Involvement of mu1 and mu2 opioid receptor subtypes in tail-pinch feeding in rats.
Tail-pinch feeding (TPF) in rats is decreased following general (naltrexone, NTX) and mu (Cys2-Tyr3-Orn5-Pen7-amide, CTOP) opioid antagonists, but not following kappa (nor-binaltorphamine. Nor-BNI) or delta (naltrindole, NTI) opioid antagonists. Because multiple mu (mu1 and mu2) and delta (delta 1 and delta 2) opioid receptor subtypes have been characterized, the present study evaluated whether TPF was differentially altered following ICV administration of general (NTX), mu (beta-funaltrexamine, B-FNA), mu1 (naloxonazine, NAZ), kappa (Nor-BNI), delta 1 ([D-Ala2, Leu5, Cys6]-enkephalin, DALCE) and delta 2 (NTI) opioid antagonists. Like the reversible mu antagonist CTOP, the irreversible mu antagonist B-FNA significantly and dose-dependently (1-20 micrograms) reduced TPF by up to 28%. In contrast, whereas NAZ (50 micrograms) reduced TPF by 32%, this effect was highly variable and failed to achieve significance. Neither NTX (5-10 mg/kg, SC), Nor-BNI (20 micrograms), DALCE (40 micrograms) nor NTI (20 micrograms) significantly altered TPF, suggesting that kappa, delta 1 and delta 2 opioid receptor subtypes were not involved. Because no antagonist altered the duration of food contact during tail pinch, it appears that the opioid effect modulates ingestive rather than activational mechanisms. The reliable inhibition of TPF by B-FNA (mu1 and mu2), together with the variable effect of naloxonazine (mu1), appears to implicate both mu binding sites in this response.
Department of Pharmacology, Mount Sinai School of Medicine, New York, NY 10029.
J E
JE
Koch
R J
RJ
Bodnar
D000818:Animals; D001143:Arousal / Q000187:drug effects / Q000502:physiology*; D016308:Enkephalin, Leucine-2-Alanine / Q000031:analogs & derivatives / Q000494:pharmacology; D005247:Feeding Behavior / Q000187:drug effects / Q000502:physiology*; D007211:Indoles / Q000494:pharmacology; D008297:Male; D009019:Morphinans / Q000494:pharmacology; D009270:Naloxone / Q000031:analogs & derivatives / Q000494:pharmacology; D009271:Naltrexone / Q000031:analogs & derivatives / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D009619:Nociceptors / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017450:Receptors, Opioid, mu / Q000145:classification / Q000187:drug effects / Q000502:physiology*
D007211:Indoles; D009019:Morphinans; D009292:Narcotic Antagonists; D017450:Receptors, Opioid, mu; C051843:binaltorphimine; C053821:enkephalin-Leu, Ala(2)-Cys(6)-; D009270:Naloxone; D009271:Naltrexone; D016308:Enkephalin, Leucine-2-Alanine; C024524:beta-funaltrexamine; C034643:naloxonazine; C055382:naltrindole