFRP-3 administration had no effect on LH levels in intact diestrus or ovariectomized, low-dose estradiol-implanted mice. Finally, peripheral administration of RFRP-3 to intact males and to females at the time of the preovulatory LH surge or during diestrus had no effect on LH secretion. Taken together, these results provide a detailed description of sex- and cycle stage-dependent effects of RFRP-3 on gonadotrophin secretion in mice. Moreover, it appears that the stimulatory effects are mediated in part by the receptor for kisspeptin, a potent stimulator of the reproductive axis.

Ontogeny of clock and KiSS-1 metastasis-suppressor (Kiss1) gene expression in the prepubertal mouse hypothalamus

Kisspeptin is crucial for the generation of the circadian-gated preovulatory gonadotrophin-releasing hormone (GnRH)-LH surge in female rodents, with expression in the anteroventral periventricular nucleus (AVPV) peaking in the late afternoon of pro-oestrus. Given kisspeptin expression is established before puberty, the aim of the present study was to investigate kisspeptin and clock gene rhythms during the neonatal period. Anterior and posterior hypothalami were collected from C57BL/6J mice on Postnatal Days (P) 5, 15 and 25, at six time points across 24h, for analysis of gene expression by reverse transcription-quantitative polymerase chain reaction. Expression of aryl hydrocarbon receptor nuclear translocator-like gene (Bmal1) and nuclear receptor subfamily 1, group D, member 2 (Rev-erbα) in the anterior hypothalamus (containing the suprachiasmatic nucleus) was not rhythmic at P5 or P15, but Bmal1 expression exhibited rhythmicity in P25 females, whereas Rev-erbα expression was rhythmic in P25 males. KiSS-1 metastasis-suppressor (Kiss1) expression did not exhibit time-of-day variation in the anterior (containing the AVPV) or posterior (containing the arcuate nucleus) hypothalami in female and male mice at P5, P15 or P25. The data indicate that the kisspeptin circadian peak in expression observed in the AVPV of pro-oestrous females does not manifest at P5, P15 or P25, likely due to inadequate oestrogenic stimuli, as well as incomplete development of clock gene rhythmicity before puberty.

Diurnal regulation of hypothalamic kisspeptin is disrupted during mouse pregnancy

Kisspeptin, the neuropeptide product of the Kiss1 gene, is critical in driving the hypothalamic-pituitary-gonadal (HPG) axis. Kisspeptin neurons in the anteroventral periventricular nucleus (AVPV) and arcuate nucleus (Arc) of the hypothalamus mediate differential effects, with the Arc regulating negative feedback of sex steroids and the AVPV regulating positive feedback, vital for the preovulatory surge and gated under circadian control. We aimed to characterize hypothalamic Kiss1 and Kiss1r mRNA expression in nonpregnant and pregnant mice, and investigate potential circadian regulation. Anterior and posterior hypothalami were collected from C57BL/6J mice at diestrus, proestrus, and days 6, 10, 14, and 18 of pregnancy, at six time points across 24h, for real-time PCR analysis of gene expression. Analysis confirmed that Kiss1 mRNA expression in the AVPV increased at ZT13 during proestrus, with a luteinizing hormone surge observed thereafter. No diurnal regulation was seen at diestrus or at any stage of pregnancy. Anterior hypothalamic Avp mRNA expression exhibited no diurnal variation, but Avpr1a peaked at 12:00h during proestrus, possibly reflecting the circadian input from the suprachiasmatic nucleus to AVPV Kiss1 neurons. Rfrp (Npvf) expression in the posterior hypothalamus did not demonstrate diurnal variation at any stage. Clock genes Bmal1 and Rev-erbα were strongly diurnal, but there was little change between diestrus/proestrus and pregnancy. Our data indicate the absence of the circadian input to Kiss1 in pregnancy, despite high gestational estradiol levels and normal clock gene expression, and may suggest a disruption of a kisspeptin-specific diurnal rhythm that operates in the nonpregnant state.

Possible Role of GnIH as a Mediator between Adiposity and Impaired Testicular Function

The aim of the present study was to evaluate the roles of gonadotropin-inhibitory hormone (GnIH) as an endocrine link between increasing adiposity and impaired testicular function in mice. To achieve this, the effect of GnIH on changes in nutrients uptake and hormonal synthesis/action in the adipose tissue and testis was investigated simultaneously by in vivo study and separately by in vitro study. Mice were treated in vivo with different doses of GnIH for 8 days. In the in vitro study, adipose tissue and testes of mice were cultured with different doses of GnIH with or without insulin or LH for 24 h at 37°C. The GnIH treatment in vivo showed increased food intake, upregulation of glucose transporter 4 (GLUT4), and increased uptake of triglycerides (TGs) in the adipose tissue. These changes may be responsible for increased accumulation of fat in white adipose tissue, resulting in increase in the body mass. Contrary to the adipose tissue, treatment with GnIH both in vivo and in vitro showed decreased uptake of glucose by downregulation of glucose transporter 8 (GLUT8) expressions in the testis, which in turn resulted in the decreased synthesis of testosterone. The GnIH treatment in vivo also showed the decreased expression of insulin receptor protein in the testis, which may also be responsible for the decreased testicular activity in the mice. These findings thus suggest that GnIH increases the uptake of glucose and TGs in the adipose tissue, resulting in increased accumulation of fat, whereas simultaneously in the testis, GnIH suppressed the GLUT8-mediated glucose uptake, which in turn may be responsible for decreased testosterone synthesis. This study thus demonstrates GnIH as mediator of increasing adiposity and impaired testicular function in mice.

The Role of Arginine-Phenylalanine-Amide-Related Peptides in Mammalian Reproduction

Until 2000 it was believed that gonadotropin-releasing hormone (GnRH) was the sole regulator of hypophyseal gonadotropes. In 2000, the discovery of a gonadotropin inhibitory hormone (GnIH) initiated a revolution in the field of reproductive physiology. Identification of GnIH homologues in mammals, the arginine-phenylalanine-amide (RFamide)-related peptides (RFRPs), indicated a similar function. Subsequently, further works conducted in various laboratories worldwide have shown that these neuropeptides inhibit the hypothalamic-hypophyseal axis. This review discusses the role of RFRPs in mammalian reproductive processes.

Construction and evaluation of the novel DNA vaccine harboring the inhibin α (1-32) and the RF-amide related peptide-3 genes for improving fertility in mice

To further improve fertility of animals, a novel gene RFRP-3 (RF-amide related peptide-3, RFRP-3) was used to construct DNA vaccines with INH α (1–32) (inhibin, INH) fragment for the first time. The aim of this study was to evaluate the effects of novel DNA vaccines on fertility in mice. Synthesized SINH and SRFRP (INH and RFRP genes were separately ligated to the C-terminus of the small envelope protein of the hepatitis B virus (HBV-S) gene) fragments were inserted into multiple cloning site of pIRES vector to develop p-SINH/SRFRP. The synthesized tissue plasminogen activator (TPA) signal sequence was then inserted into the p-SINH/SRFRP to construct p-TPA-SINH/TPA-SFRFP. Meanwhile, p-SINH was prepared and considered as positive control. Forty Kunming mice were equally divided into four groups and respectively immunized by electroporation with p-SINH, p-SINH/SRFRP and p-TPA-SINH/TPA-SRFRP vaccine (three times at 2 weeks interval) and saline as control. Results showed that the average antibodies (P/N value) of anti-INH and anti-RFRP in mice inoculated with p-TPA-SINH/TPA-SFRFP were significantly higher (P<0.05) than those inoculated with p-SINH/SRFRP and the positive rates were 100% (anti-INH) and 90% (anti-RFRP) respectively, at 2 weeks after the third immunization. Litter size of mice immunized with the three recombinant plasmids was higher (P<0.05) than that of the control, and litter size of mice immunized with p-TPA-SINH/TPA-SRFRP significantly increased (P<0.05) compared with p-SINH. These results suggested that the p-TPA-SINH/TPA-SRFRP harboring INH and RFRP genes was successfully constructed and had good immunogenicity, and might effectively increase litter size.

Hypothalamus as an endocrine organ

The endocrine hypothalamus constitutes those cells which project to the median eminence and secrete neurohormones into the hypophysial portal blood to act on cells of the anterior pituitary gland. The entire endocrine system is controlled by these peptides. In turn, the hypothalamic neuroendocrine cells are regulated by feedback signals from the endocrine glands and other circulating factors. The neuroendocrine cells are found in specific regions of the hypothalamus and are regulated by afferents from higher brain centers. Integrated function is clearly complex and the networks between and amongst the neuroendocrine cells allows fine control to achieve homeostasis. The entry of hormones and other factors into the brain, either via the cerebrospinal fluid or through fenestrated capillaries (in the basal hypothalamus) is important because it influences the extent to which feedback regulation may be imposed. Recent evidence of the passage of factors from the pars tuberalis and the median eminence casts a new layer in our understanding of neuroendocrine regulation. The function of neuroendocrine cells and the means by which pulsatile secretion is achieved is best understood for the close relationship between gonadotropin releasing hormone and luteinizing hormone, which is reviewed in detail. The secretion of other neurohormones is less rigid, so the relationship between hypothalamic secretion and the relevant pituitary hormones is more complex.

Developmental variations in environmental influences including endocrine disruptors on pubertal timing and neuroendocrine control: Revision of human observations and mechanistic insight from rodents

Puberty presents remarkable individual differences in timing reaching over 5 years in humans. We put emphasis on the two edges of the age distribution of pubertal signs in humans and point to an extended distribution towards earliness for initial pubertal stages and towards lateness for final pubertal stages. Such distortion of distribution is a recent phenomenon. This suggests changing environmental influences including the possible role of nutrition, stress and endocrine disruptors. Our ability to assess neuroendocrine effects and mechanisms is very limited in humans. Using the rodent as a model, we examine the impact of environmental factors on the individual variations in pubertal timing and the possible underlying mechanisms. The capacity of environmental factors to shape functioning of the neuroendocrine system is thought to be maximal during fetal and early postnatal life and possibly less important when approaching the time of onset of puberty.

Food availability, energetic constraints and reproductive development in a wild seasonally breeding songbird

In many organisms, food availability is a proximate cue that synchronizes seasonal development of the reproductive system with optimal environmental conditions. Growth of the gonads and secondary sexual characteristics is orchestrated by the hypothalamic–pituitary–gonadal (HPG) axis. However, our understanding of the physiological mechanisms by which food availability modulates activity of the HPG axis is limited.

It is thought that many factors, including energetic status, modulate seasonal reproductive activation. We tested the hypothesis that food availability modulates the activity of the HPG axis in a songbird. Specifically, we food‐restricted captive adult male Abert's Towhees Melozone aberti for 2 or 4 weeks during photoinduced reproductive development. A third group (control) received ad libitum food throughout. We measured multiple aspects of the reproductive system including endocrine activity of all three levels of the HPG axis [i.e. hypothalamic gonadotropin‐releasing hormone‐I (GnRH‐I), plasma luteinizing hormone (LH) and testosterone (T)], and gonad morphology. Furthermore, because gonadotropin‐inhibitory hormone (GnIH) and neuropeptide Y (NPY; a potent orexigenic peptide) potentially integrate information on food availability into seasonal reproductive development, we also measured the brain levels of these peptides.

At the hypothalamic level, we detected no effect of food restriction on immunoreactive (ir) GnRH‐I, but the duration of food restriction was inversely related to the size of ir‐GnIH perikarya. Furthermore, the number of ir‐NPY cells was higher in food‐restricted than control birds. Food restriction did not influence photoinduced testicular growth, but decreased plasma LH and T, and width of the cloacal protuberance, an androgen‐sensitive secondary sexual characteristic. Returning birds to ad libitum food availability had no effect on plasma LH or T, but caused the cloacal protuberance to rapidly increase in size to that of ad libitum‐fed birds.

Our results support the tenet that food availability modulates photoinduced reproductive activation. However, they also suggest that this modulation is complex and depends upon the level of the HPG axis considered. At the hypothalamic level, our results are consistent with a role for the GnIH and NPY systems in integrating information on energetic status. There also appears to be a role for endocrine function at the anterior pituitary gland and testicular levels in modulating reproductive development in the light of energetic status and independently of testicular growth.

Rational design of triazololipopeptides analogs of kisspeptin inducing a long-lasting increase of gonadotropins

New potent and selective KISS1R agonists were designed using a combination of rational chemical modifications of the endogenous neuropeptide kisspeptin 10 (KP10). Improved resistance to degradation and presumably reduced renal clearance were obtained by introducing a 1,4-disubstituted 1,2,3-triazole as a proteolysis-resistant amide mimic and a serum albumin-binding motif, respectively. These triazololipopeptides are highly potent full agonists of KISS1R and are >100 selective over the closely related NPFF1R. When injected in ewes with a quiescent reproductive system, the best compound of our series induced a much prolonged increase of luteinizing hormone release compared to KP10 and increased follicle-stimulating hormone plasma concentration. Hence, this KISS1R agonist is a new valuable pharmacological tool to explore the potential of KP system in reproduction control. Furthermore, it represents the first step to develop drugs treating reproductive system disorders due to a reduced activity of the hypothalamo-pituitary-gonadal axis such as delayed puberty, hypothalamic amenorrhea, and hypogonadotropic hypogonadism.

Dissecting the Roles of Gonadotropin-Inhibitory Hormone in Mammals: Studies Using Pharmacological Tools and Genetically Modified Mouse Models

Reproduction is essential for perpetuation of the species and, hence, is controlled by a sophisticated network of regulatory factors of central and peripheral origin that integrate at the hypothalamic-pituitary-gonadal (HPG) axis. Among the central regulators of reproduction, kisspeptins, as major stimulatory drivers of gonadotropin-releasing hormone (GnRH) neurosecretion, have drawn considerable interest in the last decade. However, the dynamic, if not cyclic (in the female), nature of reproductive function and the potency of kisspeptins and other stimulatory signals of the HPG axis make tenable the existence of counterbalance inhibitory mechanisms, which may keep stimulation at check and would allow adaptation of reproductive maturation and function to different endogenous and environmental conditions. In this context, discovery of the gonadotropin-inhibitory hormone (GnIH) in birds, and its mammalian homolog, RFRP, opened up the exciting possibility that this inhibitory signal might operate centrally to suppress, directly or indirectly, GnRH/gonadotropin secretion, thus reciprocally cooperating with other stimulatory inputs in the dynamic regulation of the reproductive hypothalamic-pituitary unit. After more than 15 years of active research, the role of GnIH/RFRP in the control of the HPG axis has been documented in different species. Yet, important aspects of the physiology of this system, especially regarding its relative importance and actual roles in the control of key facets of reproductive function, remain controversial. In the present work, we aim to provide a critical review of recent developments in this area, with special attention to studies in rodent models, using pharmacological tools and functional genomics. In doing so, we intend to endow the reader with an updated view of what is known (and what is not known) about the physiological role of GnIH/RFRP signaling in the control of mammalian reproduction.

Photoperiodic co-regulation of kisseptin, neurokinin B and dynorphin in the hypothalamus of a seasonal rodent

In many species, sexual activity varies on a seasonal basis. Kisspeptin (Kp), a hypothalamic neuropeptide acting as a strong activator of gonadotrophin-releasing hormone neurones, plays a critical role in this adaptive process. Recent studies report that two other neuropeptides, namely neurokinin B (NKB) and dynorphin (DYN), are co-expressed with Kp (and therefore termed KNDy neurones) in the arcuate nucleus and that these peptides are also considered to influence GnRH secretion. The present study aimed to establish whether hypothalamic NKB and DYN expression is photoperiod-dependent in a seasonal rodent, the Syrian hamster, which exhibits robust seasonal rhythms in reproductive activity. The majority of Kp neurones in the arcuate nucleus co-express NKB and DYN and the expression of all three peptides is decreased under a short (compared to long) photoperiod, leading to a 60% decrease in the number of KNDy neurones under photo-inhibitory conditions. In seasonal rodents, RFamide-related peptide (RFRP) neurones of the dorsomedial hypothalamus are also critical for seasonal reproduction. Interestingly, NKB and DYN are also expressed in the dorsomedial hypothalamus but do not co-localise with RFRP-immunoreactive neurones, and the expression of both NKB and DYN is higher under a short photoperiod, which is opposite to the short-day inhibition of RFRP expression. In conclusion, the present study shows that NKB and DYN display different photoperiodic variations in the Syrian hamster hypothalamus. In the arcuate nucleus, NKB and DYN, together with Kp, are down-regulated under a short photoperiod, whereas, in the dorsomedial hypothalamus, NKB and DYN are up-regulated under a short photoperiod.

Physiological roles of gonadotropin-inhibitory hormone signaling in the control of mammalian reproductive axis: studies in the NPFF1 receptor null mouse

RF-amide-related peptide-3 (RFRP-3), the mammalian ortholog of the avian gonadotropin-inhibiting hormone (GnIH), operates via the NPFF1 receptor (NPFF1R) to repress the reproductive axis, therefore acting as counterpart of the excitatory RF-amide peptide, kisspeptin (ligand of Gpr54). In addition, RFRP-3 modulates feeding and might contribute to the integrative control of energy homeostasis and reproduction. Yet, the experimental evidence supporting these putative functions is mostly indirect, and the physiological roles of RFRP-3 remain debatable and obscured by the lack of proper analytical tools and models. To circumvent these limitations, we characterize herein the first mouse line with constitutive inactivation of NPFF1R. Ablation of NPFF1R did not compromise fertility; rather, litters from NPFF1R null mice were larger than those from wild-type animals. Pubertal timing was not altered in NPFF1R deficient mice; yet, pre-pubertal knockout (KO) males displayed elevated LH levels, which normalized after puberty. Adult NPFF1R null male mice showed increased Kiss1 expression in the hypothalamic arcuate nucleus, higher serum FSH levels, and enhanced LH responses to GnRH. However, genetic elimination of NPFF1R was unable to reverse the state of hypogonadism caused by the lack of kisspeptin signaling, as revealed by double NPFF1R/Gpr54 KO mice. NPFF1R null mice displayed altered feedback responses to gonadal hormone withdrawal. In addition, metabolic challenges causing gonadotropin suppression, such as short-term fasting and high-fat diet, were less effective in dampening LH secretion in NPFF1R-deficient male mice, suggesting that absence of this inhibitory pathway partially prevented gonadotropin suppression by metabolic stress. Our data are the first to document the impact of elimination of GnIH signaling on reproductive parameters and their modulation by metabolic challenges. Whereas, in keeping with its inhibitory role, the NPFF1R pathway seems dispensable for preserved puberty and fertility, our results surface different alterations due to the lack of GnIH signaling that prominently include changes in the sensitivity to fasting- and obesity-associated hypogonadotropism.

Hypothalamic Kiss1 and RFRP gene expressions are changed by a high dose of lipopolysaccharide in female rats

Reproductive function is suppressed by several types of stress. Hypothalamic kisspeptin, which is a product of the Kiss1 gene, and GnIH/RFRP have pivotal roles in the regulation of GnRH and gonadotropins through their receptors Kiss1r and GPR147 in many species. However, alterations of these factors under stress conditions have not been fully evaluated. This study investigated the mechanisms of immune stress-induced reproductive dysfunction, especially focusing on the changes of Kiss1 and RFRP gene expression. Serum LH levels and hypothalamic Kiss1 and GnRH mRNA levels were decreased, while hypothalamic RFRP and GPR147 mRNA levels were increased by administration of a high dose of LPS (5mg/kg) in both ovariectomized and gonadal intact female rats. In this condition, Kiss1 and/or RFRP mRNA levels were positively and negatively correlated with GnRH expression, respectively. In contrast, hypothalamic Kiss1, RFRP, and GPR147 mRNA levels were not changed by administration of a moderate dose of LPS (500μg/kg) in ovariectomized rats. Rats with high-dose LPS injection showed more prolonged fever responses and severe anorexia compared with rats with moderate-dose LPS injection, indicating that more energy was used for the immune response in the former. These results suggest that the underlying mechanisms of dysfunction of gonadotropin secretion are changed according to the severity of immune stress, and that changes of some reserved factors, such as kisspeptin and RFRP, begin to participate in the suppression of GnRH and gonadotropin in severe conditions. As reproduction needs a large amount of energy, dysfunction of gonadotropin secretion under immune stress may be a biophylatic mechanism by which more energy is saved for the immune response.

At the crossroads of physiology and ecology: food supply and the timing of avian reproduction

This article is part of a Special Issue “Energy Balance”. The decision of when to breed is crucial to the reproductive success and fitness of seasonally breeding birds. The availability of food for adults prior to breeding has long been thought to play a critical role in timing the initiation of seasonal reproductive events, in particular laying. However, unequivocal evidence for such a role remains limited and the physiological mechanisms by which an increase in food availability results in seasonal activation of the reproductive system are largely speculative. This lack of mechanistic information partly reflects a lack of integration of ecological and physiological approaches to study seasonal reproduction. Indeed, most work pertaining to the role of food availability for adults on the timing of avian reproduction has been ecological and has focused almost exclusively on female traits associated with reproductive timing (e.g., lay date and clutch size). By contrast, most work on the physiological bases of the relationship between food availability and the timing of reproduction has investigated male traits associated with reproductive development (e.g., reproductive hormones and gonadal development). To advance our understanding of these topics, we review the role of proximate factors including food availability, social factors, and ambient temperature in the control of breeding decisions, and discuss the role of three potential candidates (leptin, glucocorticoids, and GnIH-neuropeptide Y) that may mediate the effects of food availability on these decisions. We emphasize that future progress in this area is heavily contingent upon the use of physiology-based approaches and their integration into current ecological frameworks.

Gonadotropin-inhibitory hormone promoter-driven enhanced green fluorescent protein expression decreases during aging in female rats

Gonadotropin-inhibitory hormone (GnIH) neurons project to GnRH neurons to negatively regulate reproductive function. To fully explore the projections of the GnIH neurons, we created transgenic rats carrying an enhanced green fluorescent protein (EGFP) tagged to the GnIH promoter. With these animals, we show that EGFP-GnIH neurons are localized mainly in the dorsomedial hypothalamic nucleus (DMN) and project to the hypothalamus, telencephalon, and diencephalic thalamus, which parallels and confirms immunocytochemical and gene expression studies. We observed an age-related reduction in c-Fos-positive GnIH cell numbers in female rats. Furthermore, GnIH fiber appositions to GnRH neurons in the preoptic area were lessened in middle-aged females (70 weeks old) compared with their younger counterparts (9-12 weeks old). The fiber density in other brain areas was also reduced in middle-aged female rats. The expression of estrogen and progesterone receptors mRNA in subsets of EGFP-GnIH neurons was shown in laser-dissected single EGFP-GnIH neurons. We then examined estradiol-17β and progesterone regulation of GnIH neurons, using c-Fos presence as a marker. Estradiol-17β treatment reduced c-Fos labeling in EGFP-GnIH neurons in the DMN of young ovariectomized adult females but had no effect in middle-aged females. Progesterone had no effect on the number of GnIH cells positive for c-Fos. We conclude that there is an age-related decline in GnIH neuron number and GnIH inputs to GnRH neurons. We also conclude that the response of GnIH neurons to estrogen diminishes with reproductive aging.

Gonadotropin inhibitory hormone (GnIH) as a regulator of gonadotropes

Gonadotropin inhibitory hormone (GnIH) has emerged as a negative regulator of gonadotrope function in a range of species. In rodents, such as rats and mice, GnIH exerts influence upon GnRH cells within the brain. In other species, however, the peptide is secreted into hypophysial portal blood to act on pituitary gonadotropes. In particular, a series of studies in sheep have demonstrated potent actions at the level of the pituitary gland to counteract the function of GnRH in terms of the synthesis and secretion of gonadotropins. This review focuses on the action of GnIH at the level of the gonadotrope.

Paradoxical effect of gonadotrophin-inhibiting hormone to negatively regulate neuropeptide Y neurones in mouse arcuate nucleus

Regulation of reproduction and energy homeostasis are linked, although our understanding of the central neural mechanisms subserving this connection is incomplete. Gonadotrophin-inhibiting hormone (GnIH) is a neuropeptide that negatively regulates reproduction and stimulates food intake. Neuropeptide Y (NPY) and products of the pro-opiomelanocortin (POMC) precursor (β-endorphin melanocortins) are appetite regulating peptides produced in the neurones of the arcuate nucleus; these peptides also regulate reproduction. In the present study, we determined the effects of GnIH on NPY and POMC neurones. Using brain slices from mice with transgenes for fluorescent tags in the two types of neurone and patch clamp electrophysiology, a predominant inhibitory effect of GnIH was observed. GnIH (100 nM) inhibited the firing rate in POMC cells, confirming the results of previous studies and consistent with the stimulatory effect of GnIH on food intake. Paradoxically (i.e. because both GnIH and NPY stimulate food intake), GnIH also had a predominantly inhibitory effect on action potential activity in NPY cells. GnIH also inhibited the secretion of NPY and α-melanocyte-stimulating hormone secretion in incubated hypothalamic blocks. GnIH (100 ng) injected into the cerebral ventricles of mice did not increase the number of NPY cells that were positively immunostained for c-Fos. Finally, dual label immunocytochemistry showed that 20% of NPY neurones had close contacts from GnIH fibres/varicosities. In conclusion, we confirm a negative effect of GnIH on POMC cells and demonstrate a paradoxical reduction of electrophysiological and functional activity in NPY cells.

Neurobiological study of fish brains gives insights into the nature of gonadotropin-releasing hormone 1-3 neurons

Accumulating evidence suggests that up to three different molecular species of GnRH peptides encoded by different paralogs of gnrh genes are expressed by anatomically distinct groups of GnRH neurons in the brain of one vertebrate species. They are called gnrh1, gnrh2, and gnrh3. Recent evidence from molecular, anatomical, and physiological experiments strongly suggests that each GnRH system functions differently. Here, we review recent advancement in the functional studies of the three different GnRH neuron systems, mainly focusing on the electrophysiological analysis of the GnRH-green fluorescent protein (GFP) transgenic animals. The introduction of GFP-transgenic animals for the electrophysiological analysis of GnRH neurons greatly advanced our knowledge on their anatomy and electrophysiology, especially of gnrh1 neurons, which has long defied detailed electrophysiological analysis of single neurons because of their small size and scattered distribution. Based on the results of recent studies, we propose that different electrophysiological properties, especially the spontaneous patterns of electrical activities and their time-dependent changes, and the axonal projections characterize the different functions of GnRH1-3 neurons; GnRH1 neurons act as hypophysiotropic neuroendocrine regulators, and GnRH2 and GnRH3 neurons act as neuromodulators in wide areas of the brain.

An eGFP-expressing subpopulation of growth hormone secretagogue receptor cells are distinct from kisspeptin, tyrosine hydroxylase, and RFamide-related peptide neurons in mice

Ghrelin acts on the growth hormone secretagogue receptor (GHSR) in the brain to elicit changes in physiological functions. It is associated with the neural control of appetite and metabolism, however central ghrelin also affects fertility. Central ghrelin injection in rats suppresses luteinizing hormone (LH) concentrations and pulse frequency. Although ghrelin suppresses LH and regulates kisspeptin mRNA in the anteroventral periventricular/periventricular nucleus (AVPV/PeN), there is no neuroanatomical evidence linking GHSR neural circuits to kisspeptin neurons. In this study, we first determined coexpression of GHSR and GnRH neurons using a GHSR-eGFP reporter mouse line. Using dual-label immunohistochemistry, we saw no coexpression. GHSR-eGFP expressing cells were present in the AVPV/PeN and over 90% of these expressed estrogen receptor-α (ERα). Despite this, we observed no evidence of GHSR-eGFP/kisspeptin coexpressing neurons in the AVPV/PeN. To further examine the phenotype of GHSR-eGFP cells in the AVPV/PeN, we determined coexpression with tyrosine hydroxylase (TH) and showed virtually no coexpression in the AVPV/PeN (<2%). We also observed no coexpression of GHSR-eGFP and RFamide-related peptide-3 (RFRP3) neurons in the dorsomedial hypothalamic nucleus. Importantly, we observed that approximately half of the GHSR-eGFP cells in the AVPV coexpressed Ghsr mRNA (as determined by in situ hybridization) so these data should be interpreted accordingly. Although ghrelin influences the hypothalamic reproductive axis, our data using a GHSR-eGFP reporter suggests ghrelin regulates neurons expressing ERα but does not directly act on GnRH, kisspeptin, TH, or RFRP3 neurons, as little or no GHSR-eGFP coexpression was observed.

Exogenous T3 Elicits Long Day–Like Alterations in Testis Size and the RFamides Kisspeptin and Gonadotropin-Inhibitory Hormone in Short-Day Siberian Hamsters

Siberian hamsters ( Phodopus sungorus) exhibit robust seasonal rhythms of reproduction driven by changes in day length. Day length is encoded endogenously by the duration of nocturnal melatonin (Mel) secretion from the pineal gland. Short duration Mel signals stimulate whereas long duration Mel signals inhibit reproduction. The mechanism by which Mel regulates the reproductive axis has not been fully characterized. In Siberian hamsters, the thyroid hormone triiodothyronine (T3) is thought to be part of the photoperiodic mechanism. The availability of T3 is decreased in hamsters housed in short day lengths, and injections of exogenous T3 stimulate testicular growth in short-day (SD) Siberian hamsters. Thus, T3 acts as a neuroendocrine intermediate between the Mel rhythm and the reproductive axis. The RFamides kisspeptin (Kiss1) and gonadotropin-inhibitory hormone (GnIH) also act as a link between the Mel rhythm and the reproductive axis. Expression of both of these neuropeptides is regulated by photoperiod and Mel. Kiss1 stimulates, and GnIH inhibits, the reproductive axis in long-day housed hamsters. It remains unknown whether T3 acts through changes in RFamide expression in the regulation of reproduction or whether these molecules act independently of one another. We tested the hypothesis that exogenous T3 administered to SD hamsters, a treatment that stimulates testicular growth, would also result in alterations in the patterns of Kiss1- and GnIH-immunoreactivity. Administration of T3 to SD hamsters resulted in significant testicular growth as well as a long day–like pattern of RFamide peptide expression. Thus, exogenous T3 elicited increased numbers of Kiss1-positive cells in the hypothalamic anteroventral periventricular nucleus, decreased numbers of Kiss1-positive cells in the arcuate nucleus, and a greater number of GnIH-positive cells in the dorsomedial hypothalamus compared with SD controls. The results are consistent with the hypothesis that T3 elicits alterations in the reproductive axis through alterations in RFamide peptide expression.

Review: regulatory mechanisms of gonadotropin-inhibitory hormone (GnIH) synthesis and release in photoperiodic animals

Gonadotropin-inhibitory hormone (GnIH) is a novel hypothalamic neuropeptide that was discovered in quail as an inhibitory factor for gonadotropin release. GnIH inhibits gonadotropin synthesis and release in birds through actions on gonadotropin-releasing hormone (GnRH) neurons and gonadotropes, mediated via the GnIH receptor (GnIH-R), GPR147. Subsequently, GnIH was identified in mammals and other vertebrates. As in birds, mammalian GnIH inhibits gonadotropin secretion, indicating a conserved role for this neuropeptide in the control of the hypothalamic-pituitary-gonadal (HPG) axis across species. Identification of the regulatory mechanisms governing GnIH expression and release is important in understanding the physiological role of the GnIH system. A nocturnal hormone, melatonin, appears to act directly on GnIH neurons through its receptor to induce expression and release of GnIH in quail, a photoperiodic bird. Recently, a similar, but opposite, action of melatonin on the inhibition of expression of mammalian GnIH was shown in hamsters and sheep, photoperiodic mammals. These results in photoperiodic animals demonstrate that GnIH expression is photoperiodically modulated via a melatonin-dependent process. Recent findings indicate that GnIH may be a mediator of stress-induced reproductive disruption in birds and mammals, pointing to a broad role for this neuropeptide in assessing physiological state and modifying reproductive effort accordingly. This paper summarizes the advances made in our knowledge regarding the regulation of GnIH synthesis and release in photoperiodic birds and mammals. This paper also discusses the neuroendocrine integration of environmental signals, such as photoperiods and stress, and internal signals, such as GnIH, melatonin, and glucocorticoids, to control avian and mammalian reproduction.

Distribution and sequence of gonadotropin-inhibitory hormone and its potential role as a molecular link between feeding and reproductive systems in the Pekin duck (Anas platyrhynchos domestica)

The reproductive status of adult Pekin drakes is very sensitive to nutritional status. Thus, the purpose of this study was to increase our understanding of the neurobiology underlying the depressive effect of fasting on the secretion of reproductive hormones. It was hypothesized that this effect was mediated by gonadotropin-inhibitory hormone (GnIH). Networks of GnIH fibers were present throughout the diencephalon, and cell bodies were present primarily, in the hypothalamic paraventricular nucleus (PVN). The duck GnIH gene was cloned and sequenced and found to encode GnIH and two GnIH-related peptides (GnIH-RP1, GnIH-RP2) which have a similar identity to those found in other avian species. Intracerebroventricular injection of GnIH, but not of GnIH-RP1, depressed plasma LH and stimulated feeding. Fasting for 48h depressed plasma LH and induced fos expression in about half the population of GnIH-ir neurons. These data suggest that GnIH neurons are mediators between feeding and reproductive systems in Pekin drakes.

Neuropeptide RFRP inhibits the pacemaker activity of terminal nerve GnRH neurons

The terminal nerve gonadotropin-releasing hormone (TN-GnRH) neurons show spontaneous pacemaker activity whose firing frequency is suggested to regulate the release of GnRH peptides and control motivation for reproductive behaviors. Previous studies of the electrophysiological properties of TN-GnRH neurons reported excitatory modulation of pacemaker activity by auto/paracrine and synaptic modulations, but inhibition of pacemaker activity has not been reported to date. Our recent study suggests that neuropeptide FF, a type of Arg-Phe-amide (RFamide) peptide expressed in TN-GnRH neurons themselves, inhibits the pacemaker activity of TN-GnRH neurons in an auto- and paracrine manner. In the present study, we examined whether RFamide-related peptides (RFRPs), which are produced in the hypothalamus, modulate the pacemaker activity of TN-GnRH neurons as candidate inhibitory synaptic modulators. Bath application of RFRP2, among the three teleost RFRPs, decreased the frequency of firing of TN-GnRH neurons. This inhibition was diminished by RF9, a potent antagonist of GPR147/74, which are candidate RFRP receptors. RFRP2 changed the conductances for Na(+) and K(+). The reversal potential for RFRP2-induced current was altered by inhibitors of the transient receptor potential canonical (TRPC) channel (La(3+) and 2-aminoethoxydiphenyl borate) and by a less selective blocker of voltage-independent K(+) channels (Ba(2+)). By comparing the current-voltage relationship in artificial cerebrospinal fluid with that under each drug, the RFRP2-induced current was suggested to consist of TRPC channel-like current and voltage-independent K(+) current. Therefore, synaptic release of RFRP2 from hypothalamic neurons is suggested to inhibit the pacemaker activity of TN-GnRH neurons by closing TRPC channels and opening voltage-independent K(+) channels. This novel pathway may negatively regulate reproductive behaviors.

Stress regulation of kisspeptin in the modulation of reproductive function

Stressful stimuli abound in modern society and have shaped evolution through altering reproductive development, behavior, and physiology. The recent identification of kisspeptin as an important component of the hypothalamic regulatory circuits involved in reproductive homeostasis sparked a great deal of research interest that subsequently implicated kisspeptin signaling in the relay of metabolic, environmental, and physiological cues to the hypothalamo-pituitary-gonadal axis. However, although it is widely recognized that exposure to stress profoundly impacts on reproductive function, the roles of kisspeptin within the complex mechanisms underlying stress regulation of reproduction remain poorly understood. We and others have recently demonstrated that a variety of experimental stress paradigms downregulate the expression of kisspeptin ligand and receptor within the reproductive brain. Coincidently, these stressors also inhibit gonadotropin secretion and delay pubertal onset-processes that rely on kisspeptin signaling. However, a modest literature is inconsistent with an exclusively suppressive influence of stress on the reproductive axis and suggests that complicated neural interactions and signaling mechanisms translate the stress response into reproductive perturbations. The purpose of this chapter is to review the evidence for a novel role of kisspeptin signaling in the modulation of reproductive function by stress and to broaden the understanding of this timely phenomenon.

Structure, synthesis, and phylogeny of kisspeptin and its receptor

The kisspeptin system is considered to be essential for successful mammalian reproduction. In addition to the Kiss1 peptide, Kiss2, the product of kiss2 (the kiss1 paralogue), has also been shown to activate kisspeptin receptor signaling pathways in nonmammalian species. Furthermore, in nonmammalian species, there are two subtypes of receptors, Gpr54-1 (known as GPR54 or Kiss1R in mammals) and Gpr54-2. Although complete understanding of the two kisspeptin-two kisspeptin receptor systems in vertebrates is not so simple, a careful examination of the phylogeny of their genes may provide insights into the functional generality and differences among the kisspeptin systems in different animal phyla. In this chapter, we first discuss the structure of kisspeptin ligands, Kiss1 and Kiss2, and their characteristics as physiologically active peptides. Then, we discuss the evolutionary traits of kiss1 and kiss2 genes and their receptor genes, gpr54-1 and gpr54-2. It appears that each animal species has selected either kiss1 or kiss2 rather randomly, leading us to propose that some of the important characteristics of kisspeptin neurons, such as steroid sensitivity and the anatomical relationship with the hypophysiotropic GnRH1 neurons, may be the keys to understanding the general functions of different kisspeptin neuronal populations throughout vertebrates. Species differences in kiss1/kiss2 may also provide insights into the evolutionary mechanisms of paralogous gene-expressing neuronal systems. Finally, because kisspeptins belong to one of the members of the RFamide peptide families, we discuss the functional divergence of kisspeptins from the other RFamide peptides, which may be explained from phylogenetic viewpoints.

Gonadotropin-inhibitory hormone (GnIH) and its receptor in the female pig: cDNA cloning, expression in tissues and expression pattern in the reproductive axis during the estrous cycle

Since its discovery, gonadotropin-inhibitory hormone (GnIH) has appeared to act as a key neuropeptide in the control of vertebrate reproduction. GnIH acts via the novel G protein-coupled receptor 147 (GPR147) to inhibit gonadotropin release and synthesis. To determine the physiological functions of GnIH in the pig, a study was conducted to clone and sequence the cDNA of the GnIH precursor and GPR147. Our results demonstrated that the cloned pig GnIH precursor cDNA encoded three LPXRF and that its receptor possessed typical transmembrane features. Subsequently, tissue expression studies revealed that GnIH was mainly expressed in the brain, corresponding largely with the tissue expression patterns of GPR147 in the pig. The expression patterns in the reproductive axis of the female pig across the estrous cycle were also systemically investigated. The hypothalamic levels of both GnIH and its receptor mRNA were lowest in estrus and peaked in the proestrus and diestrus phases. The highest pituitary GnIH mRNA level was detected in the metestrus, and its receptor displayed a somewhat similar pattern of expression to that of the ligand. However, the expression patterns of GnIH and GPR147 were negatively correlated in the ovary. Immunolocalization in the ovary during the estrous cycle revealed that the immunoreactivities of GnIH and GPR147 were mainly localized in the granulosa and theca cells of the antral follicles during proestrus and estrus and in the luteal cells during metestrus and diestrus. Taken together, this research provided molecular and morphological data for further study of GnIH in the pig.

Gonadotropin-inhibitory hormone (GnIH): discovery, progress and prospect

A hypothalamic neuropeptide, gonadotropin-releasing hormone (GnRH), is the primary factor regulating gonadotropin secretion. An inhibitory hypothalamic neuropeptide for gonadotropin secretion was, until recently, unknown, although gonadal sex steroids and inhibin can modulate gonadotropin secretion. Findings from the last decade, however, indicate that GnRH is not the sole hypothalamic regulatory neuropeptide of vertebrate reproduction, with gonadotropin-inhibitory hormone (GnIH) playing a key role in the inhibition of reproduction. GnIH was originally identified in birds and subsequently in mammals and other vertebrates. GnIH acts on the pituitary and on GnRH neurons in the hypothalamus via a novel G protein-coupled receptor (GPR147). GnIH decreases gonadotropin synthesis and release, inhibiting gonadal development and maintenance. Such a down-regulation of the hypothalamo-pituitary-gonadal (HPG) axis may be conserved across vertebrates. Recent evidence further indicates that GnIH operates at the level of the gonads as an autocrine/paracrine regulator of steroidogenesis and gametogenesis. More recent evidence suggests that GnIH also acts both upstream of the GnRH system and at the level of the gonads to appropriately regulate reproductive activity across the seasons and during times of stress. The discovery of GnIH has fundamentally changed our understanding of hypothalamic control of reproduction. This review summarizes the discovery, progress and prospect of GnIH, a key regulator of vertebrate reproduction.