Contribution of ASIC channels to intrinsic chemosensitivity of NTS neurons

描述(申请人提供)：呼吸起着不可或缺的生物功能，决定着基本的生理参数，如pH值和二氧化碳分压(PCO2)。中枢化学感觉神经元检测大脑pH值的变化，作为二氧化碳分压变化的替代，并引起呼吸的代偿性变化，以维持这些参数的动态平衡。这些神经元的功能障碍会导致严重的发病率，并与先天性中枢性低通气综合征和婴儿猝死综合征等疾病有关。然而，化疗敏感性背后的确切分子机制在很大程度上仍然难以捉摸。特别是，调节中枢化学接收的离子通道的同一性是 目前尚不清楚。我的初步结果表明，酸感觉离子通道(ASIC)在孤束核(NTS)的神经元亚群中扮演化学感受器的角色，NTS是已知在体内对化学药物敏感的脑干区域。然而，这引发了一个重要的担忧：如果ASIC通道即使在与此过程无关的大脑区域也广泛表达，它们如何对中枢化学接收做出贡献。我推测，ASIC通道特性的独特组合赋予了必要的pH敏感性和特定的解剖特征(如树突定向和轴突投射)，可能允许NTS神经元亚群在功能上对中枢化学接收做出贡献。目的1：ASIC通道的哪些特征赋予NTS神经元亚群化疗敏感性？生物物理、药理学和分子工具将被用来确定在对pH 7.0有反应的NTS神经元中表达的ASIC通道的特性之间的差异(响应者)和那些不响应的神经元(非响应者)之间的差异。这将有助于确定这些特性的差异是如何赋予NTS神经元化疗敏感性的。目的2：化疗敏感的NTS神经元是否表现出与其功能相适应的独特解剖特性？这些实验将结合电生理学、解剖学和成像工具，揭示体外对化疗敏感的NTS神经元的解剖特性。仅有pH敏感通道的表达不能促进中枢化学感受。因此，化学敏感神经元是否具有独特的树突特性，使它们能够采样脑pH和正确的轴突投射模式，为呼吸节律产生神经元提供突触驱动，将被确定。 与公共卫生相关：先天性中枢低通气综合征(CCHS)和婴儿猝死综合征(SDS)是以呼吸缺乏自律性为特征的呼吸系统疾病，中枢化学接收功能障碍被认为是其主要原因之一。然而，化学敏感神经元检测大脑PCO2/pH变化的确切细胞和分子机制并不完全清楚。了解参与中枢化学感受的离子通道将使我们能够评估这些通道的破坏是否参与了CCHS的病理生理学，并可能为药物或基因治疗干预提供新的靶点。

DESCRIPTION (provided by applicant): Breathing serves an indispensable biological function and determines essential physiological parameters such as pH and partial pressure of carbon dioxide (PCO2). Central chemosensory neurons detect changes in brain pH as a proxy for changes in PCO2 and cause compensatory changes in respiration to maintain homeostasis of these parameters. Dysfunction of these neurons results in severe morbidity and is implicated in disorders such as congenital central hypoventilation syndrome and sudden infant death syndrome. Yet, the exact molecular mechanisms underlying chemosensitivity have remained largely elusive. In particular, the identity of ion channels that mediate central chemoreception is currently unknown. My preliminary results suggest that the acid-sensing ion channel (ASIC) acts as a chemoreceptor in a subset of neurons located in the nucleus tractus solitarus (NTS), a brainstem region known to be chemosensitive in vivo. However, this raises an important concern: how can ASIC channels contribute to central chemoreception if they are widely expressed even in brain areas not implicated in this process. I hypothesize that a unique combination of ASIC channel properties that confer the requisite pH sensitivity and specific anatomical characteristics (such as dendritic orientation, and axonal projections) may allow a subpopulation of NTS neurons to functionally contribute to central chemoreception. Aim 1: Which features of ASIC channels confer chemosensitivity onto a subpopulation of NTS neurons? Biophysical, pharmacological, and molecular tools will be used to determine differences between properties of ASIC channels expressed in NTS neurons that respond to pH 7.0 (responders) and those that do not (non-responders). This will help establish how differences in these properties confer chemosensitivity to only a subset of NTS neurons. Aim 2: Do chemosensitive NTS neurons display unique anatomical properties befitting their function? These experiments will combine electrophysiology with anatomical and imaging tools to uncover the anatomical properties of NTS neurons that are chemosensitive in-vitro. Mere expression of pH sensitive channels cannot contribute to central chemoreception. Therefore, whether chemosensitive neurons have unique dendritic properties that would allow them to sample brain pH and the correct axonal projection pattern to provide synaptic drive to respiratory rhythm generating neurons will be determined. PUBLIC HEALTH RELEVANCE: Congenital central hypoventilation syndrome (CCHS) and sudden infant death syndrome (SIDS) are respiratory disorders characterized by a lack of breathing automaticity and dysfunction of central chemoreception has been proposed to be one of their main causes. Yet, the exact cellular and molecular mechanisms underlying detection of changes in brain PCO2/pH by chemosensitive neurons are not entirely known. Understanding the ion channels involved in central chemoreception will allow us to evaluate if disruption of these channels is involved in the pathophysiology of CCHS and may provide novel targets for pharmacological or gene therapy interventions.