Melanin-concentrating hormone is a potent anorectic peptide regulated by food-deprivation and glucopenia in the rat

Changes in rat melanin-concentrating hormone and dynorphin messenger ribonucleic acids induced by food deprivation

Melanin-concentrating hormone (MCH) and dynorphin genes are expressed in two discrete neuron populations of the rat lateral hypothalamus. Their roles remain hypothetical in mammals. In order to analyse changes in MCH and dynorphin gene expression, a multiplex competitive semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) was developed to assay their mRNAs. This technique was used to examine MCH and dynorphin mRNA content in 24-h and 48-h food-deprived rats compared to controls. A two-fold induction of dynorphin mRNA by 24 h, followed by a sharp decrease at 48 h were observed. A moderate increase in MCH mRNA content was noticed by 24 h; 48 h of fasting restored the control levels.

The melanin-concentrating hormone gene in human: flanking region analysis, fine chromosome mapping, and tissue-specific expression

Genomic sequences encoding the human melanin-concentrating hormone (MCH) were isolated from a YAC library and subcloned in pUC vector using a novel E. coli transformation method. A 4.1-kb fragment encompassing approximately 1.0 kb of the 5'-end-flanking region, the three exons-two introns of the coding region and approximately 1.7 kb of the 3'-end-flanking region, was sequenced. Comparison with the rat MCH gene indicated strong conservation in the 5'-flanking region, in particular over the putative TATA box, CAAT box, GRE and AP-1 elements that could potentially regulate MCH gene expression. FISH with a fluorescent MCH genomic probe on human chromosomes and PCR analysis of a YAC panel mapped MCH to chromosome 12q23.1 in a region flanked by D12S1074 and D12S1030 markers. Expression of the MCH RNA species and pro-MCH-derived peptides (MCH and NEI) was investigated in human tissues by combining Northern blotting, RT-PCR, in situ hybridization, immunohistochemistry and RIA. In the human brain, MCH mRNA and MCH/NEI peptides were predominantely expressed in the lateral hypothalamus in agreement with the known distribution of MCH expression in rat. In addition, MCH gene products were detected in extra-hypothalamic sites, such as the pallidum, neocortex and cerebellum. In peripheral tissues, MCH mRNA was identified in several organs, including the thymus, brown adipose tissue, duodenum and testis. An additional shorter MCH gene transcript, likely the result of alternate splicing, was revealed in several brain areas and peripheral tissues. While only fully processed MCH and NEI were found in hypothalamus, a different peptide form, bearing MCH and NEI epitopes, was detected in peripheral organs. This represents the first evidence for differential processing of pro-MCH in mammals.

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.

Exploring the expression of the melanin-concentrating hormone messenger RNA in the rat lateral hypothalamus after goldthioglucose injection

Melanin-concentrating hormone (MCH) is expressed in a large neuronal population of the rat lateral hypothalamus. This area is known to be implicated in the regulation of thirst and hunger and to contain glucose-sensitive cells. In the present study, we investigated the effects of goldthioglucose (GTG), a toxic form of glucose, on the expression of the MCH gene in the rat lateral hypothalamus by immunocytochemistry, in situ hybridization and competitive RT-PCR. We observed that the MCH immunoreactivity and the level of MCH mRNA were not changed after intraperitoneal GTG injection (0.35 mg/g body weight). These results together with previous data suggest that the glucose-sensitive cells of the lateral hypothalamus are different from the MCH neurons and remain to be identified.

Immunocytochemical detection of the neurokinin B receptor (NK3) on melanin-concentrating hormone (MCH) neurons in rat brain

The presence of the neurokinin B receptor (NK3 receptor) in the rat lateral hypothalamus and the zona incerta was previously reported. The aim of the present study was to define its cellular localization in these areas. Investigations, coupling immunocytochemical and in situ hybridization techniques, focussed on two neuron populations: the melanin-concentrating hormone (MCH) neurons and a population of neurons recognized by an ovine prolactin antiserum (PRL-ir neurons). While PRL-ir neurons did not exhibit NK3 immunoreactivity, 57% +/- 6% of MCH neurons were strongly stained by the NK3 antiserum. These results suggest that neurokinin B is involved in the regulation of MCH neuron activity via the NK3 receptor; they provide new bases for further investigations on MCH role in the control of food and water intake.

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

The intraventricular (i.c.v.) administration of the neuropeptide melanocyte stimulating hormone (alpha-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 alpha-MSH can be antagonized by the neuropeptide melanin-concentrating hormone (MCH). We therefore examined whether MCH or its sister peptide neuro-peptide E-I (NEI), derived from the same precursor molecule, would modulate the effect of alpha-MSH on grooming and motor activity in the rat, or perhaps elicit some responses of their own. Rats were injected i.c.v. with either artificial cerebrospinal fluid, alpha-MSH, MCH, NEI, or with two peptides together, and behavioral responses were monitored over the next 65 min. The i.c.v. injection of 1 microgram 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 alpha-MSH or NEI. alpha-MSH also antagonized the locomotor and rearing behavior induced by NEI. The physiological significance of these observations is discussed.

Distribution of melanin-concentrating hormone (MCH)-like immunoreactivity in neurons of the diencephalon of sheep

An immunohistochemical study with an antiserum raised against salmon melanin concentrating-hormone has demonstrated the presence of numerous melanin concentrating-hormone-immunoreactive neurons in the lateral hypothalamic areas of the sheep. The pattern of distribution of these perikarya is similar to that of rodents and primates. In sheep, however, melanin concentrating-hormone-immunoreactive neurons appeared to form two gatherings: the first is situated ventromedially to the internal capsule and the second in the dorsolateral hypothalamus. In these areas, numerous immunostained perikarya are observed. Compared to the rats, labelled neurons extended more caudally in the ventral tegmental area and more rostrally above the optic chiasma. Compared to primates, these neurons are less numerous in the periventricular area. In our study, dense networks of melanin concentrating-hormone-immunoreactive varicose fibers were observed in the supramamillary nucleus, the lateral hypothalamus, the nucleus medialis thalami and nucleus reuniens and in the bed nucleus of the stria terminalis.