Neuronal basis of cardiorespiratory control in vertebrates

心肺控制对所有脊椎动物的生存至关重要，但我们对其中涉及的神经元回路的了解还很初级，部分原因是除了哺乳动物之外，几乎没有数据来指导我们。我的NSERC资助的研究计划通过研究低等脊椎动物的心肺节律产生来解决这一重要的知识鸿沟。我们的大部分工作都集中在牛蛙呼吸节律的产生上，使用的是一种孤立的脑干准备。这种准备产生的呼吸运动模式与完整动物的呼吸运动模式相似，持续至少24小时。蝌蚪的这种韧性和发育的可及性使青蛙成为教授神经科学和研究脊椎动物神经元发育和功能的理想选择。我们发现牛蛙和哺乳动物在控制呼吸的神经元回路上有着惊人的相似之处，尽管它们的呼吸机制存在根本差异。我们发现了三个对节律发生必不可少的离散部位(即振荡器)；一个用于口腔呼吸，另外两个用于肺充气。这些振荡器之间的相互作用(即，它们的耦合)是正常呼吸运动模式所必需的。在哺乳动物中也发现了三个耦合的呼吸振荡器，两个用于吸气，另一个用于呼气。此外，哺乳动物和牛蛙大脑中的振荡器是双向重复的，占据相似的后脑菱形脑位置，似乎有几个共同的功能特性。最近，我的研究生们发现：(A)网络兴奋的轻微增加会导致口腔振荡器转变为分布式节奏生成网络(即口腔振荡器部位的神经元活动不再是节奏生成的关键)，以及(B)青蛙神经系统中脊髓神经(SN)III水平的第四个双边重复振荡器，它可能是交感神经系统的一部分。这项研究的总体目标是通过对网络激励将离散的呼吸和交感振荡器转化为分布式网络的假设进行批判性评估，以增加我们对心肺循环的理解。在接下来的5年里，我和我的受训者将：(A)将交感振荡器精确定位到脊髓中的特定神经元群体；(B)测试网络兴奋是否会将肺和交感振荡器转换为分布式网络，就像它对口腔所做的那样；以及(C)测试在更完整的准备中，哪种架构-振荡器和分布式-最有可能。这项研究将(A)在细胞和比较神经科学方面提供极好的培训机会；(B)为青蛙的心肺节律产生网络提供新的线索；(C)有可能确定哺乳动物的交感振荡器的身份--这是加深对我们如何呼吸和调节组织灌流的机械理解的重要新知识。

Cardiorespiratory control is essential for survival of all vertebrates, yet our understanding of the neuronal circuits involved is rudimentary, in part because there is little data beyond mammals to guide us. My NSERC-funded research program addresses this important knowledge gap by investigating cardiorespiratory rhythm generation in lower vertebrates. Most of our efforts have focused on respiratory rhythm generation in the bullfrog by using an isolated brainstem preparation. This preparation produces breathing motor patterns resembling those of intact animals for at least 24 hours. This resilience and the developmental accessibility of tadpoles makes frogs ideal for teaching neuroscience and for studying neuronal development and function in vertebrates. We discovered striking similarities in the neuronal circuits controlling breathing between bullfrogs and mammals, despite fundamental differences in their breathing mechanics. We found three discrete sites essential for rhythmogenesis (i.e., oscillators); one is for buccal ventilation, the other two are for lung inflation. Interactions between these oscillators (i.e.., their coupling) is required for the normal breathing motor patterns. Three coupled respiratory oscillators in mammals have also been identified, two for inspiration, the other for expiration. Moreover, the oscillators in the mammal and bullfrog brainstems are bilaterally iterated, occupy similar hindbrain rhombomere locations, and appear to share several functional properties. Recently, my graduate students discovered (a) that a mild increase in network excitation causes the buccal oscillator to transform into a distributed rhythm generating network (i.e. neuronal activity at the site of the buccal oscillator is no longer critical for rhythm generation) and (b) a fourth bilaterally-iterated oscillator in the frog nervous system at the level of Spinal Nerve (SN) III that is likely part of the sympathetic nervous system. The overall objective of the proposed research is to increase our understanding of cardiorespiratory circuits by critically evaluating the hypothesis that network excitation transforms discrete respiratory and sympathetic oscillators into distributed networks. In the next 5 years, my trainees and I will (a) pinpoint sympathetic oscillators to specific neuronal populations in the spinal cord; (b) test if network excitation transforms lung and sympathetic oscillators into distributed networks, as it does the buccal; and (c) test which architecture - oscillator vs distributed - is most likely in more intact preparations. This research will (a) provide excellent training opportunities in cellular and comparative neuroscience; (b) shed new light on cardiorespiratory rhythm generating networks in frogs; and (c) have the potential to determine the identity of the sympathetic oscillator in mammals - important new knowledge for a deeper mechanistic understanding of how we breathe and regulate tissue perfusion.