Mechanisms of ventilatory adaptations to chronic hypercapnia

慢性高碳酸血症的通气适应机制

• 批准号: 9032082
• 负责人: HUBERT V FORSTER
• 金额: --
• 依托单位: CLEMENT J. ZABLOCKI VA MEDICAL CENTER
• 依托单位国家: 美国
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-01-01 至 2019-12-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/9032082
• 关键词: Acute; Adult; Air; Asthma; Attenuated; Blood gas; Brain; Brain Stem; Breathing; Canis familiaris; Carbon Dioxide; Carotid Body; Cell Nucleus; Cerebrospinal Fluid; Chemicals; Chronic; Chronic Obstructive Airway Disease; Complex; Control Groups; Data; Denervation; Development; Disease; Dysbarism; Environmental air flow; Enzymes; Euthanasia; Excision; Excitatory Amino Acid Antagonists; Functional disorder; Generations; Glutamate Receptor; Glutamates; Goals; Goat; HTR2A gene; Heart failure; Hippocampus (Brain); Hypercapnia; Hypercapnic respiratory failure; Hyperpnea; Hypertension; Hypoxia; Implant; Injection of therapeutic agent; Intervention; Kynurenic Acid; Liquid substance; Lung; Lung diseases; Maintenance; Mammals; Measures; Mechanical ventilation; Mediating; Microtubules; Molecular; N-Methylaspartate; Neck; Nervous System Physiology; Neuraxis; Neuromodulator; Neuromuscular Diseases; Neuronal Plasticity; Organ; Patients; Process; Quality of life; Recovery; Respiratory Muscles; Serotonin; Site; Sleep; Synapses; System; Testing; Time; Tissues; Tryptophan 5-monooxygenase; Veterans; Wakefulness; Western Blotting; attenuation; awake; base; brain repair; improved; lung injury; neurochemistry; novel therapeutics; public health relevance; receptor; respiratory; respiratory distress syndrome; response; standard care

 DESCRIPTION (provided by applicant) Chronic hypercapnia due to lung or neuromuscular disease or iatrogenic intervention is common in Veteran's Affairs patients. Permissive hypercapnia from low volume mechanical ventilation is standard care for protection against barotrauma in the lung, but the effects of chronic hypercapnia on the brain are largely unknown. Our goal is to understand the time course and molecular mechanisms of the central nervous system's response to chronic hypercapnia in order to extend and improve the quality of life in VA patients with chronic CO2 retention. Our central hypothesis is that chronic hypercapnia elicits adaptive and/or maladaptive neuroplasticity within the respiratory control network. Compensatory processes in the hippocampus depend on changes in glutamate receptor subunit (GluA, GluN) expression or activity state altering synaptic strength/network function. Other forms of neuroplasticity require changes in the serotonin (5-HT) system (TPH, SERT). Our studies on carotid body denervated (CBD) goats characterized effects of hypoventilation-induced hypercapnia on neurochemicals. Over 30 days after CBD, the expression of glutamate receptor subunits and markers of the 5-HT system were altered in respiratory-related and non-respiratory brainstem nuclei, indicating that hypercapnia per se contributed to these changes. Thus, we will test our central hypothesis by completing three Specific Aims (SA) on adult goats during both wakefulness and NREM sleep. SA 1 tests whether changes in glutamate receptor subunits and markers of the 5-HT system correlate with adaptive or maladaptive changes in ventilatory control during chronic hypercapnia. We hypothesize that over 30 days of increased inspired CO2 (InCO2) of 6% there will be: a) multiphasic changes in ventilation which will positively correlate with multiphasic changes in the activation state of GluA or GluN subunits within brainstem respiratory nuclei, b) a decrease over days in the ventilatory CO2 chemoreflex which will positively correlate with a decrease in markers of the 5-HT system, and c) a greater than normal difference in PaCO2, ventilation, and respiratory muscle activity between wakefulness and NREM sleep. Ventilation, arterial blood gases, and respiratory muscle activity (awake and asleep), and the CO2 chemoreflex (awake) will be measured before and during up to 30 days of chronic 6% CO2 exposure or 30 days of room air breathing. At 5, 15, and 30 days of chronic hypercapnia, 30 days of chronic normocapnia, and in an unoperated control group, goats will be euthanized and tissue punches from brainstem nuclei will be extracted for Western blot analyses of glutamate receptor subunits, 5-HT marker expression, and molecules that initiate neuroplasticity. SA 2 functionally tests if the adaptive/maladaptive changes in ventilatory control during chronic hypercapnia correlate with changes in glutamate receptor responsiveness within key sites that contribute to CO2 chemoreception and respiratory rhythm generation. We hypothesize that the hyperpnea during chronic increased InCO2, in awake goats will be attenuated by injection of a glutamate receptor antagonist into the retrotrapezoid nucleus (RTN) or preBötzinger Complex (preBötC), and the attenuation will positively correlate with the ventilation prior to injections. Microtubule (MT's) will be chronically implanted for injections of the glutamate receptor antagonist kynurenic acid (KynA) during increased InCO2 before, during, and 2-5 days after 30 days of chronic hypercapnia or 30 days of chronic normocapnia (control). SA 3 functionally tests if changes in ventilatory control during chronic hypercapnia correlate with changes in neuromodulators within the RTN or preBötC and/or are dependent upon 5-HT2A receptor neuromdoulation. We hypothesize InCO2 hypercapnia will decrease excitatory neuromodulators and the ventilatory response to a 5-HT2A receptor antagonist dialyzed into the RTN and preBötC. Through implanted MT's, mock cerebrospinal fluid will be dialyzed with or without antagonist before, during, and after 30 days of hypercapnia or normocapnia. Effluent dialyzed fluid will be analyzed for neuromodulator content.

 描述（由申请人提供） 由于肺部或神经肌肉疾病或医源性干预导致的慢性高碳酸血症在退伍军人事务部患者中很常见。低容量机械通气引起的允许性高碳酸血症是预防肺部气压伤的标准护理，但慢性高碳酸血症对大脑的影响在很大程度上尚不清楚。我们的目标是了解中枢神经系统对慢性高碳酸血症反应的时间过程和分子机制，以延长和改善患有慢性二氧化碳潴留的 VA 患者的生活质量。 我们的中心假设是，慢性高碳酸血症会引起呼吸控制网络内的适应性和/或适应不良的神经可塑性。海马体的代偿过程取决于谷氨酸受体亚基（GluA、GluN）表达或活动状态的变化，从而改变突触强度/网络功能。其他形式的神经可塑性需要改变血清素 (5-HT) 系统（TPH、SERT）。我们对颈动脉体去神经 (CBD) 山羊的研究表征了通气不足引起的高碳酸血症对神经化学物质的影响。 CBD后30多天，呼吸相关和非呼吸脑干核中谷氨酸受体亚基和5-HT系统标记物的表达发生变化，表明高碳酸血症本身导致了这些变化。因此，我们将通过在成年山羊清醒和 NREM 睡眠期间完成三个特定目标 (SA) 来测试我们的中心假设。 SA 1 测试谷氨酸受体亚基和 5-HT 系统标记物的变化是否与慢性高碳酸血症期间通气控制的适应性或适应不良变化相关。我们假设，吸入二氧化碳 (InCO2) 增加 6% 的时间超过 30 天，将会出现：a) 通气多相变化，这与脑干呼吸核内 GluA 或 GluN 亚基激活状态的多相变化呈正相关；b) 通气 CO2 化学反射在几天内减少，这与 5-HT 系统标记物的减少呈正相关；以及 c) 清醒状态和 NREM 睡眠状态下 PaCO2、通气量和呼吸肌活动的差异大于正常值。将在长达 30 天的慢性 6% CO2 暴露或 30 天的室内空气呼吸之前和期间测量通气量、动脉血气、呼吸肌活动（清醒和睡眠）以及 CO2 化学反射（清醒）。在慢性高碳酸血症第 5、15 和 30 天，慢性正常碳酸血症第 30 天，以及在未手术的对照组中，将对山羊实施安乐死，并从脑干核中提取组织孔，用于谷氨酸受体亚基、5-HT 标记物表达和启动神经可塑性的分子的蛋白质印迹分析。 SA 2 功能测试慢性高碳酸血症期间通气控制的适应性/适应不良变化是否与有助于 CO2 化学感受和呼吸节律产生的关键位点内谷氨酸受体反应性的变化相关。我们假设，在清醒山羊中，慢性 InCO2 增加期间的呼吸过度会通过将谷氨酸受体拮抗剂注射到后梯形核 (RTN) 或 preBötzinger Complex (preBötC) 中而减弱，并且减弱将与注射前的通气量呈正相关。将长期植入微管 (MT)，以在 30 天慢性高碳酸血症或 30 天慢性正常碳酸血症（对照）之前、期间和之后 2-5 天的 InCO2 增加期间注射谷氨酸受体拮抗剂犬尿酸 (KynA)。 SA 3 功能测试慢性高碳酸血症期间通气控制的变化是否与 RTN 或 preBötC 内神经调节剂的变化相关和/或依赖于 5-HT2A 受体神经调节。我们假设 InCO2 高碳酸血症会降低兴奋性神经调节剂以及对透析至 RTN 和 preBötC 的 5-HT2A 受体拮抗剂的通气反应。通过植入的 MT，在高碳酸血症或正常碳酸血症之前、期间和之后 30 天，将在有或没有拮抗剂的情况下对模拟脑脊液进行透析。将分析流出的透析液的神经调节剂含量。