Influence of TRPV-1 on thermal nociception in rats with temporomandibular joint persistent inflammation evaluated by the operant orofacial pain assessment device (OPAD)

Abstract

Orofacial pain has a high prevalence associated with debilitating disorders in modern society involving the neck, face, head and all intra-oral structures. In addition, temporomandibular joint (TMJ)-associated inflammation is considered to be one of the reasons for the pain reported by patients with temporomandibular disorders (TMD). To study orofacial pain mechanisms, although many animal models were development, pain assessment involves the use of tests originally developed for other regions of the body, therefore adapted tests to orofacial area. To overcome limitations and expand the knowledge in orofacial pain, the research group led by Dr. Robert M. Caudle, at the University of Florida validated and characterized an operant assessment paradigm in rats with both hot and cold stimuli as well mechanical stimuli. Nevertheless, the persistent inflammation of TMJ has not been evaluated by this operant orofacial pain assessment device (OPAD). It is noteworthy that persistent inflammation in the TMJ induced by Complete Freund Adjuvant (CFA) correlates anxiety like behavior and pain responses. Moreover, the OPAD is the first assay that correlates orofacial pain with psychological processes. The general aim of this study is to characterize the thermal orofacial sensitivity during development of TMJ using the operant behavior. In additional, we want evaluate the role of transient receptor potential vanilloid 1 (TRPV1) on nociception response of rats with TMJ persistent inflammation. Finally, we will evaluate the response of rats with TMJ inflammation with and without analgesic treatment. The experiments will be performed with hairless Sprague-Dawley rats (250-300g) with or not TMJ inflammation induced by CFA. The orofacial pain will be evaluated on the OPAD in the presence of a range of cold, neutral and hot stimuli. Resiniferatoxin (RTX) will be administered into TMJs prior CFA to lesion TRPV1-expressing neurons. And independet groups of rats will be treated or not with morphine or pregabalin to evaluate the nociceptive behavior on OPAD in rats with TMJ inflammation induced by CFA. (AU)