SOMATOSENSORY SYSTEMS, PAINMorphine inhibits herpetic allodynia through μ-opioid receptors induced in Aβ-fiber neuronsSasaki, Atsushia; Nakashima, Yasutakaa; Takasaki, Ichiroc; Andoh, Tsugunobua; Shiraki, Kimiyasub; Kuraishi, Yasushia dAuthor Information Departments of aApplied Pharmacology bVirology, Graduate School of Medicine and Pharmaceutical Sciences cDivision of Molecular Genetics Research, Life Science Research Center d21st Century COE Program, University of Toyama, Toyama, Japan Correspondence to Dr Yasushi Kuraishi, Department of Applied Pharmacology, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, 2630 Sugitani, Toyama 930-0194, Japan Tel: +81 76 434 7510; fax: +81 76 434 5045; e-mail: [email protected] Received 15 March 2008 accepted 1 April 2008 NeuroReport: June 11, 2008 - Volume 19 - Issue 9 - p 975-979 doi: 10.1097/WNR.0b013e328302f123 Buy Metrics Abstract Peripheral action of μ-opioid receptor agonist inhibits mechanical allodynia in mice with herpetic pain. Mechanical allodynia is mainly mediated by Aβ fibers, whereas μ-opioid receptors are present in C and Aδ fibers. This study was conducted to address this dis-crepancy. Neonatal capsaicin treatment, which almost abolished aversive response to capsaicin, did not affect herpetic allodynia and antiallodynic effect of local injection of morphine. Although μ-opioid receptor was chiefly expressed in small-sized and medium-sized sensory neurons in naive mice, it was induced in large sensory neurons in mice with herpetic pain. Viral propagation in the sensory ganglion may induce μ-opioid receptor expression in Aβ fibers, which may be responsible for the inhibitory action of local opioids on mechanical allodynia in mice with herpetic pain. © 2008 Lippincott Williams & Wilkins, Inc.