Department of Physiology, Hebei Medical University, Shijiazhuang, Hebei, 050017, China.
School of Nursing, Hebei Medical University, Shijiazhuang, Hebei, 050000, China.
J Neurosci. 2019 Apr 10;39(15):2837-2846. doi: 10.1523/JNEUROSCI.2048-18.2018. Epub 2019 Jan 9.
The nucleus tractus solitarii (NTS) is implicated in the control of breathing, but the neuronal phenotype and circuit mechanism involved in such a physiological function remain incompletely understood. This study focused on the respiratory role of paired-like homeobox 2b gene (Phox2b)-expressing NTS neurons and sought to determine whether selective stimulation of this set of neurons activates breathing in male mice. A Cre-dependent vector encoding a Gq-coupled human M3 muscarinic receptor (hM3Dq) was microinjected into the NTS of Phox2b-Cre transgenic mice. The hM3Dq-transduced neurons were pharmacologically activated in conscious mice while respiratory effects were measured by plethysmography. We demonstrate that chemogenetic stimulation of Phox2b-expressing NTS neurons significantly increased baseline minute volume via an increase in respiratory frequency rather than tidal volume. Chemogenetic stimulation also synergized with moderate CO stimulation to enhance pulmonary ventilatory response. Selective ablation of Phox2b-expressing NTS neurons notably attenuated a hypercapnic ventilatory response. Moreover, histological evidence revealed that stimulation of Phox2b-expressing NTS neurons increased neuronal activity of the preBötzinger complex. Finally, we presented the neuroanatomical evidence of direct projection of Phox2b-expressing NTS neurons to putative respiratory central pattern generator. Overall, these findings suggest that selective activation of Phox2b-expressing NTS neurons potentiates baseline pulmonary ventilation via an excitatory drive to respiratory central pattern generator and this group of neurons is also required for the hypercapnic ventilatory response. The nucleus tractus solitarii (NTS) has been implicated in the control of breathing. The paired-like homeobox 2b gene (Phox2b) is the disease-defining gene for congenital central hypoventilation syndrome and is restrictively present in brainstem nucleus, including the NTS. Using a chemogenetic approach, we demonstrate herein that selective stimulation of Phox2b-expressing NTS neurons vigorously potentiates baseline pulmonary ventilation via an excitatory drive to respiratory central pattern generator in rodents. Genetic ablation of these neurons attenuates the hypercapnic ventilatory response. We also suggest that a fraction of Phox2b-expressing neurons exhibit CO sensitivity and presumably function as central respiratory chemoreceptors. The methodology is expected to provide a future applicability to the patients with sleep-related hypoventilation or apnea.
孤束核（NTS）参与呼吸控制，但涉及这种生理功能的神经元表型和回路机制仍不完全清楚。本研究集中于配对同源盒 2b 基因（Phox2b）表达的 NTS 神经元的呼吸作用，并试图确定选择性刺激这组神经元是否会激活雄性小鼠的呼吸。一种依赖 Cre 的载体，编码一种与 Gq 偶联的人 M3 毒蕈碱受体（hM3Dq），被微注射到 Phox2b-Cre 转基因小鼠的 NTS 中。在清醒的小鼠中，通过使用测胸廓容积描记法来测量呼吸效应，对 hM3Dq 转导的神经元进行药理学激活。我们证明，化学遗传刺激 Phox2b 表达的 NTS 神经元通过增加呼吸频率而不是潮气量显著增加了基础分钟通气量。化学遗传刺激还与适度的 CO 刺激协同作用，增强了肺通气反应。选择性消融 Phox2b 表达的 NTS 神经元显著减弱了高碳酸血症性通气反应。此外，组织学证据表明，刺激 Phox2b 表达的 NTS 神经元增加了 PreBötzinger 复合体的神经元活动。最后，我们提供了 Phox2b 表达的 NTS 神经元直接投射到呼吸中枢模式发生器的神经解剖学证据。总的来说，这些发现表明，选择性激活 Phox2b 表达的 NTS 神经元通过对呼吸中枢模式发生器的兴奋性驱动来增强基础肺通气，并且这群神经元对于高碳酸血症性通气反应也是必需的。孤束核（NTS）被认为与呼吸控制有关。配对同源盒 2b 基因（Phox2b）是先天性中枢性低通气综合征的致病基因，在脑干核，包括 NTS 中都有表达。本文采用化学遗传方法证明，在啮齿动物中，选择性刺激 Phox2b 表达的 NTS 神经元通过对呼吸中枢模式发生器的兴奋性驱动，强烈增强基础肺通气。这些神经元的遗传消融减弱了高碳酸血症性通气反应。我们还提出，一部分 Phox2b 表达的神经元表现出 CO 敏感性，可能作为中枢呼吸化学感受器发挥作用。该方法有望为睡眠相关低通气或呼吸暂停的患者提供未来的适用性。
