Melanin-concentrating hormone is the cognate ligand for the orphan G-protein-coupled receptor SLC-1.

The underlying causes of obesity are poorly understood but probably involve complex interactions between many neurotransmitter and neuropeptide systems involved in the regulation of food intake and energy balance. Three pieces of evidence indicate that the neuropeptide melanin-concentrating hormone (MCH) is an important component of this system. First, MCH stimulates feeding when injected directly into rat brains; second, the messenger RNA for the MCH precursor is upregulated in the hypothalamus of genetically obese mice and in fasted animals; and third, mice lacking MCH eat less and are lean. MCH antagonists might, therefore, provide a treatment for obesity. However, the development of such molecules has been hampered because the identity of the MCH receptor has been unknown until now. Here we show that the 353-amino-acid human orphan G-protein-coupled receptor SLC-1 expressed in HEK293 cells binds MCH with sub-nanomolar affinity, and is stimulated by MCH to mobilize intracellular Ca2+ and reduce forskolin-elevated cyclic AMP levels. We also show that SLC-1 messenger RNA and protein is expressed in the ventromedial and dorsomedial nuclei of the hypothalamus, consistent with a role for SLC-1 in mediating the effects of MCH on feeding.

Rat melanin-concentrating hormone messenger ribonucleic acid expression: marked changes during development and after stress and glucocorticoid stimuli.

Melanin-concentrating hormone (MCH) is a cyclic neuropeptide first isolated from fish and rats. MCH may be involved in the control of the hypothalamic-pituitary-adrenocortical axis and, more generally, of specific goal-oriented behaviors and homeostatic functions in mammals. In this paper we examine 1) the cellular distribution of MCH gene transcripts in the rat central nervous system, 2) the changes in neuronal expression of MCH mRNA during rat development, and 3) the effects of stress and hormonal stimuli on rat MCH (rMCH) gene activity. Northern blot analysis and in situ hybridization histochemistry show that mature rMCH mRNA (1.0 kilobase) is very abundant in the zona incerta and the dorsolateral hypothalamus. While this is in agreement with previous peptide mapping by immunohistochemical techniques, a surprising new result is that a few clusters of rMCH mRNA-containing cells are found outside the hypothalamus, in the olfactory tubercle and the pontine tegmentum. Developmentally, rMCH mRNA is detected on embryonic day 18; its level increases gradually during early postnatal life and rises abruptly at weaning to reach a constant value in adult rats. In addition, striking variations in rMCH mRNA length occur during postnatal development and are found to be variations in the polyadenylate tail. Interestingly, this structural modification appears to be independent of the increase in rMCH mRNA levels. The regulation of rMCH mRNA expression by glucocorticoids and chronic stress is examined by Northern blot analysis. Chronic intermittent footshock stress causes a 58% or 29% decrease in rMCH mRNA content in the whole hypothalamus after a 1- or 3-day regimen, respectively. In contrast, the rMCH mRNA level returns to normal after a 7-day regimen. Two weeks after adrenalectomy (ADX) the whole hypothalamus rMCH mRNA content decreases 2.5-fold, but rises close to the control value 3 weeks after ADX. Dexamethasone administration 2 weeks after ADX not only reverses the fall in rMCH mRNA, it even provokes a slight increase (123% of control). No change in rMCH mRNA length is observed after chronic stress or ADX and dexamethasone injection. These results provide evidence for a negative regulation of rMCH gene expression by stress and suggest a major role for glucocorticoids in a positive feedback control of rMCH gene activity.