Neural and Chemical Basis of Pathological Pain

描述（由申请人提供）：腰痛是一种常见的问题，对社会具有很高的发病率成本，许多患者从目前的治疗中几乎得不到缓解。在腰背部疼痛的临床前模型中，感觉神经元的异常自发活动在慢性疼痛状态的建立中起着关键作用，该模型中疼痛行为是由腰椎背根神经节（DRG）局部炎症引起的。这种活性依赖于一种特殊的钠通道异构体Nav1.6，它可以介导持续和再生的钠电流，而钠电流反过来又可以成为高频/突发活动的基础。迄今为止，这个通道作为治疗靶点在很大程度上被忽视了；然而，在体内用小干扰RNA敲除DRG中的这一通道，可以完全阻断局部DRG炎症诱导的疼痛行为的发展，而不影响正常动物的行为或运动功能。参与炎症过程的分子，如细胞因子/趋化因子，对感觉神经元的兴奋性和疼痛有直接影响。然而，潜在的机制在很大程度上尚未被探索。我们假设DRG的局部炎症通过调节一部分感觉神经元中的Nav1.6来增加炎症细胞因子的表达/释放，并增强高频/爆发性放电，从而导致疼痛和超敏反应。1)表征正常和炎症感觉神经节中Nav1.6钠通道的功能、性质和解剖分布，验证该通道通过介导持续电流和复苏电流在异常自发活动中起关键作用的假设。免疫染色方法将用于验证炎症神经节中的破裂细胞富含Nav1.6+神经元和先前与疼痛相关的分子（如神经肽Y和CGRP）的假设。2)确定促炎细胞因子如何调节Nav1.6的功能特性和Nav1.6介导的自发活性。我们假设GRO/KC是一种在几种疼痛模型和广泛疼痛综合征患者中上调的趋化因子，通过调节Nav1.6来增加自发活动。3)评估Nav1.6在病理性疼痛中的作用。我们将使用新的行为评估方法，结合局部siRNA敲低和选择性药物阻断，来确定该通道是否在DRG炎症后疼痛的发生和持续中发挥作用。此外，它将在另一个背部疼痛模型和神经性疼痛模型中进行测试。这些目标将通过结合电生理、行为、显微镜和分子方法来实现。特别是，我们实验室新建立的用药物或小干扰rna在体内操纵感觉神经节的技术，以高度局部化的方式，结合行为测量和电生理学，为理解慢性疼痛机制提供了一个强大的综合方法。由于炎症过程在许多类型的慢性疼痛中起作用，因此这些发现不仅与了解腰痛有关，而且与了解其他类型的疼痛有关。

DESCRIPTION (provided by applicant): Low back pain is a common problem with high morbidity costs to society, and many patients receive little relief from current therapies. Abnormal spontaneous activity of sensory neurons plays a key role in establishing the chronic pain state in a preclinical model relevant to low back pain, in which pain behaviors are induced by locally inflaming the lumbar dorsal root ganglion (DRG). This activity depends on a particular sodium channel isoform, Nav1.6, which can mediate persistent and resurgent sodium currents that in turn can underlie high- frequency/bursting activity. To date this channel has been largely ignored as a therapeutic target; however, knocking down this channel in the DRG in vivo with small interfering RNA can completely block development of pain behaviors induced by local DRG inflammation, without affecting behavior in the normal animal or motor function. Molecules involved in the inflammation process, such as cytokines/chemokines, have direct effects on sensory neuron excitability and pain. However, the underlying mechanisms are largely unexplored. We hypothesize that local inflammation of the DRG increases expression/release of inflammatory cytokines and enhances high-frequency/bursting discharges by regulating Nav1.6 in a subset of sensory neurons and leads to pain and hypersensitivity. The hypothesis will be tested in 3 Specific Aims: 1) Characterize functional and properties and anatomical distributions of Nav1.6 sodium channel in normal and inflamed sensory ganglia, testing the hypothesis that this channel plays a crucial role in abnormal spontaneous activity by mediating persistent and resurgent currents. Immunostaining methods will be used to test the hypothesis that bursting cells in inflamed ganglia are enriched in Nav1.6+ neurons and in molecules previously linked to pain, such as neuropeptide Y and CGRP. 2) Determine how pro-inflammatory cytokines regulate functional properties of Nav1.6 and Nav1.6-mediated spontaneous activity. We hypothesize that GRO/KC, a chemokine that is up- regulated in several pain models and in human patients with wide-spread pain syndromes, acts to increase spontaneous activity by regulating Nav1.6. 3) Assess the role of Nav1.6 in pathological pain. We will use novel behavioral assessment methods combined with local siRNA knockdown, and selective pharmacological block to determine whether this channel plays a role in the development and persistence of pain after DRG inflammation. Additionally, it will be tested in another back pain model and in a model of neuropathic pain. These aims will be carried out using combined electrophysiological, behavioral, microscopy, and molecular methods. In particular, our laboratory's newly established techniques of manipulating the sensory ganglia in vivo with drugs or small interfering RNAs, in a highly localized fashion, combined with behavioral measurements and electrophysiology, provide a powerful integrated approach to understanding chronic pain mechanisms. Because inflammatory processes play a role in many types of chronic pain, the findings will be relevant not only to understanding low back pain, but other types of pain as well.