Nerve conduction block in cold-responsive sensory neurons

描述（由申请人提供）：薄荷醇受体TRPM8被认为是哺乳动物感觉神经元中主要的冷传感器，因为缺乏TRPM8功能的动物会缺乏寒冷和冷痛行为。然而，一些残余的冷敏感性仍然存在，表明可能存在与trpm8无关的冷转导机制。其他细胞类型，如表达TRPV1和TRPA1通道的细胞，对体感觉信号传导至关重要，并与冷感觉的某些方面有关。确定这些通道和细胞类型作用的遗传方法是复杂的，因为所得到的表型要么是在操作后许多天进行研究，要么是在发育不同的背景下进行研究。最近，一种优雅的方法被设计出来，它将细胞内的钠（Na+）通道阻滞剂仅靶向于介导疼痛的初级感觉神经元（伤害感受器）。具体来说，当受到伤害感受器特异性TRPV1和TRPA1通道的激动剂刺激时，大分子如带电的利多卡因衍生物QX-314通过这些通道渗透，从而选择性地阻断这些神经元群的神经传导。先前的报道未能发现大分子通过TRPM8通道进入，这表明TRPM8神经元不能以这种方式靶向。我们的基本假设，由我们新的初步数据支持，是当通道被强效激动剂激活时，大分子通过TRPM8渗透细胞，我们建议确定是否可以通过选择性阻断这些和其他神经元群的神经传导来改善寒冷和冷痛。目的1将确定TRPM8通道在体外渗透大阳离子的机制，并将其作为将Na+通道阻滞剂靶向TRPM8神经元的手段。目的2将确定靶向TRPM8神经元中的Na+通道阻滞剂是否会改变小鼠的冷感觉，并确定其他初级感觉神经元是否也会导致冷。目的3将扩展这些行为分析，以确定是否可以通过将Na+通道阻滞剂靶向TRPM8、TRPV1或TRPA1神经元来改善损伤引起的慢性冷痛。通过这些研究，我们将确定冷痛和冷痛是否可以通过选择性进入大细胞非意味性麻醉剂来特异性抑制，并使用这种新方法进一步定义冷痛和冷痛的细胞基础，包括识别与这种体感觉模态有关的trpm8独立神经元群。

DESCRIPTION (provided by applicant): The menthol receptor TRPM8 is considered the principal cold sensor in mammalian sensory neurons as animals lacking TRPM8 function are deficient in cold and cold pain behaviors. However some residual cold sensitivity remains, indicating the possible presence of TRPM8-independent cold transduction mechanisms. Other cell types, such as those expressing TRPV1 and TRPA1 channels, are critical for somatosensory signaling, and have been implicated in certain aspects of cold sensation. Genetic approaches to determine the role of these channels and cell-types are complicated by the fact that the resulting phenotypes are investigated either many days after manipulation, or in developmentally disparate backgrounds. An elegant approach has recently been devised that targets cell impermeant sodium (Na+) channel blockers to only primary sensory neurons mediating pain (nociceptors). Specifically, when stimulated with agonists for nociceptor-specific TRPV1 and TRPA1 channels, large molecules such as the charged lidocaine derivative QX-314 permeate through these channels, thereby selectively blocking nerve conduction in just these neuronal populations. Previous reports failed to find large molecule entry through TRPM8 channels, suggesting that TRPM8 neurons cannot be targeted in this manner. Our underlying hypothesis, supported by our novel preliminary data, is that large molecules permeate cells through TRPM8 when the channel is activated by potent agonists, and we propose to determine if cold and cold pain can be ameliorated by selectively blocking nerve conduction of these and other neuronal populations. Aim 1 will determine the mechanisms whereby TRPM8 channels permeate large cations in vitro and be used as a means to target Na+-channel blockers to TRPM8 neurons. Aim 2 will determine if targeting Na+-channel blockers in TRPM8 neurons alters cold sensation in mice, and determine if other primary sensory neurons also contribute to cold. Aim 3 will extend these behavioral analyses to determine if chronic cold pain induced by injury can be ameliorated by targeting Na+-channel blockers to TRPM8, TRPV1, or TRPA1 neurons. With these studies we will determine if cold and cold pain can be specifically inhibited by the selective entry of large, cell impermeant anesthetics, as well as use this novel approach to further define the cellular basis for cold and cold pain, including identifying TRPM8-independent neuronal populations that contribute to this somatosensory modality.