The melanin-concentrating hormone system and its physiological functions

Glutamatergic heterogeneity in the neuropeptide projections from the lateral hypothalamus to the mouse olfactory bulb

The direct pathway from the lateral hypothalamus to the mouse olfactory bulb (OB) includes neurons that express the neuropeptide orexin-A, and others that do not. The OB-projecting neurons that do not express orexin-A are present in an area of the lateral hypothalamus known to contain neurons that express the neuropeptide melanin-concentrating hormone (MCH). We used virally mediated anterograde tract tracing and immunohistochemistry for orexin-A and MCH to demonstrate that the OB is broadly innervated by axon projections from both populations of neurons. Orexin-A and MCH were expressed in each OB layer across its anterior to posterior axis. Both orexin-A and MCH neurons are genetically heterogeneous, with subsets that co-express an isoform of vesicular glutamate transporter (VGLUT). We used high-resolution confocal imaging to test whether the projections from orexin-A and MCH neurons to the OB reflect this glutamatergic heterogeneity. The majority (~57%) of putative orexin-A axon terminals overlapped with VGLUT2, with smaller proportions that co-expressed VGLUT1, or that did not overlap with either VGLUT1 or VGLUT2. In contrast, only ~26% of putative MCH axon terminals overlapped with VGLUT2, with the majority not overlapping with either VGLUT. Therefore, the projections from the lateral hypothalamus to the OB are genetically heterogeneous and include neurons that can release two different neuropeptides. The projections from both populations are themselves genetically heterogeneous with distinct ratios of glutamatergic and non-glutamatergic axon terminals.

Is melanin-concentrating hormone in the medial preoptic area a signal for the decline of maternal care in late postpartum?

This manuscript proposes that melanin-concentrating hormone (MCH) in the medial preoptic area (MPOA) is an neurochemical signal evolved to trigger the declining process of maternal care. MCH in the MPOA appears only after parturition and is progressively increased with the progression of lactation, while maternal behavior declines progressively. Intra-MPOA injection of MCH decreases active maternal responses. MCH is also highly responsive to infant characteristics and maternal condition. Behavioral changes induced by MCH in late postpartum period are conducive to the decline of infant-directed maternal behavior. The MPOA MCH system may mediate the maternal behavior decline by suppressing the maternal approach motivation and/or increasing maternal withdrawal via its inhibitory action onto the mesolimbic dopamine D1/D2 receptors and its stimulating action on serotonin 5-HT2C receptors in the ventral tegmental area. Research into the MCH maternal effects will enhance our understanding of the neurochemical mechanisms underlying the maternal behavior decline.

The Orexin/Hypocretin System, the Peptidergic Regulator of Vigilance, Orchestrates Adaptation to Stress

The orexin/hypocretin neuropeptide family has emerged as a focal point of neuroscientific research following the discovery that this family plays a crucial role in a variety of physiological and behavioral processes. These neuropeptides serve as powerful neuromodulators, intricately shaping autonomic, endocrine, and behavioral responses across species. Notably, they serve as master regulators of vigilance and stress responses; however, their roles in food intake, metabolism, and thermoregulation appear complementary and warrant further investigation. This narrative review provides a journey through the evolution of our understanding of the orexin system, from its initial discovery to the promising progress made in developing orexin derivatives. It goes beyond conventional boundaries, striving to synthesize the multifaceted activities of orexins. Special emphasis is placed on domains such as stress response, fear, anxiety, and learning, in which the authors have contributed to the literature with original publications. This paper also overviews the advancement of orexin pharmacology, which has already yielded some promising successes, particularly in the treatment of sleep disorders.

Histamine and histamine receptors: Roles in major depressive disorder

Although the incidence of major depressive disorder (MDD) is high and its social impact is great, we still know very little about the pathophysiology of depression. The monoamine hypothesis of depression suggests that 5-HT, NE, and DA synergistically affect mood, which is the basis of current drug therapy for depression. However, histamine as a monoamine transmitter is rarely studied. Our review is the first time to illustrate the effect of histaminergic system on depression in order to find the way for the development of new antidepressant drugs. The brain neurotransmitter histamine is involved in MDD, and the brain histaminergic system operates through four receptors. Histamine and its receptors can also regulate the immune response to improve symptoms of depression. In addition, H3R can interact with other depression-related transmitters (including 5-HT, DA, GLU, and MCH); thus, histamine may participate in the occurrence of depression through other neural circuits. Notably, in rodent studies, several H3R and H1R antagonists were found to be safe and effective in alleviating depression-like behavior. To highlight the complex functions of histamine in depression, and reveals that histamine receptors can be used as new targets for antidepressant therapy.

Synergy of melanin and vitamin-D may play a fundamental role in preventing SARS-CoV-2 infections and halt COVID-19 by inactivating furin protease

Since the birth of Christ, in these 2019 years, the man on earth has never experienced a survival challenge from any acellular protist compared to SARS-CoV-2. No specific drugs yet been approved. The host immunity is the only alternative to prevent and or reduce the infection and mortality rate as well. Here, a novel mechanism of melanin mediated host immunity is proposed having potent biotechnological prospects in health care management of COVID-19. Vitamin D is known to enhance the rate of melanin synthesis; and this may concurrently regulate the expression of furin expression. In silico analyses have revealed that the intermediates of melanin are capable of binding strongly with the active site of furin protease. On the other hand, furin expression is negatively regulated via 1-α-hydroxylase (CYP27B1), that belongs to vitamin-D pathway and controls cellular calcium levels. Here, we have envisaged the availability of biological melanin and elucidated the bio-medical potential. Thus, we propose a possible synergistic application of melanin and the enzyme CYP27B1 (regulates vitamin D biosynthesis) as a novel strategy to prevent viral entry through the inactivation of furin protease and aid in boosting our immunity at the cellular and humoral levels.

Effects of Veratrilla baillonii Extract on Hepatic Gene Expression Profiles in Response to Aconitum brachypodum-Induced Liver Toxicity in Mice

This manuscript was aimed to explore the hepato-protective effect of water extract of Veratrilla baillonii Franch. (Gentianaceae) (WVBF) on serious hepatic toxicity induced in mice treated with Aconitum brachypodum Diels (Ranunculaceae) at transcriptome level. The physiological and pathological symptoms were evaluated as the markers for hepato toxicity induced by A. brachypodum Diels (CFA) extracted compounds. Moreover, gene chip method was used to compare and investigate the gene expression level of WVBF on CFA induced-liver toxicity to identify the potential target of WVBF and CFA on liver. The results showed that WVBF had a significant detoxification effect on CFA-induced acute hepatic toxicity. There were 130 genes with lower expression and 124 genes expressed at higher rate in CFA treated group as compared with normal control group, while there are 67 genes down-regulated and 74 genes up-regulated in WVBF treated group in comparison with CFA treated group. WVBF could attenuate CFA-induced liver damage in mice through regulating oxidative stress, inflammatory injury and cell apoptosis/necrosis pathways. On the other hand, WVBF and CFA may have potential synergetic effects on the target genes of certain diseases such as inflammation, cancer and diabetes.

Melanin-Concentrating Hormone (MCH) and MCH-R1 in the Locus Coeruleus May Be Involved in the Regulation of Depressive-Like Behavior

BACKGROUND

Previous anatomical and behavioral studies have shown that melanin-concentrating hormone is involved in the modulation of emotional states. However, little is known about brain regions other than the dorsal raphe nucleus that relate the melanin-concentrating hormone-ergic system to depressive states. Numerous studies have shown that the locus coeruleus is involved in the regulation of depression and sleep. Although direct physiological evidence is lacking, previous studies suggest that melanin-concentrating hormone release in the locus coeruleus decreases neuronal discharge. However, remaining unclear is whether the melanin-concentrating hormone-ergic system in the locus coeruleus is related to depressive-like behavior.

METHOD

We treated rats with an intra-locus coeruleus injection of melanin-concentrating hormone, intracerebroventricular injection of melanin-concentrating hormone, or chronic subcutaneous injections of corticosterone to induce different depressive-like phenotypes. We then assessed the effects of the melanin-concentrating hormone receptor 1 antagonist SNAP-94847 on depressive-like behavior in the forced swim test and the sucrose preference test.

RESULTS

The intra-locus coeruleus and intracerebroventricular injections of melanin-concentrating hormone and chronic injections of corticosterone increased immobility time in the forced swim test and decreased sucrose preference in the sucrose preference test. All these depressive-like behaviors were reversed by an intra-locus coeruleus microinjection of SNAP-94847.

CONCLUSIONS

These results suggest that the melanin-concentrating hormone-ergic system in the locus coeruleus might play an important role in the regulation of depressive-like behavior.

Nicotinic Cholinergic System in the Hypothalamus Modulates the Activity of the Hypothalamic Neuropeptides During the Stress Response

BACKGROUND

The hypothalamus harbors high levels of cholinergic neurons and axon terminals. Nicotinic acetylcholine receptors, which play an important role in cholinergic neurotransmission, are expressed abundantly in the hypothalamus. Accumulating evidence reveals a regulatory role for nicotine in the regulation of the stress responses. The present review will discuss the hypothalamic neuropeptides and their interaction with the nicotinic cholinergic system. The anatomical distribution of the cholinergic neurons, axon terminals and nicotinic receptors in discrete hypothalamic nuclei will be described. The effect of nicotinic cholinergic neurotransmission and nicotine exposure on hypothalamic-pituitaryadrenal (HPA) axis regulation at the hypothalamic level will be analyzed in view of the different neuropeptides involved.

METHODS

Published research related to nicotinic cholinergic regulation of the HPA axis activity at the hypothalamic level is reviewed.

RESULTS

The nicotinic cholinergic system is one of the major modulators of the HPA axis activity. There is substantial evidence supporting the regulation of hypothalamic neuropeptides by nicotinic acetylcholine receptors. However, most of the studies showing the nicotinic regulation of hypothalamic neuropeptides have employed systemic administration of nicotine. Additionally, we know little about the nicotinic receptor distribution on neuropeptide-synthesizing neurons in the hypothalamus and the physiological responses they trigger in these neurons.

CONCLUSION

Disturbed functioning of the HPA axis and hypothalamic neuropeptides results in pathologies such as depression, anxiety disorders and obesity, which are common and significant health problems. A better understanding of the nicotinic regulation of hypothalamic neuropeptides will aid in drug development and provide means to cope with these diseases. Considering that nicotine is also an abused substance, a better understanding of the role of the nicotinic cholinergic system on the HPA axis will aid in developing improved therapeutic strategies for smoking cessation.

Novel analgesic effects of melanin-concentrating hormone on persistent neuropathic and inflammatory pain in mice

The melanin-concentrating hormone (MCH) is a peptidergic neuromodulator synthesized by neurons in the lateral hypothalamus and zona incerta. MCHergic neurons project throughout the central nervous system, indicating the involvements of many physiological functions, but the role in pain has yet to be determined. In this study, we found that pMCH^-/- mice showed lower baseline pain thresholds to mechanical and thermal stimuli than did pMCH^+/+ mice, and the time to reach the maximum hyperalgesic response was also significantly earlier in both inflammatory and neuropathic pain. To examine its pharmacological properties, MCH was administered intranasally into mice, and results indicated that MCH treatment significantly increased mechanical and thermal pain thresholds in both pain models. Antagonist challenges with naltrexone (opioid receptor antagonist) and AM251 (cannabinoid 1 receptor antagonist) reversed the analgesic effects of MCH in both pain models, suggesting the involvement of opioid and cannabinoid systems. MCH treatment also increased the expression and activation of CB1R in the medial prefrontal cortex and dorsolateral- and ventrolateral periaqueductal grey. The MCH1R antagonist abolished the effects induced by MCH. This is the first study to suggest novel analgesic actions of MCH, which holds great promise for the application of MCH in the therapy of pain-related diseases.

Understanding sleep-wake mechanisms and drug discovery

INTRODUCTION

Although not discernible at first glance, sleep is a highly active and regulated brain state. Although we spend practically one third of our lifetimes in this stage, its importance is often taken for granted. Sleep loss can lead to disease, error and economic loss. Our understanding of how sleep is achieved has greatly advanced in recent years, and with that, the management of sleep disorders has improved. There is still room for improvement and recently many new compounds have reached clinical trials with a few being approved for commercial use. Areas covered: In this review, the authors make the case of sleep disorders as a matter of public health. The mechanisms of sleep transition are discussed emphasizing the wake and sleep promoting interaction of different brain regions. Finally, advances in pharmacotherapy are examined in the context of chronic insomnia and narcolepsy. Expert opinion: The orexinergic system is an example of a breakthrough in sleep medicine that has catalyzed drug development. Nevertheless, sleep is a topic still with many unanswered questions. That being said, the melanin-concentrating hormone system is becoming increasingly relevant and we speculate it will be the next target of sleep medication.

Nesfatin-1 regulates the lateral hypothalamic area melanin-concentrating hormone-responsive gastric distension-sensitive neurons and gastric function via arcuate nucleus innervation

Nesfatin-1, a recently discovered neuropeptide involved in satiety. Recent studies have revealed that central nesfatin-1 inhibits gastric emptying and gastric acid secretion, though the mechanisms involved in these processes are not known. We aim to explore the effects of nesfatin-1 on a population of gastric distension (GD)-sensitive neurons in the lateral hypothalamus (LHA), gastric motility, and gastric secretion and the role for an arcuate nucleus (Arc)-LHA neural pathway in these processes. Single unit extracellular discharge recordings were made in of LHA. Further, gastric motility and gastric secretion in rats were monitored. Retrograde tracing and fluorescent immunohistochemical staining were used to explore nesfatin-1 neuron projection. The results revealed that administration of nesfatin-1 to the LHA or electric stimulation of the Arc could alter the neuronal activity of melanin-concentrating hormone (MCH)-responsive, GD-responsive neurons in LHA, which could be blocked by pretreatment with MCH receptor-1 antagonist PMC-3881-PI or weakened by pretreatment of a nesfatin-1 antibody in LHA. Administration of nesfatin-1 into LHA could inhibit gastric motility and gastric secretion, and these effects could be enhanced by administration of PMC-3881-PI. Electrical stimulation of Arc promoted the gastric motility and gastric secretion. Nesfatin-1 antibody or PMC-3881-PI pretreatment to LHA had no effect on Arc stimulation-induced gastric motility, but these pretreatments did alter Arc stimulation-induced effects on gastric secretion. Our findings suggest that nesfatin-1 signaling in LHA participates in the regulation of efferent information from the gastrointestinal tract and gastric secretion which also involve MCH signaling. Further, they show that a nesfatin-1-positive Arc to LHA pathway is critical for these effects.

Functional Connectivity of Basolateral Amygdala Neurons Carrying Orexin Receptors and Melanin-concentrating Hormone Receptors in Regulating Sociability and Mood-related Behaviors

Chronic stress induces changes in neuronal functions in specific brain regions regulating sociability and mood-related behaviors. Recently we reported that stress-induced persistent upregulation of the neuropeptides orexin and melanin-concentrating hormone (MCH) in the basolateral amygdala (BLA) and the resulting activation of orexin receptors or MCH receptors within the BLA produced deficits in sociability and mood-related behaviors. In the present study, we investigated the neural targets that were innervated by BLA neurons containing orexin receptors or MCH receptors. The viral vector system AAV2-CaMKII-ChR2-eYFP was injected into the BLA to trace the axonal tracts of BLA neurons. This axon labeling analysis led us to identify the prelimbic and infralimbic cortices, nucleus accumbens (NAc), dorsal striatum, paraventricular nucleus (PVN), interstitial nucleus of the posterior limb of the anterior commissure, habenula, CA3 pyramidal neurons, central amygdala, and ventral hippocampus as the neuroanatomical sites receiving synaptic inputs of BLA neurons. Focusing on these regions, we then carried out stimulus-dependent c-Fos induction analysis after activating orexin receptors or MCH receptors of BLA neurons. Stereotaxic injection of an orexin receptor agonist or an MCH receptor agonist in the BLA induced c-Fos expression in the NAc, PVN, central amygdala, ventral hippocampus, lateral habenula and lateral hypothalamus, which are all potentially important for depression-related behaviors. Among these neural correlates, the NAc, PVN and central amygdala were strongly activated by stimulation of orexin receptors or MCH receptors in the BLA, whereas other BLA targets were differentially and weakly activated. These results identify a functional connectivity of BLA neurons regulated by orexin and MCH receptor systems in sociability and mood-related behaviors.

Physical Exercise Counteracts Stress-induced Upregulation of Melanin-concentrating Hormone in the Brain and Stress-induced Persisting Anxiety-like Behaviors

Chronic stress induces anxiety disorders, whereas physical exercise is believed to help people with clinical anxiety. In the present study, we investigated the mechanisms underlying stress-induced anxiety and its counteraction by exercise using an established animal model of anxiety. Mice treated with restraint for 2 h daily for 14 days exhibited anxiety-like behaviors, including social and nonsocial behavioral symptoms, and these behavioral impairments lasted for more than 12 weeks after the stress treatment was removed. Despite these lasting behavioral changes, wheel-running exercise treatment for 1 h daily from post-stress days 1 - 21 counteracted anxiety-like behaviors, and these anxiolytic effects of exercise persisted for more than 2 months, suggesting that anxiolytic effects of exercise stably induced. Repeated restraint treatment up-regulated the expression of the neuropeptide, melanin-concentrating hormone (MCH), in the lateral hypothalamus, hippocampus, and basolateral amygdala, the brain regions important for emotional behaviors. In an in vitro study, treatment of HT22 hippocampal cells with glucocorticoid increased MCH expression, suggesting that MCH upregulation can be initially triggered by the stress hormone, corticosterone. In contrast, post-stress treatment with wheel-running exercise reduced the stress-induced increase in MCH expression to control levels in the lateral hypothalamus, hippocampus and basolateral amygdala. Administration of an MCH receptor antagonist (SNAP94847) to stress-treated mice was therapeutic against stress-induced anxiety-like behaviors. These results suggest that repeated stress produces long-lasting anxiety-like behaviors and upregulates MCH in the brain, while exercise counteracts stress-induced MCH expression and persisting anxiety-like behaviors.

Subchronical treatment with Fluoxetine modifies the activity of the MCHergic and hypocretinergic systems. Evidences from peptide CSF concentration and gene expression

In the postero-lateral hypothalamus are located two neuronal systems that utilize the neuropeptides melanin-concentrating hormone (MCH) and hypocretins (also called orexins) as neuromodulators. These systems have reciprocal connections between them, and project throughout the central nervous system. MCH has been involved in the generation of sleep, mainly REM sleep, while hypocretins have a critical role in the generation of wakefulness. MCHergic activity is also involved in the pathophysiology of major depressive disorder (MD). In this regards, intracerebral administration of MCH promotes pro-depressive behaviors (i.e., immobility in the forced swimming test) and REM sleep hypersomnia, which is an important trait of depression. Furthermore, the antagonism of the MCHR-1 receptor has a reliable antidepressant effect, suggesting that MCH is a pro-depressive factor. Hypocretins have been also involved in mood regulation; however, their role in depression is still on debate. Taking these data into account, we explored whether systemic subchronical treatment with Fluoxetine (FLX), a serotonergic antidepressant, modifies the concentration of MCH in the cerebrospinal fluid (CSF), as well as the preproMCH mRNA expression. We also evaluated the hypocretinergic system by quantifying the hypocretin-levels in the CSF and the preprohypocretin mRNA expression. Compared to control, FLX increased the levels of preprohypocretin mRNA without affecting the hypocretin-1 CSF levels. On the contrary, FLX significantly decreased the MCH CSF concentration without affecting the preproMCH gene expression. This result is in agreement with the fact that MCH serum level diminishes during the antidepressant treatment in MD, and supports the hypothesis that an increase in the MCHergic activity could have pro-depressive consequences.

Recent advances in understanding the roles of vascular endothelial cells in allergic inflammation

Allergic disorders commonly involve both chronic tissue inflammation and remodeling caused by immunological reactions to various antigens on tissue surfaces. Due to their anatomical location, vascular endothelial cells are the final responders to interact with various exogenous factors that come into contact with the epithelial surface, such as pathogen-associated molecular patterns (PAMPs) and antigens. Recent studies have shed light on the important roles of endothelial cells in the development and exacerbation of allergic disorders. For instance, endothelial cells have the greatest potential to produce several key molecules that are deeply involved in allergic inflammation, such as periostin and thymus and activation-regulated chemokine (TARC/CCL17). Additionally, endothelial cells were recently shown to be important functional targets for IL-33--an essential regulator of allergic inflammation. Notably, almost all endothelial cell responses and functions involved in allergic inflammation are not suppressed by corticosteroids. These corticosteroid-refractory endothelial cell responses and functions include TNF-α-associated angiogenesis, leukocyte adhesion, IL-33-mediated responses and periostin and TARC production. Therefore, these unique responses and functions of endothelial cells may be critically involved in the pathogenesis of various allergic disorders, especially their refractory processes. Here, we review recent studies, including ours, which have elucidated previously unknown pathophysiological roles of vascular endothelial cells in allergic inflammation and discuss the possibility of endothelium-targeted therapy for allergic disorders.

MCH levels in the CSF, brain preproMCH and MCHR1 gene expression during paradoxical sleep deprivation, sleep rebound and chronic sleep restriction

Neurons that utilize melanin-concentrating hormone (MCH) as neuromodulator are located in the lateral hypothalamus and incerto-hypothalamic area. These neurons project throughout the central nervous system and play a role in sleep regulation. With the hypothesis that the MCHergic system function would be modified by the time of the day as well as by disruptions of the sleep-wake cycle, we quantified in rats the concentration of MCH in the cerebrospinal fluid (CSF), the expression of the MCH precursor (Pmch) gene in the hypothalamus, and the expression of the MCH receptor 1 (Mchr1) gene in the frontal cortex and hippocampus. These analyses were performed during paradoxical sleep deprivation (by a modified multiple platform technique), paradoxical sleep rebound and chronic sleep restriction, both at the end of the active (dark) phase (lights were turned on at Zeitgeber time zero, ZT0) and during the inactive (light) phase (ZT8). We observed that in control condition (waking and sleep ad libitum), Mchr1 gene expression was larger at ZT8 (when sleep predominates) than at ZT0, both in frontal cortex and hippocampus. In addition, compared to control, disturbances of the sleep-wake cycle produced the following effects: paradoxical sleep deprivation for 96 and 120 h reduced the expression of Mchr1 gene in frontal cortex at ZT0. Sleep rebound that followed 96 h of paradoxical sleep deprivation increased the MCH concentration in the CSF also at ZT0. Twenty-one days of sleep restriction produced a significant increment in MCH CSF levels at ZT8. Finally, sleep disruptions unveiled day/night differences in MCH CSF levels and in Pmch gene expression that were not observed in control (undisturbed) conditions. In conclusion, the time of the day and sleep disruptions produced subtle modifications in the physiology of the MCHergic system.

Ongoing behavioral state information signaled in the lateral habenula guides choice flexibility in freely moving rats

The lateral habenula (LHb) plays a role in a wide variety of behaviors ranging from maternal care, to sleep, to various forms of cognition. One prominent theory with ample supporting evidence is that the LHb serves to relay basal ganglia and limbic signals about negative outcomes to midbrain monoaminergic systems. This makes it likely that the LHb is critically involved in behavioral flexibility as all of these systems have been shown to contribute when flexible behavior is required. Behavioral flexibility is commonly examined across species and is impaired in various neuropsychiatric conditions including autism, depression, addiction, and schizophrenia; conditions in which the LHb is thought to play a role. Therefore, a thorough examination of the role of the LHb in behavioral flexibility serves multiple functions including understanding possible connections with neuropsychiatric illnesses and additional insight into its role in cognition in general. Here, we assess the LHb’s role in behavioral flexibility through comparisons of the roles its afferent and efferent pathways are known to play. Additionally, we provide new evidence supporting the LHb contributions to behavioral flexibility through organization of specific goal directed actions under cognitively demanding conditions. Specifically, in the first experiment, a majority of neurons recorded from the LHb were found to correlate with velocity on a spatial navigation task and did not change significantly when reward outcomes were manipulated. Additionally, measurements of local field potential (LFP) in the theta band revealed significant changes in power relative to velocity and reward location. In a second set of experiments, inactivation of the LHb with the gamma-aminobutyric acid (GABA) agonists baclofen and muscimol led to an impairment in a spatial/response based repeated probabilistic reversal learning task. Control experiments revealed that this impairment was likely due to the demands of repeated switching behaviors as rats were unimpaired on initial discrimination acquisition or retention of probabilistic learning. Taken together, these novel findings compliment other work discussed supporting a role for the LHb in action selection when cognitive or emotional demands are increased. Finally, we discuss future mechanisms by which a superior understanding of the LHb can be obtained through additional examination of behavioral flexibility tasks.

Transient expression of neuropeptide W in postnatal mouse hypothalamus--a putative regulator of energy homeostasis

Neuropeptide B and W (NPB and NPW) are cognate peptide ligands for NPBWR1 (GPR7), a G protein-coupled receptor. In rodents, they have been implicated in the regulation of energy homeostasis, neuroendocrine/autonomic responses, and social interactions. Although localization of these peptides and their receptors in adult rodent brain has been well documented, their expression in mouse brain during development is unknown. Here we demonstrate the transient expression of NPW mRNA in the dorsomedial hypothalamus (DMH) of postnatal mouse brain and its co-localization with neuropeptide Y (NPY) mRNA. Neurons expressing both NPW and NPY mRNAs begin to emerge in the DMH at about postnatal day 0 (P-0) through P-3. Their expression is highest around P-14, declines after P-21, and by P-28 only a faint expression of NPW and NPY mRNA remains. In P-18 brains, we detected NPW neurons in the region spanning the subincertal nucleus (SubI), the lateral hypothalamic (LH) perifornical (PF) areas, and the DMH, where the highest expression of NPW mRNA was observed. The majority of these postnatal hypothalamic NPW neurons co-express NPY mRNA. A cross of NPW-iCre knock-in mice with a Cre-dependent tdTomato reporter line revealed that more than half of the reporter-positive neurons in the adult DMH, which mature from the transiently NPW-expressing neurons, are sensitive to peripherally administrated leptin. These data suggest that the DMH neurons that transiently co-express NPW and NPY in the peri-weaning period might play a role in regulating energy homeostasis during postnatal development.

Involvement of melanin-concentrating hormone 2 in background color adaptation of barfin flounder Verasper moseri

In teleosts, melanin-concentrating hormone (MCH) plays a key role in skin color changes. MCH is released into general circulation from the neurohypophysis, which causes pigment aggregation in the skin chromatophores. Recently, a novel MCH (MCH2) precursor gene, which is orthologous to the mammalian MCH precursor gene, has been identified in some teleosts using genomic data mining. The physiological function of MCH2 remains unclear. In the present study, we cloned the cDNA for MCH2 from barfin flounder, Verasper moseri. The putative prepro-MCH2 contains 25 amino acids of MCH2 peptide region. Liquid chromatography-electrospray ionization mass spectrometry with a high resolution mass analyzer were used for confirming the amino acid sequences of MCH1 and MCH2 peptides from the pituitary extract. In vitro synthesized MCH1 and MCH2 induced pigment aggregation in a dose-dependent manner. A mammalian cell-based assay indicated that both MCH1 and MCH2 functionally interacted with both the MCH receptor types 1 and 2. Mch1 and mch2 are exclusively expressed in the brain and pituitary. The levels of brain mch2 transcript were three times higher in the fish that were chronically acclimated to a white background than those acclimated to a black background. These results suggest that in V. moseri, MCH1 and MCH2 are involved in the response to changes in background colors, during the process of chromatophore control.

Identification of neuropeptide receptors expressed by melanin-concentrating hormone neurons

Melanin-concentrating hormone (MCH) is a 19-amino-acid cyclic neuropeptide that acts in rodents via the MCH receptor 1 (MCHR1) to regulate a wide variety of physiological functions. MCH is produced by a distinct population of neurons located in the lateral hypothalamus (LH) and zona incerta (ZI), but MCHR1 mRNA is widely expressed throughout the brain. The physiological responses and behaviors regulated by the MCH system have been investigated, but less is known about how MCH neurons are regulated. The effects of most classical neurotransmitters on MCH neurons have been studied, but those of most neuropeptides are poorly understood. To gain insight into how neuropeptides regulate the MCH system, we investigated which neuropeptide receptors are expressed by MCH neurons by using double in situ hybridization. In all, 20 receptors, selected based on either a suspected interaction with the MCH system or demonstrated high expression levels in the LH and ZI, were tested to determine whether they are expressed by MCH neurons. Overall, 11 neuropeptide receptors were found to exhibit significant colocalization with MCH neurons: nociceptin/orphanin FQ opioid receptor (NOP), MCHR1, both orexin receptors (ORX), somatostatin receptors 1 and 2 (SSTR1, SSTR2), kisspeptin recepotor (KissR1), neurotensin receptor 1 (NTSR1), neuropeptide S receptor (NPSR), cholecystokinin receptor A (CCKAR), and the κ-opioid receptor (KOR). Among these receptors, six have never before been linked to the MCH system. Surprisingly, several receptors thought to regulate MCH neurons displayed minimal colocalization with MCH, suggesting that they may not directly regulate the MCH system.

Can neuropeptides treat obesity? A review of neuropeptides and their potential role in the treatment of obesity

Obesity is a major worldwide public health issue. The physiological systems that regulate body weight are thus of great interest as targets for anti-obesity agents. Peptidergic systems are critical to the regulation of energy homeostasis by key regions in the hypothalamus and brainstem. A number of neuropeptide systems have therefore been investigated as potential treatments for obesity. Blocking orexigenic peptide signals such as neuropeptide Y, melanin-concentrating hormone, orexins, relaxin-3 and galanin-like peptide or stimulating anorectic signalling pathways used by peptides such as the melanocortins, ciliary neurotrophic factor and brain-derived neurotrophic factor, are approaches that have shown some promise, but which have also highlighted possible concerns. Manipulation of central peptidergic systems poses a number of therapeutic problems, including brain access and side effects. Given that the homeostatic defence of body weight may limit the effectiveness of any single-target therapy developed, a combination therapy approach may offer the best hope for the effective prevention and treatment of obesity.

LINKED ARTICLES

This article is part of a themed section on Neuropeptides. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2013.170.issue-7.

The role of melanin concentrating hormone (MCH) in the central chemoreflex: a knockdown study by siRNA in the lateral hypothalamus in rats

Melanin concentrating hormone (MCH), a neuropeptide produced mainly in neurons localized to the lateral hypothalamic area (LHA), has been implicated in the regulation of food intake, energy balance, sleep state, and the cardiovascular system. Hypothalamic MCH neurons also have multisynaptic connections with diaphragmatic motoneurons and project to many central chemoreceptor sites. However, there are few studies of MCH involvement in central respiratory control. To test the hypothesis that MCH plays a role in the central chemoreflex, we induced a down regulation of MCH in the central nervous system by knocking down the MCH precursor (pMCH) mRNA in the LHA using a pool of small interfering RNA (siRNA), and measured the resultant changes in breathing, metabolic rate, body weight, and blood glucose levels in conscious rats. The injections of pMCH-siRNA into the LHA successfully produced a ∼62% reduction of pMCH mRNA expression in the LHA and a ∼43% decrease of MCH levels in the cerebrospinal fluid relative to scrambled-siRNA treatment (P = 0.006 and P = 0.02 respectively). Compared to the pretreatment baseline and the scrambled-siRNA treated control rats, knockdown of MCH resulted in: 1) an enhanced hypercapnic chemoreflex (∼42 & 47% respectively; P < 0.05) only in wakefulness; 2) a decrease in body weight and basal glucose levels; and 3) an unchanged metabolic rate. Our results indicate that MCH participates not only in the regulation of glucose and sleep-wake homeostasis but also the vigilance-state dependent regulation of the central hypercapnic chemoreflex and respiratory control.

Relaxin-3/RXFP3 networks: an emerging target for the treatment of depression and other neuropsychiatric diseases?

Animal and clinical studies of gene-environment interactions have helped elucidate the mechanisms involved in the pathophysiology of several mental illnesses including anxiety, depression, and schizophrenia; and have led to the discovery of improved treatments. The study of neuropeptides and their receptors is a parallel frontier of neuropsychopharmacology research and has revealed the involvement of several peptide systems in mental illnesses and identified novel targets for their treatment. Relaxin-3 is a newly discovered neuropeptide that binds, and activates the G-protein coupled receptor, RXFP3. Existing anatomical and functional evidence suggests relaxin-3 is an arousal transmitter which is highly responsive to environmental stimuli, particularly neurogenic stressors, and in turn modulates behavioral responses to these stressors and alters key neural processes, including hippocampal theta rhythm and associated learning and memory. Here, we review published experimental data on relaxin-3/RXFP3 systems in rodents, and attempt to highlight aspects that are relevant and/or potentially translatable to the etiology and treatment of major depression and anxiety. Evidence pertinent to autism spectrum and metabolism/eating disorders, or related psychiatric conditions, is also discussed. We also nominate some key experimental studies required to better establish the therapeutic potential of this intriguing neuromodulatory signaling system, including an examination of the impact of RXFP3 agonists and antagonists on the overall activity of distinct or common neural substrates and circuitry that are identified as dysfunctional in these debilitating brain diseases.

The hypocretins (orexins) mediate the "phasic" components of REM sleep: A new hypothesis

In 1998, a group of phenotypically distinct neurons were discovered in the postero-lateral hypothalamus which contained the neuropeptides hypocretin 1 and hypocretin 2 (also called orexin A and orexin B), which are excitatory neuromodulators. Hypocretinergic neurons project throughout the central nervous system and have been involved in the generation and maintenance of wakefulness. The sleep disorder narcolepsy, characterized by hypersomnia and cataplexy, is produced by degeneration of these neurons. The hypocretinergic neurons are active during wakefulness in conjunction with the presence of motor activity that occurs during survival-related behaviors. These neurons decrease their firing rate during non-REM sleep; however there is still controversy upon the activity and role of these neurons during REM sleep. Hence, in the present report we conducted a critical review of the literature of the hypocretinergic system during REM sleep, and hypothesize a possible role of this system in the generation of REM sleep.

Relaxin-3/RXFP3 Signaling and Neuroendocrine Function - A Perspective on Extrinsic Hypothalamic Control

Complex neural circuits within the hypothalamus that govern essential autonomic processes and associated behaviors signal using amino acid and monoamine transmitters and a variety of neuropeptide (hormone) modulators, often via G-protein coupled receptors (GPCRs) and associated cellular pathways. Relaxin-3 is a recently identified neuropeptide that is highly conserved throughout evolution. Neurons expressing relaxin-3 are located in the brainstem, but broadly innervate the entire limbic system including the hypothalamus. Extensive anatomical data in rodents and non-human primate, and recent regulatory and functional data, suggest relaxin-3 signaling via its cognate GPCR, RXFP3, has a broad range of effects on neuroendocrine function associated with stress responses, feeding and metabolism, motivation and reward, and possibly sexual behavior and reproduction. Therefore, this article aims to highlight the growing appreciation of the relaxin-3/RXFP3 system as an important "extrinsic" regulator of the neuroendocrine axis by reviewing its neuroanatomy and its putative roles in arousal-, stress-, and feeding-related behaviors and links to associated neural substrates and signaling networks. Current evidence identifies RXFP3 as a potential therapeutic target for treatment of neuroendocrine disorders and related behavioral dysfunction.

Microinjection of melanin concentrating hormone into the lateral preoptic area promotes non-REM sleep in the rat

The ventrolateral preoptic area (VLPO) has been recognized as one of the key structures responsible for the generation of non-REM (NREM) sleep. The melanin-concentrating hormone (MCH)-containing neurons, which are located in the lateral hypothalamus and incerto-hypothalamic area, project widely throughout the central nervous system and include projections to the VLPO. The MCH has been associated with the central regulation of feeding and energy homeostasis. In addition, recent findings strongly suggest that the MCHergic system promotes sleep. The aim of the present study was to determine if MCH generates sleep by regulating VLPO neuronal activity. To this purpose, we characterized the effect of unilateral and bilateral microinjections of MCH into the VLPO on sleep and wakefulness in the rat. Unilateral administration of MCH into the VLPO and adjacent dorsal preoptic area did not modify sleep. On the contrary, bilateral microinjections of MCH (100 ng) into these areas significantly increased light sleep (LS, 39.2±4.8 vs. 21.6±2.5 min, P<0.05) and total NREM sleep (142.4±23.2 vs. 86.5±10.5 min, P<0.05) compared to control (saline) microinjections. No effect was observed on REM sleep. We conclude that MCH administration into the VLPO and adjacent dorsal lateral preoptic area promotes the generation of NREM sleep.

The role of melanin-concentrating hormone and its receptors in energy homeostasis

Extensive studies in rodents with melanin-concentrating hormone (MCH) have demonstrated that the neuropeptide hormone is a potent orexigen. Acutely, MCH causes an increase in food intake, while chronically it leads to increased weight gain, primarily as an increase in fat mass. Multiple knockout mice models have confirmed the importance of MCH in modulating energy homeostasis. Animals lacking MCH, MCH-containing neurons, or the MCH receptor all are resistant to diet-induced obesity. These genetic and pharmacologic studies have prompted a large effort to identify potent and selective MCH receptor antagonists, initially as tool compounds to probe pharmacology in models of obesity, with an ultimate goal to identify novel anti-obesity drugs. In animal models, MCH antagonists have consistently shown efficacy in reducing food intake acutely and inhibiting body-weight gain when given chronically. Five compounds have proceeded into clinical testing. Although they were reported as well-tolerated, none has advanced to long-term efficacy and safety studies.

Identification of mRNAs coding for mammalian-type melanin-concentrating hormone and its receptors in the scalloped hammerhead shark Sphyrna lewini

Melanin-concentrating hormone (MCH) is a neuromodulator, synthesized in the hypothalamus, that regulates both appetite and energy homeostasis in mammals. MCH was initially identified in teleost fishes as a pituitary gland hormone that induced melanin aggregation in chromatophores in the skin; however, this function of MCH has not been observed in other vertebrates. Recent studies suggest that MCH is involved in teleost feeding behavior, spurring the hypothesis that the original function of MCH in early vertebrates was appetite regulation. The present study reports the results of cDNAs cloning encoding preproMCH and two MCH receptors from an elasmobranch fish, Sphyrna lewini, a member of Chondrichthyes, the earliest diverged class in gnathostomes. The putative MCH peptide is composed of 19 amino acids, similar in length to the mammalian MCH. Reverse-transcription polymerase chain reaction revealed that MCH is expressed in the hypothalamus in S. lewini MCH cell bodies and fibers were identified by immunochemistry in the hypothalamus, but not in the pituitary gland, suggesting that MCH is not released via the pituitary gland into general circulation. MCH receptor genes mch-r1 and mch-r2 were expressed in the S. lewini hypothalamus, but were not found in the skin. These results indicate that MCH does not have a peripheral function, such as a melanin-concentrating effect, in the skin of S. lewini hypothalamic MCH mRNA levels were not affected by fasting, suggesting that feeding conditions might not affect the expression of MCH in the hypothalamus.

Projections from melanin-concentrating hormone (MCH) neurons to the dorsal raphe or the nuclear core of the locus coeruleus in the rat

Brainstem aminergic and cholinergic nuclei are essential components of reticular activating system which are under the control of hypothalamic sleep/arousal centers. In contrast to well-known role of hypocretin (Hcrt) as a potent wake-promoting substance, only recent reports stated that melanin-concentrating hormone (MCH) plays a role in the maintenance of rapid eye movement (REM) sleep. As the sequel to our report concerning the MCH/Hcrt projection to the brainstem cholinergic nuclei (Hong et al., 2011), in the present study we examined the differential projection from MCH/Hcrt neurons in medial and lateral subdivisions of the lateral hypothalamus (LH) to the dorsal raphe (DR) or the nuclear core of the locus coeruleus (LC) of the rat. Following the injection of Red Retrobeads into the LC core (n=6), the proportions of retrogradely labeled (retro-) MCH neurons over the total retro-cells were 4.4% ± 0.5% (medial subdivision) and 7.4% ±0 .6% (lateral one), whereas those of retro-Hcrt cells over the total retro-cells were 69.4% ± 3.6% (medial) and 64.4% ± 5.2% (lateral). Following midline-DR injections (n=6), the proportions of retro-MCH neurons over the total retro-cells were 14.3% ± 2.9% (medial) and 12.3% ± 1.6% (lateral), while those of retro-Hcrt cells over the total retro-cells were 46.5% ± 6.2% (medial) and 51.3% ± 9.5% (lateral). Following lateral wing-DR injections (n=3), the proportions of retro-MCH neurons over the total retro-cells were 15.5% ± 1.2% (medial) and 11.9% ± 3.1% (lateral), while those of retro-Hcrt cells over the total retro-cells were 48.5% ± 2.7% (medial) and 52.8% ± 2.3% (lateral). The statistical analysis showed that MCH neurons projecting to the LC core or DR were outnumbered by Hcrt cells (P<0.01) and that retro-MCH cells exhibited lateral predominance in LC injection cases (P<0.05). Based on our present as well as previous (Hong et al., 2011) observations, we suggested that MCH and Hcrt neurons in the LH provide preferential projections to the brainstem cholinergic and aminergic nuclei, respectively and that MCH projections to the nuclear core of the LC exhibit differential distribution within LH subdivisions.

A truncating mutation of Alms1 reduces the number of hypothalamic neuronal cilia in obese mice

Primary cilia are ubiquitous cellular antennae whose dysfunction collectively causes various disorders, including vision and hearing impairment, as well as renal, skeletal, and central nervous system anomalies. One ciliopathy, Alström syndrome, is closely related to Bardet-Biedl syndrome (BBS), sharing amongst other phenotypic features morbid obesity. As the cellular and molecular links between weight regulation and cilia are poorly understood, we used the obese mouse strain foz/foz, bearing a truncating mutation in the Alström syndrome protein (Alms1), to help elucidate why it develops hyperphagia, leading to early onset obesity and metabolic anomalies. Our in vivo studies reveal that Alms1 localizes at the base of cilia in hypothalamic neurons, which are implicated in the control of satiety. Alms1 is lost from this location in foz/foz mice, coinciding with a strong postnatal reduction (∼70%) in neurons displaying cilia marked with adenylyl cyclase 3 (AC3), a signaling protein implicated in obesity. Notably, the reduction in AC3-bearing cilia parallels the decrease in cilia containing two appetite-regulating proteins, Mchr1 and Sstr3, as well as another established Arl13b ciliary marker, consistent with progressive loss of cilia during development. Together, our results suggest that Alms1 maintains the function of neuronal cilia implicated in weight regulation by influencing the maintenance and/or stability of the organelle. Given that Mchr1 and Sstr3 localization to remaining cilia is maintained in foz/foz animals but known to be lost from BBS knockout mice, our findings suggest different molecular etiologies for the satiety defects associated with the Alström syndrome and BBS ciliopathies.

Differential distribution of melanin-concentrating hormone (MCH)- and hypocretin (Hcrt)-immunoreactive neurons projecting to the mesopontine cholinergic complex in the rat

Hypocretin (Hcrt or orexin) and melanin-concentrating hormone (MCH) containing neurons are located in the hypothalamus and are implicated in the regulation of feeding behavior, energy homeostasis, and sleep-wake cycle. MCH and Hcrt are not co-localized within the same neuron, but these neurons project widely throughout the brain, especially to brain regions regulating arousal. Recent data indicate that HCRT and MCH neurons located medially with respect to the fornix have a differential projection pattern compared to those located lateral to the fornix. To further elucidate the projection of these neurons in the present study we use retrograde tracing methods combined with double immunofluorescence to determine the differential distribution of Hcrt- and MCH-immunoreactive neurons projecting to the pedunculopontine tegmental (PPTg) or laterodorsal tegmental (LDTg) nuclei. In rats where the retrograde tracer was confined to the PPTg/LDTg we found that there were more MCH neurons projecting to these targets compared to HCRT neurons (P<0.01). When the retrograde tracer was confined to the PPTg, there were more retrogradely labeled MCH neurons lateral to the fornix compared to MCH neurons in the medial LH subdivision (P<0.05). On the average, only about 4.5% of MCH neurons versus 6.1% of HCRT neurons project to PPTg/LDTg. Thus, very few of the MCH or HCRT neurons project to these arousal populations. Although there were significantly more MCH neurons projecting to the mesopontine cholinergic arousal zone compared to the HCRT neurons, the HCRT neurons also exert an indirect influence via the tuberomammillary nucleus. Based on the present and previous (Hong and Lee, 2011) observations, we suggest that both MCH and HCRT neurons exert a potent influence on the PPTg/LDTg, which might play an important role in arousal.

Melanin-concentrating hormone: a new sleep factor?

Neurons containing the neuropeptide melanin-concentrating hormone (MCH) are mainly located in the lateral hypothalamus and the incerto-hypothalamic area, and have widespread projections throughout the brain. While the biological functions of this neuropeptide are exerted in humans through two metabotropic receptors, the MCHR1 and MCHR2, only the MCHR1 is present in rodents. Recently, it has been shown that the MCHergic system is involved in the control of sleep. We can summarize the experimental findings as follows: (1) The areas related to the control of sleep and wakefulness have a high density of MCHergic fibers and receptors. (2) MCHergic neurons are active during sleep, especially during rapid eye movement (REM) sleep. (3) MCH knockout mice have less REM sleep, notably under conditions of negative energy balance. Animals with genetically inactivated MCHR1 also exhibit altered vigilance state architecture and sleep homeostasis. (4) Systemically administered MCHR1 antagonists reduce sleep. (5) Intraventricular microinjection of MCH increases both slow wave sleep (SWS) and REM sleep; however, the increment in REM sleep is more pronounced. (6) Microinjection of MCH into the dorsal raphe nucleus increases REM sleep time. REM seep is inhibited by immunoneutralization of MCH within this nucleus. (7) Microinjection of MCH in the nucleus pontis oralis of the cat enhances REM sleep time and reduces REM sleep latency. All these data strongly suggest that MCH has a potent role in the promotion of sleep. Although both SWS and REM sleep are facilitated by MCH, REM sleep seems to be more sensitive to MCH modulation.

Vertebrate melanophores as potential model for drug discovery and development: a review

Drug discovery in skin pharmacotherapy is an enormous, continually expanding field. Researchers are developing novel and sensitive pharmaceutical products and drugs that target specific receptors to elicit concerted and appropriate responses. The pigment-bearing cells called melanophores have a significant contribution to make in this field. Melanophores, which contain the dark brown or black pigment melanin, constitute an important class of chromatophores. They are highly specialized in the bidirectional and coordinated translocation of pigment granules when given an appropriate stimulus. The pigment granules can be stimulated to undergo rapid dispersion throughout the melanophores, making the cell appear dark, or to aggregate at the center, making the cell appear light. The major signals involved in pigment transport within the melanophores are dependent on a special class of cell surface receptors called G-protein-coupled receptors (GPCRs). Many of these receptors of adrenaline, acetylcholine, histamine, serotonin, endothelin and melatonin have been found on melanophores. They are believed to have clinical relevance to skin-related ailments and therefore have become targets for high throughput screening projects. The selective screening of these receptors requires the recognition of particular ligands, agonists and antagonists and the characterization of their effects on pigment motility within the cells. The mechanism of skin pigmentation is incredibly intricate, but it would be a considerable step forward to unravel its underlying physiological mechanism. This would provide an experimental basis for new pharmacotherapies for dermatological anomalies. The discernible stimuli that can trigger a variety of intracellular signals affecting pigment granule movement primarily include neurotransmitters and hormones. This review focuses on the role of the hormone and neurotransmitter signals involved in pigment movement in terms of the pharmacology of the specific receptors.

Molecular annotation of integrative feeding neural circuits

The identity of higher-order neurons and circuits playing an associative role to control feeding is unknown. We injected pseudorabies virus, a retrograde tracer, into masseter muscle, salivary gland, and tongue of BAC-transgenic mice expressing GFP in specific neural populations and identified several CNS regions that project multisynaptically to the periphery. MCH and orexin neurons were identified in the lateral hypothalamus, and Nurr1 and Cnr1 in the amygdala and insular/rhinal cortices. Cholera toxin β tracing showed that insular Nurr1(+) and Cnr1(+) neurons project to the amygdala or lateral hypothalamus, respectively. Finally, we show that cortical Cnr1(+) neurons show increased Cnr1 mRNA and c-Fos expression after fasting, consistent with a possible role for Cnr1(+) neurons in feeding. Overall, these studies define a general approach for identifying specific molecular markers for neurons in complex neural circuits. These markers now provide a means for functional studies of specific neuronal populations in feeding or other complex behaviors.

Cellular models for the study of the pharmacology and signaling of melanin-concentrating hormone receptors

Cellular models for the study of the neuropeptide melanin-concentrating hormone (MCH) have become indispensable tools for pharmacological profiling and signaling analysis of MCH and its synthetic analogues. Although expression of MCH receptors is most abundant in the brain, MCH-R(1) is also found in different peripheral tissues. Therefore, not only cell lines derived from nervous tissue but also from peripheral tissues that naturally express MCH receptors have been used to study receptor signaling and regulation. For screening of novel compounds, however, heterologous expression of MCH-R(1) or MCH-R(2) genes in HEK293, Chinese hamster ovary, COS-7, or 3T3-L1 cells, or amplified MCH-R(1) expression/signaling in IRM23 cells transfected with the G(q) protein gene are the preferred tools because of more distinct pharmacological effects induced by MCH, which include inhibition of cAMP formation, stimulation of inositol triphosphate production, increase in intracellular free Ca(2+) and/or activation of mitogen-activated protein kinases. Most of the published data originate from this type of model system, whereas data based on studies with cell lines endogenously expressing MCH receptors are more limited. This review presents an update on the different cellular models currently used for the analysis of MCH receptor interaction and signaling.

Immunoneutralization of melanin-concentrating hormone (MCH) in the dorsal raphe nucleus: effects on sleep and wakefulness

Hypothalamic neurons that utilize melanin-concentrating hormone (MCH) as a neuromodulator exert a positive control over energy homeostasis, inducing feeding and decreasing metabolism. Recent studies have shown also that this system plays a role in the generation and/or maintenance of sleep. MCHergic neurons project to the serotonergic dorsal raphe nucleus (DR), a neuroanatomical structure involved in several functions during wakefulness (W), and in the regulation of rapid-eye movements (REM) sleep. Recently, we determined the effect of MCH microinjected into the DR on sleep variables in the rat. MCH produced a marked increment of REM sleep, whereas slow wave sleep (SWS) showed only a moderate increase. In the present study, we analyze the effect of immunoneutralization of MCH in the DR on sleep and W in the rat. Compared to the control solution, microinjections of anti-MCH antibodies (1/100 solution in 0.2 μl) induced a significant increase in REM sleep latency (31.2±7.1 vs. 84.2±24.8 min, p<0.05) and a decrease of REM sleep time (37.8±5.4 vs. 17.8±2.9 min, p<0.05) that was related to the reduction in the number of REM sleep episodes. In addition, there was an increase of total W time (49.8±4.6 vs. 72.0±5.7 min, p<0.01). Light sleep and SWS remained unchanged. The intra-DR administration of a more diluted solution of anti-MCH antibodies (1/500) or rabbit pre-immune serum did not modify neither W nor REM sleep variables. Our findings strongly suggest that MCH released in the DR facilitates the occurrence of REM sleep.

Mechanism of the anti-obesity effects induced by a novel melanin-concentrating hormone 1-receptor antagonist in mice

BACKGROUND AND PURPOSE

Melanin-concentrating hormone (MCH) is an orexigenic neuropeptide expressed in the lateral hypothalamus that is involved in feeding and body weight regulation. Intracerebroventricular infusion of a peptidic MCH1 receptor antagonist ameliorated obesity in murine models. Recently, small molecule MCH1 receptor antagonists have been developed and characterized for the treatment of obesity. However, little is known of the mechanism of the anti-obesity effects of MCH1 receptor antagonists.

EXPERIMENTAL APPROACH

To examine the mechanisms of action of the anti-obesity effect of MCH1 receptor antagonists more precisely, we conducted a pair-feeding study in mice with diet-induced obesity (DIO), chronically treated with an orally active and highly selective MCH1 receptor antagonist and examined changes in mRNA expression levels in liver, brown and white adipose tissues. We also assessed the acute effects of the MCH1 receptor antagonist in energy expenditure under thermoneutral conditions.

KEY RESULTS

Treatment with the MCH1 receptor antagonist at 30 mg.kg(-1) for 1 month moderately suppressed feeding and significantly reduced body weight by 24%. In contrast, pair-feeding resulted in a smaller weight reduction of 10%. Treatment with the MCH1 receptor antagonist resulted in a higher body temperature compared with the pair-fed group. TaqMan and calorimetry data suggested that the MCH1 receptor antagonist also stimulated thermogenesis.

CONCLUSIONS AND IMPLICATIONS

Our results indicate that an MCH1 receptor antagonist caused anti-obesity effects im mice by acting on both energy intake and energy expenditure.

Animals models of MCH function and what they can tell us about its role in energy balance

Melanin-concentrating hormone (MCH) has attracted considerable attention because of its effects on food intake and body weight and the MCH receptor (MCHR1) remains one of the viable targets for obesity therapy. This review summarizes the literature examining the effects of MCH on body weight, food intake and energy expenditure in rodent models, and the central sites where MCH acts in regulating energy homeostasis. Emphasis is given on the discrepancies between the genetic and pharmacologic models of MCHR1 inactivation. We propose some solutions to resolve these discrepancies and discuss some future directions in MCH research.

MCH and feeding behavior-interaction with peptidic network

Numerous works associate the MCH peptide, and the hypothalamic neurons that produce it, to the feeding behavior and energy homeostasis. It is commonly admitted that MCH is an orexigenic peptide, and MCH neurons could be under the control of arcuate NPY and POMC neurons. However, the literature data is not always concordant. In particular questions about the intrahypothalamic circuit involving other neuropeptides and about the mechanisms through which MCH could act are not yet clearly answered. For example, which receptors mediate a MCH response to NPY or alpha-MSH, does MCH act alone, is there any local anatomical organization within the tuberal LHA? A review of the current literature is then needed to help focus attention on these unresolved and often neglected issues.

S38151 [p-guanidinobenzoyl-[Des-Gly(10)]-MCH(7-17)] is a potent and selective antagonist at the MCH(1) receptor and has anti-feeding properties in vivo

Structure-activity relationships studies have established the minimal sequence of melanin-concentrating hormone (MCH) that retains full agonist potency at the MCH(1), to be the dodecapeptide MCH(6-17). The alpha-amino function is not required for activity since arginine(6) can be replaced by p-guanidinobenzoyl, further improving activity. We report that the deletion of glycine in this short potent agonist (EC(50) 3.4nM) turns it into a potent and new MCH(1) antagonist (S38151, K(B) 4.3nM in the [(35)S]-GTPgammaS binding assay), which is selective versus MCH(2). A compared Ala-scan of the agonist and antagonist sequences reveals major differences in the residues that are mandatory for affinity, including arginine(11) and tyrosine(13) for the agonist and leucine(9) for the antagonist, whereas methionine(8) was necessary for both agonist and antagonist activities. A complete molecular study of the antagonist behavior is described in the present report, with a particular focus on the description of several analogues, attempting to find structure-activity relationships. Finally, S38151 antagonizes food intake when injected intra-cerebroventricularly in the rat. This is in agreement with the in vitro data and with our previous demonstration of a good correlation between in vitro and in vivo data on MCH(1) agonists.

Molecular cloning and expression of two melanin-concentrating hormone receptors in goldfish

Melanin-concentrating hormone (MCH) is a neurohypophysial hormone and induces melanin aggregation in the skin in teleosts. MCH also has multiple roles in the central regulation of food intake in teleosts and mammals. MCH receptors (MCH-R) are among type I G-protein-coupled receptors. Here, we cloned two MCH receptors from goldfish, Carassius auratus. The amino acid sequence of goldfish MCH-R1 had 57-88% homology with fish MCH-R1 and 49-50% homology with mammalian MCH-R1, while the amino acid sequence of goldfish MCH-R2 had 72-92% homology with fish MCH-R2 and 32% homology with human MCH-R2. Phylogenetic analysis showed that these two MCH-Rs are orthologous to the respective mammalian MCH-Rs. The common amino acid residues for ligand binding, signal transduction, and receptor conformation were well conserved in these receptors, although some intracellular basic-amino-acid-rich domains, which have been shown to exist in human MCH-R1 and MCH-R2, were absent in goldfish MCH-R2. When stably expressed in HEK293 cells, both goldfish MCH-R1 and MCH-R2 displayed a strong, dose-dependent, transient elevation of intracellular calcium in response to salmon MCH (EC(50)=0.8nM and 31.8nM, respectively). In contrast to goldfish MCH-R2, goldfish MCH-R1 signaling is not sensitive to pertussis toxin, suggesting an exclusive Galphaq coupling of goldfish MCH-R1 in the mammalian cell-based assay. Reverse transcriptase PCR revealed that both MCH-R1 and MCH-R2 mRNA are distributed in various tissues in goldfish. The various tissues including the brain and skin express both MCH-R1 and MCH-R2. These results suggest that these functional receptors mediate multiple effects of MCH in goldfish.

Melanin-concentrating hormone 1-receptor antagonist suppresses body weight gain correlated with high receptor occupancy levels in diet-induced obesity mice

Melanin-concentrating hormone (MCH), which is a neuropeptide expressed in the hypothalamus of the brain, is involved in regulating feeding behavior and energy homeostasis via the MCH(1) receptor in rodents. It is widely considered that MCH(1) receptor antagonists are worthy of development for medical treatment of obesity. Here we report on the development of an ex vivo receptor occupancy assay using a new radiolabeled MCH(1) receptor antagonist, [(35)S]-compound D. An MCH(1) receptor antagonist inhibited the binding of [(35)S]-compound D to brain slices in a dose-dependent manner. The result showed a good correlation between the receptor occupancy levels and plasma or brain levels of the MCH(1) receptor antagonist, suggesting that the ex vivo receptor binding assay using this radioligand is practical. Quantitative analysis in diet-induced obese mice showed that the efficacy of body weight reduction correlated with the receptor occupancy levels at 24h. Furthermore, more than 90% occupancy levels of MCH(1) receptor antagonists during 24h post-dosing are required for potent efficacy on body weight reduction. The present occupancy assay could be a useful pharmacodynamic marker to quantitatively estimate anti-obese efficacy, and would accelerate the development of MCH(1) receptor antagonists for treatment of obesity.

Lithium treatment elongates primary cilia in the mouse brain and in cultured cells

The molecular mechanisms underlying the therapeutic effects of lithium, a first-line antimanic mood stabilizer, have not yet been fully elucidated. Treatment of the algae Chlamydomonas reinhardtii with lithium has been shown to induce elongation of their flagella, which are analogous structures to vertebrate cilia. In the mouse brain, adenylyl cyclase 3 (AC3) and certain neuropeptide receptors colocalize to the primary cilium of neuronal cells, suggesting a chemosensory function for the primary cilium in the nervous system. Here we show that lithium treatment elongates primary cilia in the mouse brain and in cultured cells. Brain sections from mice chronically fed with Li(2)CO(3) were subjected to immunofluorescence study. Primary cilia carrying both AC3 and the receptor for melanin-concentrating hormone (MCH) were elongated in the dorsal striatum and nucleus accumbens of lithium-fed mice, as compared to those of control animals. Moreover, lithium-treated NIH3T3 cells and cultured striatal neurons exhibited elongation of the primary cilia. The present results provide initial evidence that a psychotropic agent can affect ciliary length in the central nervous system, and furthermore suggest that lithium exerts its therapeutic effects via the upregulation of cilia-mediated MCH sensing. These findings thus contribute novel insights into the pathophysiology of bipolar mood disorder and other psychiatric diseases.