Neurophysiology and plasticity of cardiorespiratory circuits to hypoxia

 描述（由申请人提供）：孤束核（nTS）是感觉反射的第一个中枢终止和整合部位，包括在慢性间歇性缺氧（CIH）和阻塞性睡眠呼吸暂停（OSA）期间增强的颈动脉体化学反射。初级传入神经元和二级NTS神经元之间的神经元能突触是高度可变的，表达多种形式的突触可塑性，并通过CIH增强。该NTS突触与星形胶质细胞（神经胶质细胞）密切相关，星形胶质细胞（神经胶质细胞）通过释放神经胶质递质和从突触间隙摄取神经递质来积极促进突触和神经元活性和可塑性。神经胶质、突触前终末和突触后神经元之间的相互作用被称为“三方突触”。已经确定了几种胶质递质，包括谷氨酸和ATP。星形胶质细胞在nTS释放谷氨酸响应传入感觉输入，以修改神经元的活动。通过其各自的转运蛋白摄取传入和网络释放的谷氨酸和GABA对于形成和同步活动以及防止兴奋性毒性至关重要。神经胶质改变突触传递以响应急性缺氧，并且长时间缺氧改变三重突触的组分的表达和/或功能，并且可能改变神经胶质-神经通信。星形胶质细胞、胶质递质及其在常氧条件下突触可塑性神经递质摄取中的作用尚不清楚，更不用说其在CIH中的增强作用了。此外，星形胶质细胞介导的突触可塑性如何增强心肺反射尚不清楚。我们的中心假设是神经胶质转运蛋白基本上抑制突触活动，但增加激活的星形胶质细胞内的三重突触增强突触和神经元功能，以增强心肺系统。CIH增强nTS神经传递和缺氧心肺反应，由于星形胶质细胞活性升高和兴奋性GT释放，并改变平衡的Glu和GABA摄取。目的1将定义nTS的大小（a）神经元和突触功能，以及它们的可塑性，由星形胶质细胞调节，并受胶质递质的影响，（B） 星形胶质细胞被神经元活动激活，（c）三重突触调节呼吸、交感神经活动及其偶联，和（d）CIH中的兴奋性由于星形胶质细胞激活而增强。目的2将确定星形胶质细胞Glu或GABA转运蛋白（a）影响nTS神经元功能，（B）激活突触和突触外受体，（c）调节心肺功能，以及（d）被CIH诱导的nTS神经传递增强改变或促成的程度。这项研究提出了一种综合的方法来探索重要的基础和临床问题，包括神经元和星形胶质细胞的记录，成像，分子生物学，光遗传学，DREADD操作和体内生理学。了解涉及心肺疾病的电路及其神经胶质-神经相互作用将促进我们对其发展的理解，并可能导致其治疗。

 DESCRIPTION (provided by applicant): The nucleus tractus solitarii (nTS) is the first central termination and integration site for sensory reflexes, including the carotid body chemoreflex that is augmented during chronic intermittent hypoxia (CIH) and obstructive sleep apnea (OSA). The glutamatergic synapse between the primary afferent and second-order nTS neuron is highly modifiable, expressing multiple forms of synaptic plasticity and enhanced by CIH. This nTS synapse is closely associated with astrocytes (glia) that actively contribute to synaptic and neuronal activity and plasticity through the release of gliotransmitters and by uptake of neurotransmitter from the synaptic cleft. The interaction among glia, presynaptic terminals and postsynaptic neurons is referred to as the "tripartite synapse". Several gliotransmitters have been identified, including glutamate and ATP. Astrocytes in the nTS release glutamate in response to afferent sensory input to modify neuronal activity. Uptake of afferent and network released glutamate and GABA by their respective transporters is critical for shaping and synchronizing activity, and preventing excitotoxicity. Glia modify synaptic transmission in response to acute hypoxia, and prolonged hypoxia alter the expression and/or function of components of the tripartite synapse, and likely glia-neural communication. The role of astrocytes, gliotransmitters and their role in neurotransmitter uptake in synaptic plasticity in normoxia, let alone its enhancement in CIH, is unknown. Moreover, how astrocyte-mediated effects on synaptic plasticity augment cardiorespiratory reflexes is unknown. Our central hypothesis is glial transporters basally restrain synaptic activity, but increased activation of astrocytes within the tripartite synapse enhances synaptic and neuronal function to augment the cardiorespiratory system. CIH enhances nTS neurotransmission and hypoxic cardiorespiratory responses due to elevated astrocyte activity and excitatory GT release, and altered balance of Glu and GABA uptake. Aim 1 will define the magnitude by which nTS (a) neuronal and synaptic function, and their plasticity, are modulated by astrocytes and influenced by gliotransmitters, (b) astrocytes are activated by neuronal activity, (c) tripartite synapses modulate respiration, sympathetic nerve activity and their coupling, and (d) excitability is augmented in CIH due to astrocyte activation. Aim 2 will determine the magnitude by which astrocyte Glu or GABA transporters (a) influence nTS neuronal function, (b) activate synaptic and extra-synaptic receptors, (c) regulate cardiorespiratory function, and (d) are altered by or contribute to CIH-induced augmentation of nTS neurotransmission. This study presents an integrative approach to exploring important basic and clinical questions, including the recording of neurons and astrocytes, imaging, molecular biology, optogenetics, DREADD manipulation and in vivo physiology. Understanding the circuits, and their glia-neural- interactions, involved in cardiorespiratory diseases will advance our understanding of its development and potentially lead to its treatment.