Central Mechanisms of Orofacial Pain

描述（由申请人提供）：与颞下颌疾病相关的疼痛是一种非常普遍的口腔面部疼痛，是一种使人衰弱的慢性疼痛状况。慢性口面部疼痛很难治疗，因为其机制仍不清楚。以往的研究表明，神经元和非神经元（胶质）元件在病理性疼痛的细胞机制中起着关键作用。研究表明，周围神经损伤和炎症可诱导脊髓胶质细胞激活，促炎细胞因子可上调脊髓n -甲基- d -天冬氨酸受体（NMDAR）的表达，至少部分通过细胞内蛋白激酶c的激活介导。我们的初步数据表明，将完全弗氏佐剂注射到大鼠的颞下颌关节（TMJ）诱导的疼痛行为的发展与增加白介素-6 （IL-6）和NMDAR在同侧三叉神经尾侧亚核内的表达。这些发现支持了神经元和神经胶质元素之间的相互作用也可能在口面部疼痛的细胞机制中起关键作用的观点。本研究拟系统研究三叉神经胶质激活与神经元NMDAR表达之间的相互作用及其在大鼠颞下颌关节疼痛行为发病机制中的作用。我们的主要假设是，TMJ炎症会诱导神经胶质活化和三叉神经尾侧亚核内IL-6等促炎细胞因子的增加，从而通过一系列细胞事件，包括IL-6受体信号、蛋白激酶C和转录核因子κ B，导致神经元NMDAR上调，从而导致TMJ疼痛行为。这一假设将使用行为学和药理学工具、免疫组织化学、Western blot、原位杂交、实时RT-PCR、蛋白激酶活性测定、电泳迁移位移测定和酶联免疫吸附测定来检验，以实现三个特定目标：1)评估神经胶质相互作用在TMJ疼痛行为中的功能作用；2)观察三叉神经胶质表达及其与TMJ炎症诱导的促炎细胞因子变化的关系；3)研究神经胶质激活后三叉神经NMDAR表达的细胞机制。预期的结果可能为治疗口腔面部疼痛提供新的治疗选择。非甾体抗炎药、三环抗抑郁药和阿片类镇痛药治疗口面部疼痛的有效性往往受到这些药物副作用的限制，在某些情况下，还会产生不必要的长期后果。这项研究的结果可能会导致新的治疗工具的发展，以治疗经常难治性和衰弱的临床口面部疼痛。

DESCRIPTION (provided by applicant): Pain related to temporomandibular disorders is a highly prevalent entity of orofacial pain, a debilitating chronic pain condition. Chronic orofacial pain is difficult to treat because its mechanisms remain largely unclear. Previous studies have indicated that both neuronal and non-neuronal (glial) elements play a critical role in the cellular mechanisms of pathological pain. It has been shown that peripheral nerve injury and inflammation can induce spinal glial activation and that proinflammatory cytokines can upregulate the expression of spinal N-methyl-D-aspartate receptors (NMDAR) mediated at least in part through activation of intracellular protein kinase C. Our preliminary data have demonstrated that the development of pain behavior induced by complete Freund's adjuvant injected into the temporomandibular joint (TMJ) in rats was associated with an increased expression of both interleukin-6 (IL-6) and NMDAR within the ipsilateral trigeminal subnucleus caudalis. These findings support the notion that interactions between neuronal and glial elements may also play a critical role in the cellular mechanisms of orofacial pain. In this grant, we propose to systematically examine the interaction between trigeminal glial activation and the expression of neuronal NMDAR and its role in the pathogenesis of TMJ pain behavior in rats. Our main hypothesis is that TMJ inflammation would induce glial activation and increases in proinflammatory cytokines such as IL-6 within trigeminal subnucleus caudalis, which would lead to the upregulation of neuronal NMDAR through a chain of cellular events including IL-6 receptor signaling, protein kinase C, and transcriptional nuclear factor-kappa B, contributing to TMJ pain behavior. This hypothesis will be examined using behavioral and pharmacological tools, immunohistochemistry, Western blot, in situ hybridization, real-time RT-PCR, protein kinase activity assay, electrophoretic mobility shift assay, and enzyme-linked immunosorbent assay to accomplish three specific aims: 1) to evaluate the functional role of glial-neuronal interactions in TMJ pain behavior; 2) to examine trigeminal glial expression and its relationship to proinflammatory cytokine changes induced by TMJ inflammation; and 3) to investigate a cellular mechanism contributing to the expression of trigeminal neuronal NMDAR following glial activation. The anticipated results could suggest new therapeutic options for managing orofacial pain. PUBLIC HEALTH RELEVANCE The effectiveness of treating orofacial pain with non-steroidal anti-inflammatory drugs, tricyclic antidepressants, and opioid analgesics is often limited by these drugs' side effects and, in some cases, unwanted long-term consequences. The outcome of this study could lead to the development of new therapeutic tools to treat often intractable and debilitating clinical orofacial pain.