Neuropeptide EI Research Articles

Melanin-concentrating hormone receptors (version 2019.4) in the IUPHAR/BPS Guide to Pharmacology Database

Melanin-concentrating hormone (MCH) receptors (provisional nomenclature as recommended by NC-IUPHAR [31]) are activated by an endogenous nonadecameric cyclic peptide identical in humans and rats (DFDMLRCMLGRVYRPCWQV; mammalian MCH) generated from a precursor (PMCH, P20382), which also produces neuropeptide EI and neuropeptide GE.

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

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

Chronic Loss of Melanin-Concentrating Hormone Affects Motivational Aspects of Feeding in the Rat

Current epidemic obesity levels apply great medical and financial pressure to the strenuous economy of obesity-prone cultures, and neuropeptides involved in body weight regulation are regarded as attractive targets for a possible treatment of obesity in humans. The lateral hypothalamus and the nucleus accumbens shell (AcbSh) form a hypothalamic-limbic neuropeptide feeding circuit mediated by Melanin-Concentrating Hormone (MCH). MCH promotes feeding behavior via MCH receptor-1 (MCH1R) in the AcbSh, although this relationship has not been fully characterized. Given the AcbSh mediates reinforcing properties of food, we hypothesized that MCH modulates motivational aspects of feeding.Here we show that chronic loss of the rat MCH-precursor Pmch decreased food intake predominantly via a reduction in meal size during rat development and reduced high-fat food-reinforced operant responding in adult rats. Moreover, acute AcbSh administration of Neuropeptide-GE and Neuropeptide-EI (NEI), both additional neuropeptides derived from Pmch, or chronic intracerebroventricular infusion of NEI, did not affect feeding behavior in adult pmch +/+ or pmch −/− rats. However, acute administration of MCH to the AcbSh of adult pmch −/− rats elevated feeding behavior towards wild type levels. Finally, adult pmch −/− rats showed increased ex vivo electrically evoked dopamine release and increased limbic dopamine transporter levels, indicating that chronic loss of Pmch in the rat affects the limbic dopamine system.Our findings support the MCH-MCH1R system as an amplifier of consummatory behavior, confirming this system as a possible target for the treatment of obesity. We propose that MCH-mediated signaling in the AcbSh positively mediates motivational aspects of feeding behavior. Thereby it provides a crucial signal by which hypothalamic neural circuits control energy balance and guide limbic brain areas to enhance motivational or incentive-related aspects of food consumption.

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

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

Neuropeptide glutamic-isoleucine (NEI) specifically stimulates the secretory activity of gonadotrophs in primary cultures of female rat pituitary cells

The neuropeptide EI (NEI) is derived from proMCH. It activates GnRH neurons, and has been shown to stimulate the LH release following intracerebroventricular administration in several experimental models. The aim of the present paper was to evaluate NEI actions on pituitary hormone secretion and cell morphology in vitro. Pituitary cells from female rats were treated with NEI for a wide range of concentrations (1–400 × 10 −8 M) and time periods (1–5 h). The media were collected and LH, FSH, PRL, and GH measured by RIA. The interaction between NEI (1, 10 and 100 × 10 −8 M) and GnRH (0.1 and 1 × 10 −9 M) was also tested. Pituitary cells were harvested for electron microscopy, and the immunogold immunocytochemistry of LH was assayed after 2 and 4 h of NEI incubation. NEI (100 × 10 −8 M) induced a significant LH secretion after 2 h of stimulus, reaching a maximum response 4 h later. A rapid and remarkable LH release was induced by NEI (400 × 10 −8 M) 1 h after stimulus, attaining its highest level at 2 h. However, PRL, GH and FSH were not affected. NEI provoked ultrastructural changes in the gonadotrophs, which showed accumulations of LH-immunoreactive granules near the plasma membrane and exocytotic images, while the other populations exhibited no changes. Although NEI (10 × 10 −8 M), caused no action when used alone, its co-incubation with GnRH (1 × 10 −9 M), promoted a slight but significant increase in LH. These results demonstrate that NEI acts at the pituitary level through a direct action on gonadotrophs, as well as through interaction with GnRH.

Anatomy, function and regulation of neuropeptide EI (NEI)

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

Melanin-concentrating hormone stimulates human growth hormone secretion: a novel effect of MCH on the hypothalamic-pituitary axis

Melanin-concentrating hormone (MCH), a 19-amino acid orexigenic (appetite-stimulating) hypothalamic peptide, is an important regulator of energy homeostasis. It is cleaved from its precursor prepro-MCH (ppMCH) along with several other neuropeptides whose roles are not fully defined. Because pituitary hormones such as growth hormone (GH), ACTH, and thyroid-stimulating hormone affect body weight and composition, appetite, insulin sensitivity, and lipoprotein metabolism, we investigated whether MCH exerts direct effects on the human pituitary to regulate energy balance using dispersed human fetal pituitaries (21-22 wk gestation) and cultured GH-secreting adenomas. We found that MCH receptor-1 (MCH-R1), but not MCH receptor-2, is expressed in both normal (fetal and adult) human pituitary tissues and in GH cell adenomas. MCH (10 nM) stimulated GH release from human fetal pituitary cultures by up to 62% during a 4-h incubation (P < 0.05). Interestingly, neuropeptide EI (10 nM), which is also cleaved from ppMCH, increased human GH secretion by up to 124% in fetal pituitaries. A milder, albeit significant, induction of GH secretion by MCH (20%) was seen in cultured GH-secreting pituitary adenomas. A comparable stimulation of GH secretion was seen when cultured mouse pituitary cells were treated with MCH. Treatment of cultured GH adenoma cells with MCH (100 nM) induced extracellular signal-regulated kinases 1 and 2 phosphorylation, suggesting activation of MCH-R1. In aggregate, these data suggest that MCH may regulate pituitary GH secretion and imply a potential cross-talk mechanism between appetite-regulating neuropeptides and pituitary hormones.

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

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

Effect of direct injection of melanin-concentrating hormone into the paraventricular nucleus: further evidence for a stimulatory role in the adrenal axis via SLC-1.

Melanin-concentrating hormone (MCH) is implicated in the control of a number of hormonal axes including the hypothalamic-pituitary adrenal (HPA) axis. Previous studies have shown that there is evidence for both a stimulatory and an inhibitory action on the HPA axis; therefore, we attempted to further characterize the effects of MCH on this axis. Intracerebroventricular injection of MCH increased circulating adrenocorticotropic hormone (ACTH) at 10 min post injection. Injection of MCH directly into the paraventricular nucleus (PVN) was found to increase both circulating ACTH and corticosterone 10 min after injection. Additionally, MCH was found to increase corticotropin-releasing factor (CRF) release from hypothalamic explants, and this effect was abolished by the specific SLC-1 antagonist SB-568849. Neuropeptide EI, a peptide from the same precursor as MCH was also found to increase CRF release from explants. These results suggest that MCH has a stimulatory role in the HPA axis via SLC-1, and that MCH exerts its effects predominantly through the PVN CRF neuronal populations

Melanin-concentrating hormone 1 receptor-deficient mice are lean, hyperactive, and hyperphagic and have altered metabolism

Melanin-concentrating hormone (MCH) is a cyclic 19-aa hypothalamic neuropeptide derived from a larger prohormone precursor of MCH (Pmch), which also encodes neuropeptide EI (NEI) and neuropeptide GE (NGE). Pmch-deficient (Pmch-/-) mice are lean, hypophagic, and have an increased metabolic rate. Transgenic mice overexpressing Pmch are hyperphagic and develop mild obesity. Consequently, MCH has been implicated in the regulation of energy homeostasis. The MCH 1 receptor (MCH1R) is one of two recently identified G protein-coupled receptors believed to be responsible for the actions of MCH. We evaluated the physiological role of MCH1R by generating MCH1R-deficient (Mch1r-/-) mice. Mch1r-/- mice have normal body weights, yet are lean and have reduced fat mass. Surprisingly, Mch1r-/- mice are hyperphagic when maintained on regular chow, and their leanness is a consequence of hyperactivity and altered metabolism. Consistent with the hyperactivity, Mch1r-/- mice are less susceptible to diet-induced obesity. Importantly, chronic central infusions of MCH induce hyperphagia and mild obesity in wild-type mice, but not in Mch1r-/- mice. We conclude that MCH1R is a physiologically relevant MCH receptor in mice that plays a role in energy homeostasis through multiple actions on locomotor activity, metabolism, appetite, and neuroendocrine function.

Melanin-concentrating hormone (MCH) suppresses thyroid stimulating hormone (TSH) release, in vivo and in vitro, via the hypothalamus and the pituitary.

Melanin-concentrating hormone (MCH) is an orexigenic peptide encoded in the pre-pro MCH gene. Targeted deletion of MCH causes a phenotype of hypophagia and leanness with an inappropriately high metabolic rate, suggesting a role for MCH in the control of energy balance. In order to further elucidate the mechanism by which MCH controls, energy expenditure, we have investigated the effects of MCH on the hypothalamic pituitary thyroid (HPT) axis. The thyroid axis is important in energy homeostasis and starvation leads to profound suppression of the HPT axis. MCH significantly reduces plasma TSH in vivo at 10 min (0.5 +/- 0.07 ng/ml, p < 0.05, n = 8) and 60 min (0.33 +/- 0.04 ng/ml, p < 0.01, n = 10) compared to saline (0.7 +/- 0.07 ng/ml and 0.69 +/- 0.07 ng/ml respectively) when administered intracerebroventricularly. Release of TRH form hypothalamic explants was significantly reduced in the presence of MCH production (7.1 +/- 0.99 fmol/explant to 2.3 +/- 0.4 fmol/explant p < 0.01, n = 18) and Neuropeptide EI (NEI) (8.47 +/- 1.28 fmol/explant to 4.6 +/- 1.13 p < 0.05, n = 16), a peptide, also encoded in the pre-pro-MCH gene. MCH was also shown to significantly reduce TRH stimulated TSH release from dispersed pituitary cell cultures (basal = 0.5 +/- 0.06 ng/ml, 100 nM TRH = 0.9 +/- 0.2 ng/ml, p < 0.05 0.1 nM MCH = 0.5 +/- 0.1 ng/ml, p < 0.05, 1 nM MCH = 0.3 +/- 0.03 ng/ml, p < 0.01, 10 nM MCH = 0.4 +/- 0.02 ng/ml, p < 0.01, 1000 nM MCH = 0.4 +/- 0.05 ng/ml, P < 0.01, n = 4), although basal release of TSH from these cultures was unaffected. These data suggest a possible role for MCH in the control of energy homeostasis via inhibition of the thyroid axis.

INTERACTION OF MELANIN-CONCENTRATING HORMONE (MCH), NEUROPEPTIDE E-I (NEI), NEUROPEPTIDE G-E (NGE), AND α-MSH WITH MELANOCORTIN AND MCH RECEPTORS ON MOUSE B16 MELANOMA CELLS

Melanin-concentrating hormone (MCH) and α-melanocyte-stimulating hormone (α-MSH) are known to exhibit mostly functionally antagonistic, but in some cases agonistic activities, e.g., in pigment cells and in the brain. Neuropeptide E-I (NEI) displays functional MCH-antagonist and MSH-agonist activity in different behavioral paradigms; the role of neuropeptide G-E (NGE) is not known. This study addressed the question of possible molecular interactions between α-MSH, MCH and the MCH-precursor-derived peptides NEI and NGE at the level of the pigment cell MCH receptor subtype (MCH-Rpc) and the different melanocortin (MC) receptors. Radioreceptor assays using [125I]MCH, [125I]α-MSH and [125I]NEI as radioligands and bioassays were performed with MC1-R-positive and MC1-R-negative mouse B16 melanoma cells and with COS cells expressing the different MC receptors. The IC50s of α-MSH and NEI or NGE for [125I]MCH displacement from mouse MCH-Rpc were 80-fold and, respectively, > 300-fold higher than that of MCH, and the IC50s for MCH and NEI or NGE for [125I]α-MSH displacement from mouse MC1-R were 50,000-fold and > 200,000-fold higher than that of α-MSH. No high-affinity binding sites for NEI were detected on B16 melanoma cells and there was no significant displacement of [125I]α-MSH by MCH, NEI or NGE with MC3-R, MC4-R and MC5-R expressed in COS cells. At concentrations of 100 nM to 10 μM, however, MCH, NEI and NGE induced cAMP formation and melanin synthesis which could be blocked by agouti protein or inhibitors of adenylate cyclase or protein kinase A. This shows that mammalian MCH-precursor-derived peptides may mimic MSH signalling via MC1-R activation at relatively high, but physiologically still relevant concentrations, as e.g. found in autocrine/paracrine signalling mechanisms.

Differential neuronal expression and projections of melanin-concentrating hormone (MCH) and MCH-gene-overprinted-polypeptide (MGOP) in the rat brain.

The rat melanin-concentrating hormone (MCH) gene may produce, through alternative splicing, either the precursor of MCH and neuropeptide EI, two neuropeptides coexpressed in the zona incerta (ZI) and lateral hypothalamus (LHA), or a putative protein we named previously MCH-gene-overprinted-polypeptide (MGOP). First, we investigated the distribution and relative expression of MCH and MGOP mRNA in the rat brain by Northern blotting, RT-PCR and in situ hybridization. MGOP gene transcripts were detected mainly in the hypothalamus only by RT-PCR. Second, different antisera were raised toward the C-terminus of MGOP and used to identify the translational products. In the rat brain, no MGOP-processed peptide could be detected based on RP-HPLC coupled to specific RIA. A polypeptide of 14 kDa was found in the secretory pathway of transfected monkey COS7 cells expressing recombinant MGOP. In the rat hypothalamus, a specific protein of 12 kDa was identified by Western blot analysis. Finally, distribution of MGOP-immunoreactivity (IR) was investigated in the rat brain. Colocalization studies demonstrated that 98% of the MGOP-expressing perikarya in ZI/LHA also synthesized MCH. In addition, numerous, strongly stained MGOP-containing neurons were encountered in the hypothalamic periventricular nucleus. Perikarya labelled with MGOP antiserum were also found scattered in the cortex, caudate putamen, amygdala and lateral septal nucleus. MCH was not detected in these MGOP-containing neurons. Strikingly, dense staining of terminals was observed with MGOP antiserum but not with MCH antibodies in the suprachiasmatic, ventromedial and arcuate nuclei, and also in the external layer of the median eminence. These results demonstrated that MGOP and MCH-IR overlapped in LHA/ZI but displayed a differential distribution in other areas. Based on this cerebral distribution, MGOP may act as a new secreted protein in regulating many neuroendocrine functions, such as nursing, feeding and growth control in associated behavioural components.

17β-Estradiol regulation of melanin-concentrating hormone and neuropeptide-E-I contents in cynomolgus monkeys: a preliminary study

Melanin-concentrating hormone (MCH) and neuropeptide-E-I (NEI) regulate several behaviors and neuroendocrine functions in rats. Possible influence of these peptides on sexual behavior and reproduction in mammals other than rodents prompted us to investigate: 1) The sites of synthesis of MCH and NEI in the brain of a non-human primate ( M. fascicularis); 2) The effect of 17β-estradiol (E 2) benzoate (E 2B) on pro-MCH-derived peptide concentrations in the hypothalamus of the ovariectomized (OVX) cynomolgus monkeys ( M. fascicularis). Expression of MCH mRNA and peptides was examined by Northern blotting, RT-PCR and RP-HPLC/RIA. Our results demonstrate that the MCH gene is predominantly expressed in hypothalamus of macaque. E 2B exposure of OVX monkeys provoked parallel phasic variations in the MCH-immunoreactivity (IR) and NEI-IR. NEI-IR and to a lesser extent MCH-IR, showed a transient increase (associated with the estradiol peak) at 30 h with a final rise of both MCH-IR and NEI-IR observed at the time (72 h post E 2B) of the luteinizing hormone (LH) surge. RP-HPLC analysis of peptide extracts revealed the presence, in addition to mature MCH and NEI, of different MCH-IR and NEI-IR forms in the hypothalami of control and E 2B-treated monkeys. Taken together, our results indicated that hypothalamic MCH and NEI contents are regulated after E 2B treatment and they suggest the possible involvement of these peptides in the regulation of the pre-ovulatory midcycle LH surge in primates.

Cellular Localization and Role of Prohormone Convertases in the Processing of Pro-melanin Concentrating Hormone in Mammals

Melanin concentrating hormone (MCH) and neuropeptide EI (NEI) are two peptides produced from the same precursor in mammals, by cleavage at the Arg145-Arg146 site and the Lys129-Arg130 site, respectively. We performed co-localization studies to reveal simultaneously the expression of MCH mRNA and proconvertases (PCs) such as PC1/3 or PC2. In the rat hypothalamus, PC2 was present in all MCH neurons, and PC1/3 was present in about 15-20% of these cells. PC1/3 or PC2 was not found in MCH-positive cells in the spleen. In GH4C1 cells co-infected with vaccinia virus (VV):pro-MCH along with VV:furin, PACE4, PC1/3, PC2, PC5/6A, PC5/6B, or PC7, we observed only efficient cleavage at the Arg145-Arg146 site to generate mature MCH. Co-expression of pro-MCH together with PC2 and 7B2 resulted in very weak processing to NEI. Comparison of pro-MCH processing patterns in PC1/3- or PC2-transfected PC12 cells showed that PC2 but not PC1/3 generated NEI. Finally, we analyzed the pattern of pro-MCH processing in PC2 null mice. In the brain of homozygotic mutants, the production of mature NEI was dramatically reduced. In contrast, MCH content was increased in the hypothalamus of PC2 null mice. In the spleen, a single large MCH-containing peptide was identified in both wild type and PC2 null mice. Together, our data suggest that pro-MCH is processed differently in the brain and in peripheral organs of mammals. PC2 is the key enzyme that produces NEI, whereas several PCs may cleave at the Arg145-Arg146 site to generate MCH in neuronal cell types.

Melanin-concentrating hormone and neuropeptide EI projections from the lateral hypothalamic area and zona incerta to the medial septal nucleus and spinal cord: a study using multiple neuronal tracers

The projection pathways of neurons containing melanin-concentrating hormone (MCH) and neuropeptide EI (NEI), two peptides colocalized in the lateral hypothalamic area (LHA) of the rat, were mapped using the retrogradely transported fluorescent dyes, true blue (TB) and diamidino yellow (DY). TB and DY were injected into the medial septum/diagonal band complex (MS/DBC) and the thoracic level of the spinal cord (SpCd), respectively. Brains from rats receiving only one or both tracer injections were immunohistochemically stained for MCH in the spinal cord and NEI in the forebrain. In the MS/DBC, NEI-immunoreactive (-ir) fibers are concentrated in the MS and in the vertical and horizontal limbs of the DBC. In the SpCd, MCH-ir fibers are concentrated primarily in lamina X. Of the diencephalic NEI-ir neurons, 37.15% project to the MS/DBC and reside in the rostromedial zona incerta (ZIm), in the LHA t and LHA p, and in the perifornical region. Of the diencephalic MCH-ir neurons, 20.2% project to the SpCd and reside in the LHA t and LHA p. In addition, 2.2% of the MCH-ir cells and 8.7% of the NEI-ir cells in the hypothalamus were labeled with both retrograde tracers and thus project to both the MS/DBC and SpCd. These dual projection neurons are located mainly in the LHA t and LHA p. Anterograde injections of the tracer Phaseolus vulgaris leucoagglutinin into the LHA t and ZIm corroborated our findings in the retrograde studies. Potential autonomic and behavioral roles of the NEI and MCH systems in the MS/DBC and the SpCd are discussed.

Behavioral effects of neuropeptide E-I (NEI) in the female rat: interactions with α-MSH, MCH and dopamine

The behavioral and neurochemical effects of NEI, and its interaction with α-MSH or MCH were investigated in the ventromedial nucleus (VMN) and medial preoptic area (MPOA) in female rats (bilateral administration, 100 ng in 0.5 μl/side). NEI in the VMN (but not in the MPOA) stimulated exploratory behavior, increased anxiety and reduced dopamine and DOPAC release. The behavioral effects were antagonized by α-MSH. NEI stimulated female sexual receptivity in the MPOA. In the VMN, NEI did not have any effect on sexual activity, but partially antagonized the stimulatory effect of MCH. These results show that NEI in the hypothalamus participates in the regulation of behavior, possibly through dopaminergic mediation.

Study of the origins of melanin-concentrating hormone and neuropeptide EI immunoreactive projections to the periaqueductal gray matter

Previous studies have described the distribution of melanin-concentrating hormone (MCH) and neuropeptide EI (NEI) in the rat central nervous system (CNS), and revealed this peptidergic system to be primarily localized in neurons within the lateral hypothalamic area (LHA) and zona incerta (ZI). Moreover, an extensive MCH- and NEI-immunoreactive (ir) fiber distribution has been described throughout the CNS, including a dense innervation within the periaqueductal gray matter (PAG). MCH and NEI have become important markers for the LHA, which harbors a variety of neuronal types as well as the medial forebrain bundle, a complex system of fibers which extends rostrocaudally throughout this area. In the present study, the projection patterns of MCH- and NEI-ir fibers within the PAG were characterized using a diamino benzidine immunoperoxidase procedure to localize each of these peptides in normal rat brain sections. MCH- and NEI-ir fibers were seen coursing through all of its subdivisions the entire length of the PAG, with a more condensed number of fibers in the periaqueductal medial zone. The primary origin(s) of these PAG afferents were determined in combined retrograde tracing immunofluorescent studies in which true blue (TB) was injected into various subdivisions of the PAG. TB-filled MCH-ir neurons were identified mainly in the rostral portion of the medial ZI (ZIm) and in the tuberal LHA (LHAt). Studies confirming this MCH-ir projection in which anterograde tracer ( Phaseolus vulgaris leucoagglutinin) was injected into various regions in and around the LHA and ZI revealed a distinction in the PAG projections arising from these nuclei. ZIm injections resulted in labeled fibers mainly within the rostral dorsomedial and dorsolateral regions of the PAG, whereas injections in the LHAt revealed an innervation at intermediate and caudal levels in the ventrolateral region. Since the MCH and NEI fiber distribution patterns in the PAG are identical, this would suggest that these peptides are colocalized within the hypothalamus. Sequential immunofluorescent staining for MCH and NEI on tissue from rats who had received TB injections into the PAG confirmed this, and revealed that approximately 15% of all tracer-filled neurons in the LHA and ZI were both MCH- and NEI-ir. In fact, the vast majority of MCH-ir neurons within these regions also colocalize with NEI. Therefore, the MCH/NEI projection patterns within the PAG arise from two major sources: the ZIm which supplies afferents via a medial pathway that enters the PAG dorsally at rostral levels, and a pathway originating in the LHA that enters the PAG ventrally at more caudal levels. The ZIm and LHA are believed to be the primary, if not the only, sources of MCH and NEI projections to the PAG.

Melanin-Concentrating Hormone (MCH) Antagonizes the Effects of α-MSH and Neuropeptide E-I on Grooming and Locomotor Activities in the Rat

Sanchez, M., B. I. Baker and M. Celis. Melanin-concentrating hormone (MCH) antagonizes the effects of α-MSH and neuropeptide E-I on grooming and locomotor activities in the rat. Peptides 18(3) 393–396, 1997.—The intraventricular (ICV) administration of the neuropeptide melanocyte stimulating hormone (α-MSH) is known to elicit a series of behaviors in the rat which include excessive grooming and other motor activities. In bony fish, the pigmentary effects of α-MSH can be antagonized by the neuropeptide melanin-concentrating hormone (MCH). We therefore examined whether MCH or its sister peptide neuropeptide E-I (NEI), derived from the same precursor molecule, would modulate the effect of α-MSH on grooming and motor activity in the rat, or perhaps elicit some responses of their own. Rats were injected ICV with either artificial cerebrospinal fluid, α-MSH, MCH, NEI, or with two peptides together, and behavioral responses were monitored over the next 65 min. The ICV injection of 1 μg MSH significantly enhanced grooming behavior. NEI at the same dose increased grooming, rearing, and locomotor activities. MCH alone had no behavioral effects but it annulled the behavioral responses induced by either α-MSH or NEI. α-MSH also antagonized the locomotor and rearing behavior induced by NEI. The physiological significance of these observations is discussed.

Diuretic and natriuretic actions of melanin concentrating hormone in conscious sheep.

Melanin concentrating hormone (MCH) is a 19 amino-acid peptide expressed in high concentrations within the dorso-lateral hypothalamus of rats, sheep and man. MCH regulates skin colour and ACTH release in teleost fish, however, its physiological relevance in mammals is unclear. The present study examined the cardiovascular and metabolic actions of intracerebroventricular (i.c.v.) infusion of MCH, and the pro-MCH derived peptide Neuropeptide-E-I (NEI), in conscious, chronically instrumented sheep. Human MCH (1-19) or NEI (1-13) was infused i.c.v. for 24 h into 6 sheep, and measurements were made every 10 min of arterial pressure, heart rate, cardiac output, stroke volume and peripheral blood flow/conductance. Recordings of water intake (H2Oin), urine volume (Uv), urinary Na (UNaV) and K excretion (UKV) were made, as well as hematocrit, plasma Na, K, osmolality, protein, glucose, ACTH, vasopressin, renin, endothelin, ANF, cortisol and aldosterone concentrations. After 24 h of infusion at 10 microg/h, MCH produced a significant increase in Uv from 0.8 +/- 0.2 to 1.4 +/- 0.3 l/day, together with an increase in UNaV from 56 +/- 8 to 107 +/- 14 mmol/day, and in UKV from 202 +/- 18 to 369 +/- 38 mmol/day. H2Oin was unchanged. Similar renal changes were observed during i.c.v. infusion of NEI. There was no change in any cardiovascular parameter, although hematocrit showed a large decrease with infusion of both peptides after 24 h infusion. Plasma osmolality increased from 291 +/- 1 to 295 +/- 1 mOsm/kg during MCH infusion, whereas total protein and plasma Na and K were unchanged. MCH increased plasma glucose from 3.4 +/- 0.2 to 3.8 +/- 0.2 mmol/l. Plasma aldosterone exhibited a 30-40% decrease following MCH or NEI infusion, whereas all other plasma concentrations remained unchanged. This study has shown that i.c.v. infusion of MCH or NEI can produce diuretic, natriuretic and kaliuretic changes in conscious sheep, triggered by a possible increase in plasma volume as indicated by the changes in hematocrit. These results, together with anatomical data reporting the presence of MCH/NEI in fluid regulatory areas of the brain, indicate that MCH/NEI may be an important peptide involved in the central control of fluid homeostasis in mammals.