Collectively, the retrotrapezoid nucleus (RTN) and adjacent C1 neurons regulate breathing, circulation and the state of vigilance, but previous methods to manipulate the activity of these neurons have been insufficiently selective to parse out their relative roles. We hypothesize that RTN and C1 neurons regulate distinct aspects of breathing (e.g., frequency, amplitude, active expiration, sighing) and differ in their ability to produce arousal from sleep. Here we use optogenetics and a combination of viral vectors in adult male and female Th-Cre rats to transduce selectively RTN (Phox2b⁺/Nmb⁺) or C1 neurons (Phox2b⁺/Th⁺) with Channelrhodopsin-2. RTN photostimulation modestly increased the probability of arousal. RTN stimulation robustly increased breathing frequency and amplitude; it also triggered strong active expiration but not sighs. Consistent with these responses, RTN innervates the entire pontomedullary respiratory network, including expiratory premotor neurons in the caudal ventral respiratory group, but RTN has very limited projections to brainstem regions that regulate arousal (locus ceruleus, CGRP⁺ parabrachial neurons). C1 neuron stimulation produced robust arousals and similar increases in breathing frequency and amplitude compared with RTN stimulation, but sighs were elicited and active expiration was absent. Unlike RTN, C1 neurons innervate the locus ceruleus, CGRP⁺ processes within the parabrachial complex, and lack projections to caudal ventral respiratory group. In sum, stimulating C1 or RTN activates breathing robustly, but only RTN neuron stimulation produces active expiration, consistent with their role as central respiratory chemoreceptors. Conversely, C1 stimulation strongly stimulates ascending arousal systems and sighs, consistent with their postulated role in acute stress responses.

SIGNIFICANCE STATEMENT The C1 neurons and the retrotrapezoid nucleus (RTN) reside in the rostral ventrolateral medulla. Both regulate breathing and the cardiovascular system but in ways that are unclear because of technical limitations (anesthesia, nonselective neuronal actuators). Using optogenetics in unanesthetized rats, we found that selective stimulation of either RTN or C1 neurons activates breathing. However, only RTN triggers active expiration, presumably because RTN, unlike C1, has direct excitatory projections to abdominal premotor neurons. The arousal potential of the C1 neurons is far greater than that of the RTN, however, consistent with C1's projections to brainstem wake-promoting structures. In short, C1 neurons orchestrate cardiorespiratory and arousal responses to somatic stresses, whereas RTN selectively controls lung ventilation and arterial Pco₂ stability.

总体而言，梯形后核（RTN）和相邻的C1神经元调节呼吸，循环和警觉状态，但是以前操纵这些神经元活动的方法选择性不足以解析其相对作用。我们假设RTN和C1神经元调节呼吸的不同方面（例如，频率，振幅，主动呼气，叹气），并且它们从睡眠中产生唤醒的能力也不同。在这里，我们使用光遗传学和成年雄性和雌性Th- Cre大鼠的病毒载体组合来选择性地转导RTN（Phox2b ⁺ / Nmb ⁺）或C1神经元（Phox2b ⁺ / Th ⁺）与Channelrhodopsin-2。RTN光刺激适度增加了唤醒的可能性。RTN刺激可强劲增加呼吸频率和幅度；它还触发了强烈的主动到期，但没有发出叹息。与这些反应一致，RTN支配整个桥突呼吸网络，包括尾腹侧呼吸组的呼气前运动神经元，但RTN对调节觉醒的脑干区域（蓝斑，CGRP ⁺臂旁神经元）的预测非常有限。与RTN刺激相比，C1神经元刺激产生了强烈的唤醒力，呼吸频率和幅度也有类似的增加，但引起了叹气，没有主动呼气。与RTN不同，C1神经元支配蓝藻所在地CGRP ⁺臂旁复杂内的过程，并且缺乏对尾腹呼吸组的预测。总而言之，刺激C1或RTN可以强烈激活呼吸，但是只有RTN神经元刺激才能产生主动呼气，这与其作为中枢呼吸化学感受器的作用一致。相反，C1刺激强烈刺激上升的觉醒系统和叹气，这与它们在急性应激反应中的假定作用一致。

重要性声明C1神经元和后梯形核（RTN）驻留在延髓腹侧延髓。两者均调节呼吸和心血管系统，但由于技术限制（麻醉，非选择性神经元致动器）而以不清楚的方式进行。使用未麻醉大鼠的光遗传学，我们发现RTN或C1神经元的选择性刺激可激活呼吸。但是，仅RTN会触发主动呼气，这可能是因为RTN与C1不同，其直接兴奋性投射到腹部运动前神经元。C1神经元的唤醒潜力远大于RTN，但与C1对脑干唤醒促进结构的预测一致。简而言之，C1神经元可调节对躯体应激的心肺和唤醒反应，而RTN选择性地控制肺通气和动脉P合作₂稳定性。