The homeostatic regulation of pulmonary ventilation, and ultimately arterial PCO2, depends on interactions between respiratory chemoreflexes and arousal state. The ventilatory response to CO2 is triggered by neurons in the retrotrapezoid nucleus (RTN) that function as sensors of central pH, which can be identified in adulthood by expression of Phox2b and Neuromedin B. Here we examine the dynamic response of genetically-defined RTN neurons to hypercapnia and arousal state in freely-behaving adult male and female mice using the calcium indicator jGCaMP7 and fiber photometry. We found that hypercapnia vigorously activates RTN neurons with a low CO2 recruitment threshold and with response kinetics that match respiratory activity whereas hypoxia had little effect. RTN activity increased transiently during wakefulness and respiratory-related arousals, rose persistently during REM sleep and their CO2 response persisted under anesthesia. Complementary studies using inhibitory optogenetics show that RTN activity supports eupneic breathing under anesthesia as well as during states of high arousal, but their activity is redundant for voluntary breathing patterns. Collectively, this study demonstrates that CO2-activated RTN neurons are exquisitely sensitive to arousal state, which determines their contribution to alveolar ventilation in relation to arterial PCO2 Significance statement Respiratory chemoreceptors stimulate neural respiratory motor output to regulate arterial PCO2 and PO2, thereby maintaining optimal gas exchange. Central chemoreceptor neurons expressing Phox2b and Neuromedin B in the Retrotrapezoid Nucleus (RTN) are required for the hypercapnia ventilatory response. However, the dynamic activity of RTN neurons in conditions of normal and elevated carbon dioxide has not been described in unanesthetized conditions. Here, we use a genetically-encoded calcium indicator to demonstrate that RTN neurons exquisitely sensitivity to hypercapnia and variations in arousal and sleep-state in freely-behaving mice. This work has implications for understanding the central control of breathing across arousal-states, particularly during sleep and anesthesia.

中文翻译：

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觉醒状态和 CO₂ 之间的相互作用决定了驱动呼吸的中枢化学感受器神经元的活动。


肺通气的稳态调节，以及最终的动脉 PCO2，取决于呼吸化学屈和觉醒状态之间的相互作用。对 CO2 的通气反应由梯形后核 （RTN） 中的神经元触发，这些神经元充当中心 pH 值的传感器，在成年后可以通过 Phox2b 和 Neuromedin B 的表达来识别。在这里，我们使用钙指示剂 jGCaMP7 和纤维光度法检查遗传定义的 RTN 神经元对行为自由的成年雄性和雌性小鼠高碳酸血症和觉醒状态的动态响应。我们发现，高碳酸血症强烈激活 RTN 神经元，具有低 CO2 募集阈值和与呼吸活动相匹配的反应动力学，而缺氧几乎没有影响。RTN 活性在清醒和呼吸相关觉醒期间短暂增加，在 REM 睡眠期间持续上升，其 CO2 反应在麻醉下持续存在。使用抑制性光遗传学的补充研究表明，RTN 活性支持麻醉下以及高度觉醒状态下的呼吸，但它们的活动对于自主呼吸模式来说是多余的。总的来说，这项研究表明，CO2 激活的 RTN 神经元对觉醒状态非常敏感，这决定了它们对与动脉 PCO2 相关的肺泡通气的贡献 意义陈述 呼吸化学感受器刺激神经呼吸运动输出以调节动脉 PCO2 和 PO2，从而维持最佳气体交换。在梯形后核 （RTN） 中表达 Phox2b 和 Neuromedin B 的中枢化学感受器神经元是高碳酸血症通气反应所必需的。 然而，在正常和升高的二氧化碳条件下，RTN 神经元的动态活动尚未在未麻醉的条件下得到描述。在这里，我们使用基因编码的钙指标来证明 RTN 神经元对行为自由的小鼠的高碳酸血症以及觉醒和睡眠状态的变化非常敏感。这项工作对于理解唤醒状态中呼吸的中枢控制具有意义，尤其是在睡眠和麻醉期间。