Beyond skin color: emerging roles of melanin-concentrating hormone in energy homeostasis and other physiological functions

Exploring the Relationship Between Antipsychotic Drug Target Genes and Epilepsy: Evidence From Food and Drug Administration Adverse Event Reporting System Database and Mendelian Randomization

BACKGROUND

The effect of antipsychotic drugs on epilepsy is controversial, and we performed Food and Drug Administration Adverse Event Reporting System (FAERS) data mining and Mendelian Randomization (MR) analyses to clarify the effects of target genes on epilepsy.

METHOD

We explored antipsychotic-induced epilepsy AE signals in FAERS. Gene expression was obtained from the eQTLGen consortium and GTEx project. Epilepsy data were obtained from FinnGen and the International League Against Epilepsy (ILAE). MR, Summary-data-based Mendelian Randomization (SMR), and colocalization analysis were sequentially performed, and meta-analysis was performed on genes with significant expression in MR or SMR to assess the causal relationship between them and epilepsy.

RESULT

Through FAERS database mining, 63 antipsychotics reported 5121 adverse events in epilepsy. MR identified potential causal associations of 14 drug target genes for epilepsy and its subtypes. MCHR1 and SIGMAR1 were still significant for epilepsy after meta-analysis with no evidence of heterogeneity or pleiotropy. SMR showed that DRD4 and ADRA1D were strongly associated with epilepsy or its subtypes however, neither gene passed the HEIDI test.

CONCLUSION

Our study indicates that antipsychotic drugs are associated with a high incidence of epilepsy-related AEs. MR demonstrated a causal relationship between drug targets and epilepsy. Providing new insights for managing epilepsy patients with psychiatric disorders.

Neuroendocrine control of brown adipocyte function by prolactin and growth hormone

Growth hormone (GH) is fundamental for growth and glucose homeostasis, and prolactin for optimal pregnancy and lactation outcome, but additionally, both hormones have multiple functions that include a strong impact on energetic metabolism. In this respect, prolactin and GH receptors have been found in brown, and white adipocytes, as well as in hypothalamic centers regulating thermogenesis. This review describes the neuroendocrine control of the function and plasticity of brown and beige adipocytes, with a special focus on prolactin and GH actions. Most evidence points to a negative association between high prolactin levels and the thermogenic capacity of BAT, except in early development. During lactation and pregnancy, prolactin may be a contributing factor that limits unneeded thermogenesis, downregulating BAT UCP1. Furthermore, animal models of high serum prolactin have low BAT UCP1 levels and whitening of the tissue, while lack of Prlr induces beiging in WAT depots. These actions may involve hypothalamic nuclei, particularly the DMN, POA and ARN, brain centers that participate in thermogenesis. Studies on GH regulation of BAT function present some controversies. Most mouse models with GH excess or deficiency point to an inhibitory role of GH on BAT function. Even so, a stimulatory role of GH on WAT beiging has also been described, in accordance with whole-genome microarrays that demonstrate divergent response signatures of BAT and WAT genes to the loss of GH signaling. Understanding the physiology of BAT and WAT beiging may contribute to the ongoing efforts to curtail obesity.

Melanin-concentrating hormone does not modulate serotonin release in primary cultures of fetal raphe nucleus neurons

Melanin-concentrating hormone (MCH) is a neuropeptide present in neurons located in the hypothalamus that densely innervate serotonergic cells in the dorsal raphe nucleus (DRN). MCH administration into the DRN induces a depressive-like effect through a serotonergic mechanism. To further understand the interaction between MCH and serotonin, we used primary cultured serotonergic neurons to evaluate the effect of MCH on serotonergic release and metabolism by HPLC-ED measurement of serotonin (5-HT) and 5-hydroxyindolacetic acid (5-HIAA) levels. We confirmed the presence of serotonergic neurons in the E14 rat rhombencephalon by immunohistochemistry and showed for the first time evidence of MCHergic fibers reaching the area. Cultures obtained from rhombencephalic tissue presented 2.2 ± 0.7% of serotonergic and 48.9 ± 5.4% of GABAergic neurons. Despite the low concentration of serotonergic neurons, we were able to measure basal cellular and extracellular levels of 5-HT and 5-HIAA without the addition of any serotonergic-enhancer drug. As expected, 5-HT release was calcium-dependent and induced by depolarization. 5-HT extracellular levels were significantly increased by incubation with serotonin reuptake inhibitors (citalopram and nortriptyline) and a monoamine-oxidase inhibitor (clorgyline), and were not significantly modified by a 5-HT1A autoreceptor agonist (8-OHDPAT). Even though serotonergic cells responded as expected to these pharmacological treatments, MCH did not induce significant modifications of 5-HT and 5-HIAA extracellular levels in the cultures. Despite this unexpected result, we consider that assessment of 5-HT and 5-HIAA levels in primary serotonergic cultures may be an adequate approach to study the effect of other drugs and modulators on serotonin release, uptake and turnover.

Toward Understanding the Repeated Occurrence of Associations between Melanin-Based Coloration and Multiple Phenotypes

Melanin is the most widespread pigment in organisms. Melanin-based coloration has been repeatedly observed to be associated with the same traits and in the same direction in different vertebrate and insect species. However, whether any factors that are common to different taxa account for the repeated evolution of melanin-phenotype associations remains unclear. We propose to approach this question from the perspective of convergent and parallel evolution to clarify to what extent different species have evolved the same associations owing to a shared genetic basis and being subjected to similar selective pressures. Our current understanding of the genetic basis of melanin-phenotype associations allows for both convergent and parallel evolution, but this understanding is still limited. Further research is needed to clarify the generality and interdependencies of the different proposed mechanisms (supergenes, pleiotropy based on hormones, or neural crest cells). The general ecological scenarios whereby melanin-based coloration is under selection-protection from ultraviolet radiation, thermoregulation in cold environments, or as a signal of social status-offer a good opportunity to study how melanin-phenotype associations evolve. Reviewing these scenarios shows that some traits associated with melanin-based coloration might be selected together with coloration by also favoring adaptation but that other associated traits might impede adaptation, which may be indicative of genetic constraints. We therefore encourage further research on the relative roles that selection and genetic constraints play in shaping multiple melanin-phenotype associations. Placed into a phylogenetic context, this will help clarify to what extent these associations result from convergent or parallel evolutionary processes and why melanin-phenotype associations are so common across the tree of life.

Sex-biased transcriptomic response of the reproductive axis to stress

Stress is a well-known cause of reproductive dysfunction in many species, including birds, rodents, and humans, though males and females may respond differently. A powerful way to investigate how stress affects reproduction is by examining its effects on a biological system essential for regulating reproduction, the hypothalamic-pituitary-gonadal (HPG) axis. Often this is done by observing how a stressor affects the amount of glucocorticoids, such as cortisol or corticosterone, circulating in the blood and their relationship with a handful of known HPG-producing reproductive hormones, like testosterone and estradiol. Until now, we have lacked a full understanding of how stress affects all genomic activity of the HPG axis and how this might differ between the sexes. We leveraged a highly replicated and sex-balanced experimental approach to test how male and female rock doves (Columba livia) respond to restraint stress at the level of their transcriptome. Females exhibit increased genomic responsiveness to stress at all levels of their HPG axis as compared to males, and these responsive genes are mostly unique to females. Reasons for this may be due to fluctuations in the female endocrine environment over the reproductive cycle and/or their evolutionary history, including parental investment and the potential for maternal effects. Direct links between genome to phenome cause and effect cannot be ascertained at this stage; however, the data we report provide a vital genomic foundation on which sex-specific reproductive dysfunction and adaptation in the face of stress can be further experimentally studied, as well as novel gene targets for genetic intervention and therapy investigations.

Role of nociceptin/orphanin FQ in thermoregulation

Nociceptin/Orphanin FQ (N/OFQ) is a 17-amino acid peptide that binds to the nociceptin receptor (NOP). N/OFQ and NOP receptors are expressed in numerous brain areas. The generation of specific agonists, antagonists and receptor-deficient mice or rats has enabled progress in elucidating the biological functions of N/OFQ. These tools have been employed to identify the biological significance of the N/OFQ system and how it interacts with other endogenous systems to regulate several body functions. The present review focuses on the role of N/OFQ in the regulation of body temperature and its relationship with energy balance. Critical evaluation of the literature data suggests that N/OFQ, acting through the NOP receptor, may cause hypothermia by influencing the complex thermoregulatory system that operates as a federation of independent thermoeffector loops to control body temperature at the hypothalamic level. Furthermore, N/OFQ counteracts hyperthermia elicited by cannabinoids or µ-opioid agonists. N/OFQ-induced hypothermia is prevented by ω-conotoxin GVIA, an N-type calcium channel blocker. Hypothermia induced by N/OFQ is considered within the framework of the complex action that this neuropeptide exerts on energy balance. Energy stores are regulated through the complex neural controls exerted on both food intake and energy expenditure. In laboratory rodents, N/OFQ stimulates consummatory behavior and decreases energy expenditure. Taken together, these studies support the idea that N/OFQ contributes to the regulation of energy balance by acting as an "anabolic" neuropeptide as it elicits effects similar to those produced in the hypothalamus by other neuropeptides such as orexins and neuropeptide Y.

Melanin-concentrating hormone inputs to the nucleus accumbens originate from distinct hypothalamic sources and are apposed to GABAergic and cholinergic cells in the Long-Evans rat brain

Melanin-concentrating hormone [MCH] is a neuropeptide that modulates several behaviors, such as feeding and reward. Because the hedonic and rewarding features of a food also influence feeding behavior, the nucleus accumbens [Acb] has been highlighted as a key area integrating these roles. Functional data confirm that MCH acts on a subdivision of the Acb; however, considering the importance of finding anatomical and neurochemical data that correlate the previously demonstrated function of MCH, we delineated this investigation based on the following points: (1) Is there a pattern of innervation by MCH fibers regarding the subregions within the Acb? (2) Specifically, which hypothalamic nuclei synthesize MCH and innervate the Acb? (3) Finally, what are the neurochemical identities of the accumbal neurons innervated by MCH inputs? We examined the MCH immunoreactivity [MCH-ir] in the Acb in rat brains using the peroxidase technique. Additionally, after injecting retrograde neuronal tracer [Fluoro-Gold® - FG®] into subdivisions of the Acb [shell or core], we mapped single- or double-labeled cells. Moreover, using a double immunoperoxidase protocol, we investigated the MCH-ir fibers for gamma-aminobutyric acid [GABA]-ir and choline acetyltransferase [ChAT]-ir cells in the shell subdivision of the Acb [AcbSh]. We found that the MCH-ir fibers preferentially innervate the medial AcbSh, particularly the septal pole. This innervation originated from the incerto-hypothalamic area [IHy], internuclear area, lateral hypothalamic area, perifornical area, periventricular nucleus and posterior hypothalamus. Moreover, the IHy has the highest relationship between double/single retrogradely labeled cells [n=5.33±0.66/16±0.93, i.e. 33.33%] in the whole hypothalamus. Furthermore, our data suggest that MCH-ir fibers are in apposition to GABAergic and cholinergic cells in the AcbSh. Therefore, we provide anatomical support to the ongoing functional studies investigating the relation among the hypothalamus, MCH transmission into the Acb and the involvement of known neuronal phenotypes within the AcbSh.

Functional characterization of two melanin-concentrating hormone genes in the color camouflage, hypermelanosis, and appetite of starry flounder

To investigate the involvement of two melanin-concentrating hormones (MCHs) in skin color change and appetite in flatfish, we isolated two forms of prepro-melanin concentrating hormone (pMCHs) mRNA in the starry flounder Platichthys stellatus and compared their amino acid structures to those of other animals. Then, we examined the relationship of the two starry flounder pMCH (sf-pMCH) with physiological color change, blind-side malpigmentation, and feeding by quantifying mRNA expression level. Sf-pMCH1 cDNA had a 387-bp open reading frame (ORF) that encoded a protein consisting of 129 amino acid residues. The sf-pMCH1 protein included a signal peptide composed of 24 amino acid residues; MCH1 encoded a protein consisting of 17 amino acids. The sf-pMCH2 cDNA had a 450-bp ORF that encoded a protein consisting of 150 amino acid residues, which included a signal peptide comprising 23 amino acid residues; MCH2 encoded a protein consisting of 23 amino acids that was structurally similar to mammalian MCH. Reverse transcription-polymerase chain reaction (RT-PCR) revealed that the strongest sf-pMCHs gene expression was observed in the brain and pituitary, but weak or no amplification was detected in other tissues. The expression of sf-pMCH1 was relatively high compared to that of sf-pMCH2 in the brain. The relative levels of mRNA were significantly lower in dark background-reared and hypermelanic fish, indicating that the two pMCHs and background color are related to the physiological and morphological color changes of skin. In term of feeding regulation, we found an obvious functional role of pMCH1 in appetite, whereas the pMCH2 gene was not found to play a role in feeding.

Oestradiol decreases melanin-concentrating hormone (MCH) and MCH receptor expression in the hypothalamus of female rats

Previous studies have shown that oestradiol (E₂) decreases the orexigenic effect of melanin-concentrating hormone (MCH). In the present study, we examined whether this action of E₂ is mediated by its ability to decrease the expression of MCH or its receptor (MCHR1). Using immunocytochemistry and western blotting, we examined whether E₂ decreases MCH-immunoreactive neurones or MCHR1 protein content in the hypothalamus of female rats. We found that both MCH and MCHR1 protein expression was decreased by acute E₂ treatment in ovariectomised rats, and by the peri-ovulatory increase in circulating E₂ in pro-oestrous rats, relative to rats at other cycle stages. To determine whether these changes in MCH/MCHR1 protein expression may be mediated by E₂'s ability to directly regulate the transcription of MCH and MCHR1 genes, the effect of E₂ treatment on MCH and MCHR1 mRNA expression in a neuronal hypothalamic cell line was examined using real-time reverse transcriptase-polymerase chain reaction. We also determined whether MCH and oestrogen receptor (ER)α are co-expressed in the hypothalamus of female rats. E₂ treatment did not decrease MCH or MCHR1 mRNA expression in vitro, and no hypothalamic neurones were identified that co-expressed MCH and ERα. We conclude that E₂-dependent decreases in hypothalamic MCH/MCHR1 protein expression mediate the ability of E₂ to decrease MCH-induced feeding. The current findings suggest, however, that E₂ exerts these actions indirectly, most likely though interactions with other neuronal systems that provide afferent input to MCH and MCHR1 neurones.

Influence of density and background color to stress response, appetite, growth, and blind-side hypermelanosis of flounder, Paralichthys olivaceus

To study the relevance of density and background color to stress response, appetite, and growth in olive flounder, Paralichthys olivaceus, we reared two duplicate groups of juveniles (total length 4.46 ± 0.06 cm, body weight 0.77 ± 0.03 g) in flat-bottom aquaria with dark-green (control) and white backgrounds for 120 days. We measured cortisol and glucose levels in blood and calculated the daily food intake, food conversion efficiency, survival rate, and growth rate. To study the relevance of density and background color to malpigmentation (hypermelanosis) on the blind side, we also compared malpigmented ratios and prepro-melanin-concentrating hormone mRNA activities in the brain between the dark-green and white background groups, as well as between a relatively lower density (60 days) and higher density (120 days). Although we measured relatively higher levels of cortisol and glucose in the white background group and over 200 % of coverage area [PCA]), the bright background failed to induce an acute stress response of more than 20 ng/ml cortisol and 40 mg/dl glucose both in 60 days and 120 days, but did enhance appetite and growth. Also, a bright background color delayed hyperpigmentation only at a low density below 200 % PCA, but did not inhibit malpigmentation at a high density of more than 200 % PCA. In addition, below 200 % PCA, expression of MCH mRNA was significantly higher in the white group, but the level was reversed and was lower in the white group at more than 200 % PCA. In conclusion, although did not induce a high stress response over 200 % PCA, the bright background color resulted in a moderate increasing of cortisol level in blood below 20 ng/ml and enhanced appetite and growth. Moreover, at a density below 200 % PCA, the bright color inhibited hypermelanosis with high MCH mRNA activity, but at more than 200 % PCA did not inhibit malpigmentation, and the fish showed low MCH mRNA activity, indicating that the inhibitory effect of a bright background color on hypermelanosis is density dependent.

Melanin-concentrating hormone receptor 1 (MCH1-R) antagonism: reduced appetite for calories and suppression of addictive-like behaviors

RATIONALE

The hypothalamic neuropeptide melanin-concentrating hormone and its MCH1 receptor have been implicated in regulation of feeding and energy homeostasis, as well as modulation of reward-related behaviors. Here, we examined whether the MCH system plays a role both in caloric and motivational aspects of sugar intake.

MATERIALS AND METHODS

The non-peptide MCH1-R antagonist GW803430 (3, 10, 30 mg/kg, i.p.) was first tested on self-administration under a fixed ratio schedule of reinforcement of both a caloric (10% w/v sucrose) and a non-caloric (0.06% w/v saccharin) sweet solution. GW803430 was then tested for its ability to alter motivational properties and seeking of sucrose. Lastly, the drug was tested to concurrently examine its effects on the escalated consumption of both sugar and food in animals following intermittent sugar access.

RESULTS

The MCH1-R antagonist reduced sucrose- but not saccharin-reinforced lever pressing, likely reflecting a decreased appetite for calories in GW803430-treated rats. GW803430 reduced sucrose self-administration under a progressive ratio schedule, and suppressed cue-induced reinstatement of sucrose seeking, suggesting effects on rewarding properties of sucrose. GW803430 attenuated food intake in rats on intermittent access to sucrose at all doses examined (3, 10, 30 mg/kg), while reduction of sugar intake was weaker in magnitude.

CONCLUSION

Together, these observations support an involvement of the MCH system in regulation of energy balance as well as mediation of sucrose reward. MCH may be an important regulator of sugar intake by acting on both caloric and rewarding components.

Design and optimization of quinazoline derivatives as melanin concentrating hormone receptor 1 (MCHR1) antagonists

Melanin concentrating hormone (MCH) is an important mediator of energy homeostasis and plays a role in metabolic and CNS disorders. The modeling-supported design, synthesis and multi-parameter optimization (biological activity, solubility, metabolic stability, hERG) of novel quinazoline derivatives as MCHR1 antagonists are described. The in vivo proof of principle for weight loss with a lead compound from this series is exemplified. Clusters of refined hMCHR1 homology models derived from the X-ray structure of the β2-adrenergic receptor, including extracellular loops, were developed and used to guide the design.

Melanin concentrating hormone (MCH) is involved in the regulation of growth hormone in Cichlasoma dimerus (Cichlidae, Teleostei)

Growth hormone (GH) is the main pituitary hormone involved in somatic growth. In fish, the neuroendocrine control of GH is multifactorial due to the interaction of multiple inhibitors and stimulators. Melanin-concentrating hormone (MCH) is a cyclic peptide involved in skin color regulation of fish. In addition, MCH has been related to the regulation of food intake in both mammals and fish. There is only one report presenting evidences on the GH release stimulation by MCH in mammals in experiments in vitro, but there are no data on non-mammals. In the present work, we report for the first time the sequence of MCH and GH cDNA in Cichlasoma dimerus, a freshwater South American cichlid fish. We detected contacts between MCH fibers and GH cells in the proximal pars distalis region of the pituitary gland by double label confocal immunofluorescence indicating a possible functional relationship. Besides, we found that MCH increased GH transcript levels and stimulated GH release in pituitary cultures. Additionally, C. dimerus exposed to a white background had a greater number of MCH neurons with a larger nuclear area and higher levels of MCH transcript than those fish exposed to a black background. Furthermore, fish reared for 3 months in a white background showed a greater body weight and total length compared to those from black background suggesting that MCH might be related to somatic growth in C. dimerus. Our results report for the first time, that MCH is involved in the regulation of the synthesis and release of GH in vitro in C. dimerus, and probably in the fish growth rate.

Cyclic peptides as potential therapeutic agents for skin disorders

There is an increasing understanding of the role of peptides in normal skin function and skin disease. With this knowledge, there is significant interest in the application of peptides as therapeutics in skin disease or as cosmeceuticals to enhance skin appearance. In particular, antimicrobial peptides and those involved in inflammatory processes provide options for the development of new therapeutic directions in chronic skin conditions such as psoriasis and dermatitis. To exploit their potential, it is essential that these peptides are delivered to their site of action in active form and in sufficient quantity to provide the desired effect. Many polymers permeate the skin poorly and are vulnerable to enzymatic degradation. Synthesis of cyclic peptide derivatives can substantially alter the physicochemical characteristics of the peptide with the potential to improve its skin permeation. In addition, cyclization can stabilize the peptide structure and thereby increase its stability. This review describes the role of cyclic peptides in the skin, examples of current cyclic peptide therapeutic products, and the potential for cyclic peptides as dermatological therapeutics and cosmeceuticals.

Sleep and metabolism: role of hypothalamic neuronal circuitry

Sleep and metabolism are intertwined physiologically and behaviorally, but the neural systems underlying their coordination are still poorly understood. The hypothalamus is likely to play a major role in the regulation sleep, metabolism, and their interaction. And increasing evidence suggests that hypocretin cells in the lateral hypothalamus may provide particularly important contributions. Here we review: 1) direct interactions between biological arousal and metabolic systems in the hypothalamus, and 2) indirect interactions between these two systems mediated by stress or reward, emphasizing the role of hypocretins. An increased understanding of the mechanisms underlying these interactions may provide novel approaches for the treatment of patients with sleep disorders and obesity, as well as suggest new therapeutic strategies for symptoms of aging, stress, or addiction.

The endogenous actions of hypothalamic peptides on brown adipose tissue thermogenesis in the rat

Although the neuronal pathways within the hypothalamus critical in controlling feeding and energy expenditure and projecting to brown adipose tissue (BAT) have been identified and their peptidergic content characterized, endogenous action of such peptides in the control of BAT activity has not been elucidated. Here male Sprague Dawley rats received infusions of either melanin-concentrating hormone antagonist (SNAP-7941) (1 microg/microl x h), orexin A receptor antagonist (SB-334867-A; 1 microg/microl x h), combined SB-334867-A (1 microg/microl x h), and SNAP-7941 (1 microg/microl x h), or melanocortin-3/4 receptor antagonist (SHU9119) (1 microg/microl x h) via an indwelling cannula in the lateral ventricle attached to s.c. implanted osmotic minipump. BAT temperature, physical activity, body weight, food intake, and changes in uncoupling protein (UCP)-1 were measured. SB-334867-A and SNAP-7941 significantly increased BAT temperature and UCP1 expression and reduced food intake and body weight. Combined infusion of SB-334867-A and SNAP-7941 produced a pronounced response that was greater than the addition of the individual effects in all parameters measured. SHU9119 significantly decreased BAT temperature and UCP1 expression and increased feeding and body weight. In a second series of experiments, the effect of SB-334867-A and SNAP-7941 alone or combination on the expression of the Fos protein was determined. SB-334867-A and SNAP-7941 increased Fos expression in key hypothalamic and brainstem feeding-related regions. In combination, these antagonists produced a greater than additive elevation of Fos expression in most of the regions evaluated. These findings support a role for endogenous orexigenic and anorexigenic hypothalamic peptides acting in concert to create a thermogenic tone via BAT activity.

Regulation of food intake by melanin-concentrating hormone in goldfish

Melanin-concentrating hormone (MCH), originally discovered in the teleost pituitary, is a hypothalamic neuropeptide involved in the regulation of body color in fish. Although MCH is also present in the mammalian brain, it has no evident function in providing pigmentation. Instead, this peptide is now recognized to be one of the key neuropeptides that act as appetite enhancers in mammals such as rodents and primates. Although there has been little information about the central action of MCH on appetite in fish, recent studies have indicated that, in goldfish, MCH acts as an anorexigenic neuropeptide, modulating the alpha-melanocyte-stimulating hormone signaling pathway through neuronal interaction. These observations indicate that there may be major differences in the mode of action of MCH between fish and mammals. This paper reviews what is currently known about the regulation of food intake by MCH in fish, especially the goldfish.

Regulation of synaptic efficacy in hypocretin/orexin-containing neurons by melanin concentrating hormone in the lateral hypothalamus

The lateral hypothalamus (LH) is a central hub that integrates inputs from, and sends outputs to, many other brain areas. Two groups of neurons in the LH, expressing hypocretin/orexin or melanin concentrating hormone (MCH), have been shown to participate in sleep regulation, energy homeostasis, drug addiction, motor regulation, stress response, and social behaviors. The elucidation of crosstalk between these two systems is essential to understand these behaviors and functions because there is evidence that there are reciprocal innervations between hypocretin/orexin and MCH neurons. In this study, we used MCH receptor-1 knock-out (MCHR1 KO) and wild-type (WT) mice expressing green fluorescent protein in hypocretin/orexin-containing neurons to examine the hypothesis that MCH modulates hypocretin/orexin-mediated effects on behavioral state and synaptic transmission in the LH. In MCHR1 KO mice, the efficacy of glutamatergic synapses on hypocretin/orexin neurons is potentiated and hypocretin-1-induced action potential firing is facilitated, potentially explaining an increased effect of modafinil observed in MCHR1 KO mice. In wild-type mice with intact MCHR1 signaling, MCH significantly attenuated the hypocretin-1-induced enhancement of spike frequency in hypocretin/orexin neurons. The MCH effect was dose dependent, pertussis toxin sensitive, and was abolished in MCHR1 KO mice. Consistent with this effect, MCH attenuated hypocretin-1-induced enhancement of the frequency of miniature EPSCs in hypocretin/orexin neurons. These data from MCHR1 KO and WT mice demonstrate a novel interaction between these two systems, implying that MCH may exert a unique inhibitory influence on hypocretin/orexin signaling as a way to fine-tune the output of the LH.

Melanin-concentrating hormone as a mediator of intestinal inflammation

Melanin-concentrating hormone (MCH) is expressed primarily in the hypothalamus and has a positive impact on feeding behavior and energy balance. Although MCH is expressed in the gastrointestinal tract, its role in this system remains elusive. We demonstrate that, compared to wild type, mice genetically deficient in MCH had substantially reduced local inflammatory responses in a mouse model of experimental colitis induced by intracolonic administration of 2,4,6 trinitrobenzene sulfonic acid (TNBS). Likewise, mice receiving treatments with an anti-MCH antibody, either prophylactically or after the establishment of colitis, developed attenuated TNBS-associated colonic inflammation and survived longer. Consistent with a potential role of MCH in intestinal pathology, we detected increased colonic expression of MCH and its receptor in patients with inflammatory bowel disease. Moreover, we found that human colonic epithelial cells express functional MCH receptors, the activation of which induces IL-8 expression. Taken together, these results clearly implicate MCH in inflammatory processes in the intestine and perhaps elsewhere.

Melanin-concentrating hormone (MCH) immunoreactivity in non-neuronal cells within the raphe nuclei and subventricular region of the brainstem of the cat

Neurons that utilize melanin-concentrating hormone (MCH) as a neuromodulator are localized within the postero-lateral hypothalamus and zona incerta. These neurons project diffusely throughout the central nervous system and have been implicated in critical physiological processes such as energy homeostasis and sleep. In the present report, we examined the distribution of MCH immunoreactivity in the brainstem of the cat. In addition to MCH+ axons, we found MCH-immunoreactive cells that have not been previously described either in the midbrain raphe nuclei or in the periaqueductal and periventricular areas. These MCH+ cells constituted: 1. ependymal cells that lined the fourth ventricle and aqueduct, 2. ependymal cells with long basal processes that projected deeply into the subventricular (subaqueductal) parenchyma, and, 3. cells in subventricular regions and the midbrain raphe nuclei. The MCH+ cells in the midbrain raphe nuclei were closely related to neuronal processes of serotonergic neurons. Utilizing Neu-N and GFAP immunohistochemistry we determined that the preceding MCH+ cells were neither neurons nor astrocytes. However, we found that vimentin, an intermediate-filament protein that is used as a marker for tanycytes, was specifically co-localized with MCH in these cells. We conclude that MCH is present in tanycytes whose processes innervate the midbrain raphe nuclei and adjacent subependymal regions. Because tanycytes are specialized cells that transport substances from the cerebrospinal fluid (CSF) to neural parenchyma, we suggest that MCH is absorbed from the CSF by tanycytes and subsequently liberate to act upon neurons of brainstem nuclei.

Alpha-melanocyte-stimulating hormone mediates melanin-concentrating hormone-induced anorexigenic action in goldfish

In goldfish, intracerebroventricular (ICV) administration of melanin-concentrating hormone (MCH) inhibits feeding behavior, and fasting decreases hypothalamic MCH-like immunoreactivity. However, while MCH acts as an anorexigenic factor in goldfish, in rodents MCH has an orexigenic effect. Therefore, we examined the involvement of two anorexigenic neuropeptides, alpha-melanocyte-stimulating hormone (alpha-MSH) and corticotropin-releasing hormone (CRH), in the anorexigenic action of MCH in goldfish, using an alpha-MSH receptor antagonist, HS024, and a CRH receptor antagonist, alpha-helical CRH((9-41)). ICV injection of HS024, but not alpha-helical CRH((9-41)), suppressed MCH-induced anorexigenic action for a 60-min observation period. We then examined, using a real-time PCR method, whether MCH affects the levels of mRNAs encoding various orexigenic neuropeptides, including neuropeptide Y (NPY), orexin, ghrelin and Agouti-related peptide (AgRP), in the goldfish diencephalon. ICV administration of MCH at a dose sufficient to inhibit food consumption decreased the expression of mRNAs for NPY and ghrelin, but not for orexin and AgRP. These results indicate that the anorexigenic action of MCH in the goldfish brain is mediated by the alpha-MSH signaling pathway and is accompanied by inhibition of NPY and ghrelin synthesis.

Single nucleotide polymorphisms of the MCHR1 gene do not affect metabolism in humans

Melanin concentrating hormone receptor-1 (MCHR1) is a centrally and peripherally expressed receptor that regulates energy expenditure and appetite. Single nucleotide polymorphisms (SNPs) of the MCHR1 gene have been previously associated with obesity, but the results are inconsistent among different populations. This study was performed to determine whether SNPs of MCHR1 affect glucose and energy metabolism. We screened six SNPs of MCHR1 in a cross-sectional study of 217 middle-age, non-diabetic Finnish subjects who were offspring of type 2 diabetic patients. Insulin secretion was evaluated by an intravenous glucose tolerance test and insulin sensitivity and energy metabolism by the hyperinsulinemic euglycemic clamp and indirect calorimetry. SNPs of MCHR1 were not associated with BMI, waist circumference, subcutaneous or intra-abdominal fat area, glucose tolerance, first-phase insulin release, insulin sensitivity, or energy metabolism. One SNP, which was in >0.50 linkage disequilibrium with the other five SNPs, was also screened in 1455 unrelated Finnish middle-age subjects in a population-based study. No differences in BMI, waist circumference, or glucose or insulin levels in an oral glucose tolerance test among the genotypes were found. In conclusion, SNPs of MCHR1 did not have effects on metabolic variables in humans.

Feeding-induced changes of melanin-concentrating hormone (MCH)-like immunoreactivity in goldfish brain

Intracerebroventricular (ICV) injection of melanin-concentrating hormone (MCH) influences feeding behavior in the goldfish and exerts an anorexigenic action in goldfish brain, unlike its orexigenic action in mammals. Despite a growing body of knowledge concerning MCH function in mammals, the role of MCH in appetite has not yet been well studied in fish. The aim of the present study was to investigate the involvement of endogenous MCH in the feeding behavior of the goldfish. We examined the distribution of MCH-like immunoreactivity (MCH-LI) in the goldfish brain and the effect of feeding status upon this distribution. Neuronal cell bodies containing MCH-LI were localized specifically to four areas of the hypothalamus. Nerve fibers with MCH-LI were found mainly in the neurohypophysis, with a few in the telencephalon, mesencephalon, and diencephalon. The number of neuronal cell bodies containing MCH-LI in the dorsal area adjoining the lateral recess of the third ventricle in the posterior and inferior lobes of the hypothalamus showed a significant decrease in fasted fish compared with that in normally fed fish, although other areas showed no evident differences. We also administered an antiserum against fish MCH (anti-MCH serum) by ICV injection and examined its immuno-neutralizing effect on food intake by using an automatic monitoring system. Cumulative food intake was significantly increased by ICV injection of the anti-MCH serum. These results indicate that MCH potentially functions as an anorexigenic neuropeptide in the goldfish brain, and that the further study of the evolutionary background of the MCH system and its role in appetite is warranted.

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.

Functions of melanin-concentrating hormone in fish

Melanin-concentrating hormone (MCH) was originally discovered in fish, in which it causes aggregation or concentration of melanin granules in melanophores, thus regulating body color. MCH is a cyclic neuropeptide synthesized as a preprohormone in the hypothalamus of all vertebrates. Mammalian MCH plays an important role as a neurotransmitter or neuromodulator in regulating food intake and energy homeostasis. MCH signaling system may involve in regulating food intake also in fish. This neuropeptide binds to G-protein-coupled seven transmembrane receptor[s] to mediate its functions. This article reviews MCH and MCH receptor signaling systems in body color change and food intake in fish.

Nonribosomal cyclic peptides: specific markers of fungal infections

Some cyclic peptides and depsipeptides are synthesized in microorganisms by large multienzymes called nonribosomal peptide synthetases. The structures of peptide products originating in this way are complex and diverse and are microorganism-specific. This work proposes the use of fungal cyclic peptides and depsipeptides as extremely specific markers of fungal infections. Since a reliable molecular tool for diagnosing fungal infections at an early stage is still missing, we present mass spectrometry as a new, modern, broadband (with respect to fungal strain) and specific tool for clinical mycologists. More than 40 different fungal species can be rapidly characterized according to specific families of cyclic peptides, and in some cases, a particular fungal strain can be identified on the basis of its cyclopeptide profile. This paper is also aimed at initiating discussion on the biological role of these secondary metabolites, especially of those synthesized by medically important strains. Proven cytotoxic, anti-inflammatory or immunosuppressive activities of some cyclic peptides indicate that these molecules may contribute to the synergistic array of fungal virulence factors and support microbial invasion during fungal infection. In addition to an overview on recent mass spectrometric protocols for cyclic peptide sequencing, the structures of new peptides from Paecilomyces and Pseudallescheria are presented.

Genetic background differences between FVB and C57BL/6 mice affect hypnotic susceptibility to pentobarbital, ketamine and nitrous oxide, but not isoflurane

BACKGROUND

Pharmacogenomics has allowed us to identify the mechanisms underlying much of the inherited variability in drug response. There have been several reports of strain-dependent anesthetic actions in rodents, indicating that significant genetic differences exist in the hypnotic and antinociceptive effects of various anesthetics.

METHODS

Loss of righting reflex was used to compare the hypnotic action of pentobarbital, ketamine, nitrous oxide and isoflurane between two genetically different populations of mice, C57BL/6 with black hair and Friends virus B (FVB) with white hair.

RESULTS

C57BL/6 mice were more susceptible than FVB mice to the hypnotic effects of ketamine, pentobarbital and nitrous oxide. However, the sensitivity to isoflurane did not differ between C57BL/6 and FVB mice.

CONCLUSION

Genetic background affects the hypnotic susceptibility to some anesthetic agents in mice. Our results indicate that there may be a different genetic basis for the operation of hypnosis between isoflurane and other anesthetics, such as pentobarbital, ketamine and nitrous oxide.

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.

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.

Effects of MCH and a MCH1-receptor antagonist on (palatable) food and water intake

Melanin concentrating hormone (MCH) is a regulator of ingestive behavior, but several issues regarding its effects on specific components of ingestive behavior remain to be elucidated. Therefore, we injected, in the 3rd ventricle of male Wistar rats, saline, MCH (5 microg), MCH (5 mug) together with a MCH1-R antagonist (A, 10 microg) and the antagonist alone (A, 10 microg). Our results show that (1) central administration of MCH stimulates food intake (lab chow and medium high fat diet) and this can be blocked by a MCH1-R antagonist; (2) the MCH-induced increase in food intake is mediated through increased meal number, meal duration and meal size; (3) the MCH1-R antagonist is able to significantly reduce the intake of a highly palatable food (condensed sweet milk) and is more effective in blocking MCH-induced food intake when rats are fed a palatable medium high fat food; and (4) MCH stimulated water intake independently from and disproportionately to food intake. In conclusion, our results point to an involvement of endogenous MCH in the enhanced intake of palatable food. Furthermore, they confirm that MCH stimulates not only food intake but also water intake.

Central administration of melanin-concentrating hormone increases alcohol and sucrose/quinine intake in rats

BACKGROUND

Alcohol is a caloric compound that can contribute to energy intake. Therefore, peptides that regulate energy balance likely modify the motivation to consume alcohol. Melanin-concentrating hormone (MCH) regulates energy homeostasis and has been implicated in other behaviors that impact alcohol consumption (i.e., anxiety, fluid balance, and reward). We tested the hypothesis that MCH would decrease the motivation to consume alcohol secondarily to reducing anxiety.

METHODS

Rats were trained to drink 10% ethanol or an isocaloric concentration of sucrose with use of a sucrose-fading technique. MCH (1, 5, or 10 microg) or its saline vehicle was administered into the third cerebral ventricle (i3vt), and intake of ethanol or sucrose and chow was assessed for 2 hr. Alcohol-naïve rats were evaluated in an elevated plus maze after i3vt MCH (10 microg), neuropeptide Y, or saline administration.

RESULTS

Contrary to the hypothesis, MCH dose-dependently increased alcohol intake: saline = 0.7 +/- 0.1 g/kg, 1 microg MCH = 1.0 +/- 0.1 g/kg, 5 microg MCH = 1.2 +/- 0.1 g/kg, and 10 microg MCH = 1.8 +/- 0.3 g/kg (p < 0.01), and this was true whether water was simultaneously available or not. MCH also significantly increased sucrose intake (saline = 1.0 +/- 0.3 g/kg, 10 mug MCH = 1.4 +/- 0.5 g/kg; p < 0.05). MCH had no effect on time spent in the open arms (54.3 +/- 11.5 sec) relative to saline (58.2 +/- 23.8 sec), whereas neuropeptide Y, a known anxiolytic, increased time spent on the open arms (119.2 +/- 22 sec, p < 0.05).

CONCLUSIONS

We conclude that MCH nonspecifically increases ingestive behavior. Furthermore, MCH had no apparent effect on anxiety. The ability of MCH to increase alcohol and/or sucrose intake may be explained by the effect of MCH on energy balance and/or reward processes.

How palatable food disrupts appetite regulation

Appetite regulation is part of a feedback system that controls the energy balance, involving a complex interplay of hunger and satiety signals, produced in the hypothalamus as well as in peripheral organs. Hunger signals may be generated in peripheral organs (e.g. ghrelin) but most of them are expressed in the hypothalamus (neuropeptide Y, orexins, agouti-related peptide, melanin concentrating hormone, endogenous opiates and dopamine) and are expressed during situations of energy deficiency. Some satiety signals, such as cholecystokinin, glucagon-like peptide 1, peptide YY and enterostatin are released from the digestive tract in response to food intake. Others, such as leptin and insulin, are mobilized in response to perturbations in the nutritional state. Still others are generated in neurones of the hypothalamus (alpha-melanocyte-stimulating hormone and serotonin). Satiety signals act by inhibiting the expression of hunger signals and/or by blunting their effect. Palatable food, i.e. food rich in fat and sugar, up-regulates the expression of hunger signals and satiety signals, at the same time blunting the response to satiety signals and activating the reward system. Hence, palatable food offsets normal appetite regulation, which may explain the increasing problem of obesity worldwide.