Department of Physiology, University of Alberta, Edmonton, AB, Canada; Women and Children's Research Institute, University of Alberta, Edmonton, AB, Canada.
Department of Physiology, University of Alberta, Edmonton, AB, Canada; Women and Children's Research Institute, University of Alberta, Edmonton, AB, Canada; Neuroscience and Mental Health Institute, University of Alberta, Edmonton, AB, Canada.
Respir Physiol Neurobiol. 2019 Jul;265:153-160. doi: 10.1016/j.resp.2018.06.010. Epub 2018 Jun 19.
Breathing at rest is typically characterized by three phases: active inspiration, post-inspiration (or stage 1 expiration), and passive expiration (or stage 2 expiration). Breathing during periods of increased respiratory demand, on the other hand, engages active expiration through recruitment of abdominal muscles in order to increase ventilation. It is currently hypothesized that different phases of the respiratory rhythm are driven by three coupled oscillators: the preBötzinger Complex, driving inspiration, the parafacial respiratory group (pFRG), driving active expiration and the post-inspiratory Complex, driving post-inspiration. In this paper we review advances in the understanding of the pFRG and its role in the generation of active expiration across different developmental stages and vigilance states. Recent experiments suggest that the abdominal recruitment varies across development depending on the vigilance state, possibly following the maturation of the network responsible for the generation of active expiration and neuromodulatory systems that influence its activity. The activity of the pFRG is tonically inhibited by GABAergic inputs and strongly recruited by cholinergic systems. However, the sources of these modulatory inputs and the physiological conditions under which these mechanisms are used to recruit active expiration and increase ventilation need further investigation. Some evidence suggests that active expiration during hypercapnia is evoked through disinhibition, while during hypoxia it is elicited through activation of catecholaminergic C1 neurons. Finally, a discussion of experiments indicating that the pFRG is anatomically and functionally distinct from the adjacent and partially overlapping chemosensitive neurons of the retrotrapezoid nucleus is also presented.
在休息时，呼吸通常具有三个阶段：主动吸气、吸气后（或 1 期呼气）和被动呼气（或 2 期呼气）。另一方面，在呼吸需求增加期间，呼吸通过募集腹部肌肉来进行主动呼气，以增加通气。目前的假设是，呼吸节律的不同阶段是由三个耦合振荡器驱动的：前 Bötzinger 复合体，驱动吸气；副外侧呼吸群（pFRG），驱动主动呼气；以及吸气后复合体，驱动吸气后。在本文中，我们回顾了对 pFRG 的理解的进展及其在不同发育阶段和警觉状态下产生主动呼气的作用。最近的实验表明，腹部募集在不同的发育阶段随警觉状态而变化，这可能是负责产生主动呼气的网络以及影响其活动的神经调制系统成熟的结果。pFRG 的活动受到 GABA 能输入的紧张性抑制，并被胆碱能系统强烈募集。然而，这些调制输入的来源以及使用这些机制来募集主动呼气和增加通气的生理条件仍需要进一步研究。一些证据表明，在高碳酸血症期间，主动呼气是通过去抑制引起的，而在缺氧期间则是通过激活儿茶酚胺 C1 神经元引起的。最后，还讨论了一些实验，这些实验表明 pFRG 在解剖学和功能上与相邻的、部分重叠的延髓呼吸神经元（retrotrapezoid nucleus）不同。
