title: Involvement of central mu-opioid system in the scratching behavior in mice, and the suppression of it by the activation of kappa-opioid system.
abstract: The role of central mu- and kappa-opioid receptors in the regulation of itch sensation was examined using pruritogen-induced mouse scratching behavior model. Intracerebroventricular administration of beta-funaltrexamine, a selective mu-opioid receptor antagonist, inhibited the scratching behavior induced by intradermal substance P, but subcutaneous administration of beta-funaltrexamine did not. Similarly, the scratching inhibitory activity of subcutaneously administered TRK-820, (-)-17-(cyclopropylmethyl)-3, 14beta-dihydroxy-4, 5alpha-epoxy-6beta-[N-methyl-trans-3-(3-furyl) acrylamido] morphinan hydrochloride, a kappa-opioid receptor agonist, was antagonized by intracerebroventricular administration of nor-binaltorphimine (10 microg/site), a kappa-opioid receptor antagonist, but was not by subcutaneous administration of nor-binaltorphimine. In addition, the scratching induced by the direct activation of central mu-opioid receptor by intracisternal morphine was significantly and dose-dependently inhibited by subcutaneous administration of TRK-820. Taken all together, it is suggested that the central mu-opioid receptors play a role in the processing of itch sensation, and the activation of central kappa-opioid receptors antagonize the central mu-opioid receptor mediated itch processing, thereby suppressing itch sensation.
mesh_terms: D000818:Animals; D000982:Antipruritics / Q000494:pharmacology; D001522:Behavior, Animal; D007276:Injections, Intraventricular; D007279:Injections, Subcutaneous; D007665:Ketotifen / Q000494:pharmacology; D008297:Male; D051379:Mice; D009019:Morphinans / Q000494:pharmacology; D009020:Morphine; D009043:Motor Activity / Q000187:drug effects; D009271:Naltrexone / Q000031:analogs & derivatives* / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D011537:Pruritus / Q000139:chemically induced / Q000503:physiopathology* / Q000523:psychology; D017473:Receptors, Opioid, kappa / Q000819:agonists*; D017450:Receptors, Opioid, mu / Q000819:agonists / Q000037:antagonists & inhibitors / Q000502:physiology*; D013141:Spiro Compounds / Q000494:pharmacology; D013373:Substance P
chemical_list: D000982:Antipruritics; D009019:Morphinans; D009292:Narcotic Antagonists; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu; D013141:Spiro Compounds; C111212:TRK 820; D013373:Substance P; C051844:norbinaltorphimine; D009271:Naltrexone; C024524:beta-funaltrexamine; D009020:Morphine; D007665:Ketotifen