TRPV1 Modulation during Craniofacial Neuropathy and its Contribution to Chronic Pain

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Project Summary Maladies such as trigeminal neuralgia are of neuropathic origin and lead to chronic pain. The detailed processes of increased nociceptive signaling leading to chronic pain are obscure. Recently a novel role for the transient receptor potential vanilloid-1 (TRPV1) has been demonstrated for mechanical hyperalgesia (excessive pain response), using a nerve-injury model for chronic orofacial pain. The study provides evidence for increased response of TRPV1 at central nociceptive terminals when activated (sensitization). Its selective inhibition alleviated mechanical hyperalgesia acutely. The sensitization was shown to be facilitated by serotonin, yet the means by which TRPV1 becomes sensitized is undetermined. Furthermore, during nerve constriction injury TRPV1 expression is reportedly increased. The functional sensitivity (and relevance) of this supplementary TRPV1 has yet to be evaluated in the trigeminal sensory system. The goal of this study is to clarify the detailed cellular and molecular mechanisms whereby TRPV1 contributes to craniofacial neuropathic pain. We hypothesize chronic pain following infraorbital nerve-chronic constriction injury (ION-CCI) is associated with plastic changes in expression or function of TRPV1 in trigeminal nociceptors. This hypothesis will be tested by multidisciplinary approaches as outlined in three aims. In aim 1, we will assess the role of TRPV1 in development and maintenance of craniofacial neuropathic pain. In aim 2, we will determine neurochemical and functional properties of TRPV1-expressing nociceptors in trigeminal ganglia following craniofacial neuropathy. In aim 3, we will determine the contribution of TRPV1 phosphorylation to chronic pain following craniofacial neuropathy. Our study offers a thorough assessment for the contribution of TRPV1 to chronic orofacial neuropathic pain, and thus potentially validates it as a therapeutic mark. It critically examines the in vivo significance for PKC phosphorylation of TRPV1, thereby resolving a proposed mechanism for its increased sensitivity. This award should provide the opportunity to develop the applicant’s career as a young investigator for further research of orofacial pain.