Mechanisms of ventilatory adaptations to chronic hypercapnia

 描述（由申请人提供） 由于肺或神经肌肉疾病或医源性干预引起的慢性高碳酸血症在退伍军人事务部患者中很常见。低容量机械通气的允许性高碳酸血症是保护肺免受气压伤的标准治疗，但慢性高碳酸血症对大脑的影响在很大程度上是未知的。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，以延长和改善慢性CO2潴留VA患者的生活质量。 我们的中心假设是，慢性高碳酸血症elevently适应和/或适应不良的神经可塑性的呼吸控制网络。海马中的补偿过程依赖于谷氨酸受体亚单位（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5-羟色胺（5-HT）系统（TPH，SERT）的变化。我们对颈动脉体去神经支配（CBD）山羊的研究表明，低通气诱导的高碳酸血症对神经化学物质的影响。CBD后超过30天，谷氨酸受体亚单位和5-HT系统的标记物的表达改变了与呼吸相关的脑干核团和非呼吸脑干核团，表明高碳酸血症本身促成了这些变化。因此，我们将测试我们的中心假设完成三个特定的目的（SA）在成年山羊在清醒和NREM睡眠。 SA 1测试在慢性高碳酸血症期间，谷氨酸受体亚单位和5-HT系统标记物的变化是否与排泄控制的适应性或不适应性变化相关。我们假设吸入CO2（InCO 2）增加6%超过30天，将出现：a）通气的多相变化，其将与脑干呼吸核内GluA或GluN亚单位的激活状态的多相变化正相关，B）呼吸性CO2化学反射随天数的减少，其将与5-HT系统的标志物的减少正相关，以及c）在清醒和NREM睡眠之间PaCO 2、通气和呼吸肌活动的大于正常的差异。在慢性6% CO2暴露或30天室内空气呼吸之前和期间，将测量通气、动脉血气和呼吸肌活动（清醒和睡眠）以及CO2化学反射（清醒）。在慢性高碳酸血症的5、15和30天，慢性正常碳酸血症的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穿孔，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Western印迹分析。 SA 2功能性测试慢性高碳酸血症期间呼吸控制的适应性/适应不良变化是否与关键部位内谷氨酸受体反应性的变化相关，这些部位有助于CO2化学感受和呼吸节律的产生。我们假设，在清醒的山羊慢性增加InCO 2期间的呼吸过度将通过将谷氨酸受体拮抗剂注射到后斜方核（RTN）或前Bötinger复合体（preBötC）而减弱，并且这种减弱与注射前的通气呈正相关。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，在InCO 2增加期间长期植入微管（MT），用于注射谷氨酸受体拮抗剂犬尿烯酸（KynA）。 SA 3功能性测试慢性高碳酸血症期间呼吸控制的变化是否与RTN或preBötC内神经调质的变化相关和/或依赖于5-HT 2A受体神经调节。我们假设InCO 2高碳酸血症将减少兴奋性神经调质和对透析到RTN和preBötC的5-HT 2A受体拮抗剂的兴奋性反应。通过植入的MT，在高碳酸血症或正常碳酸血症30天之前、期间和之后，在有或没有拮抗剂的情况下透析模拟脑脊液。将分析流出透析液的神经调节剂含量。

 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.