Intracellular pH Responses of Central Chemoreceptors

描述(申请人提供)：高碳酸血症(二氧化碳增加)是一种主要的呼吸刺激，由几个脑干区域的特殊神经元感受到，称为化学敏感神经元。我们一直在研究这些神经元感知二氧化碳的离子通路。基于我们的发现，我们提出了一种新的化疗敏感信号模型--多因素模型。这个模型的主要原理是，化学敏感神经元对高碳酸血症的反应涉及多个信号通路，这些信号通路针对多个离子通道。本修订申请中的工作分为4个目标：1)通过测量一个脑干区域神经元的内在化疗敏感性，直接测试参与化疗敏感信号的多种信号，特别是关注phi保持不变的神经元对酸性刺激的反应和CaI的作用；2)确定哪些离子通道作为化疗敏感信号的靶标并测量其性质，使用免疫细胞化学和电压钳技术相结合来描述化疗敏感神经元中存在哪些通道以及哪些通道受到高碳酸血症的影响；3)比较目标1中研究的蓝斑(低化疗敏感性)、孤束核(中等化疗敏感性)和斜方后核(高化疗敏感性)三个不同脑干区域神经元的信号通路，并建立一个数学模型来描述哺乳动物化疗敏感神经元的反应，该模型结合了为每个区域的神经元所描述的多个信号和离子通道靶标；以及4)结合逆行标记和细胞内记录确定二氧化碳化疗敏感神经元的传出投射。这些研究将首次在几个脑干区域的神经元中使用相同的技术，这些区域具有非常不同的内在化疗敏感性，应该会对决定化疗敏感性的细胞属性产生有价值的新见解。此外，我们的结果应该定义神经元中化疗敏感性的细胞信号通路和离子通道靶点，并用于测试多因素模型。许多疾病，包括睡眠呼吸暂停和婴儿猝死综合症，被认为在一定程度上涉及中枢呼吸控制障碍，但目前还没有可用的药物治疗来改变这一控制途径。我们的研究应该为药物治疗提出新的潜在靶点，并很可能表明联合用药在改变中枢呼吸驱动方面最有效。总结：脑干神经元感觉到的二氧化碳增加是驱动呼吸的主要刺激因素。这种反应的改变被认为在一定程度上与睡眠呼吸暂停等疾病有关，但目前还没有药物可以影响这种反应。我们正在研究神经元对二氧化碳的反应方式，以识别新的药物靶点，并测试这一途径涉及几种不同信号的新理论。

DESCRIPTION (provided by applicant): Hypercapnia (increased CO2) is a major stimulus for breathing and is sensed by specialized neurons, called chemosensitive neurons, from several brainstem regions. We have been studying the ionic pathways by which these neurons sense CO2. Based on our findings, we have proposed a new model of chemosensitive signaling, the multiple factors model. The main tenet of this model is that the response of chemosensitive neurons to hypercapnia involves multiple signaling pathways that target multiple ion channels. The work in this revised application is divided into 4 aims: 1) test directly that there are multiple signals involved in chemosensitive signaling, by measuring the intrinsic chemosensitivity of neurons from one brainstem region, focusing especially on neuronal responses to acidic stimuli with pHi held constant and on the role of Cai; 2) determine which ion channels act as targets of chemosensitive signaling and measure their properties, using a combination of immunocytochemistry and voltage clamp techniques to describe which channels are present in chemosensitive neurons and which are affected by hypercapnia; 3) compare the signaling pathways studied in Aim 1 in neurons from three different brainstem regions, the locus coeruleus (low chemosensitivity), the nucleus tractus solitarius (intermediate chemosensitivity) and the retrotrapezoid nucleus (high chemosensitivity) and develop a mathematical model to describe the response of mammalian chemosensitive neurons which combines the multiple signals and ion channel targets described for the neurons from each region; and 4) determine the efferent projections of CO2-chemosensitive neurons combining retrograde labeling with intracellular recordings. These studies will be the first to employ identical techniques in neurons from several brainstem regions which have widely different intrinsic chemosensitivitv, and should yield valuable new insights into the cellular properties that determine chemosensitivity. Further, our results should define the cellular signaling pathways and ion channel targets of chemosensitivitv in neurons and serve to test the multiple factors model. Many diseases, including sleep apnea and Sudden Infant Death Syndrome (SIDS) are believed to involve, in part, disordered central respiratory control, and yet no current drug treatments are available to modify this control pathway. Our studies should suggest new potential targets for drug treatment and may well indicate that a combination of drugs is most effective in modifying central respiratory drive. Lay Summary: Increased CO2, sensed by brainstem neurons, is a major stimulus that drives breathing. Alterations of this response are thought to be involved, in part, in diseases like sleep apnea, but no drugs are now available to affect this response. We are studying the ways in which neurons respond to CO2 to identify novel drug targets and to test a new theory that this pathway involves several different signals.