Retrotrapezoid nucleus and central chemoreception

描述(申请人提供)：在睡眠期间维持呼吸和实现血气平衡的中枢神经机制与先天性中枢低通气综合征(CCHS)、中枢性和阻塞性睡眠呼吸暂停(OSA)、婴儿猝死综合征(SID)以及阿片类药物治疗疼痛具有相当大的临床相关性。在这笔赠款的赞助下，我们已经确定并广泛描述了一组低等脑干神经元(ccRTN神经元)，这些神经元可能在二氧化碳介导的呼吸调节中发挥关键作用。这些神经元的活动在体内对二氧化碳非常敏感，因为它们直接对周围pH的变化做出反应，并从感知氧气和二氧化碳的颈动脉小体获得强大的输入。此外，我们已经证明，ccRTN神经元为呼吸模式生成器(RPG)提供了强大的兴奋性驱动，并且它们的缺失消除了麻醉下的RPG活动，而无论二氧化碳水平如何。最近对CCHS有重大意义的发现表明，ccRTN神经元对清醒哺乳动物的二氧化碳稳态可能比预期的更重要。如果没有这些神经元的输入，睡眠时可能就不可能呼吸。2006年，我们证明了在啮齿动物中，ccRTN神经元表达PHOX2B，这是2003年在CCHS中发现的定义突变基因。CCHS的主要症状是白天低通气量、完全睡眠呼吸暂停和二氧化碳对呼吸的刺激消失。2008/2009年，遗传学家发现，在CCHS小鼠模型中，ccRTN神经元在出生时选择性地缺失。换句话说，就我们目前所知，ccRTN神经元的输入输出特性似乎正好适合这些细胞通过呼吸促进二氧化碳的动态平衡。遗传性疾病CCHS表明，这些神经元在这方面至关重要，特别是在睡眠期间。这些可能性是令人着迷的，值得彻底测试，不仅是因为它们在CCHS中的重要性，还因为它们在正常动物睡眠期间对呼吸的控制。因此，这一更新应用的主要目标是：a)评估ccRTN神经元在不同警觉状态下对非自主呼吸的重要性，b)确定ccRTN神经元如何控制呼吸，特别是它们针对哪些呼吸神经元，以及c)进一步研究ccRTN神经元的活动是如何调节的，特别是它们受5-羟色胺控制的情况，5-羟色胺是参与呼吸的另一种主要神经递质。拟议实验的结果将有助于确定，当低通气量对健康有害时，选择性刺激这些神经元是否可以提供治疗机会，例如OSA。为了解决这些问题，我们将继续使用我们在前几年开发的大量神经生理学和神经解剖学方法，并将大量使用新的慢病毒载体方法在体内选择性地操纵ccRTN神经元，这种方法使我们能够释放光遗传学的力量来研究心肺控制。 与公共卫生相关：维持呼吸自动化的机制对生命至关重要，不幸的是，在相当大一部分人口中存在功能障碍。例如阻塞性睡眠呼吸暂停，这是一种常见的情况，即反复的呼吸道塌陷阻碍适当的氧合作用，导致睡眠中断、疲劳、高血压和代谢紊乱，婴儿猝死综合征(SIDS)，先天性中枢低通气综合征，一种遗传性疾病，出生时完全无法在睡眠中呼吸，疼痛使用阿片类药物治疗。所有这些例子都涉及到呼吸的神经控制和血气调节的问题。这项研究的重点是大脑中包含这方面最重要神经元的部分，并将探索刺激呼吸以维持人体足够的组织氧合的新方法。

DESCRIPTION (provided by applicant): The central neural mechanisms that maintain breathing and achieve blood gas homeostasis during sleep have considerable clinical relevance for congenital central hypoventilation syndrome (CCHS), central and obstructive sleep apnea (OSA), sudden infant death syndrome (SIDS) and the treatment of pain with opiates. Under the auspices of this grant, we have identified and extensively characterized a population of lower brainstem neurons (ccRTN neurons) that could be playing a pivotal role in the CO2-mediatedregulation of breathing. The activity of these neurons is exquisitely sensitive to CO2 in vivo due to the fact that they respond directly to changes in the surrounding pH and receive powerful input from the oxygen and CO2- sensing carotid bodies. Furthermore, we have shown that the ccRTN neurons provide a strong excitatory drive to the respiratory pattern generator (RPG) and that their absence eliminates RPG activity under anesthesia regardless of the level of CO2. Recent findings of major significance to CCHS suggest that the ccRTN neurons may be even more important for CO2 homeostasis in conscious mammals than anticipated. Without input from these neurons, breathing may not be possible during sleep. In 2006, we demonstrated that, in rodents, the ccRTN neurons express Phox2b, the defining mutated gene in CCHS identified in 2003. The cardinal signs of CCHS are day time hypoventilation, total sleep apnea and loss of breathing stimulation by CO2. In 2008/9, geneticists found that the ccRTN neurons are selectively absent at birth in a mouse model of CCHS. In other words, the input-output properties of the ccRTN neurons, as we understand them currently, seem precisely appropriate for these cells to contribute to CO2 homeostasis via breathing. The genetic disease, CCHS, suggests that these neurons are critical in this regard, especially during sleep. These possibilities are fascinating and deserve to be thoroughly tested, not merely for their importance in CCHS but for their control of breathing during sleep in normal animals. Accordingly, the main objectives of this renewal application are: a) to assess the importance of the ccRTN neurons for involuntary breathing during various states of vigilance, b) to determine how the ccRTN neurons control breathing, specifically which respiratory neurons they target, and c) to further examine how the activity of the ccRTN neurons is regulated with special focus on their control by serotonin, another major neurotransmitter involved in breathing. The results from the proposed experiments will help to determine whether selective stimulation of these neurons could offer a therapeutic opportunity when hypoventilation is detrimental to health, e.g. OSA. To address these issues we will continue using the large repertoire of neurophysiological and neuroanatomical methods that we have developed in prior years and we will make heavy use of a new lentiviral vector approach to manipulate ccRTN neurons selectively in vivo, a method that has allowed us to unleash the power of optogenetics for the study of cardiorespiratory control. PUBLIC HEALTH RELEVANCE: The mechanisms that maintain breathing automaticity are critical to life and are unfortunately dysfunctional in a significant proportion of the population. Examples include obstructive sleep apnea, a common condition in which repeated airway collapse prevents proper oxygenation and causes sleep disruption, fatigue, hypertension and metabolic perturbations, sudden infant death syndrome (SIDS), congenital central hypoventilation syndrome, a genetic disease in which one is born with the total inability to breathe during sleep, and when pain is treated with opiates. All these examples involve some problem with the neural control of breathing and its regulation by blood gases. This research focuses on the part of the brain that contains the most important neurons in this regard and will explore novel ways by which breathing could be stimulated to maintain adequate tissue oxygenation in humans.