Ontogenetic development of the diencephalic MCH neurons: a hypothalamic 'MCH area' hypothesis

The ontogeny of rat diencephalic melanin-concentrating hormone (MCH) neuron s has been analysed, using the bromodeoxyuridine method to determine the pe riod of birth of these neurons, and using in situ hybridization and immunoh istochemistry to study their chemical differentiation. The spatiotemporal p attern of MCH neuron generation is complex, although it is broadly laterome dial with a peak between embryonic days (E) 12 and E13. The first expressio n of the MCH gene has been detected on E13 in neurons in the presumptive la teral hypothalamic area. But the adult-like pattern was observed from E18. Medial-most MCH neurons express the peptide CART (cocaine-amphetamine-regul ated transcript) from E18, and the receptor neurokinin 3 (NK3) from between postnatal day (P) 0 and P5. These results are discussed and compared with data from the literature to better understand the organization of the 'MCH- containing area'.