Activity Of Melanin-concentrating Hormone Research Articles

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

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

Prolactin-Releasing Peptide Contributes to Stress-Related Mood Disorders and Inhibits Sleep/Mood Regulatory Melanin-Concentrating Hormone Neurons in Rats.

Stress disorders impair sleep and quality of life; however, their pathomechanisms are unknown. Prolactin-releasing peptide (PrRP) is a stress mediator; we therefore hypothesized that PrRP may be involved in the development of stress disorders. PrRP is produced by the medullary A1/A2 noradrenaline (NA) cells, which transmit stress signals to forebrain centers, and by non-NA cells in the hypothalamic dorsomedial nucleus. We found in male rats that both PrRP and PrRP-NA cells innervate melanin-concentrating hormone (MCH) producing neurons in the dorsolateral hypothalamus (DLH). These cells serve as a key hub for regulating sleep and affective states. Ex vivo, PrRP hyperpolarized MCH neurons and further increased the hyperpolarization caused by NA. Following sleep deprivation, intracerebroventricular PrRP injection reduced the number of REM sleep-active MCH cells. PrRP expression in the dorsomedial nucleus was upregulated by sleep deprivation, while downregulated by REM sleep rebound. Both in learned helplessness paradigm and after peripheral inflammation, impaired coping with sustained stress was associated with (1) overactivation of PrRP cells, (2) PrRP protein and receptor depletion in the DLH, and (3) dysregulation of MCH expression. Exposure to stress in the PrRP-insensitive period led to increased passive coping with stress. Normal PrRP signaling, therefore, seems to protect animals against stress-related disorders. PrRP signaling in the DLH is an important component of the PrRP's action, which may be mediated by MCH neurons. Moreover, PrRP receptors were downregulated in the DLH of human suicidal victims. As stress-related mental disorders are the leading cause of suicide, our findings may have particular translational relevance.SIGNIFICANCE STATEMENT Treatment resistance to monoaminergic antidepressants is a major problem. Neuropeptides that modulate the central monoaminergic signaling are promising targets for developing alternative therapeutic strategies. We found that stress-responsive prolactin-releasing peptide (PrRP) cells innervated melanin-concentrating hormone (MCH) neurons that are crucial in the regulation of sleep and mood. PrRP inhibited MCH cell activity and enhanced the inhibitory effect evoked by noradrenaline, a classic monoamine, on MCH neurons. We observed that impaired PrRP signaling led to failure in coping with chronic/repeated stress and was associated with altered MCH expression. We found alterations of the PrRP system also in suicidal human subjects. PrRP dysfunction may underlie stress disorders, and fine-tuning MCH activity by PrRP may be an important part of the mechanism.

Sex differences in feeding behavior in rats: the relationship with neuronal activation in the hypothalamus.

There is general agreement that the central nervous system in rodents differs between sexes due to the presence of gonadal steroid hormone during differentiation. Sex differences in feeding seem to occur among species, and responses to fasting (i.e., starvation), gonadal steroids (i.e., testosterone and estradiol), and diet (i.e., western-style diet) vary significantly between sexes. The hypothalamus is the center for controlling feeding behavior. We examined the activation of feeding-related peptides in neurons in the hypothalamus. Phosphorylation of cyclic AMP response element-binding protein (CREB) is a good marker for neural activation, as is the Fos antigen. Therefore, we predicted that sex differences in the activity of melanin-concentrating hormone (MCH) neurons would be associated with feeding behavior. We determined the response of MCH neurons to glucose in the lateral hypothalamic area (LHA) and our results suggested MCH neurons play an important role in sex differences in feeding behavior. In addition, fasting increased the number of orexin neurons harboring phosphorylated CREB in female rats (regardless of the estrous day), but not male rats. Glucose injection decreased the number of these neurons with phosphorylated CREB in fasted female rats. Finally, under normal spontaneous food intake, MCH neurons, but not orexin neurons, expressed phosphorylated CREB. These sex differences in response to fasting and glucose, as well as under normal conditions, suggest a vulnerability to metabolic challenges in females.

Association between the activation of MCH and orexin immunorective neurons and REM sleep architecture during REM rebound after a three day long REM deprivation

Rapid eye movement (REM) sleep rebound following REM deprivation using the platform-on-water method is characterized by increased time spent in REM sleep and activation of melanin-concentrating hormone (MCH) expressing neurons. Orexinergic neurons discharge reciprocally to MCH-ergic neurons across the sleep-wake cycle. However, the relation between REM architecture and the aforementioned neuropeptides remained unclear. MCH-ergic neurons can be divided into two subpopulations regarding their cocaine- and amphetamine-regulated transcript (CART) immunoreactivity, and among them the activation of CART-immunoreactive subpopulation is higher during the REM rebound. However, the possible role of stress in this association has not been elucidated.Our aims were to analyze the relationship between the architecture of REM rebound and the activation of hypothalamic MCH-ergic and orexinergic neurons. We also intended to separate the effect of stress and REM deprivation on the subsequent activation of subpopulations of MCH-ergic neurons. In order to detect neuronal activity, we performed MCH/cFos and orexin/cFos double immunohistochemistry on home cage, sleep deprived and sleep-rebound rats using the platform-on-water method with small and large (stress control) platforms. Furthermore, REM architecture was analyzed and a triple MCH/CART/cFos immunohistochemistry was also performed on the rebound groups in the same animals.We found that the activity of MCH- and orexin-immunoreactive neurons during REM rebound was positively and negatively correlated with the number of REM bouts, respectively. A negative reciprocal correlation was also found between the activation of MCH- and orexin-immunoreactive neurons during REM rebound. Furthermore, difference between the activation of CART-immunoreactive (CART-IR) and non-CART-immunoreactive MCH-ergic neuron subpopulations was found only after selective REM deprivation, it was absent in the large platform (stress control) rebound group.These results support the role of CART-IR subpopulation of MCH-ergic neurons and the inverse relationship of MCH and orexin in the regulation of REM sleep after REM sleep deprivation.

GIRK channel-mediated inhibition of melanin-concentrating hormone neurons by nociceptin/orphanin FQ

Targeting the melanin-concentrating hormone (MCH) system has been suggested as a potential treatment for obesity, anxiety disorders, as well as addiction. Despite the therapeutic potential of MCH agonists and antagonists, the endogenous factors regulating MCH activity, in particular those implicated in anxiety and reward, are ill-defined. The present study investigated the cellular effects of nociceptin/orphanin FQ (N/OFQ), an endogenous opioid with anxiolytic and antireward properties, on MCH neurons. We found that N/OFQ induced a concentration-dependent reversible outward current in MCH neurons (EC(50) = 50.7 nM), an effect that was blocked by the competitive antagonist of the nociceptin opioid peptide (NOP) receptor UFP-101. N/OFQ-induced outward currents persisted in TTX, reversed near the potassium equilibrium potential, and displayed inward rectification, suggesting direct postsynaptic potassium channel activation. Tertiapin-Q completely abolished the N/OFQ effect, whereas glibenclamide did not, implicating protein G-dependent inwardly rectifying potassium (GIRK) and not ATP-sensitive potassium (K(ATP)) channels as the effector ion channel. The N/OFQ-induced outward current desensitized during repeated applications and occluded the inhibitory effect of dynorphin, suggesting that dynorphin and N/OFQ activate the same pathway. N/OFQ also reversibly inhibited voltage-gated calcium currents in MCH neurons. In conclusion, our study indicates N/OFQ as a robust endogenous regulator of MCH neurons, which may play a role in anxiety and drug addiction.

Two Naturally Occurring Mutations in the Type 1 Melanin-Concentrating Hormone Receptor Abolish Agonist-Induced Signaling

The melanin-concentrating hormone (MCH) receptor type 1 (MCHR1) is a seven-transmembrane domain protein that modulates orexigenic activity of MCH, the corresponding endogenous peptide agonist. MCH antagonists are being explored as a potential treatment for obesity. In the current study, we examined the pharmacological impact of 11 naturally occurring mutations in the human MCHR1. Wild-type and mutant receptors were transiently expressed in human embryonic kidney 293 cells. MCHR1-mediated, Gα(i)-dependent signaling was monitored by using luciferase reporter gene assays. Two mutants, R210H and P377S, failed to respond to MCH. Five other variants showed significant alterations in MCH efficacy, ranging from 44 to 142% of the wild-type value. At each of the MCH-responsive mutants, agonist potency and inhibition by (S)-methyl 3-((3-(4-(3-acetamidophenyl)piperidin-1-yl)propyl)carbamoyl)-4-(3,4-difluorophenyl)-6-(methoxymethyl)-2-oxo-1,2,3,4-tetrahydropyrimidine-5-carboxylate (SNAP-7941), an established MCHR1 small-molecule antagonist, were similar to wild type. To explore the basis for inactivity of the R210H and P377S mutants, we examined expression levels of these receptors. Assessment by enzyme-linked immunosorbent assay revealed that cell surface expression of both nonfunctional receptors was comparable with wild type. Overnight treatment with SNAP-7941, followed by washout of antagonist, enhanced MCH induced signaling by the wild-type receptor and restored MCH responsiveness of the P377S but not the R210H variant. It is of note that the two loss-of-function mutants were identified in markedly underweight individuals, raising the possibility that a lean phenotype may be linked to deficient MCHR1 signaling. Formal association studies with larger cohorts are needed to explore the extent to which signaling-deficient MCHR1 variants influence the maintenance of body weight.

MCH receptors/gene structure-in vivo expression

Melanin-concentrating hormone (MCH) is a cyclic peptide which was originally discovered in fish to lighten skin color by affecting melanosomes aggregation. This peptide is highly conserved and also found in rodents whose gene is overexpressed upon fasting. However, the site of MCH action remained obscure until its receptor was discovered in 1999 as a G protein-coupled receptor. After this receptor structure was identified, the functional domains important for MCH-MCHR interaction were revealed. Moreover, the cloning of the MCH receptor led us to identify the in vivo sites of MCH action which suggested potential physiological functions of the MCH system. Furthermore, the MCH receptor identification allow for designing surrogate molecules which can block MCH activity. Studies using these molecules revealed various physiological functions of the MCH system not only in feeding but also in other physiological responses such as stress and emotion. This review will discuss how the MCH receptor was discovered and its impact on many studies investigating the MCH receptor's structure, signaling pathways, and expression pattern.

Dysregulation of the Mesolimbic Dopamine System and Reward in MCH−/− Mice

The hypothalamic neuropeptide melanin-concentrating hormone (MCH) plays a critical role in energy homeostasis. Abundant expression of the MCH receptor is observed outside the hypothalamus, especially in the dorsal and the ventral striatum, raising the possibility that MCH modulates the function of the midbrain dopamine neurons and associated circuitry. The MCH receptor 1 (MCHR1) expression was assessed by in situ hybridization. Expression of dopamine transporter (DAT) and the dopamine D1 and D2 receptor (D1R and D2R) subtypes in the caudate-putamen (CPu) and the nucleus accumbens (Acb) was evaluated by immunoblotting. Amperometry in ex vivo slices of the Acb was used to measure evoked-dopamine release in MCH-/ - mice. Catalepsy in MCH+/+ and MCH-/- mice was assessed by the bar test after haloperidol injection. Locomotor activity was measured after acute and chronic treatment with amphetamine and after dopamine reuptake inhibitor GBR 12909 administration. The psychostimulant amphetamine caused enhanced behavioral sensitization in MCH-/- mice. We found significantly elevated expression of the DAT in the Acb of MCH-/- mice. The DAT-mediated uptake of dopamine was also enhanced in MCH-/- mice consistent with increased expression of DAT. We also found that evoked dopamine release is significantly increased in the Acb shell of MCH-/- mice. The GBR 12909 administration increased the locomotor activity of MCH-/- mice significantly above that of MCH+/+ mice. These results demonstrate that MCH, in addition to its known role in feeding and weight regulation, plays a critical role in regulating Acb dopamine signaling and related behavioral responses.

Protein‐Kinase C Mediates MCH Signal Transduction in Teleost, Synbranchus marmoratus, Melanocytes

MCH (melanin concentrating hormone) is a heptadecapeptide, Asp-Thr-Met-Arg-Cys-Met-Val-Gly-Arg-Val-Tyr-Arg-Pro-Cys-Trp-Glu-Val, which stimulates melanosome (melanin granule) aggregation to a perinuclear position within teleost fish integumental melanocytes, resulting in lightening of the skin. The mechanisms of action of MCH are unknown. Drugs that affect the diacylglycerol/inositol triphosphate pathway were used to investigate the possible roles of this pathway in the mechanisms of action of MCH on Synbranchus marmoratus (teleost) melanocytes. The shift of the dose-response curve to MCH in the presence of various concentrations of 4-bromophenacyl bromide and neomycin sulphate, phospholipase C inhibitors, suggests that phospholipase C is stimulated after MCH receptor activation. Low concentrations (10(-9) to 10(-8) M) of the phorbol ester TPA exhibited MCH-like activity, eliciting a dose-dependent melanosome aggregation. Higher doses, however, displaced to the right the dose-response curve to MCH, as did the protein kinase C inhibitors, dibucaine and 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7). These results support the assumption that protein kinase C mediates the pigment aggregating activity of MCH. Both MCH and norepinephrine lightening actions were abolished by beta-glycerophosphate, a phosphatase inhibitor, suggesting that a protein dephosphorylation occurs during melanosome aggregation, and is, therefore, a common event triggered by MCH and norepinephrine, although both agonists act through separate receptors and exhibit different transduction mechanisms.

Melanin concentrating hormone (MCH): Structure-function aspects of its melanocyte stimulating hormone-like (MSH-like) activity

Melanin concentrating hormone (MCH) is a heptadecapeptide, Asp-Thr-Met-Arg- Cys-Met-Val-Gly-Arg-Val-Tyr-Arg-Pro-Cys -Trp-Glu-Val, synthesized in the brain and secreted from the pars nervosa of teleost fish. This hormone stimulates melanosome (melanin granule) aggregation within integumental melanocytes of fishes but, in contrast, stimulates melansome dispersion within tetrapod (frog and lizard) melanocytes. We determined the message sequence of the primary structure of MCH which is responsible for its MSH-like component of activity. Removal of the N-terminal amino acid results in an almost total loss of MSH-like activity. The C-terminal amino acid is also essential for full MSH-like activity since the analogue, MCH(1–16), is about 100 times less active than MCH. Therefore, the entire heptadecapeptide sequence of MCH appears to contribute to the MSH-like activity of MCH. Ring-contracted analogues (e.g., [Ala 5,Cys 10]MCH) of MCH are almost devoid of any melanosome aggregating (MCH-like) activity but generally possess considerable or as great an MSH-like activity as MCH. Racemization of MCH by heat-alkali treatment drastically reduces the MCH-like activity of MCH, but does not enhance the MSH-like activity of the hormone.

Ionic requirements for melanin concentrating hormone (MCH) actions on teleost Poecilia reticulata melanophores.

Melanin concentrating hormone (MCH) is a cyclic heptadecapeptide, Asp-Thr-Met-Arg-Cys-Met-Val-Gly-Arg-Val-Tyr-Arg-Pro-Cys-Trp-Glu-Val, synthesized in the hypothalamus and released by the neurohypophysis of teleost fish. This hormone is a potent lightening agent of fish skin. This lightening results from the stimulation of a centripetal melanosome (melanin granule) migration to a perinuclear position within integumental melanophores. MCH and related fragment analogues, MCH5-17 and MCH1-14 were used to investigate the ionic requirements for receptor activation by MCH on dermal melanophores of the fish Poecilia reticulata. In calcium-free saline, the sensitivity of the melanophores to MCH and MCH1-14 increased, whereas the sensitivity of the cells to MCH5-17 decreased. Verapamil diminished the sensitivity to MCH5-17, but did not affect melanophore responses to MCH or MCH1-14. The melanosome aggregating response to MCH was not affected in the presence of tetrodotoxin or in sodium- or potassium-free (choline-substituted) saline. These results suggest that neither TTX-sensitive sodium channels nor extracellular sodium or potassium ions play a role in MCH-induced melanosome aggregation. It is known that MCH and MCH1-14 also exhibit MSH-like melanosome dispersion within melanophores, skin darkening activity on fish melanophores whereas MCH5-17 lacks this characteristic. Since the darkening activity of MCH and MCH1-14 requires calcium, these analogues exhibited a diminished lightening (MCH-like) activity in the presence of the divalent cation. In the absence of the N-terminal tetrapeptide sequence (necessary for the expression of MSH-like activity), a role for calcium on melanosome aggregation became evident. These results demonstrate a bifunctional role of calcium on melanosome movements.

Melanin concentrating hormone analogues: Contraction of the cyclic structure. II. Antagonist activity

Asp-Thr-Met-Arg-Cys-Met-Val-Gly-Arg-Val-Tyr-Arg-Pro-Cys-Trp-Glu-Val, melanin concentrating hormone (MCH), is a cyclic hormone possessing both MCH-like (melanin granule aggregating effect) and melanocyte stimulating hormone (MSH)-like (melanin granule dispersing effect) activities. Nine ring-contracted analogues were synthesized and characterized for their melanotropic activity on the fish ( Synbranchus marmoratus ) and frog ( Rana pipiens ) bioassays. In most cases, these analogues were totally devoid of MCH-like agonist activity, demonstrating the essential role of the disulfide bridge between residues 5 and 14 of the hormone. [Ala 5, Cys 10]MCH, for example, was totally devoid of MCH-like activity. This analogue, like α-MSH, however, antagonized the melanosome aggregating actions of MCH on fish melanocytes. The antagonistic activity of the analogue, like that of α-MSH, was Ca 2+-dependent. Evidence suggested that this antagonism of MCH activity was related to the intrinsic MSH-like activity of the analogue. These results suggest that MCH and α-MSH may be structurally and, therefore, evolutionarily related.

Melanocyte stimulating hormone and melanin concentrating hormone may be structurally and evolutionarily related

Two melanotropic peptides, melanin concentrating hormone (MCH) and α-melanocyte stimulating hormone (α-MSH), exert opposing actions on melanosome (melanin granule) movements within teleost pigment cells, melanocytes (melanophores). MCH stimulates melanosome aggregation to the cell center whereas α-MSH stimulates pigment organelle dispersion out into the dendritic processes of the melanocytes. The actions of α-MSH are dependent upon extracellular calcium (Ca 2+), whereas those of MCH are actually enhanced in the absence of the cation. At high concentrations (10 −5–10 −8 M) MCH also exhibits MSH-like activity (autoantagonism), an effect which is abolished in the absence of Ca 2+. Therefore, MCH exhibits MCH-like as well as MSH-like activity depending on the presence or absence of extracellular Ca 2+. An analogue of MCH, [Ala 5, Cys 10]MCH, has been synthesized which is totally devoid of MCH activity but still exhibits MSH-like activity. These results suggest that the two melanotropic peptides share some component of structural similarity and may be evolutionarily related.

Characterization of melanin concentrating hormone in teleost hypothalamus

Melanin concentrating hormone (MCH) is a heptadecapeptide isolated from chum salmon ( Oncorhynchus keta) pituitaries. The peptide has been isolated from whole brain extract at a low yield of 1.2 μg/1300 brains. MCH activity in the hypothalamus was characterised by in vitro scale bioassay and radioimmunoassay. Specificity of these assay systems was examined with neurotransmitters such as epinephrine, norepinephrine, and dopamine, hypothalamic hormones such as somatostatin, isotocin, Arg-vasotocin, oxytocin, and Arg-vasopressin, and salmon prolactin and its chymotryptic peptide or salmon PRL 176–187. Among them only salmon PRL 176–187 exhibited weak activities in both assays. The neurotransmitters were 10 4 to 10 5 times less potent than MCH in the bioassay. MCH concentrations in a pituitary and a hypothalamus were estimated as 5300 ± 750 ng (ca. 106 μg/g) and 48 ± 9.5 ng (ca. 1.6 μg/g), respectively, by radioimmunoassay. Lysyl endopeptidase digestion of the hypothalamic extract resulted in a significant increase of biological activity as well as of immunoreactivity. Gel filtration of the hypothalamic extract and subsequent enzymatic digestion revealed that the fractions at higher molecular weight were contributory to the increase in the activities.

Differential structural requirements for the MSH and MCH activities of melanin concentrating hormone

▪ melanin concentrating hormone (MCH), exhibits both melanin granule concentrating and dispersing (MSH-like) activities. Fragment analogues of MCH were synthesized as described herein and the melanotropic activities of the peptides were determined. In the frog ( Rana pipiens ) and lizard ( Anolis carolinensis ) skin bioassays, the 5–17 and 5–14 fragments of MCH were inactive (at concentrations of 10 −5M or less), whereas the 1–14 sequence exhibited minimal (about 10%) MSH-like activity compared to MCH, which, as reported previously, was about 600 times less active than α-MSH. In the teleost (fish) skin bioassay, the MCH 5–17 analogue was equipotent to MCH, whereas the 1–14 analogue was 10–30 times and the cyclic N- and C- terminal truncated analogue, MCH 5–14, was about 300 times less active than MCH. These results suggest that the N-terminal sequence is particularly critical to MSH-like activity in the tetrapod species studied, whereas other structural regions of MCH, particularly in the C-terminal, are more related to MCH activity in teleosts.