title: Capsaicin prevents the hyperalgesia induced by peripheral group I mGluRs activation.
abstract: Group 1 metabotropic glutamate receptors (mGluRs) are expressed in peripheral and central neural tissues and involved in peripheral and central sensitization in various pain models. However, there are limited reports that activation of peripheral group I mGluRs could evoke pain. Furthermore, any behavioral evidences could not be found out, showing what kind of afferent fibers are involved in peripheral mGluRs-mediated hyperalgesia. This study was undertaken to clarify whether peripherally injected group I mGluRs agonists could induce pain-related behaviors and capsaicin-sensitive afferent fibers might be involved in the hyperalgesia. To assess pain sensitivity, mechanical threshold for paw withdrawal response (PWT) was measured and number of spontaneous flinching behavior was counted. Intraplantar injection of group I mGluR agonist, (RS)-3,5-dihydroxyphenylglycine (DHPG) and mGluR5 agonist, (RS)-2-chloro-5-hydroxyphenyglycine (CHPG) immediately induced pain-like behaviors, such as decrease of PWT and increased number of flinchings. These agonists-induced pain-like behaviors were blocked by group I mGluRs antagonist, (RS)-1-aminoindan-1,5-dicarboxylic acid (AIDA) and mGluR5 antagonist, 2-methyl-6-(phenylethynyl) pyridine hydrochloride (MPEP). Perineural pretreatment of 1% capsaicin solution significantly reduced pain-related behaviors induced by DHPG and CHPG, proposing that capsaicin-sensitive primary afferent fibers could be responsible for the hyperalgesia induced by activation of peripheral group I mGluRs. This study presents the first behavioral evidence that peripheral group I mGluRs activation could induce spontaneous as well as mechanical hyperalgesia and capsaicin-sensitive afferent fiber could be implicated the group I mGluR mediated hyperalgesia.
authors: Department of Physiology, College of Medicine, Hanyang University, Seoul 133-791, South Korea.
authors: Soo Suk
authors: SS
authors: Jung
authors: Ki Woon
authors: KW
authors: Sung
authors: Seo Eun
authors: SE
authors: Lee
authors: Hong Kee
authors: HK
authors: Shin
mesh_terms: D000344:Afferent Pathways; D000818:Animals; D002211:Capsaicin / Q000494:pharmacology*; D006930:Hyperalgesia / Q000378:metabolism / Q000503:physiopathology*; D008297:Male; D009412:Nerve Fibers / Q000187:drug effects / Q000502:physiology; D017288:Pain Threshold / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D018094:Receptors, Metabotropic Glutamate / Q000819:agonists* / Q000037:antagonists & inhibitors; D012584:Sciatic Nerve / Q000187:drug effects / Q000503:physiopathology; D014110:Touch
chemical_list: D018094:Receptors, Metabotropic Glutamate; D002211:Capsaicin