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.

由于缺乏围绕关键转换的信息，追踪与脊椎动物通风相关的中枢节律发生器的演变受到阻碍。首先，仅在来自四个脊椎动物群、七鳃鳗、无尾目两栖动物、海龟和哺乳动物（主要是啮齿动物）的少数物种中详细研究了中枢节律的产生。其次，缺乏关于从呼吸水的鱼到呼吸空气的羊膜动物（爬行动物、鸟类和哺乳动物）的转变的信息。具体来说，鱼的呼吸节律发生器似乎是单个振荡器，能够产生呼吸周期的两个阶段（扩张和压缩）并投射到支配颊咽肌的颅神经中的运动神经元。在羊膜中，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）并投射到延髓腹外侧的前运动神经元，然后投射到支配胸部和腹部肌肉（爬行动物、鸟类和哺乳动物）的脊髓运动神经元）。对处于这一过渡阶段的一组两栖动物（无尾龙）的研究提出了有趣的可能性，但由于我们探索的各种原因，也提出了未解决的问题。在这篇综述中，我们总结了与呼吸相关的节律产生回路的已知信息，这些回路来自每个不同脊椎动物类别的不同菱形节段。假设在发育过程中，每只脊椎动物的每一对菱形体中都会形成振荡回路，