MELANIN-CONCENTRATING HORMONE (MCH) ANTAGONIZES THE EFFECTS OF ALPHA-MSH AND NEUROPEPTIDE E-I ON GROOMING AND LOCOMOTOR ACTIVITIES IN THE RAT

The intraventricular (ICV) administration of the neuropeptide melanocy te stimulating hormone (alpha-MSH) is known to elicit a series of beha viors in the rat which include excessive grooming and other motor acti vities. In bony fish, the pigmentary effects of a-MSH can be antagoniz ed by the neuropeptide melanin-concentrating hormone (MCH). We therefo re examined whether MCH or its sister peptide neuropeptide 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 elici t some responses of their own. Rats were injected ICV with either arti ficial cerebrospinal fluid, alpha-MSH, MCH, NEI, or with two peptides together, and behavioral responses were monitored over the next 65 min . The ICV injection of 1 mu g MSH significantly enhanced grooming beha vior. NEI at the same dose increased grooming, rearing, and locomotor activities. MCH alone had no behavioral effects but it annulled the be havioral responses induced by either alpha-MSH or NEI. alpha-MSH also antagonized the locomotor and rearing behavior induced by NEI. The phy siological significance of these observations is discussed. (C) 1997 E lsevier Science Inc.