title: Increased expression of mu opioid receptors in animals susceptible to diet-induced obesity.
abstract: Stimulation of mu opioid receptors preferentially increases the intake of a high fat diet. In this paper we investigated whether there was a difference in the expression of mu opioid receptors between animals susceptible (Osborne-Mendel) or resistant (S5B/Pl) to obesity induced by eating a high fat diet. Immunohistochemical studies demonstrated that Osborne-Mendel rats eating a chow diet had an increased number of mu opioid receptors in the arcuate nucleus when compared to S5B/Pl rats. These immunohistochemical findings were supported by Real Time-PCR which demonstrated that the mRNA level of mu opioid receptors was also increased in the hypothalamus of Osborne-Mendel rats compared to S5B/Pl rats. Low doses of the mu opioid receptor agonist DAMGO [d-Ala(2)-N-Me-Phe(4)-Glycol(5)]-enkephalin administered to Osborne-Mendel rats caused a significant increase in the preference for a diet high in fat. The same doses of DAMGO switched the diet preference of S5B/Pl rats to high fat but did not significantly increase food intake. The combination of these findings suggests that the increased levels of hypothalamic mu opioid receptors in Osborne-Mendel rats may contribute to their preference for a diet high in fat and increase their susceptibility to becoming obese.
authors.affiliation: Pennington Biomedical Research Center, Dietary Obesity Laboratory, Baton Rouge, LA 70808, USA. barnesmj@pbrc.edu
authors.forename: Maria J
authors.initials: MJ
authors.lastname: Barnes
authors.forename: Gregory
authors.initials: G
authors.lastname: Holmes
authors.forename: Stefany D
authors.initials: SD
authors.lastname: Primeaux
authors.forename: David A
authors.initials: DA
authors.lastname: York
authors.forename: George A
authors.initials: GA
authors.lastname: Bray
mesh_terms: D000818:Animals; D004032:Diet; D020022:Genetic Predisposition to Disease; D008297:Male; D009765:Obesity / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D017450:Receptors, Opioid, mu / Q000096:biosynthesis / Q000235:genetics*
chemical_list: D017450:Receptors, Opioid, mu