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

WITHDRAWN: Distribution of the Novel RFRP-3/receptors system in the epididymis of the seasonal desert rodent, Gerbillus tarabuli, during sexual activity

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Chemogenetic Activation of RFRP Neurons Reduces LH Pulse Frequency in Female but not Male Mice

Context

The neuropeptide RFRP-3 (RFamide-related peptide-3) is thought to play a role in the negative regulation of fertility. However, the exogenous administration of RFRP-3 yields varying results depending on the dose and route of administration, sex of the subject, and many other variables. Manipulation of in vivo neuronal activity using DREADDs (designer receptor exclusively activated by designer drugs) technology enables investigation of cell type-specific neuronal activation in a manner that better reflects endogenous neuronal activity.

Objective

To test the effects of RFRP neuronal activation on pulsatile luteinizing hormone (LH) secretion.

Methods

We generated mice expressing the stimulatory hM3Dq designer receptor exclusively in RFRP cells using 2 different Cre-loxP-mediated approaches: (1) we bred mice to express hM3Dq in all Rfrp-Cre-expressing cells, including some that transiently expressed Rfrp-Cre neonatally (RFRP × hM3Dq mice), and (2) we stereotaxically injected Cre-dependent hM3Dq into the dorsomedial nucleus of RFRP-Cre mice to drive hM3Dq expression exclusively in a subpopulation of adult Rfrp-Cre neurons (RFRP-AAV-hM3Dq mice). We then investigated the effects of acute hM3Dq activation on LH pulse frequency in RFRP × hM3Dq mice, RFRP-AAV-hM3Dq mice, and their respective controls.

Results

In both female RFRP × hM3Dq and RFRP-AAV-hM3Dq mice, chemogenetic activation of Cre-driven hM3Dq led to a significant 35% to 50% reduction in LH pulse frequency compared with controls, while no differences in pulse amplitude or mean LH concentration were observed. In marked contrast, RFRP activation did not cause any changes to LH pulse dynamics in male mice.

Conclusions

These data show for the first time that activation of neurons that have expressed Rfrp, or of a subset of adult RFRP neurons, can independently suppress LH pulsatility in female, but not male mice.

The Role of RFRP Neurons in the Allostatic Control of Reproductive Function

Reproductive function is critical for species survival; however, it is energetically costly and physically demanding. Reproductive suppression is therefore a physiologically appropriate adaptation to certain ecological, environmental, and/or temporal conditions. This 'allostatic' suppression of fertility enables individuals to accommodate unfavorable reproductive circumstances and safeguard survival. The mechanisms underpinning this reproductive suppression are complex, yet culminate with the reduced secretion of gonadotropin-releasing hormone (GnRH) from the hypothalamus, which in turn suppresses gonadotropin release from the pituitary, thereby impairing gonadal function. The focus of this review will be on the role of RFamide-related peptide (RFRP) neurons in different examples of allostatic reproductive suppression. RFRP neurons release the RFRP-3 peptide, which negatively regulates GnRH neurons and thus appears to act as a 'brake' on the neuroendocrine reproductive axis. In a multitude of predictable (e.g., pre-puberty, reproductive senescence, and seasonal or lactational reproductive quiescence) and unpredictable (e.g., metabolic, immune and/or psychosocial stress) situations in which GnRH secretion is suppressed, the RFRP neurons have been suggested to act as modulators. This review examines evidence for and against these roles.

Circadian and kisspeptin regulation of the preovulatory surge

Fertility in mammals is ultimately controlled by a small population of neurons - the gonadotropin-releasing hormone (GnRH) neurons - located in the ventral forebrain. GnRH neurons control gonadal function through the release of GnRH, which in turn stimulates the secretion of the anterior pituitary gonadotropins luteinizing hormone (LH) and follicle-stimulating hormone (FSH). In spontaneous ovulators, ovarian follicle maturation eventually stimulates, via sex steroid feedback, the mid-cycle surge in GnRH and LH secretion that causes ovulation. The GnRH/LH surge is initiated in many species just before the onset of activity through processes controlled by the central circadian clock, ensuring that the neuroendocrine control of ovulation and sex behavior are coordinated. This review aims to give an overview of anatomical and functional studies that collectively reveal some of the mechanisms through which the central circadian clock regulates GnRH neurons and their afferent circuits to drive the preovulatory surge.

Hypothalamic Kisspeptin Neurons: Integral Elements of the GnRH System

Highly sophisticated and synchronized interactions of various cells and hormonal signals are required to make organisms competent for reproduction. GnRH neurons act as a common pathway for multiple cues for the onset of puberty and attaining reproductive function. GnRH is not directly receptive to most of the signals required for the GnRH secretion during the various phases of the ovarian cycle. Kisspeptin neurons of the hypothalamus convey these signals required for the synchronized release of the GnRH. The steroid-sensitive anteroventral periventricular nucleus (AVPV) kisspeptin and arcuate nucleus (ARC) KNDy neurons convey steroid feedback during the reproductive cycle necessary for GnRH surge and pulse, respectively. AVPV region kisspeptin neurons also communicate with nNOS synthesizing neurons and suprachiasmatic nucleus (SCN) neurons to coordinate the process of the ovarian cycle. Neurokinin B (NKB) and dynorphin play roles in the GnRH pulse stimulation and inhibition, respectively. The loss of NKB and kisspeptin function results in the development of neuroendocrine disorders such as hypogonadotropic hypogonadism (HH) and infertility. Ca²⁺ signaling is essential for GnRH pulse generation, which is propagated through gap junctions between astrocytes-KNDy and KNDy-KNDy neurons. Impaired functioning of KNDy neurons could develop the characteristics associated with polycystic ovarian syndrome (PCOS) in rodents. Kisspeptin-increased synthesis led to excessive secretion of the LH associated with PCOS. This review provides the latest insights and understanding into the role of the KNDy and AVPV/POA kisspeptin neurons in GnRH secretion and PCOS.

Circadian Regulation of Hormonal Timing and the Pathophysiology of Circadian Dysregulation

Circadian rhythms are endogenously generated, daily patterns of behavior and physiology that are essential for optimal health and disease prevention. Disruptions to circadian timing are associated with a host of maladies, including metabolic disease and obesity, diabetes, heart disease, cancer, and mental health disturbances. The circadian timing system is hierarchically organized, with a master circadian clock located in the suprachiasmatic nucleus (SCN) of the anterior hypothalamus and subordinate clocks throughout the CNS and periphery. The SCN receives light information via a direct retinal pathway, synchronizing the master clock to environmental time. At the cellular level, circadian rhythms are ubiquitous, with rhythms generated by interlocking, autoregulatory transcription-translation feedback loops. At the level of the SCN, tight cellular coupling maintains rhythms even in the absence of environmental input. The SCN, in turn, communicates timing information via the autonomic nervous system and hormonal signaling. This signaling couples individual cellular oscillators at the tissue level in extra-SCN brain loci and the periphery and synchronizes subordinate clocks to external time. In the modern world, circadian disruption is widespread due to limited exposure to sunlight during the day, exposure to artificial light at night, and widespread use of light-emitting electronic devices, likely contributing to an increase in the prevalence, and the progression, of a host of disease states. The present overview focuses on the circadian control of endocrine secretions, the significance of rhythms within key endocrine axes for typical, homeostatic functioning, and implications for health and disease when dysregulated. © 2022 American Physiological Society. Compr Physiol 12: 1-30, 2022.

GnRH and the photoperiodic control of seasonal reproduction: Delegating the task to kisspeptin and RFRP-3

Synchronization of mammalian breeding activity to the annual change of photoperiod and environmental conditions is of the utmost importance for individual survival and species perpetuation. Subsequent to the early 1960s, when the central role of melatonin in this adaptive process was demonstrated, our comprehension of the mechanisms through which light regulates gonadal activity has increased considerably. The current model for the photoperiodic neuroendocrine system points to pivotal roles for the melatonin-sensitive pars tuberalis (PT) and its seasonally-regulated production of thyroid-stimulating hormone (TSH), as well as for TSH-sensitive hypothalamic tanycytes, radial glia-like cells located in the basal part of the third ventricle. Tanycytes respond to TSH through increased expression of thyroid hormone (TH) deiodinase 2 (Dio2), which leads to heightened production of intrahypothalamic triiodothyronine (T3) during longer days of spring and summer. There is strong evidence that this local, long-day driven, increase in T3 links melatonin input at the PT to gonadotropin-releasing hormone (GnRH) output, to align breeding with the seasons. The mechanism(s) through which T3 impinges upon GnRH remain(s) unclear. However, two distinct neuronal populations of the medio-basal hypothalamus, which express the (Arg)(Phe)-amide peptides kisspeptin and RFamide-related peptide-3, appear to be well-positioned to relay this seasonal T3 message towards GnRH neurons. Here, we summarize our current understanding of the cellular, molecular and neuroendocrine players, which keep track of photoperiod and ultimately govern GnRH output and seasonal breeding.

The electrophysiologic properties of gonadotropin-releasing hormone neurons

For about two decades, recordings of identified gonadotropin-releasing hormone (GnRH) neurons have provided a wealth of information on their properties. We describe areas of consensus and debate the intrinsic electrophysiologic properties of these cells, their response to fast synaptic and neuromodulatory input, Ca2+ imaging correlates of action potential firing, and signaling pathways regulating these aspects. How steroid feedback and development change these properties, functions of GnRH neuron subcompartments and local networks, as revealed by chemo- and optogenetic approaches, are also considered.

Central and peripheral neuropeptide RFRP-3: A bridge linking reproduction, nutrition, and stress response

This article is an amalgamation of the current status of RFRP-3 (GnIH) in reproduction and its association with the nutrition and stress-mediated changes in the reproductive activities. GnIH has been demonstrated in the hypothalamus of all the vertebrates studied so far and is a well-known inhibitor of GnRH mediated reproduction. The RFRP-3 neurons interact with the other hypothalamic neurons and the hormonal signals from peripheral organs for coordinating the nutritional, stress, and environmental associated changes to regulate reproduction. RFRP-3 has also been shown to regulate puberty, reproductive cyclicity and senescence depending upon the nutritional status. A favourable nutritional status and the environmental cues which are permissive for the successful breeding and pregnancy outcome keep RFRP-3 level low, whereas unfavourable nutritional status and stressful conditions increase the expression of RFRP-3 which impairs the reproduction. Still our knowledge about RFRP-3 is incomplete regarding its therapeutic application for nutritional or stress-related reproductive disorders.

Age-dependent change of RFRP-3 neuron numbers and innervation in female mice

In female mammals, reproductive senescence is a complex process involving progressive ovarian dysfunction, associated with altered central control of the hypothalamic-pituitary-gonadal axis and desynchronization of the circadian system. The objective of this study was to investigate age-dependent changes in the daily regulation of Arg-Phe amide-related peptide-3 (RFRP-3), a hypothalamic peptide involved in reproduction, in female C57BL/6 J mice of different age groups (4, 13, and 19 months old) sampled at their diestrus stage. We found an age-dependent decrease in the total number of RFRP-3 neurons and in the relative number of activated (i.e. c-Fos-positive) RFRP-3 neurons. RFRP-3 neuronal activation exhibited a daily variation in young and middle-aged mice, which was abolished in 19-month-old mice. We also found a daily variation in the number of RFRP-3 neurons receiving close vasopressin (AVP)- and vasoactive intestinal peptide (VIP)-ergic fiber appositions in mice aged 4 and 13 months, but not in 19-month-old mice. However, we found no daily or age-dependent changes in the AVP and VIP fiber density in the dorsomedial hypothalamus. Plasma LH levels were similar in mice aged 4 and 13 months, but were markedly increased in 19-month-old mice. The present findings indicate that the number of RFRP-3 positive neurons is downregulated during old age and that the daily changes in their innervation by the circadian peptides AVP and VIP are abolished. This age-associated reduced (rhythmic) activity of the inhibitory RFRP-3 system could be implicated in the elevated LH secretion observed during reproductive senescence.

Male subfertility effects of sub-chronic ethanol exposure during stress in a rat model

BACKGROUND

Stressful conditions increase alcohol consumption in men. Clinical studies link disruption of the neuroendocrine stress system with alcoholism, but the effect of alcohol in a stress condition on male fertility is still relatively poorly understood. This project was undertaken to evaluate the effect of sub-chronic alcohol in a stress condition on male fertility in a rat model.

METHODS

Male Sprague-Dawley rats were randomly divided into a control group, a stress group that was exposed to restraint stress, an ethanol group that was injected with ethanol daily, and a stress + ethanol group that was injected with ethanol daily and was exposed to restraint stress, simultaneously. Furthermore, testis tissue was evaluated histomorphometrically and immunohistochemically for apoptosis using a TUNEL assay after 12 days. Epididymis sperm analysis was done. Blood cortisol and testosterone were measured and expression of hypothalamic kisspeptin (Kiss1), RFRP-3, and MC4R mRNA were evaluated.

RESULTS

Ethanol exposure during restraint stress did not alter body weight. Ethanol exposure decreased the cellular diameter and area, and stress increased the cellular diameter and area, in comparison with the control group. In the stress group, in comparison with the other groups, the number of seminiferous tubules decreased and the numerical density of seminiferous tubules increased. In addition, ethanol exposure and/or stress reduced semen analysis parameters (sperm viability and motility), but did not change serum testosterone concentrations. Apoptosis increased in spermatogonia with ethanol exposure, but spermatocytes were not affected. Our data present the novel finding that ethanol and stress reduced hypothalamic Kiss1 mRNA expression, while ethanol exposure decreased hypothalamic RFRP-3 and MC4R mRNA expression.

CONCLUSIONS

Ethanol decreased cortisol hormone level during the restraint stress condition and attenuated hypothalamic reproductive-related gene expressions. Therefore, ethanol exposure may induce reduction of sperm viability, increased sperm mortality, and increased apoptosis, with long-term effects, and may induce permanent male subfertility.

Gene expression pattern of Kisspeptin and RFamide-related peptide (Rfrp) in the male Damaraland mole-rat hypothalamus

Damaraland mole-rats (Fukomys damarensis) are cooperatively breeding, subterranean mammals, which exhibit high reproductive skew. Reproduction is monopolized by the dominant female of the group, while subordinates are anovulatory. Similarly, male subordinates within the colony show no sexual behaviour although they have functional gonads and do not differ from reproductive males in circulating levels of pituitary hormones and testosterone. However, reproductive status affects the neuroendocrine phenotype of males with breeders possessing increased mRNA expression of androgen and progesterone receptors compared to non-breeders in several forebrain regions implicated in the regulation of reproductive behaviour. The RFamide peptides kisspeptin and RFRP-3, encoded by the Kiss1 and Rfrp gene, are considered potent regulators of gonadotropin release. In females, reproductive inhibition is associated with reduced Kiss1 expression within the arcuate nucleus (ARC) and increased Rfrp expression in the anterior hypothalamus. To assess whether differential gene expression of Kiss1 and Rfrp underlies the difference in reproductive behaviour of males, we studied the expression of both genes by means of in situ hybridisation in wild-caught male Damaraland mole-rats with different reproductive status. The distribution of Kiss1 and Rfrp within the hypothalamus was found to be similar to females. Quantification of the Kiss1 hybridisation signal revealed no significant differences in relation to reproductive status. However, there was a significant positive correlation between testis mass and the number of Kiss1-expressing cells in the ARC and the mRNA content per cell, respectively. Analysis of the Rfrp hybridisation signal along the rostro-caudal extent of the hypothalamus revealed that non-reproductive males possessed an increased number of Rfrp-expressing cells at the level of the dorsomedial hypothalamic nucleus (DMH) than reproductive males. These data suggest the Kiss1 expression within the ARC is not associated with reproductive quiescence in subordinate males but instead, inhibitory effects may be mediated by Rfrp-expressing cells in the DMH.

Neuroendocrine interactions of the stress and reproductive axes

Reproduction is controlled by a sequential regulation of the hypothalamo-pituitary-gonadal (HPG) axis. The HPG axis integrates multiple inputs to maintain proper reproductive functions. It has long been demonstrated that stress alters fertility. Nonetheless, the central mechanisms of how stress interacts with the reproductive system are not fully understood. One of the major pathways that is activated during the stress response is the hypothalamo-pituitary-adrenal (HPA) axis. In this review, we discuss several aspects of the interactions between these two neuroendocrine systems to offer insights to mechanisms of how the HPA and HPG axes interact. We have also included discussions of other systems, for example GABA-producing neurons, where they are informative to the overall picture of stress effects on reproduction.

WITHDRAWN: Age-dependent modulation of RFRP-3 neurons in female mice

This article has been withdrawn: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been withdrawn at the request of the editor and publisher. The publisher regrets that an error occurred which led to the premature publication of this paper. This error bears no reflection on the article or its authors. The publisher apologizes to the authors and the readers for this unfortunate error.

Role of central kisspeptin and RFRP-3 in energy metabolism in the male Wistar rat

Kisspeptin (Kp) and (Arg)(Phe) related peptide 3 (RFRP-3) are two RF-amides acting in the hypothalamus to control reproduction. In the past 10 years, it has become clear that, apart from their role in reproductive physiology, both neuropeptides are also involved in the control of food intake, as well as glucose and energy metabolism. To investigate further the neural mechanisms responsible for these metabolic actions, we assessed the effect of acute i.c.v. administration of Kp or RFRP-3 in ad lib. fed male Wistar rats on feeding behaviour, glucose and energy metabolism, circulating hormones (luteinising hormone, testosterone, insulin and corticosterone) and hypothalamic neuronal activity. Kp increased plasma testosterone levels, had an anorexigenic effect and increased lipid catabolism, as attested by a decreased respiratory exchange ratio (RER). RFRP-3 also increased plasma testosterone levels but did not modify food intake or energy metabolism. Both RF-amides increased endogenous glucose production, yet with no change in plasma glucose levels, suggesting that these peptides provoke not only a release of hepatic glucose, but also a change in glucose utilisation. Finally, plasma insulin and corticosterone levels did not change after the RF-amide treatment. The Kp effects were associated with an increased c-Fos expression in the median preoptic area and a reduction in pro-opiomelanocortin immunostaining in the arcuate nucleus. No effects on neuronal activation were found for RFRP-3. Our results provide further evidence that Kp is not only a very potent hypothalamic activator of reproduction, but also part of the hypothalamic circuit controlling energy metabolism.

An Inhibitory Circuit From Brainstem to GnRH Neurons in Male Mice: A New Role for the RFRP Receptor

RFamide-related peptides (RFRPs, mammalian orthologs of gonadotropin-inhibitory hormone) convey circadian, seasonal, and social cues to the reproductive system. They regulate gonadotropin secretion by modulating gonadotropin-releasing hormone (GnRH) neurons via the RFRP receptor. Mice lacking this receptor are fertile but exhibit abnormal gonadotropin responses during metabolic challenges, such as acute fasting, when the normal drop in gonadotropin levels is delayed. Although it is known that these food intake signals to the reproductive circuit originate in the nucleus tractus solitarius (NTS) in the brainstem, the phenotype of the neurons conveying the signal remains unknown. Given that neuropeptide FF (NPFF), another RFamide peptide, resides in the NTS and can bind to the RFRP receptor, we hypothesized that NPFF may regulate GnRH neurons. To address this question, we used a combination of techniques: cell-attached electrophysiology on GnRH-driven green fluorescent protein-tagged neurons in acute brain slices; calcium imaging on cultured GnRH neurons; and immunostaining on adult brain tissue. We found (1) NPFF inhibits GnRH neuron excitability via the RFRP receptor and its canonical signaling pathway (Gi/o protein and G protein-coupled inwardly rectifying potassium channels), (2) NPFF-like fibers in the vicinity of GnRH neurons coexpress neuropeptide Y, (3) the majority of NPFF-like cell bodies in the NTS also coexpress neuropeptide Y, and (4) acute fasting increased NPFF-like immunoreactivity in the NTS. Together these data indicate that NPFF neurons within the NTS inhibit GnRH neurons, and thus reproduction, during fasting but prior to the energy deficit.

Daily and Estral Regulation of RFRP-3 Neurons in the Female Mice

Female reproductive success relies on proper integration of circadian- and ovarian- signals to the hypothalamic-pituitary-gonadal axis in order to synchronize the preovulatory LH surge at the end of the ovarian follicular stage with the onset of the main active period. In this study, we used a combination of neuroanatomical and electrophysiological approaches to assess whether the hypothalamic neurons expressing Arg-Phe amide-related peptide (RFRP-3), a gonadotropin inhibitory peptide, exhibit daily and estrous stage dependent variations in female mice. Furthermore, we investigated whether arginine vasopressin (AVP), a circadian peptide produced by the suprachiamatic nucleus regulates RFRP-3 neurons. The number of c-Fos–positive RFRP-3 immunoreactive neurons is significantly reduced at the day-to-night transition with no difference between diestrus and proestrus. Contrastingly, RFRP neuron firing rate is higher in proestrus as compared to diestrus, independently of the time of the day. AVP immunoreactive fibers contact RFRP neurons with the highest density observed during the late afternoon of diestrus and proestrus. Application of AVP increases RFRP neurons firing in the afternoon (ZT6-10) of diestrus, but not at the same time point of proestrus, indicating that AVP signaling on RFRP neurons may depend on circulating ovarian steroids. Together, these studies show that RFRP neurons integrate both daily and estrogenic signals, which downstream may help to properly time the preovulatory LH surge.

Immunodistribution of RFamide-related peptide-3 (RFRP-3) during the seminiferous epithelium cycle in a desert rodent Psammomys obesus

The Sand rat, Psammomys obesus, living northwest of the Algerian Sahara, presents a seasonal reproductive cycle. The purposes of this study were firstly to determine the stages of seminiferous epithelium cycle (SEC) by histological and morphometric analysis and secondly to investigate, for the first time, the testicular expression of RFamide-related peptide-3 (RFRP-3) during the SEC by immunohistochemistry. The results showed that the SEC consists of 14 stages according to the tubular morphology method. RFRP-3 was observed in both testicular compartments: the tubular and the interstitial. Leydig cells exhibited the highest RFRP-3 signal (30.73 % ± 4.80) compared to Sertoli cells (13-15 %). In the germline, RFRP-3 was detected during the late prophase I of meiosis in late pachytene, diplotene and metaphasic spermatocytes I. In addition, only round and triangular spermatids were positive during spermiogenesis. Referring to the SEC, it was found that the increased staining of RFRP-3 in spermatocytes I coincided with late pachytene of XI and XII stages (16.90 % ± 0.69 and 16.61 % ± 0.28, respectively). In spermatids, the labeling decreased in the triangular ones at stage IX (8.04 % ± 0.42). These results suggest the involvement of RFRP-3 in the control of SEC in P. obesus.

RFamide-related peptides' gene expression, polymorphism, and their association with reproductive traits in chickens

RFamide-related peptides (RFRP) are synthesized by the hypothalamus and have a regulatory role in gonad development. The goal of this study was to investigate the association between SNP of the RFRP gene and the reproductive traits and hormone levels of Zhenning yellow chickens. The mRNA expression levels were detected based on different tissues, ages, and genotypes. Eleven mutation sites were detected in the RFRP gene, 4 of which were significantly related to reproductive traits and hormone levels. Association analysis revealed that A276G was associated with egg production at 300 d of age (EP300) and amount of prehierarchical follicles (P < 0.05). G1396A was associated with egg weight at 300 d of age and luteinizing hormone (LH) and prolactin levels (P < 0.05). G1694A showed significant associations with fertilization rate and LH levels (P < 0.05), and A2659G was associated with EP300 (P < 0.05). The results of expression analysis showed that the RFRP mRNA expression levels in the hypothalamus were higher than those in other tissues (P < 0.01). The expression in immature individuals was higher than that in mature ones (P < 0.01). There were also differences in mRNA expression levels between different genotypes (P < 0.05). In summary, the results of this study might provide potential markers and a theoretical basis for the improvement of chicken reproductive traits.

Expression of genes for Kisspeptin (KISS1), Neurokinin B (TAC3), Prodynorphin (PDYN), and gonadotropin inhibitory hormone (RFRP) across natural puberty in ewes

Expression of particular genes in hypothami of ewes was measured across the natural pubertal transition by in situ hybridization. The ewes were allocated to three groups (n = 4); prepubertal, postpubertal and postpubertally gonadectomized (GDX). Prepubertal sheep were euthanized at 20 weeks of age and postpubertal animals at 32 weeks. GDX sheep were also euthanized at 32 weeks, 1 week after surgery. Expression of KISS1, TAC3, PDYN in the arcuate nucleus (ARC), RFRP in the dorsomedial hypothalamus and GNRH1 in the preoptic area was quantified on a cellular basis. KISS1R expression by GNRH1 cells was quantified by double-label in situ hybridization. Across puberty, detectable KISS1 cell number increased in the caudal ARC and whilst PDYN cell numbers were low, numbers increased in the rostral ARC. TAC3 expression did not change but RFRP expression/cell was reduced across puberty. There was no change across puberty in the number of GNRH1 cells that expressed the kisspeptin receptor (KISS1R). GDX shortly after puberty did not increase expression of any of the genes of interest. We conclude that KISS1 expression in the ARC increases during puberty in ewes and this may be a causative factor in the pubertal activation of the reproductive axis. A reduction in expression of RFRP may be a factor in the onset of puberty, removing negative tone on GNRH1 cells. The lack of changes in expression of genes following GDX suggest that the effects of gonadal hormones may differ in young and mature animals.

The Role of GnIH in Biological Rhythms and Social Behaviors

Gonadotropin-inhibitory hormone (GnIH) was first discovered in the Japanese quail, and peptides with a C-terminal LPXRFamide sequence, the signature protein structure defining GnIH orthologs, are well conserved across vertebrate species, including fish, reptiles, amphibians, avians, and mammals. In the mammalian brain, three RFamide-related proteins (RFRP-1, RFRP-2, RFRP-3 = GnIH) have been identified as orthologs to the avian GnIH. GnIH is found primarily in the hypothalamus of all vertebrate species, while its receptors are distributed throughout the brain including the hypothalamus and the pituitary. The primary role of GnIH as an inhibitor of gonadotropin-releasing hormone (GnRH) and pituitary gonadotropin release is well conserved in mammalian and non-mammalian species. Circadian rhythmicity of GnIH, regulated by light and seasons, can influence reproductive activity, mating behavior, aggressive behavior, and feeding behavior. There is a potential link between circadian rhythms of GnIH, anxiety-like behavior, sleep, stress, and infertility. Therefore, in this review, we highlight the functions of GnIH in biological rhythms, social behaviors, and reproductive and non-reproductive activities across a variety of mammalian and non-mammalian vertebrate species.

RFamide-Related Peptide Neurons Modulate Reproductive Function and Stress Responses

RF-amide related peptide 3 (RFRP-3) is a neuropeptide thought to inhibit central regulation of fertility. We investigated whether alterations in RFRP neuronal activity led to changes in puberty onset, fertility, and stress responses, including stress and glucocorticoid-induced suppression of pulsatile luteinizing hormone secretion. We first validated a novel RFRP-Cre mouse line, which we then used in combination with Cre-dependent neuronal ablation and DREADD technology to selectively ablate, stimulate, and inhibit RFRP neurons to interrogate their physiological roles in the regulation of fertility and stress responses. Chronic RFRP neuronal activation delayed male puberty onset and female reproductive cycle progression, but RFRP-activated and ablated mice exhibited apparently normal fertility. When subjected to either restraint- or glucocorticoid-induced stress paradigms. However, we observed a critical sex-specific role for RFRP neurons in mediating acute and chronic stress-induced reproductive suppression. Female mice exhibiting RFRP neuron ablation or silencing did not exhibit the stress-induced suppression in pulsatile luteinizing hormone secretion observed in control mice. Furthermore, RFRP neuronal activation markedly stimulated glucocorticoid secretion, demonstrating a feedback loop whereby stressful stimuli activate RFRP neurons, which in turn further activate the stress axis. These data provide evidence for a neuronal link between the stress and reproductive axes.

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.

Rfamide-related peptide-3 suppresses the substance P-induced promotion of the reproductive performance in female rats modulating hypothalamic Kisspeptin expression

RFamide-related peptide-3 (RFRP-3) has been postulated as the suppressor of the reproductive axis at hypothalamic, pituitary and gonadal levels. Considering the hypothalamic level, RFRP-3 can suppress the activity of gonadotropin-releasing hormone (GnRH) neurons and their upstream neuronal stimulator, namely; the kisspeptin neurons. The effects of the RFRP-3 on the other regulators of GnRH neurons, however, are not completely investigated. Furthermore, substance P (SP) has been known as one of the coordinators of GnRH/ luteinizing hormone (LH) and the kisspeptin/G protein-coupled receptor 54 (GPR54) systems. The present study was aimed at investigating the impacts of RFRP-3 on the effects of SP on the reproductive performance in ovariectomized female rats. After intracerebroventricular (ICV) cannulation, the rats were subjected to the ICV injection of either SP or RFRP-3 and simultaneous injection of them and their selective antagonists. Blood and hypothalamic samplings and also sexual behavioral test were carried out on two main groups of rats. The analyses of the results of LH radioimmunoassay, gene expression assay for hypothalamic Gnrh1, Kisspeptin and Gpr54 accompanied by sexual behavioral examination revealed that the SP administration promotes reproductive behavior and GnRH/LH system and upregulates Kisspeptin expression. The RFRP-3 administration suppressed reproductive behavior, GnRH / LH system and Kisspeptin expression; however, the simultaneous injection of SP and RFRP-3 was devoid of significant alterations in the assessed parameters. The results showed that RFRP-3 can modulates the impacts of SP on the reproductive performance in ovariectomized female rats in part through adjusting Kisspeptin expression.

RFRP3 increases food intake in a sex-dependent manner in the seasonal hamster Phodopus sungorus

In addition to its regulatory role in luteinising hormone secretion, Rfamide-related peptide 3 (RFRP3) has also been reported to modulate food intake in several mammalian species. Djungarian hamsters (Phodopus sungorus), similar to other seasonal mammals, display a remarkable inhibition of RFRP3 expression in winter short-day conditions, associated with decreased food intake and bodyweight. This species is therefore a valuable model for assessing whether RFRP3 might be involved in the seasonal control of feeding behaviour and investigating its possible brain targets. We found that, although both male and female animals exhibit the same robust reduction in Rfrp expression in short- (SD) compared to long-day (LD) conditions, acute central administration of RFRP3 displays sex-dependent effects on food intake. RFRP3 increased food intake in female hamsters in SD or in LD dioestrus, but not in LD pro-oestrus, indicating that the orexigenic effect of RFRP3 is observed in conditions of low circulating oestradiol levels. In male hamsters, food intake was not changed by acute injections of RFRP3, regardless of whether animals were in SD or LD conditions. Analysing the gene expression of various metabolic neuropeptides in the brain of RFRP3-injected Djungarian hamsters revealed that Npy expression was increased in female but not in male animals. The present study suggests that, in Djungarian hamsters, RFRP3 exhibits a sex-dependent orexigenic effect possibly by inducing increased Npy expression.

Effect of GABA-T on Reproductive Function in Female Rats

This study explored the role of γ-aminobutyric acid transaminase (GABA-T) in the puberty and reproductive performance of female rats. Immunofluorescence technique, quantitative real-time PCR (RT-qPCR) and enzyme-linked immunosorbent assay (ELISA) were used to detect the distribution of GABA-T and the expression of genes and hormones in female rats, respectively. The results showed that GABA-T was mainly distributed in the arcuate nucleus (ARC), paraventricular nucleus (PVN) and periventricular nucleus (PeN) of the hypothalamus, and in the adenohypophysis, ovarian granulosa cells and oocytes. Abat mRNA level at 28 d was lowest in the hypothalamus and the pituitary; at puberty, it was lowest in the ovary. Abat mRNA level was highest in adults in the hypothalamus; at infancy and puberty, it was highest in the pituitary; and at 21 d it was highest in the ovary. After vigabatrin (GABA-T irreversible inhibitor) was added to hypothalamus cells, the levels of Abat mRNA and Rfrp-3 mRNA were significantly reduced, but Gnrh mRNA increased at the dose of 25 and 50 μg/mL; Kiss1 mRNA was significantly increased but Gabbr1 mRNA was reduced at the 50 μg/mL dose. In prepubertal rats injected with vigabatrin, puberty onset was delayed. Abat mRNA, Kiss1 mRNA and Gnrh mRNA levels were significantly reduced, but Rfrp-3 mRNA level increased in the hypothalamus. Vigabatrin reduced the concentrations of GABA-T, luteinizing hormone (LH) and progesterone (P₄), and the ovarian index. Lactation performance was reduced in adult rats with vigabatrin treatment. Four hours after vigabatrin injection, the concentrations of GABA-T and LH were significantly reduced in adult and 25 d rats, but follicle-stimulating hormone (FSH) increased in 25 d rats. In conclusion, GABA-T affects the reproductive function of female rats by regulating the levels of Gnrh, Kiss1 and Rfrp-3 in the hypothalamus as well as the concentrations of LH and P₄.

Photoperiodic regulation in a wild-derived mouse strain

Mus musculus molossinus (MSM) is a wild-derived mouse strain which maintains the ability to synthesize melatonin in patterns reflecting the ambient photoperiod. The objective of this study was to characterize the effects of photoperiodic variation on metabolic and reproductive traits, and the related changes in pituitary-hypothalamic gene expression in MSM mice. MSM mice were kept in long (LP) or short photoperiod (SP) for 6 weeks. Our results demonstrate that MSM mice kept in LP, as compared to mice kept in SP, display higher expression of genes encoding thyrotropin (TSH) in the pars tuberalis, thyroid hormone deiodinase 2 (dio2) in the tanycytes, RFamide-related peptide (RFRP3) in the hypothalamus and lower expression of dio3 in the tanycytes, along with larger body and reproductive organ mass. Additionally, to assess the effects of the gestational photoperiodic environment on the expression of these genes, we kept MSM mice in LP or SP from gestation and studied offspring. We show that the gestational photoperiod affects the TSH/dio pathway in newborn MSM mice in a similar way to adults. This result indicates a transgenerational effect of photoperiod from the mother to the fetus in utero. Overall, these results indicate that photoperiod can influence neuroendocrine regulation in a melatonin-proficient mouse strain, in a manner similar that documented in other seasonal rodent species. MSM mice may therefore become a useful model for research into the molecular basis of photoperiodic regulation of seasonal biology.

Time-of-day-dependent sensitivity of the reproductive axis to RFamide-related peptide-3 inhibition in female Syrian hamsters

In spontaneously ovulating rodent species, the timing of the luteinising hormone (LH) surge is controlled by the master circadian pacemaker in the suprachiasmatic nucleus (SCN). The SCN initiates the LH surge via the coordinated control of two opposing neuropeptidergic systems that lie upstream of the gonadotrophin-releasing hormone (GnRH) neuronal system: the stimulatory peptide, kisspeptin, and the inhibitory peptide, RFamide-related peptide-3 (RFRP-3; the mammalian orthologue of avian gonadotrophin-inhibitory hormone [GnIH]). We have previously shown that the GnRH system exhibits time-dependent sensitivity to kisspeptin stimulation, further contributing to the precise timing of the LH surge. To examine whether this time-dependent sensitivity of the GnRH system is unique to kisspeptin or a more common mechanism of regulatory control, we explored daily changes in the response of the GnRH system to RFRP-3 inhibition. Female Syrian hamsters were ovariectomised to eliminate oestradiol (E₂ )-negative-feedback and RFRP-3 or saline was centrally administered in the morning or late afternoon. LH concentrations and Lhβ mRNA expression did not differ between morning RFRP-3-and saline-treated groups, although they were markedly suppressed by RFRP-3 administration in the afternoon. However, RFRP-3 inhibition of circulating LH at the time of the surge does not appear to act via the GnRH system because no differences in medial preoptic area Gnrh or RFRP-3 receptor Gpr147 mRNA expression were observed. Rather, RFRP-3 suppressed arcuate nucleus Kiss1 mRNA expression and potentially impacted pituitary gonadotrophs directly. Taken together, these findings reveal time-dependent responsiveness of the reproductive axis to RFRP-3 inhibition, possibly via variation in the sensitivity of arcuate nucleus kisspeptin neurones to this neuropeptide.

Brain mapping of the gonadotropin-inhibitory hormone-related peptide 2 with a novel antibody suggests a connection with emotional reactivity in the Japanese quail (Coturnix japonica, Temminck & Schlegel, 1849)

Gonadotropin-inhibitory hormone (GnIH) is a neuropeptide first discovered in the quail brain that is involved in the control of reproductive physiology and behaviors, and stress response. GnIH gene encodes a second peptide, GnIH-related peptide-2 (RP2), the distribution and function of which remain unknown. We therefore studied GnIH-RP2 distribution by immunohistochemistry using a novel antibody capable of discriminating between GnIH and GnIH-RP2. The overall distribution of GnIH-RP2 is similar to that of GnIH. The vast majority of labeled neurons is located in the paraventricular nucleus (PVN) of the hypothalamus. Labeling of fibers is conspicuous in the diencephalon, but present also in the mesencephalon and telencephalon. Several regions involved in the control of reproduction and stress response (the PVN, septum, bed nucleus of the stria terminalis and nucleus commissura pallii) showed a dense network of immunolabeled fibers. To investigate the potential function of GnIH-RP2 we compared its expression in two quail lines genetically selected for divergence in their emotional reactivity. A quantitative analysis in the above-mentioned brain regions showed that the density of fibers was similar in the two lines. However, the number of GnIH-RP2 labeled neurons was higher in the median portion of the PVN in birds with higher emotional reactivity. These results point to a possible involvement of GnRH-RP2 in modulating stress response and/or emotional reactivity.

The dromedary camel displays annual variation in hypothalamic kisspeptin and Arg-Phe-amide-related peptide-3 according to sex, season, and breeding activity

The dromedary camel (Camelus dromedarius) is a desert mammal whose cycles in reproductive activity ensure that the offspring's birth and weaning coincide with periods of abundant food resources and favorable climate conditions. In this study, we assessed whether kisspeptin (Kp) and arginine-phenylalanine (RF)-amide related peptide-3 (RFRP-3), two hypothalamic peptides known to regulate the mammalian hypothalamo-pituitary gonadal axis, may be involved in the seasonal control of camel's reproduction. Using specific antibodies and riboprobes, we found that Kp neurons are present in the preoptic area (POA), suprachiasmatic (SCN), and arcuate (ARC) nuclei, and that RFRP-3 neurons are present in the paraventricular (PVN), dorsomedial (DMH), and ventromedial (VMH) hypothalamic nuclei. Kp fibers are found in various hypothalamic areas, notably the POA, SCN, PVN, DMH, VMH, supraoptic nucleus, and the ventral and dorsal premammillary nucleus. RFRP-3 fibers are found in the POA, SCN, PVN, DMH, VMH, and ARC. POA and ARC Kp neurons and DMH RFRP-3 neurons display sexual dimorphism with more neurons in female than in male. Both neuronal populations display opposed seasonal variations with more Kp neurons and less RFRP-3 neurons during the breeding (December-January) than the nonbreeding (July-August) season. This study is the first describing Kp and RFRP-3 in the camel's brain with, during the winter period lower RFRP-3 expression and higher Kp expression possibly responsible for the HPG axis activation. Altogether, our data indicate the involvement of both Kp and RFRP-3 in the seasonal control of the dromedary camel's breeding activity.

Central Substance P Attenuates RF-amid-related Peptide-3 Impacts on the Serum Level of Luteinizing Hormone in Wistar Rats

Introduction: It is well-established that gonadotropin-inhibitory hormone (GnIH) and its mammalian orthologues (RFRP: RF-amid related peptides) can decrease gonadotrophin secretion. Moreover, substance P (SP) is another modulator of the secretion of gonadotropins in a species-dependent manner. This study aimed to find out the impacts of concomitant infusion of RFRP-3 and SP on luteinizing hormone (LH) concentration. Methods: Forty-two rats were arbitrarily assigned to 7 groups (n=6 per group). Animals in the experimental groups were intracerebroventricularly injected with saline +DMSO, SP, RFRP-3, SP + RFRP-3, SP + RF9 (RFRP-3 receptor antagonist), SP + P234 (kisspeptin receptor antagonist) + RFRP-3 and SP + CP-96,345 (SP receptor antagonist) + RFRP-3 in a final volume of 3 µL. Blood samples were collected at 30-minute intervals after injections, and serum was used to measure the LH concentration by radioimmunoassay. Results: According to the results, injections led to the elevation of LH serum concentration at 30-minute post injection (P<0.05) in the SP and SP+RF9 groups. Moreover, administration of either RFRP-3 or SP + RFRP-3 + SP receptor antagonist strikingly decreased the LH mean serum concentration at 30-minute after injections (P<0.05). On the contrary, the infusion of SP+RFRP-3 and SP+RFRP-3+P234 caused no dramatic changes in the LH mean serum concentration. Conclusion: In general, the data showed that SP suppresses the impacts of RFRP-3 on the serum levels of LH.

Molecular Mechanisms of Gonadotropin-Inhibitory Hormone (GnIH) Actions in Target Cells and Regulation of GnIH Expression

Since gonadotropin-inhibitory hormone (GnIH) was discovered in 2000 as the first hypothalamic neuropeptide that actively inhibits gonadotropin release, researches conducted for the last 18 years have demonstrated that GnIH acts as a pronounced negative regulator of reproduction. Inhibitory effect of GnIH on reproduction is mainly accomplished at hypothalamic-pituitary levels; gonadotropin-releasing hormone (GnRH) neurons and gonadotropes are major targets of GnIH action based on the morphological interaction with GnIH neuronal fibers and the distribution of GnIH receptor. Here, we review molecular studies mainly focusing on the signal transduction pathway of GnIH in target cells, GnRH neurons, and gonadotropes. The use of well-defined cellular model systems allows the mechanistic study of signaling pathway occurring in target cells by demonstrating the direct cause-and-effect relationship. The insights gained through studying molecular mechanism of GnIH action contribute to deeper understanding of the mechanism of how GnIH communicates with other neuronal signaling systems to control our reproductive function. Reproductive axis closely interacts with other endocrine systems, thus GnIH expression levels would be changed by adrenal and thyroid status. We also briefly review molecular studies investigating the regulatory mechanisms of GnIH expression to understand the role of GnIH as a mediator between adrenal, thyroid and gonadal axes.

Functional Implications of RFRP-3 in the Central Control of Daily and Seasonal Rhythms in Reproduction

Adaptation of reproductive activity to environmental changes is essential for breeding success and offspring survival. In mammals, the reproductive system displays regular cycles of activation and inactivation which are synchronized with seasonal and/or daily rhythms in environmental factors, notably light intensity and duration. Thus, most species adapt their breeding activity along the year to ensure that birth and weaning of the offspring occur at a time when resources are optimal. Additionally, female reproductive activity is highest at the beginning of the active phase during the period of full oocyte maturation, in order to improve breeding success. In reproductive physiology, it is therefore fundamental to delineate how geophysical signals are integrated in the hypothalamo-pituitary-gonadal axis, notably by the neurons expressing gonadotropin releasing hormone (GnRH). Several neurochemicals have been reported to regulate GnRH neuronal activity, but recently two hypothalamic neuropeptides belonging to the superfamily of (Arg)(Phe)-amide peptides, RFRP-3 and kisspeptin, have emerged as critical for the integration of environmental cues within the reproductive axis. The goal of this review is to survey the current understanding of the role played by RFRP-3 in the temporal regulation of reproduction, and consider how its effect might combine with that of kisspeptin to improve the synchronization of reproduction to environmental challenges.

Regulation of LH secretion by RFRP-3 - From the hypothalamus to the pituitary

RFamide-related peptides (RFRPs) have long been identified as inhibitors of the hypothalamus-pituitary-gonad axis in mammals. However, less progress has been made in the detailed roles of RFRPs in the control of LH secretion. Recent studies have suggested that RFRP-3 neurons in the hypothalamus can regulate the secretion of LH at different levels, including kisspeptin neurons, GnRH neurons, and the pituitary. Additionally, conflicting results regarding the effects of RFRP-3 on these levels exist. In this review, we collect the latest evidence related to the effects of RFRP-3 neurons in regulating LH secretion by acting on kisspeptin neurons, GnRH neurons, and the pituitary and discuss the potential role of the timely reduction of RFRP-3 signaling in the modulation of the preovulatory LH surge.

Immunolocalization of RFamide-related peptide 3 in a desert rodent Gerbillus tarabuli during seminiferous epithelium cycle

Gerbillus tarabuli is a nocturnal seasonal breeder desert rodent with a main breeding season in spring and summer, and sexual quiescence in winter. This species is an interesting model for studying testis function in rodents. Therefore, the present study was performed firstly to investigate the stages of seminiferous epithelium cycle of Gerbillus tarabuli with a histological, morphometric and statistical study. And secondly to investigate the expression and possible variations in cellular distribution of RFamide-related peptide-3 (RFRP-3) - the mammalian ortholog of avian gonadotropin-inhibitory hormone (GnIH) - during seminiferous epithelium cycle using immunohistochimestry. Our results showed for the first time that the seminiferous epithelium cycle in Gerbillus tarabuli comprises 14 well-defined stages according to the tubular morphology method. The seminiferous epithelium thickness showed a significant difference during the epithelium cycle, thus it was the only morphometric classification criterion of seminiferous epithelium cycle in Gerbillus tarabuli. The immunohistochemical study reveals, for the first time, the presence of RFRP-3 in Gerbillus tarabuli testes, in both testicular compartments: the tubular and the interstitial. RFRP-3 is expressed differently according to the seminiferous epithelium cycle, RFRP-3 seemed to be more expressed at the stages V-VII and XIII. RFRP-3 was detected in Sertoli cells (≈12%), spermatocytes I (≈19%), round and elongated spermatids (≈13%), and with a more important signal in Leydig cells (26.87%±0.07). These results indicated the importance of RFRP-3 in testicular function in Gerbillus tarabuli; its expression at the interstitial and germinal levels argues in favor of an involvement in androgens synthesis and in spermatogenesis specifically in meiosis and spermiogenesis. This action seems primordial from stages V-VII and XIII. Also, the study of the seminiferous epithelium cycle will enrich the histological identity of the species.

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.

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.

Daily rhythms count for female fertility

Female ovulation depends on a surge in circulating luteinizing hormone (LH) which occurs at the end of the resting period and requests high circulating estradiol. This fine tuning involves both an estradiol feedback as an indicator of oocyte maturation, and the master circadian clock of the suprachiasmatic nuclei as an indicator of the time of the day. This review describes the mechanisms through which daily time cues are conveyed to reproductive hypothalamic neurons to time the pre-ovulatory surge. In female rodents, neurotransmitters released by the suprachiasmatic nuclei activate the stimulatory kisspeptin neurons and reduce the inhibitory RFRP neurons precisely at the end of the afternoon of proestrus to allow a full surge in LH secretion. From these findings, the impact of circadian disruptions (during shift or night work) on female reproductive performance and fertility should now being investigated in both animal models and humans.