The role of the hypothalamic melanocortin system in behavioral appetitive processes.
Much evidence suggests that the hypothalamic melanocortin (MC) system plays an important role in the control of food intake. However, investigations of the potential behavioral mechanisms have been limited to measures of aversion. The purpose of the present experiment was to assess whether other behavioral consequences of administration of MC peptides were similar to those produced by 0- or 24-h food deprivation, respectively. Rats were first trained while food deprived that a tone predicted the delivery of peanut oil. They then received exposure to oil under food deprivation, satiation, intra-third-cerebroventricular (i3vt) infusion of MTII (a potent MC agonist) or SHU-9119 (a potent MC antagonist). All rats were then tested during extinction for levels of responding to the tone under food satiation. Previous results demonstrated that sated exposure reduces subsequent test responding to the tone. During the present extinction test, rats that received sated exposure exhibited reduced responding to the tone, relative to rats that received deprived exposure. Unlike satiation, rats that received exposure after MTII exhibited continued high levels of responding to the tone. Further, rats that received SHU-9119 exhibited a small reduction in responding. These data suggest that MTII and SHU-9119 do not influence intake via the same mechanisms as hunger and food satiation, respectively.
Benoit
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SC
Department of Psychiatry, University of Cincinnati, PO Box 670559, Cincinnati OH 45267-0559, USA. benoits@email.uc.edu
Tracy
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Air
E L
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Kinzig
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Seeley
R J
RJ
Davidson
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D000818:Animals; D001070:Appetitive Behavior / Q000187:drug effects / Q000502:physiology*; D004435:Eating / Q000187:drug effects / Q000502:physiology; D007031:Hypothalamus / Q000187:drug effects / Q000502:physiology*; D008297:Male; D009074:Melanocyte-Stimulating Hormones / Q000494:pharmacology; D009842:Oligopeptides / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D018043:Receptors, Corticotropin / Q000819:agonists / Q000037:antagonists & inhibitors / Q000502:physiology*; D044101:Receptors, Melanocortin; D020542:Third Ventricle / Q000187:drug effects / Q000502:physiology; D000521:alpha-MSH / Q000031:analogs & derivatives
D009842:Oligopeptides; D018043:Receptors, Corticotropin; D044101:Receptors, Melanocortin; C105974:acetyl-norleucyl(4)-(aspartyl(5)-histidyl(6)-phenylalanyl(7)-arginyl(8)-tryptophyl(9)-lysyl(10))cyclo-alpha-MSH(4-10)amide; C103272:SHU 9119; D000521:alpha-MSH; D009074:Melanocyte-Stimulating Hormones