Opioids in the nucleus of the solitary tract are involved in feeding in the rat

We evaluated the effect of selective opioid peptides and naltrexone on feeding when injected into the nucleus of the solitary tract (NTS). Doses of 0, 1, 2, 4, and 8 nmol of [D-Ala ²,N-Me-Phe ⁴,Gly ⁵-ol]enkephalin (DAMGO, μ-agonist), dynorphin A-(1-17) (DynA-(l-17), κ-agonist), and [D-Ser ²]leucine enkephalin-thr, (S-agonist) were injected into the NTS in satiated male rats, and food intake was measured at 1, 2, and 4 h. Only DAMGO significantly increased feeding above control levels at doses of 2, 4, and 8 nmol. Doses of 10 and 50 μg naltrexone in the NTS significantly decreased 18-h deprivation-induced feeding. These data suggest that NTS opioid receptors (primarily μ) may be involved in the regulation of feeding. [D-Ala ₂, N-Mc-Phe ⁴,Gly ⁵-ol]enkephalin; [D-Ser ²]leucine enkephalin-thr; dynorphin A-(1-17); naltrexone