title: Capsaicin-induced joint inflammation is not blocked by local anesthesia.
abstract: The purpose of this study was to evaluate the effect of local anesthetic blockade of afferent innervation on the development of capsaicin-induced edema in the rat temporomandibular joint (TMJ) region and on reflex jaw muscle activity. Under halothane anesthesia, 64 male Sprague-Dawley rats were prepared for monitoring of edema development by lateral movement of a needle overlying the left TMJ region and for acute recording of electromyographic activity in ipsilateral digastric and masseter muscles. A double-barrel catheter was inserted into the TMJ region for delivery of saline or 0.5% bupivacaine from 1 needle, followed with the injection of 1% capsaicin, 0.1% capsaicin, or vehicle control from the other needle 5 minutes later. Application of capsaicin into the saline pretreated TMJ region led to dose-dependent edema development and reflex jaw muscle activity; however, only 1% capsaicin solution resulted in significant tissue expansion and muscle activity when compared with the vehicle control. Pretreatment of the rat TMJ region with bupivacaine failed to inhibit capsaicin-induced edema development, although successful blockade of nerve conduction was confirmed with the absence of reflex jaw muscle activity. Capsaicin-induced edema of the rat TMJ region developed independent of axonal conduction, suggesting neurogenic inflammation may arise regardless of functional nerve conduction.
authors.affiliation: Faculty of Dentistry, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Michelle L Y
authors.initials: ML
authors.lastname: Tang
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Haas
authors.forename: James W
authors.initials: JW
authors.lastname: Hu
mesh_terms: D000704:Analysis of Variance; D000779:Anesthetics, Local / Q000494:pharmacology*; D000818:Animals; D002045:Bupivacaine / Q000494:pharmacology; D002211:Capsaicin / Q000008:administration & dosage / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004487:Edema / Q000139:chemically induced*; D004576:Electromyography; D007509:Irritants / Q000008:administration & dosage / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D008297:Male; D008406:Masseter Muscle / Q000187:drug effects; D009334:Neck Muscles / Q000187:drug effects; D009431:Neural Conduction / Q000187:drug effects; D020078:Neurogenic Inflammation / Q000139:chemically induced* / Q000503:physiopathology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012026:Reflex, Stretch / Q000187:drug effects; D013704:Temporomandibular Joint / Q000187:drug effects*
chemical_list: D000779:Anesthetics, Local; D007509:Irritants; D002211:Capsaicin; D002045:Bupivacaine