STUDY OF ACTIVITY-DEPENDENT SYMPATHETIC SPROUTING

描述(申请人提供)：许多慢性疼痛状况仍然难以治疗，给社会带来了很高的负担。交感神经活动可维持或加重复杂的区域疼痛综合征等情况。交感神经和感觉神经元之间异常联系的发现，例如周围神经损伤后交感神经纤维发芽进入感觉神经节(DRG)，提供了一个可能的解释，但对这种影响的研究得出了相互矛盾的结果。现在有了新的工具和知识来克服这一领域以前工作的一些局限性，如所建议的：1)将检查除去甲肾上腺素(NE)以外的交感神经递质的贡献。以前的许多研究仅仅依赖于NE拮抗剂，而忽略了已知的交感神经共递质，如在病理条件下特别重要的ATP。针对特定ATP受体亚型的新试剂将有助于研究其作用。2)交感-感觉神经元联系的功能研究非常有限。这项拟议的研究将使用一种描述的新制剂来刺激已发芽进入背根节的交感纤维，同时在细胞内记录感觉神经元兴奋性的许多参数。3)卫星胶质细胞和交感芽之间可能的相互作用尚未被研究。激活的胶质细胞在病理性疼痛中的重要性直到最近才被认识到。实验将测试发芽的交感纤维、感觉神经元和卫星胶质细胞之间的回响相互作用可能在启动病理性疼痛状态中发挥关键作用的可能机制。4)感觉神经元的交感神经效应可能从早期的兴奋作用转变为后来的抑制作用，这是相互矛盾的发现的原因。这种转变发生在慢性炎症的其他模型系统中。交感芽在以后的时间点上的功能将被研究。5)局部炎症在促进交感神经萌发中的作用尚未得到充分认识。局部背根节炎症足以诱导发芽，并可增强由神经切断引起的发芽。在疼痛模型中交感-感觉神经元相互作用的功能机制和行为相关性将通过三个具体目标进行研究：SA1：描述交感纤维对DRG兴奋性、自发活动和疼痛行为的功能影响，包括确定一种非常有限的外科交感神经切除术的效果，该手术形式消除了单个DRG中的发芽。SA2：确定交感神经递质和去甲肾上腺素是否在交感-感觉神经元异常相互作用中起重要的兴奋作用，重点研究ATP和卫星神经胶质细胞的可能作用。SA3：确定局部炎症、交感神经生长和神经病理性疼痛之间的相互作用。我们将确定交感神经喷嘴是否在两种疼痛模型的早期阶段调节炎症反应，正如在其他慢性炎症模型中的工作所表明的那样。拟议的实验将重振慢性疼痛条件下交感-感觉相互作用的研究，并有助于找到解决这一严重临床问题的新方法。 与公共卫生相关：慢性疼痛状况，如CRPS，是常见的、持续的和虚弱的。我们建议继续神经病理性疼痛中交感神经成分的研究。使用大鼠/小鼠模型，我们将确定异常活动、炎症、ATP释放如何影响交感神经生长和感受疼痛的神经元。

DESCRIPTION (provided by applicant): Many chronic pain conditions remain difficult to treat, presenting a high burden to society. Conditions such as complex regional pain syndrome may be maintained or exacerbated by sympathetic activity. The discovery of abnormal connections between sympathetic and sensory neurons, e.g. the sprouting of sympathetic fibers into the sensory ganglia (DRG) after peripheral nerve injury, offered a possible explanation, but studies of this effect yielded conflicting findings. New tools and knowledge are now available to overcome some limitations of previous work in this field, as proposed: 1) The contribution of sympathetic transmitters other than norepinephrine (NE) will be examined. Many previous studies relied solely on NE antagonists, ignoring known sympathetic co-transmitters such as ATP, which is particularly important in pathological conditions. New reagents for specific ATP receptor subtypes will help investigate its role. 2) Functional studies of the sympathetic-sensory neuron connection were very limited. The proposed research will use a described new preparation for stimulating the sympathetic fibers that have sprouted into the DRG while recording intracellularly many parameters of sensory neuron excitability. 3) The possible interaction of satellite glial cells and sympathetic sprouts has not been investigated. The importance of activated glia in pathological pain has been recognized only recently. Experiments will test possible mechanisms by which reverberating interactions between sprouting sympathetic fibers, sensory neurons, and satellite glia cells might play key roles in initiating the pathological pain state. 4) Sympathetic effects on sensory neurons may shift from early excitatory to later inhibitory ones, accounting for conflicting findings. This shift occurs in other model systems of chronic inflammation. The function of sympathetic sprouts at later time points will be examined. 5) The role of local inflammation in promoting sympathetic sprouting has not been fully recognized. Local DRG inflammation is sufficient to induce sprouting, and can enhance sprouting caused by axotomy. Functional mechanisms and behavioral relevance of sympathetic - sensory neuron interactions in pain models will be examined using 3 specific aims: SA1: To characterize functional effects of sympathetic fibers on DRG excitability, spontaneous activity and pain behavior, including determining the effects of a very limited form of surgical sympathectomy that eliminates sprouting in a single DRG. SA2: To determine whether sympathetic transmitters in addition to NE play important excitatory roles in abnormal sympathetic-sensory neuron interactions, focusing on possible roles of ATP and satellite glia cells. SA3: To determine the interactions between localized inflammation, sympathetic outgrowth and neuropathic pain. We will determine whether sympathetic spouts regulate inflammatory responses in the early phases of two pain models, as suggested by work in other models of chronic inflammation. The proposed experiments will reinvigorate the study of sympathetic-sensory interactions in chronic pain conditions, and help find new approaches to this serious clinical problem. PUBLIC HEALTH RELEVANCE: Chronic pain conditions such as CRPS are common, long-lasting, and debilitating. We propose to continue the study of sympathetic component in neuropathic pain. Using a rat/mouse model, we will determine how abnormal activity, inflammation, ATP release affect sympathetic outgrowth and the neurons that sense pain.