Central Mechanisms of Orofacial Pain

描述（由申请人提供）：与颞下颌关节紊乱病相关的疼痛是一种非常普遍的口面疼痛，是一种使人衰弱的慢性疼痛状况。慢性口面疼痛很难治疗，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）元素在病理性疼痛的细胞机制中起着至关重要的作用。已经显示，周围神经损伤和炎症可以诱导脊髓神经胶质细胞活化，并且促炎细胞因子可以上调至少部分通过细胞内蛋白激酶C的活化介导的脊髓N-甲基-D-天冬氨酸受体（NMDAR）的表达。我们的初步数据表明，完全弗氏佐剂注射到大鼠颞下颌关节（TMJ）引起的疼痛行为的发展与同侧三叉神经尾侧亚核内白细胞介素-6（IL-6）和NMDAR的表达增加有关。这些发现支持了神经元和神经胶质细胞之间的相互作用也可能在口面疼痛的细胞机制中发挥关键作用的观点。本研究拟系统地研究三叉神经胶质细胞活化与神经元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。我们的主要假设是颞下颌关节炎症将诱导胶质细胞活化和三叉神经尾侧亚核内促炎细胞因子如IL-6的增加，这将通过一系列细胞事件（包括IL-6受体信号传导、蛋白激酶C和转录核因子-κ B）导致神经元NMDAR的上调，从而导致颞下颌关节疼痛行为。本研究将采用免疫组化、Western blot、原位杂交、实时定量RT-PCR、蛋白激酶活性测定、电泳迁移率变动分析和酶联免疫吸附试验等方法对这一假说进行验证，以实现以下三个具体目标：1）评估胶质-神经元相互作用在TMJ疼痛行为中的功能作用; 2）检查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;和3）研究胶质活化后促进三叉神经神经元NMDAR表达的细胞机制。预期的结果可能会提出新的治疗选择管理口面疼痛。使用非甾体类抗炎药、三环类抗抑郁药和阿片类镇痛药治疗口面疼痛的有效性通常受到这些药物副作用的限制，在某些情况下，还受到不必要的长期后果的限制。这项研究的结果可能会导致新的治疗工具的发展，以治疗往往顽固性和衰弱的临床口面疼痛。

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.