Retrotrapezoid nucleus and central chemoreception

描述（由申请人提供）：在睡眠期间维持呼吸和实现血气稳态的中枢神经机制与先天性中枢性通气不足综合征（CCHS）、中枢性和阻塞性睡眠呼吸暂停（OSA）、婴儿猝死综合征（SIDS）和阿片类药物治疗疼痛具有相当大的临床相关性。在这项资助的支持下，我们已经确定并广泛表征了一群下脑干神经元（ccRTN神经元），这些神经元可能在CO2介导的呼吸调节中发挥关键作用。这些神经元的活动对体内CO2非常敏感，因为它们直接响应周围pH值的变化，并从氧和CO2传感颈动脉体接收强大的输入。此外，我们已经表明，ccRTN神经元为呼吸模式发生器（RPG）提供了强烈的兴奋性驱动，并且无论CO2水平如何，它们的缺失都会消除麻醉下的RPG活动。对CCHS具有重大意义的最新研究结果表明，ccRTN神经元对有意识哺乳动物的CO2稳态可能比预期的更重要。如果没有这些神经元的输入，睡眠期间可能无法呼吸。在2006年，我们证明，在啮齿动物中，ccRTN神经元表达Phox 2b，这是2003年在CCHS中发现的定义突变基因。CCHS的主要症状是白天通气不足，完全睡眠呼吸暂停和CO2呼吸刺激丧失。在2008/9年，遗传学家发现ccRTN神经元在CCHS小鼠模型中出生时选择性缺失。换句话说，ccRTN神经元的输入-输出特性，正如我们目前所理解的那样，似乎正好适合这些细胞通过呼吸促进CO2稳态。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。这些可能性令人着迷，值得进行彻底的测试，不仅因为它们在CCHS中的重要性，而且因为它们在正常动物睡眠期间对呼吸的控制。因此，本续期申请的主要目的为：a）评估ccRTN神经元对于在各种警觉状态期间的不自主呼吸的重要性，B）确定ccRTN神经元如何控制呼吸，具体地，它们靶向哪些呼吸神经元，以及c）进一步检查ccRTN神经元的活性如何被调节，特别关注它们通过血清素的控制，另一种与呼吸有关的主要神经递质。从拟议的实验结果将有助于确定是否选择性刺激这些神经元可以提供一个治疗的机会时，通气不足是有害的健康，如阻塞性睡眠呼吸暂停综合征。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，我们将大量使用新的慢病毒载体方法来选择性地在体内操纵ccRTN神经元，这种方法使我们能够释放光遗传学的力量用于心肺控制的研究。 公共卫生相关性：维持呼吸自主性的机制对生命至关重要，不幸的是，在相当大比例的人群中功能失调。例子包括阻塞性睡眠呼吸暂停，一种常见的情况，其中反复的气道塌陷阻止适当的氧合并导致睡眠中断，疲劳，高血压和代谢紊乱，婴儿猝死综合征（SIDS），先天性中枢性通气不足综合征，一种遗传性疾病，其中一个人出生时在睡眠期间完全无法呼吸，以及当疼痛用鸦片治疗时。所有这些例子都涉及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的神经元的部分，并将探索刺激呼吸以维持人体足够组织氧合的新方法。

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.