Interrelationships between μ opioid and melanocortin receptors in mediating food intake in rats

The present study examined the interrelationships between feeding responses produced by g opioid receptor agonists and melanocortin-3 or 4 (MC-3/4) receptor antagonists. Feeding induced by the g-sensitive opioid peptide, beta-endorphin (betaEND, 10 mug, icv) was significantly and dose-dependently reduced by pretreatment with the MC-3/4 receptor agonist, melanotan-II (MTII 0.01-10 nmol, icv). Moreover, the selective p opioid antagonist, beta-funaltrexamine (betaFNA: 2-20 mug, icv), significantly and dose-dependently reduced feeding and weight gain elicited by the potent MC-3/4 receptor antagonist, SHU-9119 (0.5 nmol, icv), especially at those intake periods (24-48 h) when SHU-9119 produced maximal ingestive effects. These data extend previous findings demonstrating interactions between opioid and melanocortin receptors in the mediation of food intake. (C) 2003 Elsevier B.V. All rights reserved.