Neural and Chemical Basis of Pathological Pain

描述(申请人提供)：下腰痛是一个常见的问题，对社会的发病率成本很高，许多患者从目前的治疗中几乎得不到缓解。在与腰背痛相关的临床前模型中，感觉神经元的异常自发活动在建立慢性疼痛状态中起着关键作用，在该模型中，疼痛行为是通过局部炎症腰背根神经节(DRG)来诱导的。这种活动依赖于一种特殊的钠通道亚型Nav1.6，它可以介导持续和复苏的钠电流，而这反过来又是高频/爆发性活动的基础。到目前为止，这一通道在很大程度上被忽视了作为治疗的靶点；然而，在体内用小干扰RNA敲除DRG中的这一通道可以完全阻止由局部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还没有被探索。我们假设，DRG的局部炎症增加了炎性细胞因子的表达/释放，并通过调节部分感觉神经元中的Nav1.6而增强了高频/爆发性放电，并导致疼痛和超敏。这一假说将在3个具体目标中得到验证：1)表征正常和炎症感觉神经节中Nav1.6钠通道的功能、特性和解剖分布，验证该通道通过调节持续和复活电流在异常自发活动中起关键作用的假说。免疫染色方法将被用来检验这一假设，即炎症神经节中的爆裂细胞富含Nav1.6+神经元以及以前与疼痛有关的分子，如神经肽Y和降钙素基因相关肽。2)确定促炎细胞因子如何调节Nav1.6和Nav1.6介导的自发活动的功能特性。我们假设Gro/KC是一种趋化因子，在几种疼痛模型和患有广泛性疼痛综合征的人类患者中上调，通过调节Nav1.6来增加自发活动。3)评价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敲除和选择性药物阻断来确定该通道是否在DRG炎症后疼痛的发展和持续中发挥作用。此外，它还将在另一个背痛模型和神经病理性疼痛模型中进行测试。这些目标将使用电生理、行为、显微镜和分子方法相结合的方法来实现。特别是，我们实验室新建立的用药物或小干扰RNA以高度局部化的方式在体内操纵感觉神经节的技术，结合行为测量和电生理学，为了解慢性疼痛的机制提供了一种强大的综合方法。由于炎症过程在许多类型的慢性疼痛中发挥作用，因此这一发现不仅与理解下腰痛有关，而且也与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.