VOLATILE ANESTHETICS AND RESPIRATORY NEUROTRANSMISSION

本提案的总体目标是表征有效的，挥发性麻醉剂在体内自发活动的哺乳动物呼吸系统中对特定突触事件的作用。这项研究的发现将带来新的知识，增加我们对挥发性麻醉药改变完整中枢神经系统神经元功能的机制的理解。这个建议是独特的，因为我们提出的研究重点是在体内条件下完整的神经网络中已知功能的特定呼吸神经元。在我们的实验范式中，突触神经递质释放的水平与呼吸中枢正常功能时的水平相同。我们的总体假设是，挥发性麻醉药对中枢呼吸输出的影响主要是由于抑制兴奋性而不是增强抑制性突触神经传递。运动前神经元的动作电位记录与神经递质激动剂和拮抗剂的局部压力微射相结合，将用于检查麻醉诱导的兴奋性和抑制性神经传递改变的相对重要性，以及突触前和突触后机制。为了验证我们的假设，我们制定了三个具体目标。在具体的目的1中，我们将确定麻醉诱导的全犬模型中吸气和呼气前运动神经元的谷氨酸能兴奋和gaba能抑制的改变量。在具体目标2中，我们将确定麻醉诱导的突触前和突触后效应对这些前运动神经元整体抑制的相对贡献。在具体目标3中，我们将描述和对比氟烷、异氟烷和七氟烷对这些前运动神经元突触机制的差异剂和位点特异性作用。我们的模型将作为在体内探索其他神经回路的范例。此外，从我们提出的研究中获得的见解将使我们能够制定合理的基于机制的治疗策略，以最大限度地减少这些药物的严重副作用，例如心肺中枢的抑制。这种机制知识也可以帮助设计更安全的麻醉剂，对呼吸的有害影响最小。

The overall goal of this proposal is to characterize the actions of the potent, volatile anesthetics on specific synaptic events within the spontaneously active mammalian respiratory system, in vivo. The findings of the proposed research will result in new knowledge that will increase our understanding of the mechanisms by which volatile anesthetics alter neuronal function in the intact central nervous system. This proposal is unique because we propose studies that focus on specific respiratory neurons of known function in an intact neuronal network under in vivo conditions. In our experimental paradigm synaptic neurotransmitters are released at levels that are present during normal function of the respiratory centers. Our overall hypothesis is that the effects of volatile anesthetics on central respiratory output are mainly due to depression of excitatory rather than enhancement of inhibitory synaptic neurotransmission. Recordings of action potentials from premotor neurons in conjunction with localized pressure microejection of neurotransmitter agonists and antagonists will be used to examine the relative importance of anesthetic-induced alterations on excitatory and inhibitory neurotransmission, and on presynaptic vs. postsynaptic mechanisms. Three specific aims have been developed to test our hypothesis. In specific aim 1, we will determine the amount of overall anesthetic-induced alterations of glutamatergic excitation and GABAergic inhibition of inspiratory and expiratory premotor neurons in a decerebrate canine model. In specific aim 2, we will determine the relative contribution of anesthetic-induced presynaptic and postsynaptic effects to the overall depression of these premotor neurons. In specific aim 3, we will characterize and contrast the differential agent-and site-specific effects of halothane, isoflurane, and sevoflurane on the synaptic mechanisms of these premotor neurons. Our model will serve as a paradigm to explore other neuronal circuits in vivo. Furthermore, the insights that will be gained from our proposed studies will allow us to develop rational mechanism- based therapeutic strategies that will minimize the serious side- effects of these agents, such as depression of the cardiorespiratory centers. Such mechanistic knowledge could also help in the design of safer anesthetic agents with the least deleterious effects on respiration.