Chronic orofacial pain is a common clinical syndrome lacking specific and effective therapeutic agents due to the fact that the cellular mechanisms of chronic orofacial pain are poorly understood. Based on data from in vitro biochemical studies and non-orofacial, nerve injury-induced chronic pain models, we hypothesize that trigeminal nerve injury leads to altered expression of the calcium channel alpha-2-delta-1 subunit (Cava2d1) and thrombospondin-4 (TSP4) in trigeminal ganglia and associated brainstem and upper cervical spinal cord that plays a functional role in the development of neuropathic pain by promoting synaptogenesis. In this exploratory proposal, we plan to test if Cava2d1 and TSP4 induction by injury plays a causal role in the genesis and/or maintenance of neuropathic pain in an orofacial neuropathic pain model. We will perform Western blot analysis, immunohistochemical studies, and real-time PCR in trigeminal ganglia and associated brainstem/spinal cord samples from sham and infraorbital nerve injured animals to determine if there is a firm correlation between Cava2d1 and TSP4 expression and development of neuropathic pain. In addition, we will apply Cava2d1 and TSP4 antisense or mismatch oligonucleotides intrathecally to the nerve injury model, in a dose-dependent manner, before and after the onset of orofacial pain states to determine if preventing and reversing Cava2d1 and/or TSP induction by injury can block orofacial neuropathic pain development and maintenance, respectively. Completion of these studies will allow us to determine the functional contribution of injury-induced Cava2d1 and TSP expression to orofacial neuropathic pain and form the foundation for further investigation of the mechanisms underlying the contribution of these proteins in orofacial pain development. The final goal of the study is to identify new targets and pathways for the development of new medications for orofacial pain management. Project Narrative: Chronic orofacial pain derived from nerve injury, or orofacial neuropathic pain, is a common clinical syndrome lacking specific and effective therapeutic agents due to the fact that its cellular mechanisms are poorly understood. Existing data from in vitro biochemical studies and non-orofacial nerve injury pain models support that trigeminal nerve injury may lead to altered expression of the calcium channel alpha-2-delta-1 subunit (Cava2d1) and thrombospondin-4 (TSP4) in trigeminal ganglia and associated brainstem and upper cervical spinal cord that plays a functional role in orofacial pain development through a novel mechanism. In this exploratory proposal, we plan to test if trigeminal nerve injury causes altered expression of the Cava2d1 and TSP4 that contributes to the genesis and/or maintenance of neuropathic pain in an orofacial neuropathic pain model. We will test this hypothesis using biochemical and behavioral pharmacology approaches. Completion of this study will provide important information for the understanding of orofacial neuropathic pain mechanisms and the development of next generation of medications for orofacial neuropathic pain management.
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