Melanin-concentrating hormone (MCH) antagonizes the effects of alpha-MSH and neuropeptide E-I on grooming and locomotor activities in the rat

Exploratory Rearing Is Governed by Hypothalamic Melanin-Concentrating Hormone Neurons According to Locus Ceruleus

Information seeking, such as standing on tiptoes to look around in humans, is observed across animals and helps survival. Its rodent analog-unsupported rearing on hind legs-was a classic model in deciphering neural signals of cognition and is of intense renewed interest in preclinical modeling of neuropsychiatric states. Neural signals and circuits controlling this dedicated decision to seek information remain largely unknown. While studying subsecond timing of spontaneous behavioral acts and activity of melanin-concentrating hormone (MCH) neurons (MNs) in behaving male and female mice, we observed large MN activity spikes that aligned to unsupported rears. Complementary causal, loss and gain of function, analyses revealed specific control of rear frequency and duration by MNs and MCHR1 receptors. Activity in a key stress center of the brain-the locus ceruleus noradrenaline cells-rapidly inhibited MNs and required functional MCH receptors for its endogenous modulation of rearing. By defining a neural module that both tracks and controls rearing, these findings may facilitate further insights into biology of information seeking.

PDGF Promotes Dermal Fibroblast Activation via a Novel Mechanism Mediated by Signaling Through MCHR1

Systemic sclerosis (SSc) is an autoimmune disease characterized by vasculopathy and excessive fibrosis of the skin and internal organs. To this day, no effective treatments to prevent the progression of fibrosis exist, and SSc patients have disabilities and reduced life expectancy. The need to better understand pathways that drive SSc and to find therapeutic targets is urgent. RNA sequencing data from SSc dermal fibroblasts suggested that melanin-concentrating hormone receptor 1 (MCHR1), one of the G protein-coupled receptors regulating emotion and energy metabolism, is abnormally deregulated in SSc. Platelet-derived growth factor (PDGF)-BB stimulation upregulated MCHR1 mRNA and protein levels in normal human dermal fibroblasts (NHDF), and MCHR1 silencing prevented the PDGF-BB-induced expression of the profibrotic factors transforming growth factor beta 1 (TGFβ1) and connective tissue growth factor (CTGF). PDGF-BB bound MCHR1 in membrane fractions of NHDF, and the binding was confirmed using surface plasmon resonance (SPR). MCHR1 inhibition blocked PDGF-BB modulation of intracellular cyclic adenosine monophosphate (cAMP). MCHR1 silencing in NHDF reduced PDGF-BB signaling. In summary, MCHR1 promoted the fibrotic response in NHDF through modulation of TGFβ1 and CTGF production, intracellular cAMP levels, and PDGF-BB-induced signaling pathways, suggesting that MCHR1 plays an important role in mediating the response to PDGF-BB and in the pathogenesis of SSc. Inhibition of MCHR1 should be considered as a novel therapeutic strategy in SSc-associated fibrosis.

Melanin-concentrating hormone in rat nucleus accumbens or lateral hypothalamus differentially impacts morphine and food seeking behaviors

BACKGROUND

Identifying neural substrates that are differentially affected by drugs of abuse and natural rewards is key to finding a target for an efficacious treatment for substance abuse. Melanin-concentrating hormone is a polypeptide with an inhibitory effect on the mesolimbic dopamine system. Here we test the hypothesis that melanin-concentrating hormone in the lateral hypothalamus and nucleus accumbens shell is differentially involved in the regulation of morphine and food-rewarded behaviors.

METHODS

Male Sprague-Dawley rats were trained with morphine (5.0 mg/kg, subcutaneously) or food pellets (standard chow, 10-14 g) to induce a conditioned place preference, immediately followed by extinction training. Melanin-concentrating hormone (1.0 µg/side) or saline was infused into the nucleus accumbens shell or lateral hypothalamus before the reinstatement primed by morphine or food, and locomotor activity was simultaneously monitored. As the comparison, melanin-concentrating hormone was also microinjected into the nucleus accumbens shell or lateral hypothalamus before the expression of food or morphine-induced conditioned place preference.

RESULTS

Microinfusion of melanin-concentrating hormone into the nucleus accumbens shell (but not into the lateral hypothalamus) prevented the reinstatement of morphine conditioned place preference but had no effect on the reinstatement of food conditioned place preference. In contrast, microinfusion of melanin-concentrating hormone into the lateral hypothalamus (but not in the nucleus accumbens shell) inhibited the reinstatement of food conditioned place preference but had no effect on the reinstatement of morphine conditioned place preference.

CONCLUSIONS

These results suggest a clear double dissociation of melanin-concentrating hormone in morphine/food rewarding behaviors and melanin-concentrating hormone in the nucleus accumbens shell. Melanin-concentrating hormone could be a potential target for therapeutic intervention for morphine abuse without affecting natural rewards.

Melanin-concentrating hormone peptidergic system: Comparative morphology between muroid species

Melanin-concentrating hormone (MCH) is a conserved neuropeptide, predominantly located in the diencephalon of vertebrates, and associated with a wide range of functions. While functional studies have focused on the use of the traditional mouse laboratory model, critical gaps exist in our understanding of the morphology of the MCH system in this species. Even less is known about the nontraditional animal model Neotomodon alstoni (Mexican volcano mouse). A comparative morphological study among these rodents may, therefore, contribute to a better understanding of the evolution of the MCH peptidergic system. To this end, we employed diverse immunohistochemical protocols to identify key aspects of the MCH system, including its spatial relationship to another neurochemical population of the tuberal hypothalamus, the orexins. Three-dimensional (3D) reconstructions were also employed to convey a better sense of spatial distribution to these neurons. Our results show that the distribution of MCH neurons in all rodents studied follows a basic plan, but individual characteristics are found for each species, such as the preeminence of a periventricular group only in the rat, the lack of posterior groups in the mouse, and the extensive presence of MCH neurons in the anterior hypothalamic area of Neotomodon. Taken together, these data suggest a strong anatomical substrate for previously described functions of the MCH system, and that particular neurochemical and morphological features may have been determinant to species-specific phenotypes in rodent evolution.

Differential effects of hypo- and hyperthyroidism on remodeling of contacts between neurons expressing the neuropeptide EI and tyrosine hydroxylase in hypothalamic areas of the male rat

The Neuropeptide EI (NEI, glutamic acid- isoleucine amide) participates in neuroendocrine function. Previously we demonstrated that NEI concentration is regulated by thyroid hormones in discrete hypothalamic areas in rats. We observed that the thyroid status affects the dopaminergic regulation of the pituitary hormones. In this study we explored possible interactions between NEI and tyrosine hydroxylase (TH) containing elements in selected hypothalamic areas of male rats. Neuronal somas, terminals and boutons were assessed by confocal microscopy, in hypo- and hyperthyroid animals. We observed a remodeling of the contacts between the TH and NEI immunoreactive elements in the incerto-hypothalamic area (IHy, also known as rostromedial zona incerta) according to thyroid function. However, in the dorsolateral zone of the peduncular part of the lateral hypothalamus (DL-PLH) the thyroid hormones affect the dendritic trees of the neurons without perturbing the overall NEI/TH contacts. Also, we demonstrated that TRH Receptor 1 (TRH-R1) is colocalized in NEI immunoreactive neurons in the peduncular part of the lateral hypothalamus (PLH) and NEI precursor mRNA expression increased by hypothyroidism indicating that NEI neurons are responsive to the feedback mechanisms of the Hypothalamic Pituitary-Thyroid Axis (HPT). In conclusion, the hypothyroid status seems to increase the interactions between the NEI neurons and the dopaminergic pathways while hyperthyroidism either decreases or displays no effects. Altogether these observations support the participation of the IHy and PLH NEI as a modulating component of the HPT suggesting that altered neuroendocrine, behavioral and cognitive dysfunctions induced by dysthyroidism could be in part mediated by NEI.

Melanin concentrating hormone modulates oxytocin-mediated marble burying

Repetitive and perseverative behaviors are common features of a number of neuropsychiatric diseases such as Angelman's syndrome, Tourette's syndrome, obsessive-compulsive disorder, and autism spectrum disorders. The oxytocin system has been linked to the regulation of repetitive behavior in both animal models and humans, but many of its downstream targets have still to be found. We report that the melanin-concentrating hormone (MCH) system is a target of the oxytocin system in regulating one repetitive behavior, marble burying. First we report that nearly 60% of MCH neurons express oxytocin receptors, and demonstrate using rabies mediated tract tracing that MCH neurons receive direct presynaptic input from oxytocin neurons. Then we show that MCH receptor knockout (MCHR1KO) mice and MCH ablated animals display increased marble burying response while central MCH infusion decreases it. Finally, we demonstrate the downstream role of the MCH system on oxytocin mediated marble burying by showing that central infusions of MCH and oxytocin alone or together reduce it while antagonizing the MCH system blocks oxytocin-mediated reduction of this behavior. Our findings reveal a novel role for the MCH system as a mediator of the role of oxytocin in regulating marble-burying behavior in mice.

Neuropeptide glutamic acid-isoleucine (NEI)-induced paradoxical sleep in rats

Neuropeptideglutamic acid-isoleucine (NEI) as well as melanin concentrating hormone (MCH) is cleaved from the 165 amino acid protein, prepro-melanin concentrating hormone (prepro-MCH). Among many physiological roles of MCH, we demonstrated that intracerebroventricular (icv) injection of MCH induced increases in REM sleep episodes as well as in non REM sleep episodes. However, there are no studies on the effect of NEI on the sleep-wake cycle. As for the sites of action of MCH for induction of REM sleep, the ventrolateral periaqueductal gray (vlPAG) has been reported to be one of its site of action. Although MCH neurons contain NEI, GABA, MCH, and other neuropeptides, we do not know which transmitter(s) might induce REM sleep by acting on the vlPAG. Thus, we first examined the effect of icv injection of NEI on the sleep-wake cycle, and investigated how microinjection of either NEI, MCH, or GABA into the vlPAG affected REM sleep in rats. Icv injection of NEI (0.61μg/5μl: n=7) significantly increased the time spent in REM episodes compared to control (saline: 5μl; n=6). Microinjection of either NEI (61ng/0.2μl: n=7), MCH (100ng/0.2μl: n=6) or GABA (250mM/0.2μl: n=7) into the vlPAG significantly increased the time spent in REM episodes and the AUC. Precise hourly analysis of REM sleep also revealed that after those microinjections, NEI and MCH increased REM episodes at the latter phase, compared to GABA which increased REM episodes at the earlier phase. This result suggests that NEI and MCH may induce sustained REM sleep, while GABA may initiate REM sleep. In conclusion, our findings demonstrate that NEI, a cleaved peptide from the same precursor, prepro-MCH, as MCH, induce REM sleep at least in part through acting on the vlPAG.

Effects of thyroid status on NEI concentration in specific brain areas related to reproduction during the estrous cycle

We previously showed that short-term hypo- and hyperthyroidism induce changes in neuropeptide glutamic-acid-isoleucine-amide (NEI) concentrations in discrete brain areas in male rats. To investigate the possible effects of hypo- and hyperthyroidism on NEI concentrations mainly in hypothalamic areas related to reproduction and behavior, female rats were sacrificed at different days of the estrous cycle. Circulating luteinizing hormone (LH), estradiol and progesterone concentrations were measured in control, hypothyroid (hypoT, treated with PTU during 7-9 days) and hyperthyroid (hyperT, l-T4 during 4-7 days) animals. Both treatments blunted the LH surge. Hypo- and hyperthyroidism increased estradiol concentrations during proestrus afternoon (P-PM), although hypoT rats showed lower values compared to control during proestrus morning (P-AM). Progesterone levels were higher in all groups at P-PM and in the hyperT during diestrus morning (D2). NEI concentrations were lower in hypoT rats during the estrous cycle except in estrus (E) in the peduncular part of the lateral hypothalamus (PLH). They were also reduced by both treatments in the perifornical part of the lateral hypothalamus (PeFLH) during P-PM. Hypothyroidism led to higher NEI concentrations during P-PM in the organum vasculosum of the lamina terminalis and anteroventral periventricular nucleus (OVLT+AVPV). The present results indicate that NEI concentration is regulated in a complex manner by hypo- and hyperthyroidism in the different areas studied, suggesting a correlation between NEI values and the variations of gonadal steroid levels during estrous cycle. These changes could be, in part, responsible for the alterations observed in the hypothalamic-pituitary-gonadal axis in these pathologies.

Olanzapine-induced changes in glucose metabolism are independent of the melanin-concentrating hormone system

Atypical antipsychotic drugs such as Olanzapine (Ola) induce weight gain and metabolic changes associated with the development of type 2 diabetes. The mechanisms underlying these undesired side-effects are currently unknown. Chagnon et al. showed that the common allele rs7973796 of the prepro-melanin-concentrating hormone (PMCH) gene is associated with a greater body mass index in Ola-treated schizophrenic patients. As PMCH encodes for the orexigenic neuropeptide melanin-concentrating hormone (MCH), it was hypothesized that MCH is involved in Ola-induced metabolic changes. We have recently reported that the intragastric infusion of Ola results in hyperglycaemia and insulin resistance in male rats. In order to test in vivo the possible involvement of the PMCH gene in the pathogenesis of Ola side-effects, we administered Ola intragastrically in wild-type (WT) and PMCH knock-out (KO) rats. Our results show that glucose and corticosterone levels, as well as endogenous glucose production, are elevated by the infusion of Ola in both WT and KO animals. Thus, the lack of MCH does not seem to affect the acute effects of Ola on glucose metabolism. On the other hand, these effects might be obliterated by compensatory changes in other hypothalamic systems. In addition, possible modulatory effects of the MCH KO on the long term effects of Ola, i.e. increased adiposity, body weight gain, have not been investigated yet.

Neurochemical heterogeneity of rats predicted by different measures to be high ethanol consumers

BACKGROUND

Alcoholism is a heterogeneous disease, with subjects possibly differing both in the best measure that predicts their excess consumption and in their most effective pharmacotherapy. Two different measures, high novelty-induced activity and high-fat-induced triglycerides (TGs), are known to identify subgroups of animals prone to consuming higher amounts of ethanol (EtOH). The question investigated here is whether these subgroups are, in fact, similar in their neurochemical phenotype that may contribute to their overconsumption.

METHODS

EtOH-naïve, Sprague-Dawley rats were subgrouped based on the 2 predictor measures of activity or TG levels, and then quantitative real-time polymerase chain reaction and digoxigenin-labeled in situ hybridization were used to measure their expression of hypothalamic peptides that affect EtOH intake. In additional subgroups subsequently trained to drink 9% EtOH, the opioid antagonist and alcoholism medication, naltrexone, was tested at a low dose (0.02 mg/kg, s.c.) to determine the rats' sensitivity to its effects.

RESULTS

The 2 measures, while both effective in predicting amount of EtOH intake, were found to identify distinctive subgroups. Rats with high compared to low activity exhibited significantly greater expression of galanin and enkephalin in the paraventricular nucleus (PVN) and of orexin in the perifornical lateral hypothalamus (PFLH), but no difference in melanin-concentrating hormone in PFLH or neuropeptide Y in arcuate nucleus. This contrasts with rats having high TG, which exhibited greater expression only of PVN galanin, along with reduced PFLH orexin. The high-activity rats with elevated enkephalin, but not high-TG rats, were also unusually sensitive to naltrexone, which significantly reduced their alcohol intake.

CONCLUSIONS

In addition to revealing differences in endogenous peptides and drug responsiveness in predicted high EtOH drinkers, this study demonstrates that these disturbances differ markedly between the 2 at-risk subgroups. This indicates that simple tests may be effective in identifying subjects most responsive to a specific pharmacotherapy.

Melanin-concentrating hormone receptor 1 antagonists: synthesis, structure-activity relationship, docking studies, and biological evaluation of 2,3,4,5-tetrahydro-1H-3-benzazepine derivatives

Melanin-concentrating hormone receptor 1 (MCHR1) antagonists have been studied as potential agents for the treatment of obesity. Initial structure-activity relationship studies of in-house hit compound 1a and subsequent optimization studies resulted in the identification of tetrahydroisoquinoline derivative 23, 1-(2-acetyl-1,2,3,4-tetrahydroisoquinolin-7-yl)-4-[4-(4-chlorophenyl)piperidin-1-yl]butan-1-one, as a potent hMCHR1 antagonist. A homology model of hMCHR1 suggests that these compounds interact with Asn 294 and Asp 123 in the binding site of hMCHR1 to enhance binding affinity. Oral administration of compound 23 dose-dependently reduced food intake in diet-induced obesity (DIO)-F344 rats.

Hypo- and hyperthyroidism affect NEI concentration in discrete brain areas of adult male rats

To date, there has been only one in vitro study of the relationship between neuropeptide EI (NEI) and the hypothalamic-pituitary-thyroid (HPT) axis. To investigate the possible relationship between NEI and the HPT axis, we developed a rat model of hypothyroidism and hyperthyroidism that allows us to determine whether NEI content is altered in selected brain areas after treatment, as well as whether such alterations are related to the time of day. Hypothyroidism and hyperthyroidism, induced in male rats, with 6-propyl-1-thiouracil and l-thyroxine, respectively, were confirmed by determination of triiodothyronine, total thyroxine, and thyrotropin levels. All groups were studied at the morning and the afternoon. In rats with hypothyroidism, NEI concentration, evaluated on postinduction days 7 and 24, was unchanged or slightly elevated on day 7 but was decreased on day 24. In rats with hyperthyroidism, NEI content, which was evaluated after 4 days of l-thyroxine administration, was slightly elevated, principally in the preoptic area in the morning and in the median eminence-arcuate nucleus and pineal gland in the afternoon, the morning and afternoon NEI contents being similar in the controls. These results provide the bases to pursue the study of the interaction between NEI and the HPT axis.

Anatomical organization of the melanin-concentrating hormone peptide family in the mammalian brain

More than 20 years ago, melanin-concentrating hormone (MCH) and its peptide family members - neuropeptide EI (NEI) and neuropeptide GE (NGE) - were described in various species, including mammals (rodents, humans, and non-human primates). Since then, most studies have focused on the role of MCH as an orexigenic peptide, as well as on its participation in learning, spatial memory, neuroendocrine control, and sleep. It has been shown that MCH mRNA or the neuropeptide MCH are present in neurons of the prosencephalon, hypothalamus and brainstem. However, most of the neurons containing MCH/NEI are within the incerto-hypothalamic and lateral hypothalamic areas. In addition, the terminals of those neurons are distributed widely throughout the central nervous system. In this review, we will discuss the relationship between those territories and the roles played by MCH/NEI, as well as the importance of MCH receptor 1 in the respective terminal fields. Certain neurochemical features of MCH- and NEI-immunoreactive (MCH-ir and NEI-ir) neurons will also be discussed. The overarching theme is the anatomical organization of an inhibitory neuropeptide colocalized with an inhibitory neurotransmitter in integrative territories of the central nervous system, such as the IHy and LHA. Although these territories have connections to few brain regions, the regions to which they are connected are relevant, being responsible for the organization of motivated behaviors. All available information on this peptidergic system (anatomical, neurochemical, hodological, physiological, pharmacological and behavioral data) suggests that MCH is intimately involved in arousal and the initiation of motivated behaviors.

Pmch expression during early development is critical for normal energy homeostasis

Postnatal development and puberty are times of strong physical maturation and require large quantities of energy. The hypothalamic neuropeptide melanin-concentrating hormone (MCH) regulates nutrient intake and energy homeostasis, but the underlying mechanisms are not completely understood. Here we use a novel rat knockout model in which the MCH precursor Pmch has been inactivated to study the effects of loss of MCH on energy regulation in more detail. Pmch(-/-) rats are lean, hypophagic, osteoporotic, and although endocrine parameters were changed in pmch(-/-) rats, endocrine dynamics were normal, indicating an adaptation to new homeostatic levels rather than disturbed metabolic mechanisms. Detailed body weight growth and feeding behavior analysis revealed that Pmch expression is particularly important during early rat development and puberty, i.e., the first 8 postnatal weeks. Loss of Pmch resulted in a 20% lower set point for body weight that was determined solely during this period and remained unchanged during adulthood. Although the final body weight is diet dependent, the Pmch-deficiency effect was similar for all diets tested in this study. Loss of Pmch affected energy expenditure in both young and adult rats, although these effects seem secondary to the observed hypophagia. Our findings show an important role for Pmch in energy homeostasis determination during early development and indicate that the MCH receptor 1 system is a plausible target for childhood obesity treatment, currently a major health issue in first world countries.

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.

Melanin-concentrating hormone and melanin-concentrating hormone receptors in mammalian skin physiopathology

To date, there is a dearth of evidence to support functions for melanin-concentrating hormone (MCH) and melanin-concentrating hormone receptors (MCH-R) in mammalian skin physiology including pigmentation, inflammation and immune responses and skin cell proliferation. Much research is therefore still needed to define the roles of the hormone and its receptors in mammalian skin. This will be a crucial step to identifying pathogenic mechanisms that may involve the MCH/MCH-R system in the context of inflammatory and autoimmune skin diseases as well as skin cancers. The following review summarizes the studies which have been carried out to examine the expression and function of MCH and MCH-R in mammalian skin. Recent findings with regard to humoral immune responses to the MCH-R1 in patients with the skin depigmenting disease vitiligo are also discussed.

Melanin-concentrating hormone: A neuropeptide hormone affecting the relationship between photic environment and fish with special reference to background color and food intake regulation

Melanin-concentrating hormone (MCH) was first discovered in the pituitary gland of the chum salmon for its role in the regulation of skin pallor. Currently, MCH is known to be present in the brains of organisms ranging from fish to mammals. MCH has been suggested to be conserved principally as a central neuromodulator or neurotransmitter in the brain. Indeed, MCH is considered to regulate food intake in mammals. In this review, profiles of MCH in the brain and pituitary gland of teleost fishes are described, focusing on the involvement of MCH in background color adaptation and in food intake regulation.

Anatomy, function and regulation of neuropeptide EI (NEI)

This review is focused on the anatomy, role and behavior of neuropeptide-glutamic acid-isoleucine (NEI), providing a general report on the neuropeptide. In addition to hormone release, this peptide also takes part in the regulation of grooming behavior and locomotor activity. NEI is produced by cleavage of prepro-MCH that probably takes place at the Lys(129)-Arg(130) and Arg(145)-Arg(146) sites (the glycine residue on the C-terminus of NEI strongly suggests that this peptide is amidated). This same prohormone is also the precursor of MCH, widely studied in relation to food and water intake, and NGE, of which little is known. NEI and MCH are extensively colocalized throughout the central nervous system (CNS), and NEI is also present in peripheral tissues. The latter is also effective in stimulating luteinizing hormone (LH) release and, to a lesser extent, FSH from primary pituitary cell cultures. In addition to releasing LH from the medial eminence, NEI also acts directly on gonadotropes. Lastly, this neuropeptide also acts at the CNS level on gonadotropin-releasing hormone (GnRH) neurons.

High-throughput screening of novel antagonists on melanin-concentrating hormone receptor-1

AIM

To find new antagonists on human melanin-concentrating hormone receptor-1 (MCHR-1) through high-throughput screening (HTS) of a diverse compound library.

METHODS

MCHR-1, [3H]SNAP7941, and FlashBlue G-protein-coupled receptor beads were used to measure the receptor-binding activities of various compounds based on scintillation proximity assay (SPA) technology. The guanosine 5'(gamma-[35S]thio) triphosphate ([35S]GTPgammaS) binding assay was subsequently applied to functionally characterize the "hits" identified by the HTS campaign.

RESULTS

Of the 48,240 compounds screened with the SPA method, 12 hits were confirmed to possess MCHR-1 binding activities, 8 were functionally studied subsequently with the [35S]GTPgammaS binding assay, and only 1 compound (NC127816) displayed moderate human MCHR-1 binding affinity (Ki=115.7 nmol/L) and relatively potent antagonism (KB=23.8 nmol/L). This compound shares a novel scaffold (1-ethoxy-2H-2-aza-1-phospha-naphthalene 1-oxide) with 3 other analogs in the group.

CONCLUSION

Considering the marked difference in molecular shape and electrostatic status between NC127816 and the structures reported elsewhere, we anticipate that its derivatives may represent a new class of potent MCHR-1 modulators.

The melanin-concentrating hormone system and its physiological functions

Melanin-concentrating hormone (MCH) is a neuropeptide that was originally isolated from salmon pituitary where it causes pigment aggregation. MCH is also abundantly present in mammalian neurons and expressed in the lateral hypothalamus and zona incerta, brain regions that are known to be at the center of feeding behavior. MCH binds to and activates two G protein-coupled receptors, MCH1R and MCH2R. Although MCH2R is non-functional in rodents, genetic and pharmacological studies have demonstrated that rodent MCH1R is involved in the regulation of feeding behavior and energy balance. Unexpectedly, some antagonists have provided evidence that MCH signaling participates in the regulation of other processes, such as emotion and stress. The discovery of MCH receptors has extensively promoted the progress of MCH studies and may represent an ideal example of how deorphanized receptors can open new directions toward more detailed physiological studies.

Possible association of the pro-melanin-concentrating hormone gene with a greater body mass index as a side effect of the antipsychotic olanzapine

Following our report of a linkage at 12q24 with a phenotype of obesity under antipsychotics, we tested the pro-melanin-concentrating hormone (PMCH) candidate gene for a possible association in humans with the body mass index (BMI; kg/m2) in unrelated schizophrenic patients (SZ) receiving antipsychotics (N = 300) and in controls (CTL; N = 150). Subjects were classified in obese (OB) (BMI > or = 30 kg/m2), overweight (25 < or = BMI < 30 kg/m2), and normal weight (BMI < 25 kg/m2) groups. Single nucleotide polymorphisms (SNP) rs7973796 and rs11111201, located 5' at -4.5 kb and 3' at +1.8 kb, respectively, of PMCH were genotyped. Interaction effects of genotypes and antipsychotic treatment on BMI were tested in a covariance analysis with age and gender as covariates. Interaction effects on the prevalence of obesity were tested in a logistic regression analysis. For subjects under 50 years, the effect of the rs7973796 genotype on BMI differed between the SZ patients taking olanzapine and CTL group (interaction P = 0.025). Olanzapine-treated SZ patients carrying the ancestral homozygote genotype showed a higher BMI for rs7973796 (P = 0.016 with the LSMeans t-test) than the variant homozygotes. Accordingly, the ORs for obesity associated with rs7973796 genotypes differed in the SZ patients taking olanzapine compared to the CTL group (interaction P = 0.0094). The G allele was associated with an increase in the odds of obesity in SZ patients taking olanzapine. No association was observed for those over 50 years, or for rs11111201. These results suggest that the common allele of PMCH rs7973796 may be associated with a greater BMI in olanzapine-treated SZ patients.

Effect of β-adrenoceptors on the behaviour induced by the neuropeptide glutamic acid isoleucine amide

Excessive grooming behaviour is induced by intracerebroventricular injections of the neuropeptide glutamic acid isoleucine amide (neuropeptide-EI), via the activation of A-10 dopaminergic neurons and the noradrenergic system. Our object was to study the latter system involved in these behaviours, using male Wistar rats weighing 250-300 g with i.c.v. implants. The results show that all the adrenoceptor antagonists "per se" do not affect excessive grooming behaviour or motor activity. Intracerebroventricular administration of propranolol, a general beta-adrenoceptor antagonist, before neuropeptide-EI, inhibited the induced excessive grooming behaviour in a dose dependent manner. Metoprolol, a beta(1)-adrenoceptor antagonist, also blocked this behaviour. However, intracerebroventricular injections of phentolamine, an alpha-adrenoceptor antagonist, and ((+/-)-1-[2,3-(Dihydro-7-methyl-1H-inden-4-yl)oxy]-3-[(1-methylethyl)amino]-2-butanol), a beta(2)-adrenoceptor antagonist, had no effect on the behaviour induced by neuropeptide-EI induced behaviour for any of the doses tested. On the other hand, isoproterenol, a general beta-adrenoceptor agonist and dobutamine, a beta(1)-adrenoceptor agonist, both elicited similar behaviours as those induced by neuropeptide-EI. These results support the hypothesis that a relationship exists between neuropeptide-EI and beta-adrenoceptors, more specifically the beta(1)-adrenoceptor, as found with other similar endogenous peptides such as neurotensin, cholecystin, substance P and alpha-melanocyte stimulating hormone. Hence, neuropeptide-EI could probably be exerting a neuromodulating effect on the central nervous system.

Effect of ppMCH derived peptides on PBMC proliferation and cytokine expression

The mRNA encoding prepro-Melanin concentrating hormone (ppMCH) is mainly expressed in the central nervous system but has also been detected at lower amount in many peripheral tissues including spleen and thymus. At the peptide level however, several forms of the precursor can be detected in these tissues and are sometimes expressed at similar levels compared to brain. In the present work, we have studied the in vitro action of a wide range of concentration (1 nM to 1 microM) of the different peptides encoded by ppMCH i.e. neuropeptide glycine-glutamic acid (NGE), neuropeptide glutamic acid-isoleucine (NEI), Melanin concentrating hormone (MCH) and the dipeptide NEI-MCH on peripheral blood mononuclear cells (PBMC) proliferation and cytokine production following anti-CD3 stimulation. Among them only MCH decreased PBMC proliferation with a maximal effect of 35% at 100 nM. Moreover as demonstrated by using ELISA, MCH significantly decreases IL-2 production by 25% but not IL-4, INF-gamma or TNF-alpha expression. Interestingly, exogenous IL-2 decreases significantly MCH-mediated inhibition, suggesting that it is an important downstream mediator of MCH action. Finally, we showed that after 7 to 9 days of incubation, MCH also inhibits proliferation of non-stimulated PBMC. Altogether, these data demonstrate that fully mature MCH modulates proliferation of anti-CD3 stimulated PBMC partially through regulation of IL-2 production.

Expanding the scales: The multiple roles of MCH in regulating energy balance and other biological functions

Melanin-concentrating hormone (MCH) is a cyclic peptide originally identified as a 17-amino-acid circulating hormone in teleost fish, where it is secreted by the pituitary in response to stress and environmental stimuli. In fish, MCH lightens skin color by stimulating aggregation of melanosomes, pigment-containing granules in melanophores, cells of neuroectodermal origin found in fish scales. Although the peptide structure between fish and mammals is highly conserved, in mammals, MCH has no demonstrable effects on pigmentation; instead, based on a series of pharmacological and genetic experiments, MCH has emerged as a critical hypothalamic regulator of energy homeostasis, having effects on both feeding behavior and energy expenditure.

The melanocortins and melanin-concentrating hormone in the central regulation of feeding behavior and energy homeostasis

A number of different neuropeptides exert powerful concerted controls on feeding behavior and energy balance, most of them being produced in hypothalamic neuronal networks under stimulation by anabolic and catabolic peripheral hormones such as ghrelin and leptin, respectively. These peptide-expressing neurons interconnect extensively to integrate the multiple opposing signals that mediate changes in energy expenditure. In the present review I have summarized our current knowledge about two key peptidic systems involved in regulating appetite and energy homeostasis, the melanocortin system (alpha-MSH, agouti and Agouti-related peptides, MC receptors and mahogany protein) and the melanin-concentrating hormone system (proMCH-derived peptides and MCH receptors) that contribute to satiety and feeding-initiation, respectively, with concurrent effects on energy expenditure. I have focused particularly on recent data concerning transgenic mice and the ongoing development of MC/MCH receptor antagonists/agonists that may represent promising drugs to treat human eating disorders on both sides of the energy balance (anorexia, obesity).

Melanin-concentrating hormone receptor 1 deficiency increases insulin sensitivity in obese leptin-deficient mice without affecting body weight

The hypothalamic peptide melanin-concentrating hormone (MCH) plays important roles in energy homeostasis. Animals overexpressing MCH develop hyperphagia, obesity, and insulin resistance. In this study, mice lacking both the MCH receptor-1 (MCHr1 knockout) and leptin (ob/ob) double-null mice (MCHr1 knockout ob/ob) were generated to investigate whether the obesity and/or the insulin resistance linked to the obese phenotype of ob/ob mice was attenuated by ablation of the MCHr1 gene. In MCHr1 knockout ob/ob mice an oral glucose load resulted in a lower blood glucose response and markedly lower insulin levels compared with the ob/ob mice despite no differences in body weight, food intake, or energy expenditure. In addition, MCHr1 knockout ob/ob mice had higher locomotor activity and lean body mass, lower body fat mass, and altered body temperature regulation compared with ob/ob mice. In conclusion, MCHr1 is important for insulin sensitivity and/or secretion via a mechanism not dependent on decreased body weight.

Evidence for a stimulatory action of melanin-concentrating hormone on luteinising hormone release involving MCH1 and melanocortin-5 receptors

The present series of studies aimed to further our understanding of the role of melanin-concentrating hormone (MCH) neurones in the central regulation of luteinising hormone (LH) release in the female rat. LH release was stimulated when MCH was injected bilaterally into the rostral preoptic area (rPOA) or medial preoptic area (mPOA), but not when injected into the zona incerta (ZI), of oestrogen-primed ovariectomised rats. In rats that were steroid-primed to generate a surge-like release of LH, MCH administration into the ZI blocked this rise in LH release: no such effect occurred when MCH was injected into the rPOA or mPOA. In vitro, MCH stimulated gonadotrophin-releasing hormone (GnRH) release from hypothalamic explants. Double-label immunohistochemistry showed GnRH-immunoreactive neurones in the vicinity of and intermingled with immunoreactive MCH processes. MCH is the endogenous ligand of the MCH type 1 receptor (MCH1-R). Previously, we have shown a role for melanocortin-5 receptors (MC5-R) in the stimulatory action of MCH, so we next investigated the involvement of both MCH1-R and/or MC5-R in mediating the actions of MCH on GnRH and hence LH release. The stimulatory action of MCH in the rPOA was inhibited by administration of antagonists for either MCH1-R or MC5-R. However, in the mPOA, the action of MCH was blocked only by the MC5-R antagonist. LH release was stimulated by an agonist for MC5-R injected into the rPOA or mPOA; this was blocked by the MC5-R antagonist but not the MCH1-R antagonist. These results indicate that both MCH1-R and MC5-R are involved in the central control of LH release by MCH.

Central administration of melanin-concentrating hormone (MCH) suppresses food intake, but not locomotor activity, in the goldfish, Carassius auratus

Melanin-concentrating hormone (MCH) is a hypothalamo-pituitary peptide, which was first identified in the salmon pituitary as a hormone affecting body color. Recently, MCH has been implicated in the regulation of feeding behavior and energy homeostasis in mammals. Despite a growing body of knowledge concerning MCH in mammals, however, there is little information about the effect of MCH on appetite and behavior in fish. The aim of the present study was to investigate the action of MCH on feeding behavior and spontaneous locomotor activity in the goldfish. We administered synthetic MCH by intracerebroventricular (ICV) injection and examined its effect on food intake and locomotor activity using an automatic monitoring system. Both types of synthetic MCH we employed, which are of fish and human origin, were effective in stimulating aggregation of melanin granules in the melanophores of goldfish scales. Cumulative food intake was significantly decreased by ICV injection of both MCHs in a dose-dependent manner. ICV injection of fish MCH at the same doses as those used for examination of food intake induced no marked changes in locomotor activity during the observation period. These results suggest that MCH influences feeding behavior, but not spontaneous locomotor activity, in the goldfish, and may exert an anorexigenic action in the goldfish brain, unlike its orexigenic action in mammals.

Identification of melanin-concentrating hormone receptor and its impact on drug discovery

The neuropeptide melanin-concentrating hormone (MCH) was originally isolated from the pituitary of salmon, in which it causes skin paling. MCH is also found abundantly in mammalian neurons, and has been detected in the lateral hypothalamus and zona incerta, brain regions that are at the center of feeding behavior. Acute central administration of MCH leads to a rapid and significant increase in food intake, while MCH expression changes in states of altered energy balance, such as fasting and obesity. Furthermore, MCH knockout mice tend toward hypophagia and leanness. In 1999, we and four other groups identified an orphan G-protein-coupled receptor (GPCR) as a specific receptor for MCH (MCH-1 receptor). Although a second MCH receptor (MCH-2 receptor) was isolated in humans, it was found to be non-functional or encode a non-functional pseudogene in non-human species, including rodents. The discovery of these MCH receptors permitted the launch of a broad array of drug screening efforts and three MCH-1 receptor antagonists were identified to reduce food intake and body weight. Interestingly, some antagonists unexpectedly produced evidence that blockade of these receptors has antidepressant and anxiolytic activities. The expressions of the MCH receptors, which have been implicated in regulating emotion, stress and motivation, make MCH an excellent candidate for integrating the various homeostatic stimuli necessary for maintaining the proper conditions of energy metabolism and other physiological functions. Finally, the speed at which MCH receptor studies have been undertaken exemplifies the impact that this deorphanized GPCR will have on setting the stage for more detailed physiological studies.

Neuropeptide glutamic acid-isoleucine may induce luteinizing hormone secretion via multiple pathways

Neuropeptide glutamic acid-isoleucine (NEI) is a 14-amino acid peptide processed from prepro-melanin-concentrating hormone (ppMCH). In males, the localization of NEI is almost identical to that of MCH, the cell bodies of both being located primarily in the lateral hypothalamic area and zona incerta, projecting fibers throughout the brain. Although MCH has been widely studied, the role that NEI plays in brain circuitry has been poorly investigated. Recently, we showed that intracerebroventricular injection of NEI increases serum luteinizing hormone (LH) levels. In order to identify the anatomical substrate underlying this effect, we used combined immunohistochemistry methods to analyze the forebrains of females on the diestrus and proestrus days, as well as those of ovariectomized females treated with estradiol benzoate, with estradiol benzoate plus progesterone or with sesame oil (control animals). We found that ovariectomized females with no steroid treatment showed an increased number of NEI-immunoreactive neurons in the medial zona incerta. In addition, we observed dense to moderate NEI innervation of areas related to reproduction, including the organum vasculosum of the lamina terminalis, the anteroventral periventricular nucleus (AVPV) and the median eminence. The NEI fibers were in close apposition with the AVPV and gonadotropin-releasing hormone (GnRH) neurons expressing Fos in the afternoon of the proestrus day or following administration of estradiol benzoate plus progesterone. In the median eminence, NEI varicosities and terminal-like structures were in close proximity to blood vessels and GnRH fibers. Our results suggest that NEI might induce LH secretion in one of the following ways: by direct release into the median eminence, by modulation of GnRH neurons located in the preoptic area, by modulation of the GnRH terminals located in the median eminence or by an additive effect involving other neurotransmitters or neurohormones. Release of NEI might also induce LH secretion indirectly by modulating AVPV neurons.

Regulation of the hypothalamic melanin-concentrating hormone neurons by sex steroids in the goldfish: possible role in the modulation of luteinizing hormone secretion

In teleost fish, melanin-concentrating hormone (MCH) is a cyclic heptadecapeptide released from the pituitary during white background adaptation. In the periphery MCH concentrates melanin granules in melanophores thus lightening the body color of fish. Evidence from mammalian studies has demonstrated the involvement of MCH in the control of energy balance and the reproductive axis. Information about the hormonal regulation of MCH neurons in non-mammalian systems is scarce and nothing is known about its role in the regulation of the reproductive axis. We here report the molecular characterization of two MCH precursors in the goldfish. Both precursors are peripherally expressed and the expression in the central nervous system is restricted to the mediobasal hypothalamus. Hypothalamic MCH-mRNA production is upregulated during white background adaptation. Both testosterone and estradiol stimulate MCH mRNA expression in the hypothalamus in a sex-dependent manner, with females showing the greatest responsiveness. In addition, in vitro experiments demonstrated that graded doses of salmon MCH stimulate LH, but not GH, secretion from dispersed pituitary cells. Results suggest that hypothalamic MCH may participate in the steroid positive feedback loop on pituitary LH secretion.

Effects of tank color on melanin-concentrating hormone levels in the brain, pituitary gland, and plasma of the barfin flounder as revealed by a newly developed time-resolved fluoroimmunoassay

A pleuronectiform fish, the barfin flounder Verasper moseri, reared in a white tank had a smaller ratio of pigmented area of the skin on non-eyed side, grew faster, and had greater melanin-concentrating hormone (MCH)-immunoreactive cell bodies and MCH gene expression in the brain than in the black tank, indicating that synthesis and release of MCH are higher in fish from a white tank. In the present study, a time-resolved fluoroimmunoassay for MCH was developed. MCH levels were assessed in the brain, pituitary gland, and plasma of barfin flounders reared in a white or black tank. A competitive assay using two antibodies was performed among secondary antibodies in the solid phase, MCH antibodies, samples, and europium-labeled MCH. Displacement curves of serially diluted extracts (brain, pituitary gland, and plasma) of the barfin flounder paralleled that of the MCH standard. MCH levels in the brain and plasma were higher in fish reared in the white tank for 5 months than in the black tank. These results suggest that synthesis and secretion of MCH are enhanced with the white background and that MCH is involved in both somatic growth and the skin pigmentation in the barfin flounder.

Increases in melanin-concentrating hormone and MCH receptor levels in the hypothalamus of dietary-obese rats

Melanin-concentrating hormone (MCH) is a hypothalamic neuropeptide that stimulates feeding and increases body weight in rodents. We studied the role of the system in energy homeostasis and its regulation by the satiety signals, leptin and insulin. We used real-time PCR to measure the hypothalamic expression of MCH and its receptor (MCHR1) in two contrasting models of altered nutritional status, namely, obesity induced by 8 weeks' voluntary overeating and food restriction for 10 days. Diet-fed rats were stratified according to final total fat-pad mass into a 'high fat gain' group (HG) and 'low fat gain' group (LG). MCH mRNA levels were increased by 31% (p>0.05) and 49% (p<0.05) in the LG and HG, respectively, compared with controls. MCHR1 mRNA levels rose by 118% in the LG (p<0.01) and 85% in the HG (p<0.01). There were significant positive correlations (p<0.05) between plasma leptin concentration and both MCH and MCHR1 mRNA levels, and between plasma insulin and MCHR1 expression. A positive correlation was also observed between MCH and MCHR1 mRNA levels (p<0.05). Food-restricted rats showed no significant alterations in the levels of either MCH mRNA or MCHR1 mRNA. In a second experiment, we measured MCH peptide levels in five discrete hypothalamic areas of dietary-obese rats. MCH concentrations were significantly increased in the arcuate nuclei of the HG (p<0.05) and the paraventricular nuclei of both the LG (p<0.05) and HG (p<0.05), compared with their lean counterparts. These results suggest that the MCH system becomes more active in dietary obesity and could be involved in enhancing appetite for palatable food. The possibility that MCH and MCHR1 expression are positively regulated by leptin and insulin, which normally inhibit feeding, is a putative explanation for how appetite for palatable food is able to override mechanisms that prevent the development of obesity.

Enhanced running wheel activity of both Mch1r- and Pmch-deficient mice

Mch1r-deficient (Mch1r(-/-)) mice are hyperphagic, hyperactive, lean, and resistant to diet-induced obesity. To examine whether the MCH1R is involved in regulating activity-based energy expenditure, we investigated voluntary wheel running (WR) activity of wild-type (WT) and Mch1r(-/-) mice basally, in response to diets with different caloric density and with different feeding schedules. We also evaluated WR activity of mice with ablation of the prepro-MCH gene (Pmch(-/-) mice). Dark cycle WR activity of Mch1r(-/-) mice fed low fat (LF) chow was increased significantly relative to WT mice. Transition to moderate high-fat (MHF) diet was associated with an increase in nocturnal WR activity in both genotypes. Both Mch1r(-/-) and WT mice exhibited food anticipatory activity (FAA) before the daily scheduled feeding time, indicating that MCH1R is not required for FAA. Naloxone (3 mg/kg, i.p.) suppressed WR activity of both genotypes, suggesting opioid regulation of locomotor activity. WR increased nocturnal dynorphin mRNA levels in Mch1r(-/-) brain. Importantly, Pmch-deficient mice had significantly enhanced WR activity relative to WT controls. These results suggest that endogenous MCH plays an inhibitory role in regulating locomotor activity. In summary, we demonstrated enhanced WR activities in mice lacking either MCH or its cognate receptor.

Intracerebroventricular injection of neuropeptide EI increases serum LH in male and female rats

Melanin concentrating hormone (MCH) precursor-derived neuropeptide EI (NEI) has not yet been extensively studied. The aim of this study was to determine the effect of neuropeptide EI on serum levels of LH in normal male rats and chronically ovariectomized (CHR-OVX) female rats treated with estrogen benzoate (EB) and with a low dose of progesterone. The peptide, administered intracerebroventricularly in male and chronically ovariectomized female rats, increased LH serum levels compared to the controls injected with artificial cerebrospinal fluid. It is important to note that there is some relation between neuropeptide EI-melanin concentrating hormone and alpha-melanocyte stimulating hormone (alpha-MSH) indicating that all three peptides are associated in a complex inter-relationship. Therefore, the question that arises is if neuropeptide EI could also be related with the receptors for melanin concentrating hormone or alpha-melanocyte stimulating hormone.

Possible involvement of melanin-concentrating hormone in food intake in a teleost fish, barfin flounder

We investigated the involvement of MCH in food intake in barfin flounder. The structure of barfin flounder MCH was determined by cDNA cloning and mass spectrometry. In fasted fish, the MCH gene expression and the number of MCH neurons in the brain were greater than controls. In white-reared fish, the MCH gene expression and the number of MCH neurons in the brain were greater than black-reared fish. Furthermore, white-reared fish grew faster than black-reared fish. These results indicate that a white background stimulated production of MCH and MCH, in turn, enhanced body growth, probably by stimulating food intake.

Comparative analysis of melanin-concentrating hormone structure and activity in fishes and mammals

A comparative analysis of the structure of the melanin-concentrating hormone (MCH) precursor reveals that this sequence has been subjected to a higher selection pressure in mammals than in teleosts, suggesting that the structural constraints have not been the same throughout the vertebrate lineage. In contrast, the MCH peptide sequence has been very well conserved in all species. A sensitive and reproducible eel skin assay was developed and allowed us to define the structural features needed for a full MCH bioactivity. It was shown that the minimal structure carrying the critical residues was the same in fishes and in mammals. A pharmacological approach confirmed that MCH receptor activation decreased the cAMP levels in the fish skin, but this effect appeared to be independent from a Galphai protein. We propose that one of the intracellular signaling pathways of the MCH receptor in fish skin is the activation of one or several cellular phosphodiesterases.

Melanin-concentrating hormone-1 receptor antagonism decreases feeding by reducing meal size

Prior work has demonstrated that melanin-concentrating hormone-1 (MCH-1) receptor antagonism decreases food intake and body weight in obese rodents. The purpose of this study was to determine if the MCH-1 receptor antagonist-mediated hypophagia was due a decrease in meal size, meal frequency, or both. We performed a meal pattern analysis in free-feeding hyperphagic diet-induced obese (DIO) rats treated with 1, 3 or 10 mg/kg p.o. of the MCH-1 receptor antagonist T-226296 (a (-)enantiomer of N-[6-(dimethylamino)-methyl]-5,6,7,8-tetrahydro-2-naphthalenyl]-4'-fluoro[1,1'-biphenyl]-4 carboxamide). Food intake was continuously monitored for 24 h using a BioDAQ food intake monitoring system. A total of 10 mg/kg T-226296 significantly decreased body weight and 24-h food intake, and had no effect on locomotor activity. The decrease in food intake was due to a reduction in meal size, not meal frequency. We conclude that MCH-1 receptor antagonism with T-226296 decreases food intake in DIO rats by selectively reducing meal size, and that the reduced food intake is not due to a generalized behavioral malaise.

Anabolic neuropeptides

The hypothalamus and other brain regions that control energy homeostasis contain neuronal populations that produce specific neuropeptides which have experimental effects on feeding behavior and body weight. Here, we describe examples of neuropeptides that exert 'anabolic' effects, notably stimulation of feeding and increased body weight. Neuropeptide Y (NPY) neurons in the hypothalamic arcuate nucleus (ARC) are inhibited by leptin and insulin, and thus are stimulated in states of energy deficit and fat loss, e.g., underfeeding. NPY neuronal overactivity contributes to enhanced hunger and food-seeking activity under these conditions. The lateral hypothalamic area (LHA) contains specific neuronal populations that affect feeding in different ways. Neurons expressing the appetite-stimulating peptide orexin A are stimulated by starvation (but not food restriction) and by hypoglycemia, but only if food is withheld. Orexin neurons are apparently activated by low glucose but are promptly inhibited by visceral feeding signals, probably mediated via vagal sensory pathway and the nucleus of the solitary tract (NTS); a short-term role in initiating feeding seems most likely. Other LHA neurons express melanin-concentrating hormone (MCH), which transiently increases food intake when injected centrally. MCH neurons may be regulated by leptin, insulin and glucose. Glucose-sensing neurons in the hypothalamus and elsewhere are sensitive to other cues of nutritional state, including visceral satiety signals (transmitted via the vagus) and orexin A. Thus, long- and short-term humoral and neural signals interact with each other to meet diverse nutritional needs, and anabolic neuropeptides are important in the overall integration of energy homeostasis. Clarifying the underlying mechanisms will be essential to understanding normal energy balance and the pathogenesis and treatment of disorders, such as obesity and cachexia.

Chronic MCH-1 receptor modulation alters appetite, body weight and adiposity in rats

Central administration of the neuropeptide melanin-concentrating hormone (MCH) stimulates feeding in rodents. We studied the effects of intracerebroventricular (i.c.v.) administration of an MCH-1 receptor agonist (Compound A) and an MCH-1 receptor antagonist (Compound B) on feeding in satiated rats. Compound B (10 microg, i.c.v.) blocked the acute orexigenic effect of Compound A (5 microg, i.c.v.). In an experiment designed to either stimulate or inhibit MCH-1 receptor signaling over an extended period, rats received continuous i.c.v. infusions of vehicle (saline), Compound A (30 microg/day), Compound B (30 or 48 microg/day) or neuropeptide Y (24 microg/day, as positive control) via implantable infusion pumps. Continuous MCH-1 receptor activation recapitulated the obese phenotype of MCH-over-expressor mice, manifest as enhanced feeding (+23%, P<0.001), caloric efficiency and body weight gain (+38%, P<0.005) over the 14-day period relative to controls. Chronic MCH-1 receptor activation also elevated plasma insulin and leptin levels significantly. Conversely, continuous MCH-1 receptor antagonism led to sustained reductions in food intake (-16%, P<0.001), body weight gain (-35%, P<0.01), and body fat gain relative to controls, without an effect on lean mass. Antagonism of the MCH-1 receptor may be an effective approach for the treatment of obesity.

Melanin-concentrating hormone functions in the nervous system: food intake and stress

Melanin-concentrating hormone (MCH) is a cyclic neuropeptide, which centrally regulates food intake and stress. MCH induces food intake in rodents and, more generally, acts as an anabolic signal in energy regulation. In addition, MCH seems to be activatory on the stress axis. Two receptors for MCH in humans have very recently been characterised, namely, MCH-R1 and MCH-R2. MCH-R1 has received considerable attention, as potent and selective antagonists acting at that receptor display anxiolytic, antidepressant and/or anorectic properties. Feeding and affective disorders are both debilitating conditions that have become serious worldwide health threats. There are as yet no efficient and/or safe cures that could contain the near-pandemia phenomen of both diseases. Thus, the discovery of MCH-R1 antagonists may lead to the development of valuable drugs to treat obesity, anxiety and depressive syndromes. In addition, it opens wide avenues to probe additional functions of the peptide, both in the brain and in the peripheral nervous system.

Behavioural analysis of melanin-concentrating hormone in rats: evidence for orexigenic and anxiolytic properties

Melanin-concentrating hormone (MCH) is a cyclic neuropeptide, predominantly expressed in hypothalamus, and recognized as a key regulator in feeding behaviour and energy balance. In this study, we examined the behavioural effects of intracerebroventricularly administered MCH on food intake, anxiety, exploratory behaviour and body core temperature in rats. MCH (0.15-10.0 microg, i.c.v.) acutely increased food intake in a dose-dependent manner. In addition, MCH (0.6-10.0 microg, i.c.v.) produced effects similar to anxiolytics in an animal model of anxiety, Vogel's punished drinking test. Thus, punished drinking episodes were significantly increased. We found no effects of MCH (5.0-20.0 microg, i.c.v.) on locomotor activity either in habituated or non-habituated animals. Furthermore, MCH did not produce any changes in body core temperature. Together, these observations further support a role for MCH as an orexigenic neuropeptide and also suggest anti-anxiety properties for MCH.

Lateral hypothalamic neuropeptides in reward and drug addiction

The hypothalamus has been long considered important in feeding and other motivated behaviors. The identification of neuropeptides expressed in the hypothalamus has initiated efforts to better elucidate the underlying molecular mechanisms involved. The neuropeptides orexin and melanin-concentrating hormone (MCH) are expressed in the lateral hypothalamus (LH) and have been implicated in regulation of feeding behavior. Neurons expressing these neuropeptides have extensive projections to regions of the brain important for behavioral responses to drugs of abuse, raising the possibility that the pathways may also be important in addiction. Regulation of LH intracellular signaling pathways in response to drugs of abuse supports a role for the LH neuropeptides in addiction.

Melanic body colour and aggressive mating behaviour are correlated traits in male mosquitofish (Gambusia holbrooki)

Correlated traits are important from an evolutionary perspective as natural selection acting on one trait may indirectly affect other traits. Further, the response to selection can be constrained or hastened as a result of correlations. Because mating behaviour and body colour can dramatically affect fitness, a correlation between them can have important fitness ramifications. In this work, melanic (black) male mosquitofishes (Gambusia holbrooki) with temperature-sensitive body-colour expression are bred in captivity. Half of the sons of each melanic sire are reared at 19 degrees C (and express a black body colour) and half are reared at 31 degrees C (and express a silver body colour). The two colour morphs are placed in the same social setting and monitored for behavioural differences. Mating behaviour and colour are correlated traits. Mating behaviour differs markedly between the two phenotypes, despite high genetic relatedness. Melanic (black) phenotypes are more aggressive towards females, chasing them and attempting more matings than their silver siblings. Females avoid melanic-male mating attempts more than silver-male mating attempts. When males with temperature-sensitive colour expression are melanic and aggressive, they probably experience a very different selective regime in nature from when they are silver and less aggressive. Under some conditions (e.g. predation), melanic coloration and/or aggression is advantageous compared with silver coloration and/or less aggressive behaviour. However, under different conditions (e.g. high-frequency melanism), melanism and/or aggression appears to be disadvantageous and melanic males have reduced survival and reproduction. Selective advantages to each morph under different conditions may enable the long-term persistence of this temperature-sensitive genotype.

Distribution of melanin-concentrating hormone neurons projecting to the medial mammillary nucleus

The melanin-concentrating hormone and neuropeptide glutamic acid-isoleucine are expressed in neurons located mainly in the hypothalamus that project widely throughout the CNS. One of the melanin-concentrating hormone main targets is the medial mammillary nucleus, but the exact origin of these fibers is unknown. We observed melanin-concentrating hormone and neuropeptide glutamic acid-isoleucine immunoreactive fibers coursing throughout the mammillary complex, showing higher density in the pars lateralis of the medial mammillary nucleus, while the lateral mammillary nucleus showed sparse melanin-concentrating hormone innervation. The origins of these afferents were determined by using implant of the retrograde tracer True Blue in the medial mammillary nucleus. Double-labeled neurons were observed in the lateral hypothalamic area, rostromedial zona incerta and dorsal tuberomammillary nucleus. A considerable population of retrogradely labeled melanin-concentrating hormone perikaryal profiles was also immunoreactive to neuropeptide glutamic acid-isoleucine (74+/-15% to 85+/-15%). The afferents from the lateral hypothalamic area, rostromedial zona incerta and dorsal tuberomammillary nucleus to the medial mammillary nucleus were confirmed using implant of the anterograde tracer Phaseolus vulgaris leucoagglutinin. In addition, using double-labeled immunohistochemistry, we found no co-localization between neurons expressing melanin-concentrating hormone and adenosine deaminase (histaminergic marker) in the dorsal tuberomammillary nucleus. We hypothesize that these melanin-concentrating hormone projections participate in spatial memory process mediated by the medial mammillary nucleus. These pathways would enable the animal to look for food during the initial moments of appetite stimulation.

Participation of the cholinergic system in the excessive grooming behavior induced by neuropeptide (N) glutamic acid (E) isoleucine (I) amide (NEI)

The neuropeptide (N) glutamic acid (E) isoleucine (I) amide (NEI) injected into the ventral tegmental area (VTA) or intraventricularly (icv) induces excessive grooming behavior (EGB) and motor activity (MA). Here, we studied whether the cholinergic system is involved in the NEI-induced behavior. The present results demonstrate that atropine, a general muscarinic antagonist, injected icv previous to NEI, suppresses the behavior provoked by icv injections of the peptide, whereas the prior icv injection of dyhidro-beta-erythroidine, a general nicotinic antagonist, did not affect the EGB and MA induced by the peptide. From the experimental evidence, it is suggested that NEI may act specifically on a cholinergic afferent to dopaminergic cells. Also, the results appear to indicate that a neural target, different from the dopamine system, may be activated by the peptide to elicit behavioral changes, such as EGB.