A novel pathway mediating the development of chronic orofacial neuropathic pain

描述（由申请人提供）：慢性口面部疼痛是一种常见的临床综合征，由于对慢性口面部疼痛的细胞机制知之甚少，缺乏特异性和有效的治疗药物。基于三叉神经损伤模型和非口面疼痛模型的初步数据，我们假设三叉神经损伤诱导三叉神经节（TG）和相关脑干/上颈脊髓（Vc/C2）中血栓sponpin -4 （TSP4）的表达，导致感觉神经元亢进和脊髓三叉神经复合体突触发生异常。这些变化是三叉神经损伤向慢性疼痛发展转变的基础。在这项提议中，我们计划确定TSP4在介导行为超敏性和脊髓神经元超兴奋性中的关键结构域。病毒驱动TSP4在TG或Vc/C2中的表达将分别用于确定TSP4在慢性疼痛加工中的作用部位。我们将使用共聚焦显微镜和电子显微镜来确定神经损伤模型中异常突触发生的程度。此外，下行调节通路和电压门控钙通道对tsp4介导的行为超敏反应和背角神经元高兴奋性的影响将通过各自的药物进行研究。TSP4对感觉神经元兴奋性、钙通道活性和细胞内钙信号的影响将在分离的神经元或神经损伤模型的完整TG中，或在TSP4治疗后进行研究。为了确定TSP4是否通过与其受体钙通道α -2- δ -1亚基（Cava2d1）的相互作用，以感觉神经元特异性的方式诱导行为超敏性和背角神经元超兴奋性，将在感觉神经元亚群中选择性缺失Cava2d1的Cava2d1条件敲除小鼠进行这些研究。这些研究的最终目标是确定三叉神经损伤后tsp4介导的向慢性疼痛状态过渡的外周和/或中枢机制。

DESCRIPTION (provided by applicant): Chronic orofacial pain is a common clinical syndrome lacking specific and effective therapeutic agents due to the fact that cellular mechanisms of chronic orofacial pain are poorly understood. Based on our preliminary data from a trigeminal nerve injury model and in non-orofacial pain models, we hypothesize that trigeminal nerve injury induced thrombospondin-4 (TSP4) expression in trigeminal ganglia (TG) and associated brainstem/upper cervical spinal cord (Vc/C2) that causes sensory neuron hyperexcitability, and abnormal synaptogenesis in the trigeminal complex in the spinal cord. These changes underlie the transition from trigeminal nerve injury to chronic pain development. In this proposal, we plan to identify the critical domain(s) of TSP4 in mediating behavioral hypersensitivity and spinal neuron hyperexcitability. Viral driven TSP4 expression in TG or Vc/C2, respectively, will be used to identify the site of the TSP4's action in chronic pain processing. We will perform confocal and electron microscopy to determine the extent of abnormal synaptogenesis in the nerve injury models. In addition, the influence of descending modulatory pathways and voltage-gated-calcium channels on TSP4-mediated behavioral hypersensitivity and dorsal horn neuron hyperexcitability will be studies using respective drugs. The influence of TSP4 on sensory neuron excitability, calcium channel activities, and intracellular calcium signaling will be studied in isolated neurons or intact TG from nerve injury models, or after TSP4 treatment. To determine if TSP4 induces behavioral hypersensitivity and dorsal horn neuron hyperexcitability through its interactions with its receptor, the calcium channel alpha-2-delta-1 subunit (Cava2d1), in a sensory neuron specific manner, Cava2d1 conditional knockout mice with selective deletion of Cava2d1 in subpopulation of sensory neurons will be used for these studies. The final goal of the proposed studies is to identify the peripheral and/or central mechanisms underlying TSP4-mediated transition to chronic pain states after trigeminal nerve injury. PUBLIC HEALTH RELEVANCE: Chronic orofacial neuropathic pain often evolves from a preceding injury of the peripheral nerves, which is accompanied by initial nociceptive pain. Identification of the mechanisms underlying this transition would be critically valuable in preventing or reversing it. We plan to study a novel pathway mediated by injury-induced expression of thrombospondin 4 in mediating orofacial neuropathic pain. Completion of this study will provide important information for identifying a novel mediator for the transition to chronic orofacial pain after nerve injury.