title: Itch-scratch responses induced by opioids through central mu opioid receptors in mice.
abstract: We examined scratch-inducing effects of intracisternal, intrathecal and intradermal injections of morphine and some opioid agonists in mice. Intracisternal injection of morphine (3 nmol/animal) and the mu-receptor agonist [D-Ala(2), N-Me-Phe(4), Gly(5)-ol]enkephalin (DAMGO; 0.2 nmol/animal) elicited scratching of the face, with little effect on scratching of the trunk. Intracisternal injection of the delta-receptor agonist [D-Pen(2,5)]enkephalin (DPDPE) and the kappa-receptor agonist U50488 were without effects. Intrathecal injection of morphine (0.1-3 nmol/animal) produced a dose-dependent increase in body scratching, with little effects on face scratching. Face scratching induced by intrathecal morphine (3 nmol/animal) was almost abolished by subcutaneous pretreatment with naloxone (1 mg/kg). Intradermal injections of morphine (3-100 nmol/site), DAMGO (1-100 nmol/site), DPDPE (10 and 100 nmol/site) and U50488 (10-100 nmol/site) did not elicit scratching of the site of injection. Intradermal injection of histamine (100 nmol/site) induced the scratching in ICR, but not ddY, mice and serotonin (30 and 50 nmol/site) elicited the scratching in either strain of mice. The results suggest that opioids induce scratching, and probably itching, through central mu-opioid receptors in the mouse.
authors.affiliation: Department of Applied Pharmacology, Faculty of Pharmaceutical Sciences, Toyama Medical and Pharmaceutical University, Toyama, Japan. kuraisiy@ms.toyama-mpu.ac.jp
authors.forename: Y
authors.initials: Y
authors.lastname: Kuraishi
authors.forename: T
authors.initials: T
authors.lastname: Yamaguchi
authors.forename: T
authors.initials: T
authors.lastname: Miyamoto
mesh_terms: D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer / Q000494:pharmacology; D000701:Analgesics, Opioid / Q000494:pharmacology; D000818:Animals; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000494:pharmacology; D020881:Enkephalin, D-Penicillamine (2,5)- / Q000494:pharmacology; D005145:Face / Q000503:physiopathology; D006632:Histamine / Q000494:pharmacology; D007279:Injections, Subcutaneous; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D008815:Mice, Inbred Strains; D009020:Morphine / Q000494:pharmacology; D009294:Narcotics / Q000819:agonists / Q000494:pharmacology*; D011537:Pruritus / Q000139:chemically induced* / Q000503:physiopathology*; D017450:Receptors, Opioid, mu / Q000502:physiology*; D012701:Serotonin / Q000494:pharmacology; D012965:Sodium Chloride / Q000008:administration & dosage / Q000494:pharmacology; D013997:Time Factors
chemical_list: D000701:Analgesics, Opioid; D009294:Narcotics; D017450:Receptors, Opioid, mu; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D012701:Serotonin; D012965:Sodium Chloride; D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; D009020:Morphine; D006632:Histamine; D020881:Enkephalin, D-Penicillamine (2,5)-