Central Mechanisms of Orofacial Pain

描述(申请人提供)：与颞下颌关节紊乱病相关的疼痛是口腔面部疼痛的一种非常普遍的实体，是一种衰弱的慢性疼痛状况。慢性口腔面部疼痛很难治疗，因为其机制在很大程度上仍不清楚。以往的研究表明，神经性和非神经性(神经胶质)成分在病理性疼痛的细胞机制中都起着关键作用。已有研究表明，周围神经损伤和炎症可诱导脊髓神经胶质细胞激活，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，至少部分是通过激活细胞内蛋白激酶C。我们的初步数据表明，将完全弗氏佐剂注射到大鼠颞下颌关节(TMJ)诱导的疼痛行为与同侧三叉神经尾侧亚核(TMJ)内IL-6和NMDAR表达增加有关。这些发现支持这样一种观点，即神经元和神经胶质元素之间的相互作用也可能在口腔面部疼痛的细胞机制中发挥关键作用。在这项研究中，我们建议系统地研究三叉神经胶质细胞激活和神经元NMDAR表达之间的相互作用及其在大鼠TMJ疼痛行为发病机制中的作用。我们的主要假设是，TMJ炎症可诱导三叉神经尾侧亚核内胶质细胞的激活和IL-6等促炎细胞因子的增加，这将通过IL-6受体信号、蛋白激酶C和转录核因子-kappaB等一系列细胞事件导致神经元NMDAR的上调，从而导致TMJ疼痛行为。这一假说将通过行为和药理学工具、免疫组织化学、Western印迹、原位杂交、实时RT-PCR、蛋白激酶活性分析、凝胶迁移率变化分析和酶联免疫吸附试验来验证，以实现三个特定目标：1)评估胶质细胞-神经元相互作用在TMJ疼痛行为中的功能作用；2)检测三叉神经节胶质细胞的表达及其与TMJ炎症诱导的促炎细胞因子变化的关系；3)探讨胶质细胞激活后三叉神经细胞NMDAR表达的细胞机制。预期的结果可能会为治疗口腔面部疼痛提供新的治疗选择。公共卫生相关性使用非类固醇抗炎药、三环类抗抑郁药和阿片类镇痛剂治疗口腔面部疼痛的有效性往往受到这些药物的副作用的限制，在某些情况下，还会产生不希望看到的长期后果。这项研究的结果可能导致新的治疗工具的开发，以治疗经常顽固性和衰弱的临床口腔面部疼痛。

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.