Excitatory amino acid receptor subtype agonists induce feeding in the nucleus accumbens shell in rats: opioid antagonist actions and interactions with mu-opioid agonists.

Administration of mu-opioid receptor subtype agonists into the nucleus accumbens shell elicits feeding which is dependent upon the normal function of mu-, delta- and kappa-opioid receptors, D(1) dopamine receptors and GABA(B) receptors in the nucleus accumbens shell for its full expression. Whereas the AMPA antagonist, DNQX administered into the nucleus accumbens shell elicits a transient, though intense feeding response, feeding is elicited by excitatory amino acid agonists administered into the lateral hypothalamus. The present study examined whether excitatory amino acid agonists elicited feeding following administration into the nucleus accumbens shell of rats, whether such feeding responses were altered by opioid antagonist pretreatment, and whether such feeding responses interacted with feeding elicited by mu-opioid agonists. Both AMPA (0.25-0.5 microg) and NMDA (1 microg) in the nucleus accumbens shell significantly and dose-dependently increased food intake over 4 h. Both feeding responses were blocked by naltrexone pretreatment in the nucleus accumbens shell. The mu-opioid agonist, [D-Ala(2),NMe-Phe(4),Gly-ol(5)]-enkephalin in the nucleus accumbens shell significantly increased food intake which was significantly enhanced by AMPA cotreatment. This enhanced feeding response was in turn blocked by pretreatment with either general or mu-selective opioid antagonists. In contrast, cotreatment of NMDA and the mu-opioid agonist in the nucleus accumbens shell elicited feeding which was significantly less than that elicited by either treatment alone. These data indicate the presence of important interactions between excitatory amino acid receptors and mu-opioid receptors in the nucleus accumbens shell in mediating feeding responses in nondeprived, ad libitum-fed rats.