Neuronal basis of bimodal ventilation in lower vertebrates

呼吸可能是哺乳动物最重要、最强健和最有节奏的行为，但有关产生呼吸节奏的节律性神经元回路的性质的关键问题在很大程度上仍未解决。这些包括：(A)产生节律的回路有多广？(B)能否将其简化为若干离散但相互作用的神经元振荡器？以及(C)电路是如何进化的？其动机是：(A)呼吸对人类的健康和福祉至关重要，(B)需要更多关于非哺乳动物物种呼吸的中枢控制的知识，以及(C)比较方法有助于阐明其他系统的生理基础的神经元机制，拟议的实验重点是低等脊椎动物的神经元控制呼吸，并解决节律电路的进化。最近的数据表明，鱼类的呼吸节律，青蛙和哺乳动物是由位于脑干内的一对神经元时钟或振荡器产生的。这提出了一种可能性，即哺乳动物中的一个或两个呼吸振荡器最早出现在4亿年前的一种古老的呼吸鱼类中。这一提议的总体目的是测试这种可能性，并通过以下方式扩大我们对低等脊椎动物呼吸节律发生的理解：(1)使用新的“绵羊浸泡”技术来快速识别和确定青蛙和其他低等脊椎动物大脑中具有重要功能的节律产生区域的药理学特性；(2)比较投射到这些区域的神经元的位置、电学性质和分子指纹与其他脊椎动物的呼吸神经元群体。

Breathing is perhaps the most vital, robust and rhythmic behavior in mammals yet key questions regarding the nature of the rhythmogenic neuronal circuit that generates the breathing rhythm remain largely unresolved. These include: (a) How extensive is the rhythmogenic circuit? (b) Can it be reduced to a number of discrete, but interacting neuronal oscillators?  And (c) how did the circuit evolve?  Motivated by (a) the fact that breathing is quintessential to human health and well-being, (b) the need for greater knowledge about central control of breathing in non-mammalian species and (c) the fact that a comparative approach has been instrumental in illuminating neuronal mechanisms underlying the physiology of other systems, the proposed experiments focus on neuronal control of breathing in lower vertebrates and address the evolution of the rhythmogenic circuit.Recent data suggest that the breathing rhythms in fish, frog and mammals is generated by pairs of neuronal clocks, or oscillators, located within the brainstem. This raises the possibility that one or both of the breathing oscillators in mammals first arose in an ancient air-breathing fish, 400 million years ago.The overall aim of this proposal is to test this possibility and expand our understanding of respiratory rhythmogenesis in lower vertebrates by:(1) Using a novel "sheep-dip" technique to quickly identify and determine the pharmacological properties of functionally important rhythmogenic regions within the isolated brainstems of frogs and other lower vertebrates, and(2) Comparing the location, electrical properties and molecular fingerprint of the neurons that project to these regions with populations of respiratory neurons in other vertebrates.