Reciprocal opioid-opioid interactions between the ventral tegmental area and nucleus accumbens regions in mediating μ, agonist-induced feeding in rats

Feeding elicited by the mu-selective agonist, [D-Ala(2), M-Phe(4), Gly-ol(5)]-encephalin administered into the nucleus accumbens is blocked by accumbal pre-treatment with mu, delta(1), delta(2) and kappa, but not mu(1) opioid antagonists. Correspondingly, mu-agonist-induced feeding elicited from the ventral tegmental area is blocked by ventral tegmental area pre-treatment with 1, and K, but not 8 opioid antagonists. A bi-directional opioid-opioid feeding interaction has been firmly established such that N.-agonist-induced feeding elicited from the ventral tegmental area is blocked by accumbal naltrexone, and that accumbal mu-agonist-induced feeding is blocked by naltrexone pre-treatment in the ventral tegmental area. To determine which opioid receptor subtypes mediate the regional bi-directional opioid-opioid feeding interactions between these two sites, the present study examined the dose-dependent ability of either general (naltrexone), mu (beta-funaltrexamine), kappa (nor-binaltorphamine) or delta (naltrindole) opioid antagonists administered into one site to block mu-agonist-induced feeding elicited from the other site. General, mu and kappa, but not delta opioid receptor antagonist pre-treatment in the ventral tegmental area dose-dependently reduced mu-agonist-induced feeding elicited from the nucleus accumbens. General, mu and delta, and to a lesser degree kappa, opioid receptor antagonist pre-treatment in the nucleus accumbens dose-dependently reduced mu-agonist-induced feeding elicited from the ventral tegmental area. Thus, multiple, but different opioid receptor subtypes are involved in mediating opioid-opioid feeding interactions between the nucleus accumbens and ventral tegmental area regions. (c) 2004 Elsevier Inc. All rights reserved.