Melanotropic peptides in the mammalian brain: the melanin-concentrating hormone

Melanin Concentrating Hormone Signaling Deficits in Schizophrenia: Association With Memory and Social Impairments and Abnormal Sensorimotor Gating

BACKGROUND

Evidence from anatomical, pharmacological, and genetic studies supports a role for the neuropeptide melanin concentrating hormone system in modulating emotional and cognitive functions. Genome-wide association studies revealed a potential association between the melanin concentrating hormone receptor (MCHR1) gene locus and schizophrenia, and the largest genome-wide association study conducted to date shows a credible genome-wide association.

METHODS

We analyzed MCHR1 and pro-melanin concentrating hormone RNA-Seq expression in the prefrontal cortex in schizophrenia patients and healthy controls. Disruptions in the melanin concentrating hormone system were modeled in the mouse brain by germline deletion of MCHR1 and by conditional ablation of melanin concentrating hormone expressing neurons using a Cre-inducible diphtheria toxin system.

RESULTS

MCHR1 expression is decreased in the prefrontal cortex of schizophrenia samples (false discovery rate (FDR) P < .05, CommonMind and PsychEncode combined datasets, n = 901) while pro-melanin concentrating hormone is below the detection threshold. MCHR1 expression decreased with aging (P = 6.6E-57) in human dorsolateral prefrontal cortex. The deletion of MCHR1 was found to lead to behavioral abnormalities mimicking schizophrenia-like phenotypes: hyperactivity, increased stereotypic and repetitive behavior, social impairment, impaired sensorimotor gating, and disrupted cognitive functions. Conditional ablation of pro-melanin concentrating hormone neurons increased repetitive behavior and produced a deficit in sensorimotor gating.

CONCLUSIONS

Our study indicates that early disruption of the melanin concentrating hormone system interferes with neurodevelopmental processes, which may contribute to the pathogenesis of schizophrenia. Further neurobiological research on the developmental timing and circuits that are affected by melanin concentrating hormone may lead to a therapeutic target for early prevention of schizophrenia.

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.

Anatomical organization of MCH connections with the pallidum and dorsal striatum in the rat

Neurons producing the melanin-concentrating hormone (MCH) are distributed in the posterior hypothalamus, but project massively throughout the forebrain. Many aspects regarding the anatomical organization of these projections are still obscure. The present study has two goals: first to characterize the topographical organization of neurons projecting into the cholinergic basal forebrain (globus pallidus, medial septal complex), and second to verify if MCH neurons may indirectly influence the dorsal striatum (caudoputamen) by innervating afferent sources to this structure. In the first series of experiments, the retrograde tracer fluorogold was injected into multiple sites in the pallidal and medial septal regions and the distribution of retrogradely labeled neurons were analyzed in the posterior lateral hypothalamus. In the second series of experiments, fluorogold was injected into the caudoputamen, and the innervation by MCH axons of retrogradely labeled cells was analyzed. Our results revealed that the MCH system is able to interact with the basal nuclei in several different ways. First, MCH neurons provide topographic inputs to the globus pallidus, medial septal complex, and substantia innominata. Second, striatal projecting neurons in the cortex, thalamus, and substantia nigra presumably receive only sparse inputs from MCH neurons. Third, the subthalamic nucleus is heavily innervated by MCH projections, thus, presumably serves as one important intermediate station to mediate MCH influence on other parts of the basal nuclei.

The melanin-concentrating hormone1 receptor antagonists, SNAP-7941 and GW3430, enhance social recognition and dialysate levels of acetylcholine in the frontal cortex of rats

Melanin-concentrating hormone (MCH)1 receptors are widely expressed in limbic structures and cortex. Their inactivation is associated with anxiolytic and antidepressive properties but little information is available concerning cognition. This issue was addressed using the selective antagonists, SNAP-7941 and GW3430, in a social recognition paradigm in rats. The muscarinic blocker, scopolamine (1.25 mg/kg s.c.), reduced social recognition, an action dose-dependently blocked by SNAP-7941 and GW3430 (0.63-10.0 and 20.0-80.0 mg/kg i.p., respectively) which did not themselves display amnesic properties. Further, in a protocol where a spontaneous deficit was induced by a prolonged inter-session delay, SNAP-7941 and GW3430 dose-dependently enhanced social recognition. In dialysis studies, SNAP-7941 (0.63-40.0 mg/kg i.p.) and GW3430 (10.0-40.0 mg/kg i.p.) elevated extracellular levels of acetylcholine (ACh) in the frontal cortex (FCX) of freely moving rats. The SNAP-7941 effect was specific, as it did not increase levels of ACh in ventral and dorsal hippocampus: moreover, it did not modify levels of noradrenaline, dopamine, serotonin and glutamate in FCX. Active doses of SNAP-7941 and GW3430 corresponded to doses (2.5-40.0 and 10.0-80.0 mg/kg i.p., respectively) exerting anxiolytic properties in Vogel conflict and ultrasonic vocalization tests, and antidepressant actions in forced swim, isolation-induced aggression and marble-burying procedures. In contrast to SNAP-7941 and GW3430, the benzodiazepine, diazepam, decreased social recognition and dialysate levels of ACh, while the tricyclic, imipramine, reduced social recognition and failed to enhance cholinergic transmission. In conclusion, at anxiolytic and antidepressant doses, SNAP-7941 and GW3430 improve social recognition and elevate extracellular ACh levels in FCX. This profile differentiates MCH1 receptor antagonists from conventional anxiolytic and antidepressant agents.

Highly regionalized neuronal expression of monocyte chemoattractant protein-1 (MCP-1/CCL2) in rat brain: evidence for its colocalization with neurotransmitters and neuropeptides

The monocyte chemoattractant protein-1 (MCP-1/CCL2) and its receptor CCR2 are key modulators of immune functions. In the nervous system, MCP-1/CCL2 is implicated in neuroinflammatory pathologies. However, cerebral functions of MCP-1/CCL2 under normal conditions are still unclear. In this study, using reverse transcriptase-polymerase chain reaction (RT-PCR) and specific rat MCP-1 enzyme-linked immunosorbent assay (ELISA) approaches, we observed that MCP-1/CCL2 mRNA and protein were expressed in different punched regions of the normal rat central nervous system. Immunohistochemical studies further revealed that this chemokine is constitutively expressed not only in astrocytes but also in neurons, in discrete neuroanatomical regions. Neuronal expression of MCP-1/CCL2 is mainly found in the cerebral cortex, globus pallidus, hippocampus, paraventricular and supraoptic hypothalamic nuclei, lateral hypothalamus, substantia nigra, facial nuclei, motor and spinal trigeminal nuclei, and gigantocellular reticular nucleus and in Purkinje cells in the cerebellum. Moreover, we obtained the first evidence that MCP-1/CCL2 is constitutively expressed in cholinergic neurons, notably in the magnocellular preoptic and oculomotor nuclei, and in dopaminergic neurons of the substantia nigra pars compacta. In addition, in the lateral hypothalamic area, MCP-1/CCL2 co-localized with melanin-concentrating hormone-expressing neurons. Interestingly, we demonstrate a co-localization of MCP-1/CCL2 with vasopressin in magnocellular neuronal cell bodies and processes in the supraoptic and paraventricular hypothalamic nuclei, as well as in processes in the internal layer of the median eminence and in the posterior pituitary. Taken together, our data suggest that MCP-1/CCL2 could act as a modulator of neuronal activity and neuroendocrine functions.

Discovery of novel chemotypes to a G-protein-coupled receptor through ligand-steered homology modeling and structure-based virtual screening

Melanin-concentrating hormone receptor 1 (MCH-R1) is a G-protein-coupled receptor (GPCR) and a target for the development of therapeutics for obesity. The structure-based development of MCH-R1 and other GPCR antagonists is hampered by the lack of an available experimentally determined atomic structure. A ligand-steered homology modeling approach has been developed (where information about existing ligands is used explicitly to shape and optimize the binding site) followed by docking-based virtual screening. Top scoring compounds identified virtually were tested experimentally in an MCH-R1 competitive binding assay, and six novel chemotypes as low micromolar affinity antagonist "hits" were identified. This success rate is more than a 10-fold improvement over random high-throughput screening, which supports our ligand-steered method. Clearly, the ligand-steered homology modeling method reduces the uncertainty of structure modeling for difficult targets like GPCRs.

MCH-containing neurons in the hypothalamus of the cat: searching for a role in the control of sleep and wakefulness

Neurons that utilize melanin-concentrating hormone (MCH) and others that employ hypocretin as neurotransmitter are located in the hypothalamus and project diffusely throughout the CNS, including areas that participate in the generation and maintenance of the states of sleep and wakefulness. In the present report, immunohistochemical methods were employed to examine the distribution of MCHergic and hypocretinergic neurons. In order to test the hypothesis that the MCHergic system is capable of influencing specific behavioral states, we studied Fos immunoreactivity in MCH-containing neurons during (1) quiet wakefulness, (2) active wakefulness with motor activity, (3) active wakefulness without motor activity, (4) quiet sleep and (5) active sleep induced by carbachol (AS-carbachol). We determined that MCHergic neuronal somata in the cat are intermingled with hypocretinergic neurons in the dorsal and lateral hypothalamus, principally in the tuberal and tuberomammillary regions; however, hypocretinergic neurons extended more in the anterior-posterior axis than MCHergic neurons. Axosomatic and axodendritic contacts were common between these neurons. In contrast to hypocretinergic neurons, which are known to be active during motor activity and AS-carbachol, Fos immunoreactivity was not observed in MCH-containing neurons in conjunction with any of the preceding behavioral conditions. Non-MCHergic, non-hypocretinergic neurons that expressed c-fos during active wakefulness with motor activity were intermingled with MCH and hypocretin-containing neurons, suggesting that these neurons are related to some aspect of motor function. Further studies are required to elucidate the functional sequela of the interactions between MCHergic and hypocretinergic neurons and the phenotype of the other neurons that were active during motor activity.

Bicyclic[4.1.0]heptanes as phenyl replacements for melanin concentrating hormone receptor antagonists

Melanin concentrating hormone (MCH) receptor antagonists have been proposed as potential treatments of obesity. MCH receptor antagonists with a biphenylamine subunit have been reported previously at Schering-Plough. Herein, we report the discovery of bicyclo[4.1.0]heptanes as replacements for the middle phenyl ring of the biphenylamine moiety in order to eliminate its potential mutagenic liability. Structure-activity relationships in this series were found to be very similar to those of the original biphenylamine series, suggesting that the two series have similar binding modes.

Further insights into the neurobiology of melanin-concentrating hormone in energy and mood balances

Melanin-concentrating hormone (MCH) is a critical hypothalamic anabolic neuropeptide, with key central and peripheral actions on energy balance regulation. The actions of MCH are, so far, known to be transduced through two seven-transmembrane-like receptor paralogues, named MCH1R and MCH2R. MCH2R is not functional in rodents. MCH1R is an important receptor involved in mediating feeding behaviour modulation by MCH in rodents. Pharmacological antagonism at MCH1R in rodents diminishes food intake and results in significant and sustained weight loss in fat tissues, particularly in obese animals. Additionally, MCH1R antagonists have been shown to have anxiolytic and antidepressant properties. The purpose of this review is to highlight the recent numerous pieces of evidence showing that pharmacological blockade at MCH1R could be a potential treatment for obesity and its related metabolic syndrome, as well as for various psychiatric disorders.

Differential distribution of hypocretin (orexin) and melanin-concentrating hormone in the goldfish brain

The orexigenic peptides hypocretin (orexin) and melanin-concentrating hormone (MCH) are involved in the control of food intake and in other homeostatic functions including sleep and arousal. In this article we study the distribution of these peptides in the brain of the goldfish (Carassius auratus), focusing on those regions particularly related to feeding, sleep, and arousal. Although the general distribution of these peptides in goldfish shows many similarities to those described previously in other species, we observed some noteworthy differences. As in other vertebrates, the peptidergic somata lie in the anterolateral hypothalamus. In goldfish, both hypocretin and MCH immunoreactive cell bodies project fibers to the ventral telencephalon, thalamus, and hypothalamus. At mesencephalic levels fibers reach the deep layers of the optic tectum and also course sparsely through the mesencephalic tegmentum. In contrast to the strong innervation of locus coeruleus and raphe in mammal, the MCH and hypocretin systems in goldfish barely innervate these aminergic populations related to the regulation of sleep and arousal. MCH, but not hypocretin, immunoreactive fibers terminate substantially in the sensory layer of the vagal gustatory lobe of goldfish, while both peptidergic systems distribute to the primary visceral sensory areas of the medulla and pons. The strong involvement of these peptidergic systems with the hypothalamus and general visceral nuclei, but not with locus coeruleus or raphe nuclei support the view that these peptides originally played a role in regulation of energy balance and evolved secondarily to influence sleep-wakefulness systems in amniote vertebrates.

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.

Translational medicine in fish-derived peptides: from fish endocrinology to human physiology and diseases

Recent studies have revealed the importance of fish-derived peptide hormones to human endocrinology. These peptides include melanin-concentrating hormone (MCH), urocortins (human urotensin-I), and urotensin-II. MCH, a hypothalamic peptide, is a potent stimulator on appetite. Urocortins, e.g. urocortin 1 and urocortin 3 (stresscopin), are endogenous ligands for the corticotropin-releasing factor (CRF) receptors, particularly CRF type 2 receptor, that mediates a vasodilator action, a positive inotropic action and a central appetite-inhibiting action. These actions mediated by CRF type 2 receptor may ameliorate the stress response. Human urotensin-II is a potent vasoconstrictor peptide, while it acts as a vasodilator on some arteries. Human urotensin-II is expressed in various types of cells and tissues, including cardiovascular tissues, as well as many types of tumor cells. Thus, these fish-derived peptides appear to play important roles in human physiology, such as appetite regulation, stress response and cardiovascular regulation, and also in diseases, for example, obesity, cardiovascular diseases and tumors. Development of antagonists/agonists against the receptors for these peptides may open new strategies for the treatment of various diseases, including obesity-related diseases, hypertension, heart failure and malignant tumors.

Identification of novel adrenomedullin in mammals: a potent cardiovascular and renal regulator

We have identified cDNA encoding a new member of the adrenomedullin (AM) family, AM2, for the first time in mammals (mouse, rat and human). The predicted precursor carried mature AM2 in the C-terminus, which had an intramolecular ring formed by an S-S bond and a possibly amidated C-terminus. Phylogenetic analyses clustered AM2 and AM into two distinct but closely related groups. Similarity of exon-intron structure and synteny of neighboring genes showed that mammalian AM2 is an ortholog of pufferfish AM2 and a paralog of mammalian AM. AM2 mRNA was expressed in submaxillary gland, kidney, stomach, ovary, lymphoid tissues and pancreas of mice, but not in adrenal and testis. Intravenous injection of synthetic mature AM2 decreased arterial pressure more potently than AM, and induced antidiuresis and antinatriuresis in mice. These results show that at least two peptides, AM and AM2, comprise an adrenomedullin family in mammals, and that AM2 may play pivotal roles in cardiovascular and body fluid regulation.

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.

Cell and molecular cell biology of melanin-concentrating hormone

Recent advances in the study of melanin-concentrating hormone (MCH) have depended largely on molecular biological techniques. In mammals, which have attracted the most attention, novel findings concern (i) the MCH gene, which can yield several peptides by either posttranslational cleavage or alternative splicing, as well as bidirectional transcription; (ii) the identification of two G protein-coupled MCH receptors in the brain and peripheral tissues; and (iii) the evidence for subpopulations of MCH neurons in the central nervous system, characterized by their chemical phenotypes, connections, and individual physiological responses to different physiological paradigms. The involvement of central MCH in various functions, including feeding, reproduction, stress, and behavior patterns, is reviewed. The stage during evolution at which MCH may have acquired hypophysiotrophic and hormonal functions in lower vertebrates is considered in light of morphological data. Evidence that MCH also has peripheral paracrine/autocrine effects in mammals is provided.

Cocaine- and amphetamine-regulated transcript peptide projections in the ventral midbrain: colocalization with gamma-aminobutyric acid, melanin-concentrating hormone, dynorphin, and synaptic interactions with dopamine neurons

To date, cocaine- and amphetamine-regulated transcript (CART) peptides have been found to influence feeding, locomotor activity, and conditioned place preference. A common brain structure that could mediate these effects is the ventral tegmental area (VTA). For a better understanding of the anatomical substrates that might underlie CART peptides' role in these behaviors, we performed a series of experiments to elucidate the source, synaptic connectivity, and neurochemical content of CART peptide-immunoreactive (CARTir) terminals in the rat VTA. Double-labeling immunofluorescence revealed that approximately 15% of CARTir terminals in the VTA contain the hypothalamic neuropeptide, melanin-concentrating hormone (MCH). Furthermore, CART peptides were also found to colocalize with GABA and, to a small extent, with dynorphin in nerve terminals in both the VTA and the substantia nigra (SN). In the VTA, CARTir terminals form both symmetric and asymmetric synapses onto dopaminergic and nondopaminergic distal dendrites, suggesting that various sources contribute to this innervation. About 30% of CARTir terminals in the VTA and only 15% in the SN appose or form synaptic contact with DA neurons, which support our previous data showing that GABAergic basal ganglia output neurons in the substantia nigra pars reticulata (SNr) receive strong CARTir input from the accumbens core. Results of these studies suggest that the most significant behavioral states influenced by CART peptides, feeding and locomotion, may be mediated by direct and/or indirect modulation of VTA dopaminergic neuronal activity.

Distribution of melanin-concentrating hormone-like immunoreactivity in the central nervous system of Rana esculenta

The distribution of salmon and rat melanin-concentrating hormone (MCH)-like and neuropeptide glutamate-isoleucine (NEI)-like immunoreactivity in the brain and spinal cord of the frog Rana esculenta was studied with immunohistochemistry. In the telencephalon, only fibers showed immunoreactivity in the olfactory bulb, lateral pallium, diagonal band, septum, and the amygdala. Immunoreactive fibers were abundant in all diencephalic structures, except the optic tract, the visual neuropils, and the habenula. Several cells in the central thalamic nucleus and a few in the suprachiasmatic nucleus were stained with the MCH antisera. Cells and their processes were intensely stained in the dorsal hypothalamus with the MCH and NEI antisera. Immunoreactive fibers were found in all tegmental nuclei and the white matter of the mesencephalon. They formed terminal plexuses in the deep layers of the optic tectum and the laminar nucleus of the torus semicircularis. Immunoreactive fibers were sparse in the rhombencephalon and the spinal cord.

Neuronal organization of the melanin-concentrating hormone system in primitive actinopterygians: evolutionary changes leading to teleosts

Hypothalamic melanin-concentrating hormone (MCH) neurones occur in all vertebrates and have an apparent neuromodulatory role. In teleost fish, however, MCH is used also as a neurohypophysial hormone, controlling skin color, and as a hypophysiotrophic peptide. This work describes the central location of immunoreactive MCH perikarya and their projections to the pituitary in a range of ancestral fish to determine the phylogenetic stage when the peptide adopted these roles. In all actinopterygians examined, including polypteriformes, chondrosteans, holosteans, and teleosts, immunoreactive fibers were abundant in the median eminence or, in the case of teleosts, within the pars distalis itself, suggesting MCH acquired a hypophysial regulatory role early in vertebrate evolution. MCH fibers appeared to be absent from the posterior neurohypophysis of the polypteriform Calamoichthys but were evident in this region in the chondrostean Acipensor, the holosteans Lepisosteus and Amia, and all teleosts, suggesting its use as a neurohypophysial hormone. The ability of MCH to induce skin pallor seems to have arisen at a later stage, probably in the preholosteans. This hormonal role coincides with the migration of MCH perikarya away from the ventricular surface and their enlargement into magnocellular neurones. In the higher teleosts, magnocellular hypothalamo-neurohypophysial neurones predominate in size and number, whereas smaller periventricular MCH neurones associated with the paraventricular organ, that are prominent in lampreys, early actinopterygians and tetrapods, are reduced in teleosts. The data suggest that, in teleost fish, earlier functions of the peptide may have become subordinate to its novel pigmentary role.

Identification and pharmacological characterization of a novel human melanin-concentrating hormone receptor, mch-r2

Melanin-concentrating hormone (MCH) is a neuropeptide highly expressed in the brain that regulates several physiological functions mediated by receptors in the G protein-coupled receptor family. Recently an orphan receptor, SLC-1, has been identified as an MCH receptor (MCH-R1). Herein we identify and characterize a novel receptor for human MCH (MCH-R2). The receptor is composed of 340 amino acids encoded by a 1023-base pair cDNA and is 35% homologous to SLC-1. (125)I-MCH specifically bound to Chinese hamster ovary cells stably expressing MCH-R2. MCH stimulated dose-dependent increases in intracellular free Ca(2+) and inositol phosphate production in these cells but did not affect cAMP production. The pharmacological profile for mammalian MCH, [Phe(13),Tyr(19)]MCH, and salmon MCH at MCH-R2 differed compared with MCH-R1 as assessed by intracellular signaling and radioligand binding assays. The EC(50) in signaling assays and the IC(50) in radioligand binding assays of salmon MCH was an order of magnitude higher than mammalian MCH at MCH-R2. By comparison, the EC(50) and IC(50) values of salmon MCH and mammalian MCH at MCH-R1 were relatively similar. Blot hybridization revealed exclusive expression of MCH-R2 mRNA in several distinct brain regions, particularly in the cortical area, suggesting the involvement of MCH-R2 in the central regulation of MCH-mediated functions.

Expression of melanin-concentrating hormone receptor messenger ribonucleic acid in tumor tissues of pheochromocytoma, ganglioneuroblastoma, and neuroblastoma

Expression of melanin-concentrating hormone (MCH) receptor messenger ribonucleic acid (mRNA) was studied by RT-PCR and Northern blot analysis in human brain; pituitary; adrenal glands; tumor tissues of adrenal tumors, ganglioneuroblastomas, and neuroblastomas; and various cultured tumor cell lines. RT-PCR analysis showed that MCH receptor mRNA was widely expressed in brain tissues, pituitary, normal portions of adrenal glands (cortex and medulla), tumor tissues of adrenocortical tumors (12 of 13 cases), pheochromocytoma (all 7 cases), ganglioneuroblastoma (1 case), neuroblastoma (all 5 cases), and various cultured tumor cell lines (6 of 7 cell lines), including 2 neuroblastoma cell lines. Northern blot analysis showed the expression of MCH receptor mRNA ( approximately 2.4 kb) only in the tumor tissues of 5 pheochromocytomas, 1 ganglioneuroblastoma, and 4 neuroblastomas, indicating that the expression levels of MCH receptor mRNA are much higher in these tumors than in the other tissues. These findings raised the possibility that MCH or MCH-like peptides may be related to the pathophysiology of these neural crest-derived tumors.

The distribution of the mRNA and protein products of the melanin-concentrating hormone (MCH) receptor gene, slc-1, in the central nervous system of the rat

Melanin-concentrating hormone (MCH), a 19 amino acid cyclic peptide, is largely expressed in the hypothalamus. It is implicated in the control of general arousal and goal-orientated behaviours in mammals, and appears to be a key messenger in the regulation of food intake. An understanding of the biological actions of MCH has been so far hampered by the lack of information about its receptor(s) and their location in the brain. We recently identified the orphan G-protein-coupled receptor SLC-1 as a receptor for the neuropeptide MCH. We used in situ hybridization histochemistry and immunohistochemistry to determine the distribution of SLC-1 mRNA and its protein product in the rat brain and spinal cord. SLC-1 mRNA and protein were found to be widely and strongly expressed throughout the brain. Immunoreactivity was observed in areas that largely overlapped with regions mapping positive for mRNA. SLC-1 signals were observed in the cerebral cortex, caudate-putamen, hippocampal formation, amygdala, hypothalamus and thalamus, as well as in various nuclei of the mesencephalon and rhombencephalon. The distribution of the receptor mRNA and immunolabelling was in good general agreement with the previously reported distribution of MCH itself. Our data are consistent with the known biological effects of MCH in the brain, e.g. modulation of the stress response, sexual behaviour, anxiety, learning, seizure production, grooming and sensory gating, and with a role for SLC-1 in mediating these physiological actions.

Phe(13),Tyr(19)-melanin-concentration hormone and the blood-brain barrier: role of protein binding

Melanin-concentrating hormone (MCH), found both peripherally and centrally, is involved in food ingestion. Although its expression in brain is increased by fasting, it is not known whether it crosses the blood-brain barrier (BBB). Use of the sensitive method of multiple-time regression analysis has shown that almost all of the peptides and polypeptides tested cross the BBB at a rate faster than the vascular marker albumin. With this same method, however, we found that the 19-amino acid 125I-Phe13,Tyr19-MCH did not cross faster than 99mTc-albumin. Several mechanisms were excluded as possible explanations for the slow rate of influx. These included degradation, association with capillary endothelial cells, and transport from brain to blood. When Phe13,Tyr19-MCH was perfused in blood-free buffer, however, it entered the brain significantly faster than albumin. This suggested protein binding as an explanation for the slow rate of influx when the MCH was administered in blood. Protein binding was confirmed by capillary zone electrophoresis, which showed that almost all of the Phe13,Tyr19-MCH added to blood migrated with a large-molecular-weight substance. Sodium dodecyl sulfate-capillary gel electrophoresis of Phe13,Tyr19-MCH in buffer additionally showed that the MCH aggregated as a trimer, a factor not preventing its influx by blood-free perfusion. Thus, the results show that blood-borne Phe13,Tyr19-MCH does not significantly cross the BBB, probably because of its binding to serum proteins.

Hypothalamic cocaine- and amphetamine-regulated transcript (CART) neurons: histochemical relationship to thyrotropin-releasing hormone, melanin-concentrating hormone, orexin/hypocretin and neuropeptide Y

Recent demonstrations of the feeding-inhibitory properties of putative peptides derived from cocaine- and amphetamine-regulated transcript (CART) raise the question of interactions between CART peptides and other messenger molecules implicated in the control of food intake. The present study investigated the histochemical relationship of CART to the neuropeptides thyrotropin-releasing hormone (TRH), melanin-concentrating hormone (MCH), orexin/hypocretin and neuropeptide Y (NPY) in the hypothalamus. Double-label in situ hybridization showed that CART to a great extent is co-expressed with TRH in hypothalamic paraventricular nucleus neurons. This technique was also used to demonstrate that MCH, but not orexin/hypocretin, mRNA colocalized with CART in neurons of the dorsomedial hypothalamic nucleus/lateral hypothalamic area. CART-peptide immunoreactive cell bodies in this region, as well as in the arcuate nucleus and the medial posterodorsal nucleus of the amygdala, were all seen to have close appositions formed by NPY-immunoreactive nerve terminals. Lastly, in a study of mice treated with the neurotoxin, monosodium glutamate, which targets the arcuate nucleus, a near-total ablation of CART peptide immunoreactive cell bodies in this nucleus was accompanied by decreased terminal staining for CART peptide in the paraventricular hypothalamic nucleus, the arcuate nucleus itself and in the dorsomedial hypothalamic nucleus. These findings further define the position of hypothalamic CART neurons within the hierarchy of brain circuitries regulating energy balance, demonstrating the presence of CART peptide in several cell populations that form putative down-stream targets of NPY terminals, including hypophysiotropic TRH neurons and lateral hypothalamic MCH neurons.

Response to novelty after i.c.v. injection of melanin-concentrating hormone (MCH) in rats

Some behavioral response of rats to spatial novelty after i.c.v. administration of melanin-concentrating hormone (MCH) were evaluated. To this purpose, an open-field test was used, as well as an elevated plus-maze to study the possible anxiolytic effect of this peptide. In the open field, the frequency of exploratory components (locomotion and rearing) increased after MCH administration in comparison to controls. Moreover, in the plus-maze, MCH increased the number of entries into the open arms as well as the time spent on them, whereas no changes in the number of entries onto the closed arms were found. The data indicate that MCH exerts an anxiolytic effect, and suggests a physiological role for this.

Melanin-concentrating hormone-producing neurons in birds

The peptidergic melanin-concentrating hormone (MCH) system was investigated by immunocytochemistry in several birds. MCH perikarya were found in the periventricular hypothalamic nucleus near the paraventricular organ and in the lateral hypothalamic areas. Immunoreactive fibers were very abundant in the ventral pallidum, in the nucleus of the stria terminalis, and in the septum/diagonal band complex, where immunoreactive pericellular nets were prominent. Many fibers innervated the whole preoptic area, the lateral hypothalamic area, and the infundibular region. Some fibers also reached the dorsal thalamus and the epithalamus. The median eminence contained only sparse projections, and the posterior pituitary was not labeled. Thus, in birds, a neurohormonal role for MCH is not likely. Immunoreactive fibers were observed in other regions, such as the intercollicular nucleus, stratum griseum periventriculare (mesencephalic tectum), central gray, nigral complex (especially the ventral tegmental area), reticular areas, and raphe nuclei. Although no physiological investigation concerning the role of MCH has been performed in birds, the distribution patterns of the immunoreactive perikarya and fibers observed suggest that MCH may be involved in functions similar to those described in rats. In particular, the projections to parts of the limbic system (ventropallidal ganglia, septal complex, hypothalamus, dorsal thalamus, and epithalamus) and to structures concerned with visceral and other sensory information integration suggest that MCH acts as a neuromodulator involved in a wide variety of physiological and behavioral adaptations (arousal) with regard to feeding, drinking, and reproduction.

The distribution of melanin-concentrating hormone in the monkey brain (Cebus apella)

Melanin-concentrating hormone was identified in the brain of Cebus monkey using immunohistochemical and in situ hybridization. MCH-immunoreactive neurons were found in the lateral hypothalamus and dorsolateral zona incerta. MCH-ir fibers were seen in the medial mammillary nucleus, and in the median eminence, and very few fibers in the globus pallidus. This is the first report describing the MCH-ir cell and fiber distribution in the monkey brain.

Melanin-concentrating hormone system in the brain of the lungfish Protopterus annectens

The neurochemical anatomy of the lungfish brain is of particular interest, because many features in these animals might be representative of the common ancestor of land vertebrates. In the present study, we have investigated the localization and biochemical characteristics of melanin-concentrating hormone (MCH)-immunoreactive material in the central nervous system of the African lungfish, Protopterus annectens. The most prominent group of MCH-immunoreactive cell bodies was found in the dorsal hypothalamus. Additional groups of MCH-immunoreactive perikarya were detected in the telencephalon within the medial and dorsal pallium, the medial subpallium, and the ventral part of the lateral subpallium. Brightly immunofluorescent nerve fibers were seen in the anterior olfactory nucleus, the ventral part of the medial pallium, the medial subpallium, and the anterior preoptic area. In the diencephalon, the hypothalamus and the medial region of the dorsal thalamus exhibited a dense accumulation of fibers. MCH-immunoreactive fibers were also found in the tectum and the tegmentum of the mesencephalon and within the reticular formation of the rhombencephalon. In the pituitary, several small groups of cells of the intermediate lobe showed a bright fluorescence. Reversed-phase high-performance liquid chromatography (HPLC) analysis of diencephalon and pituitary extracts resolved a major MCH-immunoreactive peak that coeluted with synthetic salmon MCH. The distribution of MCH in the brain of P. annectens suggests that, in lungfishes, this peptide may exert neuromodulator or neurotransmitter functions. The presence of MCH-like immunoreactivity in the intermediate lobe of the pituitary indicates that, in dipnoans, MCH may also act as a typical pituitary hormone.

Lithium increases melanin-concentrating hormone mRNA stability and inhibits tyrosine hydroxylase gene expression in PC12 cells

Melanin-concentrating hormone (MCH) is a cyclic peptide involved in the regulation of food-intake behaviour and stress response in mammals. Expression of the MCH gene predominates in hypothalamic neurons. Mechanisms governing the regulation of expression of MCH gene in established cell lines were not explored yet. Here, we analysed the actions of nerve growth factor (NGF), dexamethasone, forskolin and lithium on MCH mRNA levels in the PC12 pheochromocytoma cell line. We compared them with those observed on tyrosine hydroxylase (TH) mRNA, constitutively expressed in PC12 cells, and neurotensin (NT) mRNA, taken as a control. In untreated cells, MCH RNA species of high molecular weight were found. Exposure of cells at a combination of NGF and lithium resulted in decreased expression of these MCH RNAs and in the transient production of mature MCH mRNA. Strikingly, after short exposure of PC12 cells to NGF, lithium per se elicited a marked increase in MCH mRNA levels whilst it exerted a potent inhibitory action on TH mRNA expression. Detailed investigations revealed that lithium enhanced MCH mRNA expression through post-transcriptional mechanisms whereas it regulated TH gene expression mainly at the level of transcription. These results demonstrate that lithium, an agent widely used for treatment of manic depressive illness, can exert an opposite effect on MCH and TH mRNA production in PC12 cells. The MCH gene system in NGF-treated PC12 cells provides a good opportunity for studying the effect of lithium on gene expression at post-transcriptional levels in a neuron-like cellular model.

Melanin-concentrating hormone (MCH) involvement in pentylenetetrazole (PTZ)-induced seizure in rat and guinea pig

Intraperitoneal injection of 60 mg/kg of pentylenetetrazole (PTZ) induced seizure in rats, but was subthreshold and did not result in seizure in guinea pigs. Three days after intracerebroventricular (i.c.v.) injection of 75 micrograms 6-hydroxydopamine (6-OHDA) in guinea pigs, PTZ induced seizures similar to those seen in rats. In both rats and 6-OHDA-treated guinea pigs, i.c.v. injection of melanin-concentrating hormone (MCH) 15 min before PTZ prevented seizure activity. These results suggest that MCH-containing neurons may participate in the neural circuits involved in expression of PTZ-induced seizure.