STUDY OF ACTIVITY-DEPENDENT SYMPATHETIC SPROUTING

描述(申请人提供)：我们研究的总体目标是调查交感神经萌发的机制及其与来自轴突扭转的感觉神经元或受损的外周轴突(神经瘤)的异位自发活动的相关性。周围神经切断后，交感神经轴突发芽进入腰椎背根神经节(DRGs)，这是神经病理性疼痛(如复杂区域疼痛综合征[CRPS])的主要现象。虽然有证据表明某些胶质细胞衍生的神经营养因子参与了交感神经末梢的萌发，但交感神经末梢的萌发在很大程度上仍不清楚。然而，有证据表明，交感神经萌发主要与大中型感觉神经元有关，这些感觉神经元在神经损伤后经常出现高频和/或爆发式放电。我们的初步研究结果显示，全身应用利多卡因(一种钠离子通道阻滞剂)可显著降低交感神经萌发的程度，而全身应用4-氨基吡啶(4-AP，一种钾通道阻滞剂)可增加交感神经萌发的自发活动。我们假设，周围神经或DRG的损伤导致大中型DRG神经元的高频和/或爆发性放电，从而触发交感神经纤维的萌发，可能是通过增强卫星神经胶质细胞的神经营养因子的表达。使用实验性神经瘤的动物模型，结合电生理学、免疫组织化学和Western印迹技术，我们将通过以下三个具体目标来验证我们的假设。具体目的1.研究周围神经切断后DRG的交感神经发芽是否表现出对高频和/或爆发性放电或兴奋性强的自发神经元的偏好。具体目的2.确定在不切断脊神经轴突的情况下，背根神经节的自发活动是否可以诱发交感神经萌发。具体目的3.评估神经胶质细胞衍生的神经营养因子在活性依赖的交感神经萌发中的作用。如果确定了自发活动、神经营养因子和交感神经萌发之间的关系，那么可以开发新的治疗方法，包括对自发活动的药物调节，以抑制感觉神经元的过度兴奋。这种疗法可以为神经病理性疼痛患者提供更有效的非阿片类止痛。

DESCRIPTION (provided by applicant): The overall goal of our research is to investigate the mechanisms underling sympathetic sprouting and its correlation with ectopic, spontaneous activity originating from axotornized sensory neurons or injured peripheral axons (neuroma). After peripheral axotomy, sympathetic axons sprout into the lumbar dorsal root ganglia (DRGs), a major phenomenon implicated in neuropathic pain (e.g., complex regional pain syndrome [CRPS]). Although there is evidence that certain glial-cell-derived neurotrophins are involved in the sympathetic sprouting, the causal factor that triggers, and possibly guides, the sprouting of sympathetic nerve endings remains largely unknown. However, evidence exists that sympathetic sprouting is associated predominately with large- and medium-sized sensory neurons, which often present with high frequency and/or bursting discharges after nerve injury. Results from our preliminary study revealed that systemic lidocaine (a Na* channel blocker) significantly reduced the extent of sympathetic sprouting, whereas systemic administration of 4-aminopyridine (4-AP, a K+ channel blocker), which enhances spontaneous activity, increased the sprouting. We hypothesize that injury of the peripheral nerve or the DRG causes high frequency and/or bursting discharges in large- and medium-sized DRG neurons that trigger the sprouting of sympathetic nerve fibers possibly through the enhanced expression of neurotrophins from satellite glial cells. Using animal models of experimental neuroma combining with electrophysiological, immunohistochemical and Western blot techniques, we will test our hypothesis via the following 3 Specific Aims. Specific Aim 1. Examine whether sympathetic sprouting in DRGs with peripheral axotomy shows any preference for spontaneously active neurons with high frequency and/or bursting discharges or hyperexcitability. Specific Aim 2. Determine whether sympathetic sprouting may be evoked by spontaneous activity in DRGs without axotomy. Specific Aim 3. Assess the role of glial cell-derived neurotrophins in activity-dependent sympathetic sprouting. If a relationship among spontaneous activity, neurotrophins, and sympathetic sprouting is identified, then new therapeutic approaches involving pharmacological modulation of spontaneous activity could be developed to suppress the hyperexcitability of sensory neurons. Such therapies could provide more effective non-opioid analgesia to patients with neuropathic pain.