Detailed distribution of neuropeptide FF receptors (NPFF1 and NPFF2) in the rat, mouse, octodon, rabbit, guinea pig, and marmoset monkey brains: a comparative autoradiographic study

Renal autocrine neuropeptide FF (NPFF) signaling regulates blood pressure

The kidney and brain play critical roles in the regulation of blood pressure. Neuropeptide FF (NPFF), originally isolated from the bovine brain, has been suggested to contribute to the pathogenesis of hypertension. However, the roles of NPFF and its receptors, NPFF-R1 and NPFF-R2, in the regulation of blood pressure, via the kidney, are not known. In this study, we found that the transcripts and proteins of NPFF and its receptors, NPFF-R1 and NPFF-R2, were expressed in mouse and human renal proximal tubules (RPTs). In mouse RPT cells (RPTCs), NPFF, but not RF-amide-related peptide-2 (RFRP-2), decreased the forskolin-stimulated cAMP production in a concentration- and time-dependent manner. Furthermore, dopamine D1-like receptors colocalized and co-immunoprecipitated with NPFF-R1 and NPFF-R2 in human RPTCs. The increase in cAMP production in human RPTCs caused by fenoldopam, a D1-like receptor agonist, was attenuated by NPFF, indicating an antagonistic interaction between NPFF and D1-like receptors. The renal subcapsular infusion of NPFF in C57BL/6 mice decreased renal sodium excretion and increased blood pressure. The NPFF-mediated increase in blood pressure was prevented by RF-9, an antagonist of NPFF receptors. Taken together, our findings suggest that autocrine NPFF and its receptors in the kidney regulate blood pressure, but the mechanisms remain to be determined.

Neuropeptide FF (NPFF)-positive nerve cells of the human cerebral cortex and white matter in controls, selected neurodegenerative diseases, and schizophrenia

We quantified and determined for the first time the distribution pattern of the neuropeptide NPFF in the human cerebral cortex and subjacent white matter. To do so, we studied n = 9 cases without neurological disorders and n = 22 cases with neurodegenerative diseases, including sporadic amyotrophic lateral sclerosis (ALS, n = 8), Alzheimer's disease (AD, n = 8), Pick's disease (PiD, n = 3), and schizophrenia (n = 3). NPFF-immunopositive cells were located chiefly, but not exclusively, in the superficial white matter and constituted there a subpopulation of white matter interstitial cells (WMIC): Pyramidal-like and multipolar somata predominated in the gyral crowns, whereas bipolar and ovoid somata predominated in the cortex surrounding the sulci. Their sparsely ramified axons were unmyelinated and exhibited NPFF-positive bead-like varicosities. We found significantly fewer NPFF-immunopositive cells in the gray matter of the frontal, cingulate, and superior temporal gyri of both sporadic ALS and late-stage AD patients than in controls, and significantly fewer NPFF-positive cells in the subjacent as well as deep white matter of the frontal gyrus of these patients compared to controls. Notably, the number of NPFF-positive cells was also significantly lower in the hippocampal formation in AD compared to controls. In PiD, NPFF-positive cells were present in significantly lower numbers in the gray and white matter of the cingulate and frontal gyrii in comparison to controls. In schizophrenic patients, lower wNPFF cell counts in the neocortex were significant and global (cingulate, frontal, superior temporal gyrus, medial, and inferior gyri). The precise functions of NPFF-positive cells and their relationship to the superficial corticocortical white matter U-fibers are currently unknown. Here, NPFF immunohistochemistry and expression characterize a previously unrecognized population of cells in the human brain, thereby providing a new entry-point for investigating their physiological and pathophysiological roles.

Brain RFamide Neuropeptides in Stress-Related Psychopathologies

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

Anorexigenic neuropeptides as anti-obesity and neuroprotective agents: exploring the neuroprotective effects of anorexigenic neuropeptides

Since 1975, the incidence of obesity has increased to epidemic proportions, and the number of patients with obesity has quadrupled. Obesity is a major risk factor for developing other serious diseases, such as type 2 diabetes mellitus, hypertension, and cardiovascular diseases. Recent epidemiologic studies have defined obesity as a risk factor for the development of neurodegenerative diseases, such as Alzheimer's disease (AD) and other types of dementia. Despite all these serious comorbidities associated with obesity, there is still a lack of effective antiobesity treatment. Promising candidates for the treatment of obesity are anorexigenic neuropeptides, which are peptides produced by neurons in brain areas implicated in food intake regulation, such as the hypothalamus or the brainstem. These peptides efficiently reduce food intake and body weight. Moreover, because of the proven interconnection between obesity and the risk of developing AD, the potential neuroprotective effects of these two agents in animal models of neurodegeneration have been examined. The objective of this review was to explore anorexigenic neuropeptides produced and acting within the brain, emphasizing their potential not only for the treatment of obesity but also for the treatment of neurodegenerative disorders.

NPFFR2-deficient mice fed a high-fat diet develop strong intolerance to glucose

A previous study on neuropeptide FF receptor 2 (NPFFR2)-deficient mice has demonstrated that NPFFR2 is involved in the control of energy balance and thermogenesis. Here, we report on the metabolic impact of NPFFR2 deficiency in male and female mice that were fed either a standard diet (STD) or a high-fat diet (HFD) and each experimental group consisted of ten individuals. Both male and female NPFFR2 knockout (KO) mice exhibited severe glucose intolerance that was exacerbated by a HFD diet. In addition, reduced insulin pathway signaling proteins in NPFFR2 KO mice fed a HFD resulted in the development of hypothalamic insulin resistance. HFD feeding did not cause liver steatosis in NPFFR2 KO mice of either sex, but NPFFR2 KO male mice fed a HFD had lower body weights, white adipose tissues, and liver and lower plasma leptin levels compared with their wild-type (WT) controls. Lower liver weight in NPFFR2 KO male mice compensated for HFD-induced metabolic stress by increased liver PPARα and plasma FGF21 hepatokine, which supported fatty acid β-oxidation in the liver and white adipose tissue. Conversely, NPFFR2 deletion in female mice attenuated the expression of Adra3β and Pparγ, which inhibited lipolysis in adipose tissue.

Search for lipidized PrRP analogs with strong anorexigenic effect: In vitro and in vivo studies

Prolactin-releasing peptide (PrRP) is an anorexigenic neuropeptide that attenuates food intake and increases energy expenditure. We designed three series of new lipidized PrRP31 analogs of different lengths of fatty acids attached at amino acids 1 or 11 directly or via linkers, part of them acetylated at the N-terminus and/or modified with dichlorophenylalanine (PheCl₂) at the C-terminus. We tested their affinity for and activation of signaling pathways relevant to receptors GPR10, NPFF-R2, and NPFF-R1, effect on food intake in fasted or freely fed mice and rats, and stability in rat plasma. We aimed to select a strong dual GPR10/NPFF-R2 agonist whose affinity for NPFF-1 was not enhanced. The selected potent analog was then tested for body weight-lowering potency after chronic administration in mice with diet-induced obesity. PrRP31 analogs lipidized by monocarboxylic fatty acids showed strong dual affinity for both GPR10 and NPFF-R2 and activated MAPK/ERK1/2, Akt and CREB in cells overexpressing GPR10 and NPFF-R2. The selected analog stabilized at N- and C-termini and palmitoylated through the TTDS linker to Lys¹¹ is a powerful dual agonist GPR10/NPFF-R2 at not enhanced affinity for NPFF-R1. It showed strong anti-obesity properties in mice with diet-induced obesity and became a potential compound for further studies.

Co-existing Neuropeptide FF and Gonadotropin-Releasing Hormone 3 Coordinately Modulate Male Sexual Behavior

Animals properly perform sexual behaviors by using multiple sensory cues. However, neural mechanisms integrating multiple sensory cues and regulating motivation for sexual behaviors remain unclear. Here, we focused on peptidergic neurons, terminal nerve gonadotropin-releasing hormone (TN-GnRH) neurons, which receive inputs from various sensory systems and co-express neuropeptide FF (NPFF) in addition to GnRH. Our behavioral analyses using knockout medaka of GnRH (gnrh3) and/or NPFF (npff) demonstrated that some sexual behavioral repertoires were delayed, not disrupted, in gnrh3 and npff single knockout males, while the double knockout appeared to alleviate the significant defects that were observed in single knockouts. We also found anatomical evidence to show that both neuropeptides modulate the sexual behavior-controlling brain areas. Furthermore, we demonstrated that NPFF activates neurons in the preoptic area via indirect pathway, which is considered to induce the increase in motivation for male sexual behaviors. Considering these results, we propose a novel mechanism by which co-existing peptides of the TN-GnRH neurons, NPFF, and GnRH3 coordinately modulate certain neuronal circuit for the control of behavioral motivation. Our results may go a long way toward understanding the functional significance of peptidergic neuromodulation in response to sensory information from the external environments.

The distribution of Neuropeptide FF and Neuropeptide VF in central and peripheral tissues and their role in energy homeostasis control

Neuropeptide FF (NPFF) and Neuropeptide VF (NPVF) are part of the extended RFamide peptide family characterized by their common arginine (R) and amidated phenylalanine (F)-motif at the carboxyl terminus. Both peptides signal through their respective high affinity G-protein coupled receptors, NPFFR2 and NPFFR1, but also show binding affinity for the other receptor due to their sequence similarity. NPFF and NPVF are highly conserved throughout evolution and can be found across the whole animal kingdom. Both have been implicated in a variety of biological mechanisms, including nociception, locomotion, reproduction, and response to pain and stress. However, more recently a new major functional role in the control of energy homeostasis has been discovered. In this article we will summarise the current knowledge on the distribution of NPFF, NPVF, and their receptors in central and peripheral tissues, as well as how this relates to the regulation of food intake and energy balance, which will help to better understand their role in these processes and thus might help finding treatments for impaired energy homeostasis disorders, such as obesity or anorexia.

Expression analysis of neuropeptide FF receptors on neuroendocrine-related neurons in the rat brain using highly sensitive in situ hybridization

RF-amide peptides, a family of peptides characterized by a common carboxy-terminal Arg-Phe-NH₂ motif, play various physiological roles in the brain including the modulation of neuroendocrine signaling. Neuropeptide FF (NPFF) receptors exhibit a high affinity for all RF-amide peptides, which suggests that the neurons expressing these NPFF receptors may have multiple functions in the brain. However, the distribution of the neurons expressing NPFF receptors in the rat brain remains poorly understood. This study aimed to determine the detailed histological distribution of mRNA that encodes the neuropeptide FF receptors (Npffr1 and Npffr2) in the rat brain using in situ hybridization. Neurons with strong Npffr1 expression were observed in the lateral septal nucleus and several hypothalamic areas related to neuroendocrine functions, including the paraventricular nucleus (PVN) and arcuate nucleus, whereas Npffr2-expressing neurons were observed mainly in brain regions involved in somatosensory pathways, such as several subnuclei of the thalamus. Npffr1 expression was observed in 70% of corticotropin-releasing hormone neurons, but in only a small population of oxytocin and vasopressin neurons in the PVN. Npffr1 expression was also observed in the dopaminergic neurons in the periventricular nucleus and the dorsal arcuate nucleus, and in the kisspeptin neurons in the anteroventral periventricular nucleus. These results suggest that NPFFR1-mediated signaling may be involved in neuroendocrine functions, such as in reproduction and stress response. In conjunction with a detailed histological map of NPFFRs, this study provides useful data for future neuroendocrine research.

Intracerebroventricular Neuropeptide FF Diminishes the Number of Apneas and Cardiovascular Effects Produced by Opioid Receptors' Activation

The opioid-induced analgesia is associated with a number of side effects such as addiction, tolerance and respiratory depression. The involvement of neuropeptide FF (NPFF) in modulation of pain perception, opioid-induced tolerance and dependence was well documented in contrast to respiratory depression. Therefore, the aim of the present study was to examine the potency of NPFF to block post-opioid respiratory depression, one of the main adverse effects of opioid therapy. Urethane-chloralose anaesthetized Wistar rats were injected either intravenously (iv) or intracerebroventricularly (icv) with various doses of NPFF prior to iv endomorphin-1 (EM-1) administration. Iv NPFF diminished the number of EM-1-induced apneas without affecting their length and without influence on the EM-1 induced blood pressure decline. Icv pretreatment with NPFF abolished the occurrence of post-EM-1 apneas and reduced also the maximal drop in blood pressure and heart rate. These effects were completely blocked by the NPFF receptor antagonist RF9, which was given as a mixture with NPFF before systemic EM-1 administration. In conclusion, our results showed that centrally administered neuropeptide FF is effective in preventing apnea evoked by stimulation of μ-opioid receptors and the effect was due to activation of central NPFF receptors. Our finding indicates a potential target for reversal of opioid-induced respiratory depression.

Neuropeptide FF receptor 2 inhibits capsaicin-induced CGRP Upregulation in mouse trigeminal ganglion

BACKGROUND

Stimulation of trigeminovascular pathway is widely used to establish the headache animal model. Headache is a common neurological disorder, in which symptomatic attacks are mediated by calcitonin-gene-related peptide (CGRP). CGRP is synthesized and released from the trigeminal ganglion to transmit pain signals under stimulation. On the other hand, Neuropeptide FF (NPFF) is a candidate transmitter/modulator for migraine, and stimulation of its receptor, NPFFR2, increases the expression and release of CGRP in mice sensory neurons. Here, we investigate the impact of NPFFR2 on trigeminal CGRP level in a capsaicin-induced headache mouse model.

METHODS

Mice were intracisternally injected with capsaicin into the cisterna magna to activate the trigeminovascular pathway and induce headache symptoms. Mice pretreated with Npffr2-shRNA or NPFFR2 knockouts were adopted to test the impact of NPFFR2 on capsaicin-induced CGRP upregulation in trigeminal ganglion. The gene silencing effect of Npffr2-shRNA in trigeminal ganglion was confirmed by real-time PCR. Trigeminal CGRP level was determined by immunofluorescence staining, and the percentage of CGRP-positive cell was calculated after setting the signal intensity threshold by Image J software. Amount of trigeminal CGRP in NPFFR2 overexpressed mice was also measured by CGRP ELISA.

FINDINGS

Infusion of capsaicin into the cisterna magna upregulated the CGRP in trigeminal ganglion and induced spontaneous pain behaviors including the reduction of locomotor activity and the increase of freezing behavior. Intracisternal injection of Npffr2-shRNA reduced the mRNA of Npffr2 in trigeminal ganglion. Mice pretreatment with Npffr2-shRNA prevented capsaicin-induced CGRP upregulation in trigeminal ganglion. Similarly, CGRP upregulation was also reduced in NPFFR2 knockout mice. On the contrary, trigeminal CGRP was increased in NPFFR2 overexpressed mice.

CONCLUSIONS

Reducing the level of NPFFR2 leads to the downregulation of capsaicin-induced CGRP in trigeminal ganglion, which would consequently attenuate the activation of trigeminovascular pathway. Thus, NPFFR2 could serve as a potential target for neuromodulation of cephalic pain.

Spinal DN-9, a Peptidic Multifunctional Opioid/Neuropeptide FF Agonist Produced Potent Nontolerance Forming Analgesia With Limited Side Effects

The development of multitarget opioid drugs has emerged as an attractive therapeutic strategy to eliminate opioid-related side effects. Our previous study developed a series of opioid and neuropeptide FF pharmacophore-containing chimeric peptides, including DN-9 (Tyr-D.Ala-Gly-NMe.Phe-Gly-Pro-Gln-Arg-Phe-NH₂), which produced potent nontolerance forming analgesia at the supraspinal level. In the present study, the antinociceptive effects of DN-9 in a series of preclinical pain models and the potential side-effects were investigated at the spinal level in mice. In the tail-flick test, intrathecal injection of DN-9 produced potent analgesia with an ED₅₀ value at 1.33 pmol, and the spinal antinociception of DN-9 was mainly mediated by μ- and κ-opioid receptors. In addition, DN-9-induced spinal antinociception was augmented by the neuropeptide FF receptors antagonist. Furthermore, DN-9 could decrease both the frequency and amplitude of sEPSCs in lamina IIo neurons of the spinal cord, which were mediated by opioid receptors. In contrast to morphine, chronic intrathecal treatments with DN-9 did not induce analgesic tolerance, c-Fos expression or microglial activation. Intrathecal injection of DN-9 showed potent analgesia with antinociceptive ED₅₀ values between .66 and 55.04 pmol in different pain models, including the formalin test, acetic acid-induced writhing test, carrageenan-induced inflammatory pain and neuropathic pain. Moreover, DN-9 did not show side effects in locomotor function and coordination, gastrointestinal transit inhibition, the cardiovascular system, and body temperature regulation at antinociceptive doses. Taken together, the present study showed DN-9 produced effective, nontolerance forming analgesia with reduced side effects at the spinal level. DN-9 might be a promising compound for developing multifunctional opioid analgesics with limited adverse effects. PERSPECTIVE: This article presents the potent and nontolerance forming analgesia effects of DN-9 in a series of preclinical pain models with less opioid related adverse effects at the spinal level in mice. This study also demonstrates that DN-9 has translational potential into an intrathecal analgesic.

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

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

Pharmacologically evoked apnoeas. Receptors and nervous pathways involved

This review analyses the knowledge about the incidence of transient apnoeic spells, induced by substances which activate vagal chemically sensitive afferents. It considers the specificity and expression of appropriate receptors, and relevant research on pontomedullary circuits contributing to a cessation of respiration. Insight is gained into an excitatory drive of 5-HT_1A serotonin receptors in overcoming opioid-induced respiratory inhibition.

Diet-induced adaptive thermogenesis requires neuropeptide FF receptor-2 signalling

Excess caloric intake results in increased fat accumulation and an increase in energy expenditure via diet-induced adaptive thermogenesis; however, the underlying mechanisms controlling these processes are unclear. Here we identify the neuropeptide FF receptor-2 (NPFFR2) as a critical regulator of diet-induced thermogenesis and bone homoeostasis. Npffr2^−/− mice exhibit a stronger bone phenotype and when fed a HFD display exacerbated obesity associated with a failure in activating brown adipose tissue (BAT) thermogenic response to energy excess, whereas the activation of cold-induced BAT thermogenesis is unaffected. NPFFR2 signalling is required to maintain basal arcuate nucleus NPY mRNA expression. Lack of NPFFR2 signalling leads to a decrease in BAT thermogenesis under HFD conditions with significantly lower UCP-1 and PGC-1α levels in the BAT. Together, these data demonstrate that NPFFR2 signalling promotes diet-induced thermogenesis via a novel hypothalamic NPY-dependent circuitry thereby coupling energy homoeostasis with energy partitioning to adipose and bone tissue.

Excess caloric intake leads to increased thermogenesis in brown adipose tissue, to limit weight gain. Here, the authors show that neuropeptide FF receptor-2 signalling promotes thermogenesis via control of NPY expression in the arcuate nucleus, and that it absence in mice leads to a failure of activation of diet-induced thermogenesis and the development of exacerbated obesity.

The role of orphan G protein-coupled receptors in the modulation of pain: A review

G protein-coupled receptors (GPCRs) comprise a large number of receptors. Orphan GPCRs are divided into six families. These groups contain orphan receptors for which the endogenous ligands are unclear. They have various physiological effects in the body and have the potential to be used in the treatment of different diseases. Considering their important role in the central and peripheral nervous system, their role in the treatment of pain has been the subject of some recent studies. At present, there are effective therapeutics for the treatment of pain including opioid medications and non-steroidal anti-inflammatory drugs. However, the side effects of these drugs and the risks of tolerance and dependence remain a major problem. In addition, neuropathic pain is a condition that does not respond to currently available analgesic medications well. In the present review article, we aimed to review the most recent findings regarding the role of orphan GPCRs in the treatment of pain. Accordingly, based on the preclinical findings, the role of GPR3, GPR7, GPR8, GPR18, GPR30, GPR35, GPR40, GPR55, GPR74, and GPR147 in the treatment of pain was discussed. The present study highlights the role of orphan GPCRs in the modulation of pain and implies that these receptors are potential new targets for finding better and more efficient therapeutics for the management of pain particularly neuropathic pain.

Female sexual behavior in mice is controlled by kisspeptin neurons

Sexual behavior is essential for the survival of many species. In female rodents, mate preference and copulatory behavior depend on pheromones and are synchronized with ovulation to ensure reproductive success. The neural circuits driving this orchestration in the brain have, however, remained elusive. Here, we demonstrate that neurons controlling ovulation in the mammalian brain are at the core of a branching neural circuit governing both mate preference and copulatory behavior. We show that male odors detected in the vomeronasal organ activate kisspeptin neurons in female mice. Classical kisspeptin/Kiss1R signaling subsequently triggers olfactory-driven mate preference. In contrast, copulatory behavior is elicited by kisspeptin neurons in a parallel circuit independent of Kiss1R involving nitric oxide signaling. Consistent with this, we find that kisspeptin neurons impinge onto nitric oxide-synthesizing neurons in the ventromedial hypothalamus. Our data establish kisspeptin neurons as a central regulatory hub orchestrating sexual behavior in the female mouse brain.

Mate preference and copulatory behavior in female rodents are coordinated with the ovulation cycles of the animal. This study shows that hypothalamic kisspeptin neurons control both mate choice and copulation, and therefore, that sexual behavior and ovulation may be synchronized by the same neuropeptide.

NPFFR2 Activates the HPA Axis and Induces Anxiogenic Effects in Rodents

Neuropeptide FF (NPFF) belongs to the RFamide family and is known as a morphine-modulating peptide. NPFF regulates various hypothalamic functions through two receptors, NPFFR1 and NPFFR2. The hypothalamic-pituitary-adrenal (HPA) axis participates in physiological stress response by increasing circulating glucocorticoid levels and modulating emotional responses. Other RFamide peptides, including neuropeptide AF, neuropeptide SF and RFamide related peptide also target NPFFR1 or NPFFR2, and have been reported to activate the HPA axis and induce anxiety- or depression-like behaviors. However, little is known about the action of NPFF on HPA axis activity and anxiety-like behaviors, and the role of the individual receptors remains unclear. In this study, NPFFR2 agonists were used to examine the role of NPFFR2 in activating the HPA axis in rodents. Administration of NPFFR2 agonists, dNPA (intracerebroventricular, ICV) and AC-263093 (intraperitoneal, IP), time-dependently (in rats) and dose-dependently (in mice) increased serum corticosteroid levels and the effects were counteracted by the NPFF receptor antagonist, RF9 (ICV), as well as corticotropin-releasing factor (CRF) antagonist, α-helical CRF(9-41) (intravenous, IV). Treatment with NPFFR2 agonist (AC-263093, IP) increased c-Fos protein expression in the hypothalamic paraventricular nucleus and induced an anxiogenic effect, which was evaluated in mice using an elevated plus maze. These findings reveal, for the first time, that the direct action of hypothalamic NPFFR2 stimulates the HPA axis and triggers anxiety-like behaviors.

Anti-opioid Effects of RFRP-3 on Magnocellular Neuron Activity in Morphine-naïve and Morphine-treated Female Rats

Neuropeptide FF receptors (NPFFR1 and NPFFR2) have been proposed to possess anti-opioid properties, and be involved in the development of opiate tolerance and dependence. However, there is no evidence to date supporting such opioid effects at the cellular level in vivo. Using in vivo electrophysiological recordings from vasopressin and oxytocin neurons in the supraoptic nucleus, we aimed to determine the effects of NPFFRs on opiate inhibition, tolerance, and dependence at a cellular level. Both vasopressin and oxytocin neurons are acutely inhibited by opioids and develop opiate tolerance. Oxytocin neurons also develop cellular opiate dependence and undergo withdrawal hyperexcitation upon cessation of opiate administration. Here, the classical μ-opioid receptor agonist, morphine robustly inhibited the spontaneous firing rate of vasopressin and oxytocin neurons, and this inhibition was attenuated by pretreatment with the NPFFR1 agonist, RFamide-related peptide-3. In rats infused with morphine for 6 d, vasopressin neurons were unresponsive to morphine, indicating the development of cellular tolerance, but pretreatment with the NPFFR antagonist, GJ14, restored acute morphine inhibition. In morphine-infused rats, RFamide related peptide-3 did not induce withdrawal excitation in oxytocin neurons and GJ14 did not reverse naloxone-precipitated withdrawal excitation. This is the first evidence of anti-opioid effects of the NPFFR system at a cellular level in vivo. Our results suggest that the anti-opioid properties of the NPFFR system reduce morphine sensitivity during tolerance but that it is not involved in dependence.

Chronic activation of NPFFR2 stimulates the stress-related depressive behaviors through HPA axis modulation

Neuropeptide FF (NPFF) is a morphine-modulating peptide that regulates the analgesic effect of opioids, and also controls food consumption and cardiovascular function through its interaction with two cognate receptors, NPFFR1 and NPFFR2. In the present study, we explore a novel modulatory role for NPFF-NPFFR2 in stress-related depressive behaviors. In a mouse model of chronic mild stress (CMS)-induced depression, the expression of NPFF significantly increased in the hypothalamus, hippocampus, medial prefrontal cortex (mPFC) and amygdala. In addition, transgenic (Tg) mice over-expressing NPFFR2 displayed clear depression and anxiety-like behaviors with hyperactivity in the hypothalamic-pituitary-adrenal (HPA) axis, reduced expression of glucocorticoid receptor (GR) and neurogenesis in the hippocampus. Furthermore, acute treatment of NPFFR2 agonists in wild-type (WT) mice enhanced the activity of the HPA axis, and chronic administration resulted in depressive and anxiety-like behaviors. Chronic stimulation of NPFFR2 also decreased the expression of hippocampal GR and led to persistent activation of the HPA axis. Strikingly, bilateral intra-paraventricular nucleus (PVN) injection of NPFFR2 shRNA predominately inhibits the depressive-like behavior in CMS-exposed mice. Antidepressants, fluoxetine and ketamine, effectively relieved the depressive behaviors of NPFFR2-Tg mice. We speculate that persistent NPFFR2 activation, in particular in the hypothalamus, up-regulates the HPA axis and results in long-lasting increases in circulating corticosterone (CORT), consequently damaging hippocampal function. This novel role of NPFFR2 in regulating the HPA axis and hippocampal function provides a new avenue for combating depression and anxiety-like disorder.

Kisspeptin Regulation of Neuronal Activity throughout the Central Nervous System

Kisspeptin signaling at the gonadotropin-releasing hormone (GnRH) neuron is now relatively well characterized and established as being critical for the neural control of fertility. However, kisspeptin fibers and the kisspeptin receptor (KISS1R) are detected throughout the brain suggesting that kisspeptin is involved in regulating the activity of multiple neuronal circuits. We provide here a review of kisspeptin actions on neuronal populations throughout the brain including the magnocellular oxytocin and vasopressin neurons, and cells within the arcuate nucleus, hippocampus, and amygdala. The actions of kisspeptin in these brain regions are compared to its effects upon GnRH neurons. Two major themes arise from this analysis. First, it is apparent that kisspeptin signaling through KISS1R at the GnRH neuron is a unique, extremely potent form or neurotransmission whereas kisspeptin actions through KISS1R in other brain regions exhibit neuromodulatory actions typical of other neuropeptides. Second, it is becoming increasingly likely that kisspeptin acts as a neuromodulator not only through KISS1R but also through other RFamide receptors such as the neuropeptide FF receptors (NPFFRs). We suggest likely locations of kisspeptin signaling through NPFFRs but note that only limited tools are presently available for examining kisspeptin cross-signaling within the RFamide family of neuropeptides.

RF-amide neuropeptides and their receptors in Mammals: Pharmacological properties, drug development and main physiological functions

RF-amide neuropeptides, with their typical Arg-Phe-NH2 signature at their carboxyl C-termini, belong to a lineage of peptides that spans almost the entire life tree. Throughout evolution, RF-amide peptides and their receptors preserved fundamental roles in reproduction and feeding, both in Vertebrates and Invertebrates. The scope of this review is to summarize the current knowledge on the RF-amide systems in Mammals from historical aspects to therapeutic opportunities. Taking advantage of the most recent findings in the field, special focus will be given on molecular and pharmacological properties of RF-amide peptides and their receptors as well as on their implication in the control of different physiological functions including feeding, reproduction and pain. Recent progress on the development of drugs that target RF-amide receptors will also be addressed.

RFRP Neurons - The Doorway to Understanding Seasonal Reproduction in Mammals

Seasonal control of reproduction is critical for the perpetuation of species living in temperate zones that display major changes in climatic environment and availability of food resources. In mammals, seasonal cues are mainly provided by the annual change in the 24-h light/dark ratio (i.e., photoperiod), which is translated into the nocturnal production of the pineal hormone melatonin. The annual rhythm in this melatonin signal acts as a synchronizer ensuring that breeding occurs when environmental conditions favor survival of the offspring. Although specific mechanisms might vary among seasonal species, the hypothalamic RF (Arg-Phe) amide-related peptides (RFRP-1 and -3) are believed to play a critical role in the central control of seasonal reproduction and in all seasonal species investigated, the RFRP system is persistently inhibited in short photoperiod. Central chronic administration of RFRP-3 in short day-adapted male Syrian hamsters fully reactivates the reproductive axis despite photoinhibitory conditions, which highlights the importance of the seasonal changes in RFRP expression for proper regulation of the reproductive axis. The acute effects of RFRP peptides, however, depend on species and photoperiod, and recent studies point toward a different role of RFRP in regulating female reproductive activity. In this review, we summarize the recent advances made to understand the role and underlying mechanisms of RFRP in the seasonal control of reproduction, primarily focusing on mammalian species.

Visualization of Kisspeptin Binding to Rat Hypothalamic Neurons

The neuropeptide kisspeptin plays an important role in fertility and the onset of puberty, stimulating gonadotropin-releasing hormone (GnRH) neurons to activate the hypothalamic–pituitary–gonadal axis. Several studies have demonstrated a morphological interaction between kisspeptin- and GnRH-expressing neurons; however, few have addressed the interaction of kisspeptin with other neuronal subtypes. We recently showed that fibers immunoreactive for kisspeptin were densely distributed in the dorsal part of the arcuate nucleus. These fibers were found in close proximity to GnRH and tuberoinfundibular dopamine (TIDA) neurons. In the present study, using biotinylated kisspeptin, we established a visualization method for identifying kisspeptin binding sites on TIDA neurons. Biotinylated kisspeptin bound to the cell bodies of TIDA neurons and surrounding fibers, suggesting that TIDA neurons express sites of action for kisspeptin. Our assay also detected biotinylation signals from kisspeptin binding to GnRH fibers in the median eminence, but not to cell bodies of GnRH neurons in the medial preoptic area. Positive signals were completely eliminated by addition of excess non-labeled kisspeptin. This method enabled us to detect kisspeptin binding sites on specific neural structures and neuronal fibers.

Sex differences in the photoperiodic regulation of RF-Amide related peptide (RFRP) and its receptor GPR147 in the syrian hamster

RF-(Arg-Phe) related peptides (RFRP-1 and -3) are considered to play a role in the seasonal regulation of reproduction; however, the effect of the peptides depends on species and gender. This study aimed at comparing the RFRP system in male and female Syrian hamsters over long and short photoperiods to investigate the neuroanatomical basis of these differential effects. The neuroanatomical distribution of RFRP neurons and fibers, revealed using an antiserum recognizing RFRP-1 and -3, as well as GPR147 mRNA, are similar in male and female Syrian hamsters. RFRP neurons are mainly found in the medial hypothalamus, whereas RFRP projections and GPR147 mRNA are observed in the preoptic area, anteroventral-periventricular nucleus, suprachiasmatic nucleus, paraventricular nucleus, bed nucleus of the stria terminalis, ventromedial hypothalamus, habenular nucleus, and arcuate nucleus. The number of RFRP neurons is higher in females than in males, and in both sexes, the number of RFRP neurons is reduced in short photoperiods. GPR147 mRNA levels are higher in females than in males and are downregulated in short photoperiods, particularly in females. Interestingly, the number of RFRP-positive fibers in the anteroventral-periventricular nucleus is higher only in females adjusted to a short photoperiod. Our results suggest that the RFRP system, which is strongly regulated by photoperiod in both male and female Syrian hamsters, is particularly important in females, with a distinct role in the anteroventral-periventricular nucleus, possibly in the regulation of the preovulatory luteinizing hormone surge via kisspeptin neurons.

Peripheral administration of palmitoylated prolactin-releasing peptide induces Fos expression in hypothalamic neurons involved in energy homeostasis in NMRI male mice

Energy homeostasis is the result of a balance between energy intake and expenditure, and the hypothalamus plays a key role in the regulation of these processes. The hypothalamic prolactin-releasing peptide (PrRP) is involved in food intake regulation and energy homeostasis, although only its lipidized analogs exert central anorexigenic effects after peripheral administration. The aim of the present study was to delineate the extent of the Fos expression as a marker of neuronal activation within the hypothalamic structures involved in food intake regulation after peripherally administered palmitoylated PrRP31 (palm-PrRP31) and to determine whether the anorexigenic effect of peripherally administered palm-PrRP31 influence the activity of hypocretin (HCRT) and oxytocin (OXY) neurons, i.e., the neuropeptides crucially involved in the regulation of energy homeostasis. The data confirmed an anorexigenic effect of palm-PrRP31 treatment (5mg/kg, s.c.) in mice. In the palm-PrRP31-treated animals, a significant increase in Fos expression was observed in the hypothalamic paraventricular (PVN), dorsomedial (DMN), and arcuate (Arc) nuclei and in the neurons of the nucleus of the solitary tract (NTS). Moreover, significant Fos expression was observed in the lateral hypothalamic area (LHA) HCRT neurons and PVN OXY neurons after palm-PrRP31 administration. The present findings may indicate that palm-PrRP31 may be involved in energy homeostasis via the activation of several hypothalamic structures. Fos activation of the hypothalamic OXY and HCRT neurons in the PVN and LHA emphasizes the importance of the areas mentioned in the central action of palm-PrRP31.

Neuropeptide FF receptors exhibit direct and anti-opioid effects on mice dorsal raphe nucleus neurons

By using acutely dissociated dorsal raphe nucleus neurons (DRN) from young mice, direct and anti-opioid effects of Neuropeptide FF (NPFF) receptors were measured. The NPFF analog 1 DMe (10 µM) had no effect on resting Ca2+ channels but reduced the magnitude of Ca2+ transients induced by depolarization in 83.3% neurons tested, of which the inhibition rate is 45.4±2.9%. Pertussis toxin treatment reduced to 18.9% the number of responding neurons and attenuated by 47% the response of 1 DMe. In contrast, cholera toxin treatment had no significant effect. Eighteen minute perfusion with 1 DMe at a very low 10 nM concentration, that did not directly inhibit Ca2+ transients triggered by depolarization in every neuron, attenuated by 78% the inhibitory effect of Nociceptin/orphanin FQ (N/OFQ) on Ca2+ transients, but not that of by serotonin. These results demonstrated for the first time that NPFF receptors on mice DRN inhibit Ca2+ transients induced by depolarization via Gi/o protein and also exhibit a specific anti-opioid activity on nociceptin receptors, and that their specific anti-opioid activity is not a direct consequence of their activity on Ca2+ transients.

The hypothalamic neuropeptide FF network is impaired in hypertensive patients

BACKGROUND

The human hypothalamus contains the neuropeptide FF (NPFF) neurochemical network. Animal experiments demonstrated that NPFF is implicated in the central cardiovascular regulation. We therefore studied expression of this peptide in the hypothalamus of individuals who suffered from essential hypertension (n = 8) and died suddenly due to acute myocardial infarction (AMI), and compared to that of healthy individuals (controls) (n = 6) who died abruptly due to mechanical trauma of the chest.

METHODS

The frozen right part of the hypothalamus was cut coronally into serial sections of 20 μm thickness, and each tenth section was stained immunohistochemically using antibody against NPFF. The central section through each hypothalamic nucleus was characterized by the highest intensity of NPFF immunostaining and thus was chosen for quantitative densitometry.

RESULTS

In hypertensive patients, the area occupied by NPFF immunostained neuronal elements in the central sections through the suprachiasmatic nucleus (SCh), paraventricular hypothalamic nucleus (Pa), bed nucleus of the stria terminalis (BST), perinuclear zone (PNZ) of the supraoptic nucleus (SON), dorso- (DMH), ventromedial (VMH) nuclei, and perifornical nucleus (PeF) was dramatically decreased compared to controls, ranging about six times less in the VMH to 15 times less in the central part of the BST (BSTC). The NPFF innervation of both nonstained neuronal profiles and microvasculature was extremely poor in hypertensive patients compared to control.

CONCLUSIONS

The decreased NPFF expression in the hypothalamus of hypertensive patients might be a cause of impairment of its interaction with other neurochemical systems, and thereby might be involved in the pathogenesis of the disease.

A high-affinity, radioiodinatable neuropeptide FF analogue incorporating a photolabile p-(4-hydroxybenzoyl)phenylalanine

A new radioiodinated photoaffinity compound, [(125)I]YE(Bpa)WSLAAPQRFNH2, derived from a peptide present in the rat neuropeptide FF (NPFF) precursor was synthesized, and its binding characteristics were investigated on a neuroblastoma clone, SH-SY5Y, stably expressing rat NPFF2 receptors tagged with the T7 epitope. The binding of the probe was saturable and revealed a high-affinity interaction (KD=0.24nM) with a single class of binding sites. It was also able to affinity label NPFF2 receptor in a specific and efficient manner given that 38% of the bound radioligand at saturating concentration formed a wash-resistant binding after ultraviolet (UV) irradiation. Photoaffinity labeling with [(125)I]YE(Bpa)WSLAAPQRFamide showed two molecular forms of NPFF2 receptor with apparent molecular weights of 140 and 95kDa in a 2:1 ratio. The comparison of the results between photoaffinity labeling and Western blot analysis suggests that all receptor forms bind the probe irreversibly with the same efficiency. On membranes of mouse olfactory bulb, only the high molecular weight form of NPFF2 receptor is observed. [(125)I]YE(Bpa)WSLAAPQRFamide is an excellent radioiodinated peptidic ligand for direct and selective labeling of NPFF2 receptors in vitro.

Involvement of Mammalian RF-Amide Peptides and Their Receptors in the Modulation of Nociception in Rodents

Mammalian RF-amide peptides, which all share a conserved carboxyl-terminal Arg-Phe-NH2 sequence, constitute a family of five groups of neuropeptides that are encoded by five different genes. They act through five G-protein-coupled receptors and each group of peptide binds to and activates mostly one receptor: RF-amide related peptide group binds to NPFFR1, neuropeptide FF group to NPFFR2, pyroglutamylated RF-amide peptide group to QRFPR, prolactin-releasing peptide group to prolactin-releasing peptide receptor, and kisspeptin group to Kiss1R. These peptides and their receptors have been involved in the modulation of several functions including reproduction, feeding, and cardiovascular regulation. Data from the literature now provide emerging evidence that all RF-amide peptides and their receptors are also involved in the modulation of nociception. This review will present the current knowledge on the involvement in rodents of the different mammalian RF-amide peptides and their receptors in the modulation of nociception in basal and chronic pain conditions as well as their modulatory effects on the analgesic effects of opiates.

The Evolution and Variety of RFamide-Type Neuropeptides: Insights from Deuterostomian Invertebrates

Five families of neuropeptides that have a C-terminal RFamide motif have been identified in vertebrates: (1) gonadotropin-inhibitory hormone (GnIH), (2) neuropeptide FF (NPFF), (3) pyroglutamylated RFamide peptide (QRFP), (4) prolactin-releasing peptide (PrRP), and (5) Kisspeptin. Experimental demonstration of neuropeptide-receptor pairings combined with comprehensive analysis of genomic and/or transcriptomic sequence data indicate that, with the exception of the deuterostomian PrRP system, the evolutionary origins of these neuropeptides can be traced back to the common ancestor of bilaterians. Here, we review the occurrence of homologs of vertebrate RFamide-type neuropeptides and their receptors in deuterostomian invertebrates - urochordates, cephalochordates, hemichordates, and echinoderms. Extending analysis of the occurrence of the RFamide motif in other bilaterian neuropeptide families reveals RFamide-type peptides that have acquired modified C-terminal characteristics in the vertebrate lineage (e.g., NPY/NPF), neuropeptide families where the RFamide motif is unique to protostomian members (e.g., CCK/sulfakinins), and RFamide-type peptides that have been lost in the vertebrate lineage (e.g., luqins). Furthermore, the RFamide motif is also a feature of neuropeptide families with a more restricted phylogenetic distribution (e.g., the prototypical FMRFamide-related neuropeptides in protostomes). Thus, the RFamide motif is both an ancient and a convergent feature of neuropeptides, with conservation, acquisition, or loss of this motif occurring in different branches of the animal kingdom.

Hypothalamic QRFP: regulation of food intake and fat selection

QRFP, a member of the RFamide-related peptide family, is a strongly conserved hypothalamic neuropeptide that has been characterized in various species. Prepro-QRFP mRNA expression is localized to select regions of the hypothalamus, which are involved in the regulation of feeding behavior. The localization of the peptide precursor has led to the assessment of QRFP on feeding behaviors and the orexigenic effects of QRFP have been detected in mice, rats, and birds. QRFP acts in a macronutrient specific manner in satiated rats to increase the intake of a high fat diet, but not the intake of a low fat diet, and increases the intake of chow in food-restricted rats. Studies suggest that QRFP's effects on food intake are mediated by the adiposity signal, leptin, and hypothalamic neuropeptides. Additionally, QRFP regulates the expression and release of hypothalamic Neuropeptide Y and proopiomelanocortin/α-Melanocyte-Stimulating Hormone. QRFP binds to receptors throughout the brain, including regions associated with food intake and reward. Taken together, these data suggest that QRFP is a mediator of motivated behaviors, particularly the drive to ingest high fat food. The present review discusses the role of QRFP in the regulation of feeding behavior, with emphasis on the intake of dietary fat.

Kisspeptin neurones do not directly signal to RFRP-3 neurones but RFRP-3 may directly modulate a subset of hypothalamic kisspeptin cells in mice

The neuropeptides kisspeptin (encoded by Kiss1) and RFamide-related peptide-3 (also known as GnIH; encoded by Rfrp) are potent stimulators and inhibitors, respectively, of reproduction. Whether kisspeptin or RFRP-3 might act directly on each other's neuronal populations to indirectly modulate reproductive status is unknown. To examine possible interconnectivity of the kisspeptin and RFRP-3 systems, we performed double-label in situ hybridisation (ISH) for the RFRP-3 receptors, Gpr147 and Gpr74, in hypothalamic Kiss1 neurones of adult male and female mice, as well as double-label ISH for the kisspeptin receptor, Kiss1r, in Rfrp-expressing neurones of the hypothalamic dorsal-medial nucleus (DMN). Only a very small proportion (5-10%) of Kiss1 neurones of the anteroventral periventricular region expressed Gpr147 or Gpr74 in either sex, whereas higher co-expression (approximately 25%) existed in Kiss1 neurones in the arcuate nucleus. Thus, RFRP-3 could signal to a small, primarily arcuate, subset of Kiss1 neurones, a conclusion supported by the finding of approximately 35% of arcuate kisspeptin cells receiving RFRP-3-immunoreactive fibre contacts. By contrast to the former situation, no Rfrp neurones co-expressed Kiss1r in either sex, and Tacr3, the receptor for neurokinin B (NKB; a neuropeptide co-expressed with arcuate kisspeptin neurones) was found in <10% of Rfrp neurones. Moreover, kisspeptin-immunoreactive fibres did not readily appose RFRP-3 cells in either sex, further excluding the likelihood that kisspeptin neurones directly communicate to RFRP-3 neurones. Lastly, despite abundant NKB in the DMN region where RFRP-3 soma reside, NKB was not co-expressed in the majority of Rfrp neurones. Our results suggest that RFRP-3 may modulate a small proportion of kisspeptin-producing neurones in mice, particularly in the arcuate nucleus, whereas kisspeptin neurones are unlikely to have any direct reciprocal actions on RFRP-3 neurones.

Endogenous mammalian RF-amide peptides, including PrRP, kisspeptin and 26RFa, modulate nociception and morphine analgesia via NPFF receptors

Mammalian RF-amide peptides are encoded by five different genes and act through five different G protein-coupled receptors. RF-amide-related peptides-1 and -3, neuropeptides AF and FF, Prolactin releasing peptides, Kisspeptins and RFa peptides are currently considered endogenous peptides for NPFF1, NPFF2, GPR10, GPR54 and GPR103 receptors, respectively. However, several studies suggest that the selectivity of these peptides for their receptors is low and indicate that expression patterns for receptors and their corresponding ligands only partially overlap. In this study, we took advantage of the cloning of the five human RF-amide receptors to systematically examine their affinity for and their activation by all human RF-amide peptides. Binding experiments, performed on membranes from CHO cells expressing GPR10, GPR54 and GPR103 receptors, confirmed their high affinity and remarkable selectivity for their cognate ligands. Conversely, NPFF1 and NPFF2 receptors displayed high affinity for all RF-amide peptides. Moreover, GTPγS and cAMP experiments showed that almost all RF-amide peptides efficiently activate NPFF1 and NPFF2 receptors. As NPFF is known to modulate morphine analgesia, we undertook a systematic analysis in mice of the hyperalgesic and anti morphine-induced analgesic effects of a representative set of endogenous RF-amide peptides. All of them induced hyperalgesia and/or prevented morphine analgesia following intracerebroventricular administration. Importantly, these effects were prevented by administration of RF9, a highly selective NPFF1/NPFF2 antagonist. Altogether, our results show that all endogenous RF-amide peptides display pain-modulating properties and point to NPFF receptors as essential players for these effects.

Kisspeptins and RFRP-3 Act in Concert to Synchronize Rodent Reproduction with Seasons

Seasonal mammals use the photoperiodic variation in the nocturnal production of the pineal hormone melatonin to synchronize their reproductive activity with seasons. In rodents, the (SD) short day profile of melatonin secretion has long been proven to inhibit reproductive activity. Lately, we demonstrated that melatonin regulates the expression of the hypothalamic peptides kisspeptins (Kp) and RFamide-related peptide-3 (RFRP-3), recently discovered as potent regulators of gonadotropin-releasing hormone (GnRH) neuron activity. In the male Syrian hamster, Kp expression in the arcuate nucleus is down-regulated by melatonin independently of the inhibitory feedback of testosterone. A central or peripheral administration of Kp induces an increase in pituitary gonadotropins and gonadal hormone secretion, but most importantly a chronic infusion of the peptide reactivates the photo-inhibited reproductive axis of Syrian hamsters kept in SD conditions. RFRP-3 expression in the dorsomedial hypothalamus is also strongly inhibited by melatonin in a SD photoperiod. Although RFRP-3 is usually considered as an inhibitory component of the gonadotropic axis, a central acute administration of RFRP-3 in the male Syrian hamster induces a marked increase in gonadotropin secretion and testosterone production. Furthermore, a chronic central infusion of RFRP-3 in SD-adapted hamsters reactivates the reproductive axis, in the same manner as Kp. Both Kp and RFRP-3 neurons project onto GnRH neurons and both neuropeptides regulate GnRH neuron activity. In addition, central RFRP-3 infusion was associated with a significant increase in arcuate Kp expression. However, the actual sites of action of both peptides in the Syrian hamster brain are still unknown. Altogether our findings indicate that Kp and RFRP neurons are pivotal relays for the seasonal regulation of reproduction, and also suggest that RFRP neurons might be the primary target of the melatoninergic message.

Physiological Roles of GPR10 and PrRP Signaling

Prolactin-releasing peptide (PrRP) was first isolated from bovine hypothalamus, and was found to act as an endogenous ligand at the G-protein-coupled receptor 10 (GPR10 or hGR3). Although originally named as it can affect the secretion of prolactin from anterior pituitary cells, the potential functions for this peptide have been greatly expanded over the past decade. Anatomical, pharmacological, and physiological studies indicate that PrRP, signaling via the GPR10 receptor, may have a wide range of roles in neuroendocrinology; such as in energy homeostasis, stress responses, cardiovascular regulation, and circadian function. This review will provide the current knowledge of the PrRP and GPR10 signaling system, its putative functions, implications for therapy, and future perspectives.

Study of the N-terminal part of peptidic selective NPFF₂ agonists

Neuropeptide FF (NPFF) has been shown to act as an endogenous anti-analgesic peptide. In this paper, several peptide analogs of the selective ligand dNP(NMe)AFLFQPQRF-NH(2) modified in the putative address segment, were designed to be selective NPFF(2) receptor probes, synthesized and assayed. One peptide dA(NMe)AAFLFQPQRF-NH(2) displays a very high affinity for NPFF(2) receptors transfected in CHO cells, and a high selectivity versus NPFF(1) receptors. The exact residues carried in the N-terminal part of the ligands are not decisive to obtain a high affinity only the length of the peptide in itself seems important to create selectivity.

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.

In Vitro Activities of Kissorphin, a Novel Hexapeptide KiSS-1 Derivative, in Neuronal Cells

The primary products of the metastasis-suppressor KiSS-1 gene are the kisspeptin (KP) peptides that stimulate gonadotrophin-releasing-hormone (GnRH) release via GPR-54 receptor activation. Recent studies have suggested that the KP-10 peptide also activates neuropeptide FF (NPFF) receptors. The aim of the current study was to determine the activities of the KiSS-1 derivative kissorphin (KSO), which contains the first six amino acids of the KP-10 peptide, is C-terminally amidated, and shares amino acid similarities with the biologically active NPFF 3–8 sequence. The KSO peptide inhibited forskolin-stimulated cyclic adenosine monophosphate (cAMP) production in ND7/23 neuroblastoma cells via an action that could be inhibited by the NPFF receptor antagonist RF9. Release of GnRH by LA-N-1 neuroblastoma cells was not altered by the KSO peptide. In ND7/23 neuroblastoma cells, the KSO peptide was able to reduce forskolin neuroprotection against H₂O₂ toxicity. The KSO peptide was also able to prevent prostaglandin E2-induced apoptosis in rat cortical neurons. The NPFF receptor antagonist RF9 could inhibit these actions of the KSO peptide in oxidative stress and apoptosis models. In conclusion, the kissorphin peptide, comprising the amino acid sequence Tyr-Asn-Trp-Asn-Ser-Phe-NH₂, has NPFF-like biological activity without showing any GnRH releasing activity and inhibits forskolin-activated cAMP release.

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.

Involvement of neuropeptide FF receptors in neuroadaptive responses to acute and chronic opiate treatments

BACKGROUND AND PURPOSE Opiates remain the most effective compounds for alleviating severe pain across a wide range of conditions. However, their use is associated with significant side effects. Neuropeptide FF (NPFF) receptors have been implicated in several opiate-induced neuroadaptive changes including the development of tolerance. In this study, we investigated the consequences of NPFF receptor blockade on acute and chronic stimulation of opioid receptors in mice by using RF9, a potent and selective antagonist of NPFF receptors that can be administered systemically. EXPERIMENTAL APPROACH The effects of RF9 were investigated on opioid pharmacological responses including locomotor activity, antinociception, opioid-induced hyperalgesia, rewarding properties and physical dependence. KEY RESULTS RF9 had no effect on morphine-induced horizontal hyperlocomotion and slightly attenuated the decrease induced in vertical activity. Furthermore, RF9 dose-dependently blocked the long-lasting hyperalgesia produced by either acute fentanyl or chronic morphine administration. RF9 also potentiated opiate early analgesic effects and prevented the development of morphine tolerance. Finally, RF9 increased morphine-induced conditioned place preference without producing any rewarding effect by itself and decreased naltrexone-precipitated withdrawal syndrome following chronic morphine treatment. CONCLUSION AND IMPLICATIONS The NPFF system is involved in the development of two major undesirable effects: tolerance and dependence, which are clinically associated with prolonged exposure to opiates. Our findings suggest that NPFF receptors are interesting therapeutic targets to improve the analgesic efficacy of opiates by limiting the development of tolerance, and for the treatment of opioid dependence.