Peripheral Sensitization Following Spinal Cord Injury

描述(申请人提供)：脊髓损伤(SCI)导致严重的运动和躯体感觉功能障碍。躯体感觉的改变包括中枢神经病理性疼痛(CNP)，这种疼痛持续患者的一生。CNP发生在大多数脊髓损伤患者中，对生活质量产生不利影响，因此自杀事件频繁发生。这是一个重大的、知之甚少的公共卫生问题，了解CNP背后的机制应该会带来干预机会，以防止这种可怕的情况。我们的总体目标是确定脊髓损伤后CNP的发生机制。我们使用啮齿动物脊髓挫伤模型，因为该模型最接近人类脊髓损伤。这个模型中的CNP包括水平以上(前肢)、水平(躯干)和水平以下(后肢)的类似于人类脊髓损伤的痛样行为。目前的学说是脊髓机制导致CNP的产生，这是由于挫伤时细胞外谷氨酸的增加而产生的。然而，我们的初步数据显示，机械和热敏化发生在肋间神经(水平)和前肢(水平以上)的初级传入伤害性感受器，后者是一个对脊髓或周围神经都没有损害的位置。我们的假设是，从损伤引起的脊髓中谷氨酸的释放开始，建立了一个回响回路。谷氨酸产生背根反射(DRRs)，引起外周神经源性炎症(通过外周释放神经肽)。神经源性炎症导致初级传入纤维的外周敏化，从而敏化背角神经元。一旦建立了这个混响循环，它就会被长期维护。为了支持这一假设，我们的初步数据显示，与对照组相比，脊髓损伤大鼠颈部传入细胞中存在异常高的DRR活性。脊髓损伤后C、A5纤维自发DRRs的放电频率显著增加，A5纤维诱发DRRs的百分比增加，而鞘内注射GABAA拮抗剂荷包牡丹碱可使其减少。这些数据提供了脊髓(损伤部位)和外周传入神经之间的关键联系。我们的具体假设是，初级传入参与了CNP的中枢敏化，阻断DRRs和/或外周敏化将减弱CNP。为了验证这一假设，目标1将确定脊髓损伤后外周和中枢敏化的时间进程；目标2将证明用谷氨酸拮抗剂治疗脊髓损伤大鼠可以减少CNP，表现为疼痛行为减少，外周和中枢敏化减弱，DRRS减少。相反，鞘内注射谷氨酸治疗幼鼠将产生这些CNP迹象。目的3将证明阻断DRRs将减轻中枢和外周的敏感化和神经源性炎症。在这项提案中，我们将阐明迄今为止未知的中枢神经病理性疼痛的机制。

DESCRIPTION (provided by applicant): Spinal cord injury (SCI) leads to severe impairments in locomotor and somatosensory function. Alterations in somatosensation include central neuropathic pain (CNP) which persists for the patient's life. CNP occurs in the majority of SCI patients, so adversely affecting the quality of life that suicide frequently ensues. This is a major, poorly understood, public health problem and understanding the mechanisms underlying CNP should lead to opportunities for intervention to prevent this terrible condition. Our overall goal is to identify mechanisms contributing to CNP following SCI. We use the rodent spinal cord contusion model since this model best approximates human SCI. CNP in this model includes above level (forelimb), at level (trunk) and below level (hindlimb) pain-like behaviors that resemble those seen in human SCI. The dogma is that spinal mechanisms give rise to CNP, generated by increased extracellular glutamate at the time of contusion. Our preliminary data, however, show that mechanical and thermal sensitization occurs in primary afferent nociceptors in the intercostal nerves (at level) and in the forelimbs (above level), the latter being a location where there is no damage to either the spinal cord or peripheral nerves. Our hypothesis is that a reverberating loop is set up beginning with injury-induced release of glutamate in the cord. The glutamate generates dorsal root reflexes (DRRs) that cause peripheral neurogenic inflammation (from release of neuropeptides peripherally). The neurogenic inflammation leads to peripheral sensitization of primary afferent fibers which sensitizes dorsal horn neurons. Once this reverberating loop is established, it is maintained chronically. In support of this hypothesis, our preliminary data demonstrate the presence of abnormally high DRR activity in cervical afferents in SCI rats compared to controls. The discharge rate of spontaneous DRRs in C and A5 fibers is significantly elevated in SCI cervical afferents, the percentage of A5 fibers with evoked DRRs is increased and these are reduced by intrathecal bicuculline, a GABAA antagonist. These data provide a critical link between the spinal cord (the site of injury) and the peripheral afferents. Our specific hypothesis is that primary afferents contribute to the central sensitization underlying CNP, and blocking DRRs and/or peripheral sensitization will attenuate CNP. To test this hypothesis, aim 1 will determine the time course of peripheral and central sensitization following SCI; aim 2 will demonstrate that treatment of SCI rats with glutamate antagonists reduces CNP, evidenced by reduced pain behaviors, attenuation of both peripheral and central sensitization and decreased DRRs. Conversely, treatment of naive rats with intrathecal glutamate will produce these signs of CNP. Aim 3 will demonstrate that blocking DRRs will attenuate central and peripheral sensitization and neurogenic inflammation. In this proposal we will elucidate mechanisms that heretofore have been unknown contributors to central neuropathic pain.