Contribution of ASIC channels to intrinsic chemosensitivity of NTS neurons

描述（由申请人提供）：呼吸具有不可或缺的生物学功能，并决定基本生理参数，如pH值和二氧化碳分压（PCO2）。中枢化学感受神经元检测脑pH值的变化作为PCO2变化的代理，并引起呼吸的代偿性变化，以维持这些参数的稳态。这些神经元的功能障碍导致严重的发病率，并与诸如先天性中枢换气不足综合征和婴儿猝死综合征等疾病有关。然而，化学敏感性的确切分子机制仍然很难理解。特别地，介导中枢化学感受的离子通道的身份是 目前未知。我的初步研究结果表明，酸敏感离子通道（ASIC）作为一个化学感受器在位于孤束核（NTS），脑干区域已知是体内化学敏感的神经元的子集。然而，这提出了一个重要的问题：ASIC通道如何有助于中央化学感受，如果他们广泛表达，甚至在大脑区域没有牵连在这个过程中。我假设ASIC通道特性的独特组合赋予必要的pH敏感性和特定的解剖特征（如树突方向和轴突投射），可能允许NTS神经元的亚群在功能上有助于中央化学感受。目的1：ASIC通道的哪些特征赋予NTS神经元亚群化学敏感性？将使用生物物理学、药理学和分子工具来确定对pH 7.0有反应（反应者）和无反应（无反应者）的NTS神经元中表达的ASIC通道特性之间的差异。这将有助于确定这些特性的差异如何仅对NTS神经元的一个子集赋予化学敏感性。目的2：化学敏感的孤束核神经元是否显示出与其功能相适应的独特解剖学特性？这些实验将联合收割机电生理学与解剖学和成像工具相结合，以揭示NTS神经元的解剖学特性，这些神经元在体外是化学敏感的。pH敏感通道的单纯表达不能促进中枢化学感受。因此，将确定化学敏感性神经元是否具有独特的树突特性，其将允许它们对脑pH进行采样，以及正确的轴突投射模式，以向呼吸节律产生神经元提供突触驱动。

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.