Department of Zoology, University of British Columbia, Canada.
Département de Pédiatrie, Université Laval, Canada.
Respir Physiol Neurobiol. 2022 Jan;295:103781. doi: 10.1016/j.resp.2021.103781. Epub 2021 Sep 1.
Tracing the evolution of the central rhythm generators associated with ventilation in vertebrates is hindered by a lack of information surrounding key transitions. To begin with, central rhythm generation has been studied in detail in only a few species from four vertebrate groups, lamprey, anuran amphibians, turtles, and mammals (primarily rodents). Secondly, there is a lack of information regarding the transition from water breathing fish to air breathing amniotes (reptiles, birds, and mammals). Specifically, the respiratory rhythm generators of fish appear to be single oscillators capable of generating both phases of the respiratory cycle (expansion and compression) and projecting to motoneurons in cranial nerves innervating bucco-pharyngeal muscles. In the amniotes we find oscillators capable of independently generating separate phases of the respiratory cycle (expiration and inspiration) and projecting to pre-motoneurons in the ventrolateral medulla that in turn project to spinal motoneurons innervating thoracic and abdominal muscles (reptiles, birds, and mammals). Studies of the one group of amphibians that lie at this transition (the anurans), raise intriguing possibilities but, for a variety of reasons that we explore, also raise unanswered questions. In this review we summarize what is known about the rhythm generating circuits associated with breathing that arise from the different rhombomeric segments in each of the different vertebrate classes. Assuming oscillating circuits form in every pair of rhombomeres in every vertebrate during development, we trace what appears to be the evolutionary fate of each and highlight the questions that remain to be answered to properly understand the evolutionary transitions in vertebrate central respiratory rhythm generation.
追踪与脊椎动物通气相关的中央节律发生器的进化受到关键转变相关信息缺失的阻碍。首先，只有来自四个脊椎动物群体（七鳃鳗、蛙类两栖动物、海龟和哺乳动物（主要是啮齿动物））的少数几种物种对中央节律产生进行了详细研究。其次，关于从水生鱼类到空气呼吸羊膜动物（爬行动物、鸟类和哺乳动物）的转变，信息也很缺乏。具体来说，鱼类的呼吸节律发生器似乎是单一振荡器，能够产生呼吸周期的两个阶段（扩张和压缩），并投射到支配口咽肌肉的颅神经运动神经元。在羊膜动物中，我们发现振荡器能够独立产生呼吸周期的不同阶段（呼气和吸气），并投射到腹外侧髓质中的前运动神经元，这些神经元反过来投射到支配胸腹部肌肉的脊髓运动神经元（爬行动物、鸟类和哺乳动物）。对处于这一转变中的一组两栖动物（蛙类）的研究提出了有趣的可能性，但由于我们探索的各种原因，也提出了尚未回答的问题。在这篇综述中，我们总结了与呼吸相关的节律产生电路的知识，这些电路源于每个不同脊椎动物类群的不同脑区节段。假设在每个脊椎动物的每一对脑区节段中都形成振荡电路，我们追踪每个脑区节段的进化命运，并突出仍然存在的问题，以正确理解脊椎动物中央呼吸节律产生的进化转变。
