title: Spinal delta 2-, but not delta 1-, mu-, or kappa-opioid receptors are involved in the tail-flick inhibition induced by beta-endorphin from nucleus raphe obscurus in the pentobarbital-anesthetized rat.
abstract: The antinociception induced by beta-endorphin given supraspinally has been previously demonstrated to be mediated by the release of [Met5]enkephalin acting on delta-opioid receptors in the spinal cord. The present study was designed to determine what type of opioid receptors in the spinal cord is involved in beta-endorphin-induced antinociception in the rat. Antinociception was induced by beta-endorphin (0.6 nmol) given into nucleus raphe obscurus and was assessed by the tail-flick test in pentobarbital-anesthesized rats. Naltriben (0.6-6.0 nmol), a selective delta 2-opioid receptor antagonist, given intrathecally dose-dependently attenuated beta-endorphin-induced inhibition of the tail-flick response. On the other hand, 7-benzylidene naltrexone (2.1-64.3 nmol), CTOP (D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2, 0.09-2.8 nmol), or nor-binaltorphimine (1.4-40.8 nmol), selective delta 1-, mu-, and kappa-opioid receptor antagonists, respectively, did not block beta-endorphin-induced antinociception. The results of present study in rats are consistent with previous experiments in mice indicating that spinal delta 2-, but not delta 1-, mu- or kappa-opioid receptors are involved in beta-endorphin-induced inhibition of the tail-flick response.
mesh_terms: D000595:Amino Acid Sequence; D000698:Analgesia; D000818:Animals; D001597:Benzylidene Compounds / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004744:Enkephalin, Methionine / Q000378:metabolism; D007276:Injections, Intraventricular; D007278:Injections, Spinal; D008297:Male; D008969:Molecular Sequence Data; D009271:Naltrexone / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000008:administration & dosage / Q000494:pharmacology; D010424:Pentobarbital / Q000008:administration & dosage / Q000494:pharmacology; D011903:Raphe Nuclei / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D017465:Receptors, Opioid, delta / Q000187:drug effects* / Q000378:metabolism; D017473:Receptors, Opioid, kappa / Q000187:drug effects* / Q000378:metabolism; D017450:Receptors, Opioid, mu / Q000187:drug effects* / Q000378:metabolism; D013004:Somatostatin / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000494:pharmacology; D013116:Spinal Cord / Q000187:drug effects / Q000378:metabolism; D013623:Tail; D001615:beta-Endorphin / Q000008:administration & dosage / Q000633:toxicity*
chemical_list: D001597:Benzylidene Compounds; D009292:Narcotic Antagonists; D017465:Receptors, Opioid, delta; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu; C049352:phenylalanyl-cyclo(cysteinyltyrosyl-tryptophyl-ornithyl-threonyl-penicillamine)threoninamide; C068868:naltrindole benzofuran; C077358:7-benzylidenenaltrexone; C051844:norbinaltorphimine; D013004:Somatostatin; D004744:Enkephalin, Methionine; D009271:Naltrexone; D001615:beta-Endorphin; D010424:Pentobarbital