title: Naloxone does not antagonize the anesthetic-induced depression of nociceptor-driven spinal cord response in spinal cats.
abstract: The effects of several anaesthetics on spinal cord nociceptive neural mechanisms and their interactions with the opiate antagonist, naloxone, were studied in acute, spinal cord transected cats. Intra-arterial injection of bradykinin was used as the noxious test stimulus. Spontaneous activity and the neural response induced by bradykinin were recorded by the multi-unit activity technique in the lateral funiculus of the spinal cord. Naloxone, 0.1 or 2.0 mg/kg i.v. had little effect on the bradykinin-induced response, but enhanced the spontaneous firing of the lateral funiculus significantly. Fentanyl, 30 micrograms/kg i.v., depressed both the bradykinin-induced response and spontaneous firing. These effects of fentanyl were antagonized completely by naloxone, 0.1 mg/kg i.v. Nitrous oxide, thiamylal, halothane and ether depressed the bradykinin-induced response considerably, but it was not antagonized by naloxone, 0.1-2.0 mg/kg i.v. Enflurane had little effect on the bradykinin-induced response. The effects of these anesthetics on spontaneous firing were divergent: nitrous oxide enhanced it while other drugs depressed it, to various degrees. All these data suggest that the neural and/or neurochemical mechanisms of anesthetic-induced analgesia differ from mechanisms related to opioids.
mesh_terms: D000777:Anesthetics / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D000818:Animals; D002415:Cats; D004737:Enflurane / Q000494:pharmacology; D004986:Ether / Q000494:pharmacology; D005260:Female; D005283:Fentanyl / Q000494:pharmacology; D006221:Halothane / Q000494:pharmacology; D008297:Male; D009270:Naloxone / Q000494:pharmacology*; D009609:Nitrous Oxide / Q000494:pharmacology; D009619:Nociceptors / Q000187:drug effects*; D011957:Receptors, Opioid / Q000187:drug effects*; D013116:Spinal Cord / Q000187:drug effects*; D013840:Thiamylal / Q000494:pharmacology
chemical_list: D000777:Anesthetics; D011957:Receptors, Opioid; D013840:Thiamylal; D004986:Ether; D009270:Naloxone; D004737:Enflurane; D009609:Nitrous Oxide; D005283:Fentanyl; D006221:Halothane