General, μ and κ opioid antagonists in the nucleus accumbens alter food intake under deprivation, glucoprivic and palatable conditions

Ventricular microinjection studies found that whereas μ (β-funaltrexamine, B-FNA), μ₁ (naloxonazine) and κ (nor-binaltorphamine, Nor-BNI) opioid receptor antagonists, but not δ antagonists, reduce deprivation-induced intake, κ and μ, but not μ₁ or δ antagonists reduce both 2-deoxy- d-glucose (2DG) hyperphagia and sucrose intake. Since opioid agonists stimulate spontaneous food intake in the accumbens, the present study examined whether administration of either naltrexone, B-FNA or Nor-BNI in the accumbens altered intake under deprivation (24 h), glucoprivic (2DG: 500 mg/kg, i.p.) or palatable sucrose (10%) conditions. Naloxonazine's effects in the accumbens were also evaluated for deprivation-induced intake. Deprivation-induced intake was significantly decreased over 4 h by naltrexone (5-20 μg, 44%), B-FNA (1-4 μg, 55%) and Nor-BNI (4 μg, 31%), but not naloxonazine (10 μg) in the accumbens. 2DG hyperphagia was significantly decreased by naltrexone (10-20 μg, 79%), B-FNA (1-4 μg, 100%) and Nor-BNI (1-4 μg, 75%) in the accumbens. Sucrose intake was significantly decreased by naltrexone (50 μg, 27%) and B-FNA (1-4 μg, 37%), but not Nor-BNI in the accumbens. These data suggest that μ receptors, and particularly the μ₂ binding site in the accumbens are responsile for the opioid modulation of these forms of intake in this nucleus, and that this control may be acting upon the amount of intake per se.