Projections of RFamide-related peptide-3 neurones in the ovine hypothalamus, with special reference to regions regulating energy balance and reproduction

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.

Glucocorticoid receptor-mediated regulation of Rfrp (GnIH) and Gpr147 (GnIH-R) synthesis in immortalized hypothalamic neurons

A novel RFamide peptide, gonadotropin-inhibitory hormone (GnIH) has emerged as a modulator of avian reproduction. However, the functional role of the mammalian homologue, RFRP-3 remains poorly understood. The RFRP-3 neuronal circuit is influenced by the stress axis. However, whether the Rfrp gene is under direct glucocorticoid (GC)-mediated transcriptional regulation, in the presence and absence of the gonadal steroid, 17β-estradiol, is unknown. We investigated the regulation of the Rfrp (GnIH) and Gpr147 (GnIH-R) transcripts by steroids in a novel hypothalamic Rfrp-expressing cell model, rHypoE-23. The GC agonist, dexamethasone increased Rfrp and Gpr147 mRNA levels. Dexamethasone acted directly on the nuclear GC receptor (GR) to mediate GC-dependent transcriptional changes, independently of de novo protein synthesis. 17β-estradiol had no significant effect on Rfrp or Gpr147 biosynthesis in these neurons. This suggests that Rfrp-expressing neurons serve as potential upstream mediators of stress-induced effects through GR-dependent mechanisms.

Effect of residual feed intake on hypothalamic gene expression and meat quality in Angus-sired cattle grown during the hot season

The relationship between heat stress, meat quality, and residual feed intake (RFI) is unknown in growing steers. To address this issue, high RFI (HRFI) and low RFI (LRFI) individuals were compared by assessing RFI in 48 Angus-sired steers during a 70-d feeding trial conducted during July through September to identify steers with calculated RFI at least 2 SD apart. The association of RFI with indices of meat quality and expression of genes within hypothalamic and adipose tissue was then determined in LRFI and HRFI steers. While on test, feed intake was recorded daily with BW and hip heights recorded every 14 d. Ultrasound measurements of rib eye area (REA) and backfat (BF) were recorded initially and before harvest. Carcass and growth data were analyzed using a mixed model with RFI level (LRFI and HRFI) as the independent variable. The least square means for RFI were -1.2 and 0.99 kg DMI/d, respectively, for the LRFI and HRFI cohorts (P < 0.0001). Dry matter intake was higher for the HRFI individuals versus the LRFI steers (P < 0.0001) while on-test gain was not different (P < 0.95). Marbling score was greater in LRFI than HRFI steers (P < 0.05). However, there were no differences in REA (P < 0.53), BF (P < 0.65), yield grade (P < 0.24), or objective Hunter color measures between LRFI and HRFI steers indicating there was no consistent relationship between RFI and indices of meat quality. Hypothalamic neuropeptide Y (NPY), agouti related protein (AGRP), relaxin-3 (RLN3), melanocortin 3 receptor, and relaxin/insulin-like family peptide receptor 1 (RXFP1) mRNA were expressed 280, 185, 202, 183, and 163% greater, respectively (P < 0.01), while proopiomelanocortin (POMC) mRNA was expressed 42% lower in LRFI than HRFI animals (P < 0.05). Hypothalamic GnRH mRNA expression was 67% lower while gonadotropin inhibiting hormone (GnIH) mRNA was 209% higher in LRFI than HRFI animals (P < 0.01). Pituitary expression of FSHβ and LHβ correlated to hypothalamic GnRH levels (P < 0.05) indicating changes in gene expression within the hypothalamus had functional consequences. Leptin mRNA expression levels were not different between adipose tissue of LRFI or HRFI steers (P < 0.84). These data indicate that animals with superior RFI evaluated during warm conditions have higher expression of orexigenic neuropeptide genes independent of the expression of adipose-derived leptin. Furthermore, the gonadotropin axis may also influence feed efficiency under these conditions.

Residual feed intake studies in Angus-sired cattle reveal a potential role for hypothalamic gene expression in regulating feed efficiency

Mechanisms underlying variation in residual feed intake (RFI), a heritable feed efficiency measure, are poorly understood while the relationship between RFI and meat quality is uncertain. To address these issues, 2 divergent cohorts consisting of High (HRFI) and Low (LRFI) RFI individuals were created by assessing RFI in 48 Angus-sired steers during a 70 d feeding trial to identify steers with divergent RFI. The association of RFI with indices of meat quality and expression of genes within hypothalamic and adipose tissue was then determined in LRFI and HRFI steers. While on test, feed intake was recorded daily with BW and hip heights recorded at 14 d intervals. Ultrasound measurements of rib eye area (REA) and backfat (BF) were recorded initially and before harvest. Carcass and growth data were analyzed using a mixed model with RFI level (LRFI, HRFI) as the independent variable. The least-square means (lsmeans) for RFI were -1.25 and 1.51 for the LRFI and HRFI cohorts (P < .0001). Dry matter intake was higher for the HRFI individuals versus the LRFI steers (P < .0001) while on test BW gain was not different between the 2 groups (P < 0.73). There were no differences detected in marbling score (P < 0.93), BF (P < 0.61), REA (P < 0.15), yield grade (P < 0.85) or objective Hunter color measures between LRFI and HRFI steers indicating that there was no relationship between RFI and meat quality. Neuropeptide-Y (NPY), relaxin-3 (RLN3), melanocortin 4 receptor (MC4R), and GnRH mRNA expression was 64%, 59%, 58%, 86% lower (P < 0.05), respectively, while gonadotropin inhibiting hormone (GnIH) and pro-opiomelanocortin (POMC) mRNA expression was 198% and 350% higher (P < 0.01) in the arcuate nucleus of LRFI steers. Expression of agouti-related protein (AGRP), relaxin/insulin-like family peptide receptor 1 (RXFP1), and melanocortin 3 receptor mRNA was similar between LRFI and HRFI animals. Pituitary expression of FSHβ (P < 0.03) and LHβ (P < 0.01) was correlated to hypothalamic GnRH levels suggesting that changes in gene expression within the arcuate nucleus had functional consequences. Leptin mRNA expression was 245% higher in the adipose tissue of LRFI steers consistent with lower levels of NPY and higher expression of POMC in their hypothalami. These data support the hypothesis that differences in hypothalamic neuropeptide gene expression underlie variation in feed efficiency in steers while the gonadotropin axis may also influence feed efficiency.

Structural and functional divergence of gonadotropin-inhibitory hormone from jawless fish to mammals

Gonadotropin-inhibitory hormone (GnIH) was discovered as a novel hypothalamic peptide that inhibits gonadotropin release in the quail. The presence of GnIH-homologous peptides and its receptors (GnIHRs) have been demonstrated in various vertebrate species including teleosts, suggesting that the GnIH-GnIHR family is evolutionarily conserved. In avian and mammalian brain, GnIH neurons are localized in the hypothalamic nuclei and their neural projections are widely distributed. GnIH acts on the pituitary and gonadotropin-releasing hormone neurons to inhibit reproductive functions by decreasing gonadotropin release and synthesis. In addition, GnIH-GnIHR signaling is regulated by various factors, such as environmental cues and stress. However, the function of fish GnIH orthologs remains inconclusive because the physiological properties of fish GnIH peptides are debatable. This review summarizes the current research progress in GnIH-GnIHR signaling and their physiological functions in vertebrates with special emphasis on non-mammalian vertebrate species.

Central pathways integrating metabolism and reproduction in teleosts

Energy balance plays an important role in the control of reproduction. However, the cellular and molecular mechanisms connecting the two systems are not well understood especially in teleosts. The hypothalamus plays a crucial role in the regulation of both energy balance and reproduction, and contains a number of neuropeptides, including gonadotropin-releasing hormone (GnRH), orexin, neuropeptide-Y, ghrelin, pituitary adenylate cyclase-activating polypeptide, α-melanocyte stimulating hormone, melanin-concentrating hormone, cholecystokinin, 26RFamide, nesfatin, kisspeptin, and gonadotropin-inhibitory hormone. These neuropeptides are involved in the control of energy balance and reproduction either directly or indirectly. On the other hand, synthesis and release of these hypothalamic neuropeptides are regulated by metabolic signals from the gut and the adipose tissue. Furthermore, neurons producing these neuropeptides interact with each other, providing neuronal basis of the link between energy balance and reproduction. This review summarizes the advances made in our understanding of the physiological roles of the hypothalamic neuropeptides in energy balance and reproduction in teleosts, and discusses how they interact with GnRH, kisspeptin, and pituitary gonadotropins to control reproduction in teleosts.

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.

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 seasonal variation in hypothalamic RF-amide peptides in a semi-desert rodent, the jerboa

The jerboa is a semi-desert rodent, in which reproductive activity depends on the seasons, being sexually active in the spring-summer. The present study aimed to determine whether the expression of two RF-amide peptides recently described to regulate gonadotrophin-releasing hormone neurone activity, kisspeptin (Kp) and RF-amide-related peptide (RFRP)-3, displays seasonal variation in jerboa. Kp and/or RFRP-3 immunoreactivity was investigated in the hypothalamus of jerboas captured in the field of the Middle Atlas mountain (Morocco), either in the spring or autumn. As in other rodents, the Kp-immunoreactive (-IR) neurones were found in the anteroventro-periventricular and arcuate nuclei. RFRP-3 neurones were noted within the dorso/ventromedial hypothalamus. A marked sexual dimorphism in the expression of Kp (but not RFRP-3) was observed. The number of Kp-IR neurones was nine-fold higher, and the density of Kp-IR fibres and terminal-like elements in the median eminence was two-fold higher in females than in males. Furthermore, a significant seasonal variation in peptide expression was obtained with an increase in both Kp- and RFRP-3-IR cell bodies in sexually active male jerboas captured in the spring compared to sexually inactive autumn animals. In the arcuate nucleus, the level of Kp-IR cells and fibres was significant higher during the sexually active period in the spring than during the autumnal sexual quiescence. Similarly, the number of RFRP-3-IR neurones in the ventro/dorsomedial hypothalamus was approximately three-fold higher in sexually active jerboa captured in the spring compared to sexually inactive autumn animals. Altogether, the present study reports the distribution of Kp and RFRP-3 neurones in the hypothalamus of a desert species and reveals a seasonal difference in their expression that correlates with sexual activity. These findings suggest that these two RF-amide peptides may act in concert to synchronise the gonadotrophic activity of jerboas with the seasons.

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.

[Effects of RFRP-3 on reproductive function and energy balance in mammals]

The hypothalamo-pituitary-gonadal (HPG) axis integrates internal and external cues via a balance of stimulatory and inhibitory neurochemical systems to regulate reproductive function in mammals. However, RFRP-3 is a unique inhibitor of HPG axis at the hypothalamuic level in mammals to date. A large number of previous studies have confirmed that RFamide-related peptide (RFRP-3) suppresses gonadotropin-releasing hormone (GnRH) system and luteinizing hormone (LH) secretion, thereby affecting the reproduction. However, whether the inhibition of LH secretion by RFRP-3 occurs at the pituitary level or the hypothalamus level is not clear. It is interesting that RFRP-3 is also related to signal pathway of melatonin modulating mammal seasonal reproduction, but little is known about the effects of melatonin on the RFRP-3 neuron up to now. In addition, RFRP-3 also plays an important role in the regulation of energy balance and behavior. The regulatory mechanism of RFRP-3 in HPG axis and role of RFRP-3 in modulating mammalian energy balance, as well as behavior, are systematically elaborated and the remaining unsolved problems are also discussed in this paper.

Disrupted organization of RFamide pathways in the hypothalamus is associated with advanced puberty in female rats neonatally exposed to bisphenol A

Hypothalamic neurons, which produce the kisspeptin family of peptide hormones (Kp), are critical for initiating puberty and maintaining estrous cyclicity by stimulating gonadotropin-releasing hormone (GnRH) release. Conversely, RFamide-related peptide-3 (RFRP3) neurons inhibit GnRH activity. It has previously been shown that neonatal exposure to bisphenol A (BPA) can alter the timing of female pubertal onset and induce irregular estrous cycles or premature anestrus. Here we tested the hypothesis that disrupted ontogeny of RFamide signaling pathways may be a mechanism underlying advanced puberty. To test this, we used a transgenic strain of Wistar rats whose GnRH neurons express enhanced green fluorescent protein. Pups were exposed by daily subcutaneous injection to vehicle, 17beta-estradiol (E2), 50 μg/kg BPA, or 50 mg/kg BPA, from Postnatal Day (PND) 0 through PND 3, and then cohorts were euthanized on PNDs 17, 21, 24, 28, and 33 (5-8 animals per age per exposure; males were collected on PNDs 21 and 33). Vaginal opening was advanced by E2 and 50 μg/kg BPA. On PND 28, females exposed to E2 and 50 μg/kg BPA had decreased RFRP-3 fiber density and contacts on GnRH neurons. RFRP3 perikarya were also decreased in females exposed to 50 μg/kg BPA. Data suggest that BPA-induced premature puberty results from decreased inhibition of GnRH neurons.

The role of kisspeptin and gonadotropin inhibitory hormone in the seasonal regulation of reproduction in sheep

Sheep are seasonal breeders, experiencing an annual period of reproductive quiescence in response to increased photoperiod during the late-winter into spring and renaissance during the late summer. The nonbreeding (anestrous) season is characterized by a reduction in the pulsatile secretion of GnRH from the brain, in part because of an increase in negative feedback activity of estrogen. Neuronal populations in the hypothalamus that produce kisspeptin and gonadotropin-inhibitory hormone (GnIH) appear to be important for the seasonal shift in reproductive activity, and the former are also mandatory for puberty onset. Kisspeptin cells in the arcuate nucleus (ARC) and preoptic area appear to regulate GnRH neurons and transmit sex-steroid feedback signals to these neurons. Moreover, kisspeptin expression in the ARC is markedly up-regulated at the onset of the breeding season, as too are the number of kisspeptin fibers in close apposition to GnRH neurons. The lower levels of kisspeptin seen during the nonbreeding season can be "corrected" by infusion of kisspeptin, which causes ovulation in seasonally acyclic females. The role of GnIH is less clear, but mounting evidence supports a role for this neuropeptide in the inhibitory regulation of both GnRH secretion and gonadotropin release from the pituitary gland. Contrary to kisspeptin, GnIH expression is markedly reduced at the onset of the breeding season. In addition, the number of GnIH fibers in close apposition to GnRH neurons also decreases during this time. Importantly, exogenous GnIH treatment can block both the pulsatile release of LH and the preovulatory LH surge during the breeding season. In summary, it is most likely the integrated function of both these neuropeptide systems that modulate the annual shift in photoperiod to a physiological change in fertility.

RFamide-related peptide-3 receptor gene expression in GnRH and kisspeptin neurons and GnRH-dependent mechanism of action

RFamide-related peptide-3 (RFRP-3) is known to inhibit the activity of GnRH neurons. It is not yet clear whether its G protein-coupled receptors, GPR147 and GPR74, are present on GnRH neurons or on afferent inputs of the GnRH neuronal network or whether RFRP-3 can inhibit gonadotropin secretion independently of GnRH. We tested the following: 1) whether GnRH is essential for the effects of RFRP-3 on LH secretion; 2) whether RFRP-3 neurons project to GnRH and rostral periventricular kisspeptin neurons in mice, and 3) whether Gpr147 and Gpr74 are expressed by these neurons. Intravenous treatment with the GPR147 antagonist RF9 increased plasma LH concentration in castrated male rats but was unable to do so in the presence of the GnRH antagonist cetrorelix. Dual-label immunohistochemistry revealed that approximately 26% of GnRH neurons from male and diestrous female mice were apposed by RFRP-3 fibers, and 19% of kisspeptin neurons from proestrous female mice were apposed by RFRP-3 fibers. Using immunomagnetic purification of GnRH and kisspeptin cells, single-cell nested RT-PCR, and in situ hybridization, we showed that 33% of GnRH neurons and 9-16% of rostral periventricular kisspeptin neurons expressed Gpr147, whereas Gpr74 was not expressed in either population. These data reveal that RFRP-3 can act at two levels of the GnRH neuronal network (i.e. the GnRH neurons and the rostral periventricular kisspeptin neurons) to modulate reproduction but is unable to inhibit gonadotropin secretion independently of GnRH.

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.

Lipopolysaccharide injection induces rapid decrease of hypothalamic GnRH mRNA and peptide, but does not affect GnIH in zebra finches

Lipopolysaccharide (LPS) is frequently used experimentally to mimic acute infection. Through activation of the host's immune response, an LPS injection has profound effects on the adrenocortical response to stress and on behaviors including reduction in activity, water and food intake, and libido. These behavioral changes occurring during infection are collectively called "sickness behavior." It is thought that adoption of sickness behavior reallocates energy from other fitness-enhancing activities, such as reproduction, for use in the immune response. Although the behavioral effects of LPS treatment are well-known, less information is available regarding the effects of LPS on the brain in terms of controlling reproductive behavior, specifically concerning a newly discovered neuropeptide, gonadotropin-inhibitory hormone (GnIH). This study investigated the effects of an LPS injection on the behavior and the hypothalamic neuropeptides controlling reproduction [GnIH and gonadotropin-releasing hormone (GnRH)] of zebra finches (Taeniopygia guttata). Overall, there was a decrease in activity in birds injected with LPS. The number of GnRH-immunoreactive neurons was significantly reduced in birds injected with LPS when compared to controls, while the number of GnIH-releasing neurons remained unchanged. At the level of gene expression, a similar pattern was found: there was reduced expression of GnRH mRNA in LPS-injected animals, whereas GnIH expression remained unchanged. Plasma testosterone did not change significantly in LPS-injected animals, nor did plasma corticosterone. Taken together, these results indicate a rapid (within 3h) inhibition of the reproductive axis during an immune challenge mimicking an infection, specifically acting on the GnRH system. The present study expands our knowledge on the interaction between the immune system and the reproductive system.

Gonadotropin-inhibitory hormone (GnIH) secretion into the ovine hypophyseal portal system

GnIH was first identified in avian species, and there is now strong evidence that it is operant in mammals as an inhibitor of reproduction. Mammalian gonadotropin-inhibitory hormone (GnIH)-3 is encoded by the RFRP gene in neurons of the dorsomedial nucleus. These neurons project to the median eminence, predicting a role as a secreted neurohormone and regulation of the pituitary gonadotropes. To determine whether GnIH-3 is a secreted neurohormone, we measured its concentration in hypophyseal portal blood in ewes during the nonbreeding (anestrous) season and during the luteal and follicular phases of the estrous cycle in the breeding season. Paired portal and jugular blood samples were collected and plasma prepared for RIA using an ovine GnIH-3 antibody. Pulsatile GnIH-3 secretion was observed in the portal blood of all animals. Mean GnIH-3 pulse amplitude and pulse frequency was higher during the nonbreeding season. GnIH-3 was virtually undetectable in peripheral blood plasma. There was a lack of association between secretory pulses of GnIH-3 (portal) and LH (peripheral). To determine the role of secreted GnIH-3, we examined its effects on GnRH-stimulated LH secretion in hypothalamo-pituitary-disconnected ewes; a significant reduction in the LH response to GnRH was observed. Finally, to identify cellular targets in the pituitary, the expression of GnIH receptor [G protein-coupled receptor 147 (GPR147)] in fractions enriched for gonadotropes somatotropes, and lactotropes was examined; expression was observed in each cell type. These data show GnIH-3 is secreted into portal blood to act on pituitary gonadotropes, reducing the action of GnRH.

Analysis on DNA sequence of goat RFRP gene and its possible association with average daily sunshine duration

Goat RFRP gene was cloned and its mutations were detected in thirteen goat breeds whose reproductive seasonality and litter size were different. Then sequence characteristics were analyzed and association analyses were performed to reveal the relationships between mutations of RFRP gene and average daily sunshine duration, reproductive seasonality as well as litter size in goats. A 4,862 bp DNA fragment of goat RFRP gene was obtained and the complete CDS of 591 bp encodes 196 amino acids, having high homology with that of other mammals. The protein was predicted to be a secreted protein with a signal peptide of 21 amino acids. Moreover, two mutations (A712G, T1493C) in 5' regulatory region and one mutation (A3438T) in exon 2 were detected. The test of genotype distribution in six selective goat breeds showed that there was no uniform significant association between the three polymorphisms and seasonal reproduction. The association just existed in some goat breeds for each locus. Interestingly, however, there was a strong positive correlation (r = 0.830, P = 0.003) between the G allele frequency of the A712G locus and average daily sunshine duration in ten local goat breeds, suggesting that RFRP gene has undergone a selective pressure in sunshine duration and may have indirect relationship with reproductive seasonality in goats. Additionally, no significant difference was found in litter size between genotypes in prolific Jining Grey goats.

Microinjection of RFRP-1 in the central nucleus of amygdala decreases food intake in the rat

Several members of the RFamide peptide family are known to have role in the regulation of feeding. For example, neuropeptide FF and prolactin-releasing peptide cause anorexigenic, while 26RFa and QRFP result in orexigenic effects in rodents. I.c.v. microinjection of neuropeptide RFRP-1 significantly reduced food and water intake in chicks. However, feeding related effects of RFRP-1 have not been studied in mammals yet. The central part of amygdala (CeA) is essentially involved in the regulation of feeding and body weight. RFRP-1 positive nerve cells were detected in the rat hypothalamus and RFRP-1 immunoreactive fibers were identified in the CeA. RFRP analogs bind with relatively high affinity to the NPFF1 and NPFF2 receptors (NPFF-R). RFRP-1 has potent activity for NPFF1. Significant expression of NPFF1 was detected in the CeA. To evaluate the role of RFRP-1 in feeding regulation rats were microinjected with different doses of RFRP-1 and their food intake were quantified over a 60min period. Liquid food intake of male Wistar rats was measured after bilateral intraamygdaloid administration of RFRP-1 (25, 50 or 100ng/side, RFRP-1 dissolved in 0.15M sterile NaCl/0.4μl, respectively). The 50ng dose of RFRP-1 microinjections resulted in significant decrease of food intake. The 25 and 100ng had no effect. Action of 50ng (37.8pmol) RFRP-1 was eliminated by 20ng (41.4pmol) RF9 NPFF-R antagonist pretreatment. In open-field test 50ng RFRP-1 did not modify spontaneous locomotor activity and general behavior of animals did not change. Our results are the first reporting that RFRP-1 injected to the CeA result in a decrease of liquid food consumption. This is a receptor-linked effect because it was eliminated by a NPFF-R selective antagonist.

Neonatal dexamethasone exposure down-regulates GnRH expression through the GnIH pathway in female mice

Synthetic glucocorticoid (dexamethasone; DEX) treatment during the neonatal stage is known to affect reproductive activity. However, it is still unknown whether neonatal stress activates gonadotropin-inhibitory hormone (GnIH) synthesizing cells in the dorsomedial hypothalamus (DMH), which could have pronounced suppressive action on gonadotropin-releasing hormone (GnRH) neurons, leading to delayed pubertal onset. This study was designed to determine the effect of neonatal DEX (1.0mg/kg) exposure on reproductive maturation. Therefore, GnRH, GnIH and GnIH receptors, G-protein coupled receptors (GPR) 147 and GPR74 mRNA levels were measured using quantitative real-time PCR in female mice at postnatal (P) days 21, 30 and in estrus stage mice, aged between P45-50. DEX-treated females of P45-50 had delayed vaginal opening, and irregular estrus cycles and lower GnRH expression in the preoptic area (POA) when compared with age-matched controls. The expression levels of GPR147 and GPR74 mRNA in the POA increased significantly in DEX-treated female mice of P21 and P45-50 compared to controls. In addition, GPR147 and GPR74 mRNA expression was observed in laser captured single GnRH neurons in the POA. Although there was no difference in GnIH mRNA expression in the DMH, immunostained GnIH cell numbers in the DMH increased in DEX-treated females of P45-50 compared to controls. Taken together, the results show that the delayed pubertal onset could be due to the inhibition of GnRH gene expression after neonatal DEX treatment, which may be accounted for in part by the inhibitory signals from the up-regulated GnIH-GnIH receptor pathway to the POA.

RNA interference of gonadotropin-inhibitory hormone gene induces arousal in songbirds

Gonadotropin-inhibitory hormone (GnIH) was originally identified in quail as a hypothalamic neuropeptide inhibitor of pituitary gonadotropin synthesis and release. However, GnIH neuronal fibers do not only terminate in the median eminence to control anterior pituitary function but also extend widely in the brain, suggesting it has multiple roles in the regulation of behavior. To identify the role of GnIH neurons in the regulation of behavior, we investigated the effect of RNA interference (RNAi) of the GnIH gene on the behavior of white-crowned sparrows, a highly social songbird species. Administration of small interfering RNA against GnIH precursor mRNA into the third ventricle of male and female birds reduced resting time, spontaneous production of complex vocalizations, and stimulated brief agonistic vocalizations. GnIH RNAi further enhanced song production of short duration in male birds when they were challenged by playbacks of novel male songs. These behaviors resembled those of breeding birds during territorial defense. The overall results suggest that GnIH gene silencing induces arousal. In addition, the activities of male and female birds were negatively correlated with GnIH mRNA expression in the paraventricular nucleus. Density of GnIH neuronal fibers in the ventral tegmental area was decreased by GnIH RNAi treatment in female birds, and the number of gonadotropin-releasing hormone neurons that received close appositions of GnIH neuronal fiber terminals was negatively correlated with the activity of male birds. In summary, GnIH may decrease arousal level resulting in the inhibition of specific motivated behavior such as in reproductive contexts.

Gonadotropin-inhibitory hormone is a hypothalamic peptide that provides a molecular switch between reproduction and feeding

OBJECTIVE

Gonadotropin-inhibitory hormone (GnIH)-3 is a neuropeptide that plays a major role in the regulation of reproduction and feeding in mammals.

MATERIALS AND METHODS

We measured endocrine and behavioural parameters of reproduction in sheep, and sexual behaviour in sheep, mice and cynomolgus monkeys. In addition, GnIH gene expression (in situ hybridization) was examined in ewes, and effects of GnIH-3 on food intake and energy expenditure were measured in various species. GnIH-3 was infused (i.v.) into ewes after an i.m. injection of estradiol benzoate to determine whether the peptide blocks the surge in luteinizing hormone (LH) secretion.

RESULTS

GnIH gene expression was reduced in the preovulatory period in ewes. Infusion (i.v.) of GnIH-3 blocked the estrogen-induced LH surge (in ewes). Intracerebroventricular infusion had no effect on female or male sexual behaviour in each of the three species, but increased food intake. There were no effects on energy expenditure in sheep or rats. GnIH increased fos protein (immunohistochemistry) was seen in orexigenic neurons (in sheep and rats), but also in anorexigenic neurons (in sheep).

CONCLUSIONS

GnIH-3 reduces reproductive hormone levels and increases food intake in mammals without reducing energy expenditure. There is minimal effect on reproductive behaviour. The dual effect on reproduction and feeding suggests that GnIH-3 provides a molecular switch between these two functions. Blockade of the positive feedback effect of estrogen with parenteral infusion indicates that this peptide may have utility as a blocker of reproductive function in mammals.

Gonadotropin-inhibitory hormone action in the brain and pituitary

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

RFamide Peptides: Structure, Function, Mechanisms and Pharmaceutical Potential

Different neuropeptides, all containing a common carboxy-terminal RFamide sequence, have been characterized as ligands of the RFamide peptide receptor family. Currently, five subgroups have been characterized with respect to their N-terminal sequence and hence cover a wide pattern of biological functions, like important neuroendocrine, behavioral, sensory and automatic functions. The RFamide peptide receptor family represents a multiligand/multireceptor system, as many ligands are recognized by several GPCR subtypes within one family. Multireceptor systems are often susceptible to cross-reactions, as their numerous ligands are frequently closely related. In this review we focus on recent results in the field of structure-activity studies as well as mutational exploration of crucial positions within this GPCR system. The review summarizes the reported peptide analogs and recently developed small molecule ligands (agonists and antagonists) to highlight the current understanding of the pharmacophoric elements, required for affinity and activity at the receptor family. Furthermore, we address the biological functions of the ligands and give an overview on their involvement in physiological processes. We provide insights in the knowledge for the design of highly selective ligands for single receptor subtypes to minimize cross-talk and to eliminate effects from interactions within the GPCR system. This will support the drug development of members of the RFamide family.

Control of GnRH secretion: one step back

The reproductive system is controlled by gonadotropin releasing hormone (GnRH) secretion from the brain, which is finely modulated by a number of factors including gonadal sex steroids. GnRH cells do not express estrogen receptor α, but feedback is transmitted by neurons that are at least 'one step back' from the GnRH cells. Modulation by season, stress and nutrition are effected by neuronal pathways that converge on the GnRH cells. Kisspeptin and gonadotropin inhibitory hormone (GnIH) neurons are regulators of GnRH secretion, the former being a major conduit for transmission of sex steroid feedback. GnIH cells project to GnRH cells and may play a role in the seasonal changes in reproductive activity in sheep. GnIH also modulates the action of GnRH at the level of the pituitary gonadotrope. This review focuses on the role that kisspeptin and GnIH neurons play, as modulators that are 'one step back' from GnRH neurons.

Food restriction dissociates sexual motivation, sexual performance, and the rewarding consequences of copulation in female Syrian hamsters

Animals can switch their behavioral priorities from ingestive to sex behaviors to optimize reproductive success in environments where energy fluctuates. We hypothesized that energy availability differentially affects the appetitive (motivation), consummatory (performance), and learned (rewarding) components of behavior. In Experiment 1, appetitive and consummatory aspects of sex behavior were dissociated in the majority of female Syrian hamsters restricted to 75% of their ad libitum food intake for between 8 and 11 days. Food restriction significantly inhibited vaginal scent marking, decreased the preference for spending time with male hamsters vs. spending time with food, and increased food hoarding with no significant effect on consummatory behaviors such as the incidence of lordosis or food intake. In Experiments 2 and 3, we attempted to use a similar level of food restriction to dissociate sexual appetite from sexual reward. In hamsters, formation of a conditioned place preference (CPP) for copulatory reward is reflected in increased nucleus accumbens (NAc) neural activation, measured as immunocytochemical staining for c-Fos, the protein product of the immediate-early gene, c-fos. In Experiment 2, neural activation increased 1h after copulation in the NAc, and did not differ significantly between 10-day food-restricted and ad libitum-fed females in any brain area examined. In Experiment 3, females were either food-restricted or fed ad libitum over 8-30 days of conditioning with copulatory stimuli. Food-restricted females showed significantly fewer appetitive behaviors, but no difference in formation of a CPP compared to females fed ad libitum. Together these data are consistent with the idea that mild levels of food restriction that inhibit appetitive behaviors fail to attenuate consummatory behaviors and the rewarding consequences of copulation. Thus, appetitive sex behaviors are, at least partially, neuroanatomically and behaviorally distinct from both consummatory behaviors and copulatory reward.

Evidence that RF-amide related peptide-3 is not a mediator of the inhibitory effects of psychosocial stress on gonadotrophin secretion in ovariectomised ewes

It is well known that stress inhibits normal reproductive function, including gonadotrophin secretion; however, the mechanisms and mediators involved are largely unknown. Stress impairs the secretion of luteinising hormone (LH), and it has been suggested that the RF-amide gonadotrophin-inhibitory hormone (GnIH), known as RF-amide related peptide-3 (RFRP-3) in mammalian species, may mediate this inhibitory effect of stress. If this is the case, the GnIH/RFRP system would likely be up-regulated during stress. We tested this hypothesis in ovariectomised ewes using a psychosocial stressor: isolation/restraint. Ewes were randomly allocated to control or stress (n=5 per group). Isolation/restraint stress was imposed for 90 min after control sampling for 4 h, whereas control ewes were sampled continuously for 5.5 h. All ewes were then euthanased and brains were collected. As expected, plasma concentrations of cortisol were increased significantly (P<0.05) by stress and plasma concentrations of LH were significantly (P<0.05) reduced. Immunohistochemistry and in situ hybridisation were conducted for RFRP-3 peptide and RFRP mRNA expression, respectively, in the paraventricular nucleus/dorsal medial hypothalamus region of the hypothalamus. There was no significant effect of stress on RFRP-3 peptide or mRNA levels, with no differences between control or stress ewes. Furthermore, there was no difference in the number of RFRP-3 cells double-labelled for Fos between control and stress ewes and there was no difference in the cellular expression of RFRP mRNA between groups. These results indicate that the GnIH/RFRP system is not activated by psychosocial stress in ewes, suggesting that it is an unlikely mediator of the effects of stress on LH secretion.

Kisspeptin is essential for the full preovulatory LH surge and stimulates GnRH release from the isolated ovine median eminence

Kisspeptins are the product of the Kiss1 gene and potently stimulate GnRH secretion. In sheep, Kiss1 mRNA-expressing cells are found in the arcuate nucleus (ARC) and dorsal-lateral preoptic area and both appear to mediate the positive feedback effect of estradiol to generate the preovulatory GnRH/LH surge. To determine the role of kisspeptin in transmitting estrogen-positive feedback in the hypothalamus, we administered the kisspeptin antagonist p-271 to ewes subjected to an estradiol benzoate-induced LH surge. Kisspeptin antagonist treatment significantly attenuated these LH surges. We further examined the response to kisspeptin treatment prior to the LH surge. Kisspeptin significantly stimulated GnRH secretion into the hypophysial portal system, but the response to kisspeptin was similar in luteal and late-follicular phase ewes. Kiss1r mRNA expression in GnRH neurons was also similar across the estrous cycle. To examine alternative pathways for kisspeptin stimulation of GnRH neurons, we examined the origin of kisspeptin neuronal fibers in the external zone of the median eminence (ME) using neuronal tracing and immunohistochemical techniques. ARC populations of kisspeptin neurons project fibers to the ME. Finally, we showed kisspeptin stimulates GnRH release from ovine ME-cultured explants. This suggests direct kisspeptin to GnRH terminal-to-terminal communication within the ME. Overall, these data indicate an essential role for kisspeptin in receiving stimulatory estrogen signals and generating the full positive feedback GnRH/LH surge. Kisspeptin neurons of the ARC project to the external zone of the ME and kisspeptin acts upon the GnRH fibers at this level.

Effects of RFamide-related peptide (RFRP)-1 and RFRP-3 on oxytocin release and anxiety-related behaviour in rats

RFamide-related peptides (RFRP-1 and RFRP-3) are localised in neurones of the dorsomedial hypothalamus in rats. The dorsomedial hypothalamus plays an essential role in neuroendocrine and behavioural stress responses. In the present study, we examined the role of RFRP in the control of neuroendocrine and behavioural responses in rats. Stressful stimuli increased expression of Fos protein in RFRP-immunoreactive neurones of the dorsomedial hypothalamus, suggesting that stressful stimuli activate RFRP neurones. Intracerebroventricular injection of RFRPs increased the expression of Fos protein in oxytocin neurones in the hypothalamus and plasma concentrations of adrenocorticotrophic hormone and oxytocin. The hypothalamic paraventricular and supraoptic nuclei expressed mRNA of GPR147, the putative RFRP receptor, and application of RFRPs to isolated supraoptic nuclei facilitated oxytocin release, suggesting that RFRPs activate oxytocin neurones directly. Furthermore, the administration of RFRPs induced anxiety-related behaviour in rats in open-field tests. All these data taken together suggest that RFRPs play a role in the control of neuroendocrine and behavioural stress responses in rats.

Recent studies of gonadotropin-inhibitory hormone (GnIH) in the mammalian hypothalamus, pituitary and gonads

The hypothalamo-pituitary-gonadal (HPG) axis integrates internal and external cues via a balance of stimulatory and inhibitory neurochemical systems to time reproductive activity. The cumulative output of these positive and negative modulators drives secretion of gonadotropin-releasing hormone (GnRH), a neuropeptide that causes pituitary gonadotropin synthesis and secretion. Ten years ago, Tsutsui and colleagues discovered a peptide in quail hypothalamus that is capable of inhibiting gonadotropin secretion in cultured quail pituitary cells. Later studies by a variety of researchers examined the presence and functional role for the mammalian ortholog of GnIH. To date, GnIH exhibits a similar distribution and functional role in all mammals investigated, including humans. This overview summarizes the role of GnIH in modulation of mammalian reproductive physiology and suggests avenues for further study by those interested in the neuroendocrine control of reproductive physiology and sexual behavior.

Seasonal breeding as a neuroendocrine model for puberty in sheep

Puberty is defined as the awakening of the hypothalamic-pituitary gonadal axis. Sheep are seasonal breeders, experiencing an annual period of reproductive quiescence and renaissance that can be utilized as a model for the onset of puberty. Kisspeptin and gonadotropin-inhibitory hormone appear to be important for the seasonal shift in reproductive activity and the former is mandatory for puberty. The non-breeding season is characterized by an increase in the negative feedback effect of estrogen on GnRH and gonadotropin secretion, as is the case in the pre-pubertal period. This effect of estrogen may be transmitted by kisspeptin cells. Additionally, dopaminergic A14/A15 neurons facilitate the seasonal change in estrogen negative feedback. Integrated function of these three groups of neurons appears to modulate the annual shift in photoperiod to a physiological change in fertility. This review compares and contrasts seasonal cycles of reproduction with the mechanisms that relate to the onset of puberty.

The roles of RFamide-related peptide-3 in mammalian reproductive function and behaviour

To maximise reproductive success, organisms restrict breeding to optimal times of the day or year, when internal physiology and external environmental conditions are suitable for the survival of both parent and offspring. To appropriately coordinate reproductive activity, internal and external standing is communicated to the hypothalamic-pituitary-gonadal axis via a coordinated balance of stimulatory and inhibitory neurochemical systems. The cumulative balance of these mediators ultimately drives the pattern of gonadotrophin-releasing hormone secretion, a neurohormone that stimulates pituitary gonadotrophin secretion. Until 2000, a complementary inhibitor of pituitary gonadotrophin secretion had not been identified. At this time, a novel, avian hypothalamic peptide capable of inhibiting gonadotrophin secretion in cultured quail pituitary cells was uncovered and named gonadotrophin-inhibitory hormone (GnIH). Subsequently, the presence and functional role for the mammalian orthologue of GnIH, RFamide-related peptide, (RFRP-3), was examined, confirming a conserved role for this peptide across several rodent species. To date, a similar distribution and functional role for RFRP-3 have been observed across all mammals investigated, including humans. This overview summarises the role that RFRP-3 plays in mammals and considers the implications and opportunities for further study with respect to reproductive physiology and the neural control of sexual behaviour and motivation.

Hypothalamic expression of KISS1 and gonadotropin inhibitory hormone genes during the menstrual cycle of a non-human primate

Kisspeptin, the product of the KISS1 gene, stimulates gonadotropin-releasing hormone (GnRH) secretion; gonadotropin inhibitory hormone (GnIH), encoded by the RF-amide-related peptide (RFRP) or NPVF gene, inhibits the reproductive axis. In sheep, kisspeptin neurons are found in the lateral preoptic area (POA) and the arcuate nucleus (ARC) and may be important for initiating the preovulatory GnRH/luteinizing hormone (LH) surge. GnIH cells are located in the ovine dorsomedial hypothalamic nucleus (DMN) and paraventricular nucleus (PVN), with similar distribution in the primate. KISS1 cells are found in the primate POA and ARC, but the function that kisspeptin and GnIH play in primates has not been elucidated. We examined KISS1 and NPVF mRNA throughout the menstrual cycle of a female primate, rhesus macaque (Macaca mulatta), using in situ hybridization. KISS1-expressing cells were found in the POA and ARC, and NPVF-expressing cells were located in the PVN/DMN. KISS1 expression in the caudal ARC and POA was higher in the late follicular phase of the cycle (just before the GnRH/LH surge) than in the luteal phase. NPVF expression was also higher in the late follicular phase. We ascertained whether kisspeptin and/or GnIH cells project to GnRH neurons in the primate. Close appositions of kisspeptin and GnIH fibers were found on GnRH neurons, with no change across the menstrual cycle. These data suggest a role for kisspeptin in the stimulation of GnRH cells before the preovulatory GnRH/LH surge in non-human primates. The role of GnIH is less clear, with paradoxical up-regulation of gene expression in the late follicular phase of the menstrual cycle.

Kisspeptin cells in the ewe brain respond to leptin and communicate with neuropeptide Y and proopiomelanocortin cells

Kisspeptin stimulates reproduction, and kisspeptin cells in the arcuate nucleus (ARC) express Ob-Rb in the mouse. Herein we report studies in ewes to determine whether kisspeptin cells express Ob-Rb and respond to leptin and whether reciprocal connections exist between kisspeptin cells and proopiomelanocortin (POMC) or neuropeptide Y (NPY) cells to modulate reproduction and metabolic function. Kiss1 mRNA was measured by in situ hybridization in ovariectomized ewes that were normal body weight, lean, or lean with leptin treatment by intracerebroventricular (icv) infusion (4 microg/h, 3 d). Kiss1 expression in the ARC and the preoptic area was lower in hypogonadotropic lean animals than animals of normal weight, and icv infusion of leptin partially restored Kiss1 expression in lean animals. Single-cell laser capture microdissection coupled with real-time PCR showed that Kiss1 cells in the preoptic area and ARC express Ob-Rb. Double-label fluorescent immunohistochemistry showed that reciprocal connections exist between kisspeptin cells and NPY and POMC cells. Accordingly, we treated ovariectomized ewes with kisspeptin (5 microg/h, icv) or vehicle for 20 h and examined POMC and NPY gene expression by in situ hybridization. Kisspeptin treatment reduced POMC and increased NPY gene expression. Thus, kisspeptin neurons respond to leptin and expression of Kiss1 mRNA is affected by leptin status. Kisspeptin cells communicate with NPY and POMC cells, altering expression of the relevant genes in the target cells; reciprocal connections also exist. This network between the three cell types could coordinate brain control of reproduction and metabolic homeostatic systems.

The action of leptin on appetite-regulating cells in the ovine hypothalamus: demonstration of direct action in the absence of the arcuate nucleus

It is widely accepted that leptin acts on first-order neurons in the arcuate nucleus (ARC) with information then relayed to other hypothalamic centers. However, the extent to which leptin mediates its central actions solely, or even primarily, via this route is unclear. We used a model of hypothalamo-pituitary disconnection (HPD) to determine whether leptin action on appetite-regulating systems requires the ARC. This surgical preparation eliminates the ARC. We measured effects of iv leptin to activate hypothalamic neurons (Fos labeling). In ARC-intact animals, leptin increased the percentage of Fos-positive melanocortin neurons and reduced percentages of Fos-positive neuropeptide Y neurons compared with saline-treated animals. HPD itself increased Fos labeling in the lateral hypothalamic area (LHA). Leptin influenced Fos labeling in the dorsomedial nucleus (DMH), ventromedial nucleus, and paraventricular nucleus (PVN) in HPD and normal animals, with effects on particular cell types varying. In the LHA and DMH, leptin decreased orexin cell activation in HPD and ARC-intact sheep. HPD abolished leptin-induced expression of Fos in melanin-concentrating hormone cells in the LHA and in CRH cells in the PVN. In contrast, HPD accentuated activation in oxytocin neurons. Our data from sheep with lesions encompassing the ARC do not suggest a primacy of action of leptin in this nucleus. We demonstrate that first order to second order signaling may not represent the predominant means by which leptin acts in the brain to generate integrated responses. We provide evidence that leptin exerts direct action on cells of the DMH, ventromedial nucleus, and PVN.

Gonadotropin inhibitory hormone function in mammals

Reproductive function depends on the stimulatory action of gonadotropin-releasing hormone (GnRH), secreted by the brain. Original work in birds identified and isolated a peptide that inhibits gonadotropin release, named gonadotropin inhibitory hormone (GnIH). There is no evidence for a similar factor operant in mammals. This mammalian orthologue of GnIH has been named RFamide-related peptide (RFRP), and negatively regulates GnRH function and gonadotropin secretion. In particular, mammalian GnIH inhibits the function of GnRH cells and acts at the level of gonadotropes. It appears to play a major role in seasonal regulation of reproduction and also to be involved in regulation of stress and food intake.

Effect of RF-amide-related peptide-3 on luteinizing hormone and follicle-stimulating hormone synthesis and secretion in ovine pituitary gonadotropes

GnRH provides the primary stimulus for the reproductive axis, but original work also revealed the existence of a gonadotropin-inhibitory hormone (GnIH) in birds. In mammals, GnIH properties are displayed by a hypothalamic dodecapeptide, which is a member of the RF-amide family, namely RF-amide-related peptide (RFRP)-3. This peptide inhibits GnRH-stimulated gonadotropin secretion from ovine pituitary cells in culture, but it is not known whether there are effects on gonadotropin synthesis. The aim of the present study was to determine the effects of RFRP-3 on the expression of genes for beta-subunits of the gonadotropins in ovine pituitary cells from gonadectomized ewes and rams. Cells in primary culture were given GnRH or vehicle pulses every 8 h for 24 h with and without RFRP-3 treatment. GnRH stimulated LH and FSH secretion, which was reduced by RFRP-3. Quantitative real-time PCR revealed increased expression of LHbeta and FSHbeta subunit genes after GnRH treatment and a specific reduction in expression after RFRP-3 treatment. There was no effect on the expression of GH, proopiomelanocortin, or prolactin genes. Western blotting showed that GnRH stimulated phosphorylation of ERK (phospho-ERK-1/2), and this effect was abolished by RFRP-3. We conclude that RFRP-3 acts on the pituitary gonadotropes to inhibit synthesis of the gonadotropins, and this effect may be mediated by a reduction in the GnRH-stimulated second messenger phospho-ERK-1/2.