Cellular Mechanisms Underlying State-Dependent Neural Inhibition with Magnetic Stimulation

重复经颅磁刺激(RTMS)神经调制技术被广泛应用于 治疗许多神经系统疾病。磁刺激的输出在很大程度上取决于 刺激参数，如磁场的持续时间、频率和强度， 因为它们影响单个神经元的兴奋、突触传递和离子通道 动力学。最近的临床证据表明，神经系统的兴奋状态在 在磁刺激的结果中起着重要作用(称为“状态依赖”)。 例如，磁刺激产生不同的感知或行为结果 取决于大脑的兴奋性水平。大脑的瞬时状态已经被用来 促进TMS有效的诱导可塑性。与临床上的成功相比，神经 依赖状态的磁刺激背后的机制在很大程度上是未知的。 以前，这个问题很难在细胞和离子通道水平上解决，因为 大尺寸TMS线圈不能提供高度特异性刺激。最新的发展动态 微线圈技术提高了线圈刺激的细胞特异性。这些亚毫米大小的 线圈允许研究单个细胞对磁刺激的反应，并观察其 国家依存性。初步数据报告了一个有趣的“国家依赖”现象 单细胞水平-处于低活跃状态的神经元更容易被相同的 磁刺激比神经元处于高活跃状态。这倡导对 大脑激发状态的动力学，用于优化设计、练习和分析磁力 对大脑的刺激。 在这个方案中，我们将使用电生理学、药理学和计算机的组合工具 模拟研究状态依赖神经的细胞和分子机制 采用新型微线圈技术的磁刺激抑制。因为神经层面的 活性在神经元对磁抑制的反应中是必不可少的，Aim 1.1将研究 体外生理/病理谱下的状态依赖性磁刺激 条件。单个神经元的生物物理性质，如大小、形状和膜 神经元的导电性，在磁刺激中起着重要作用。不同类型的细胞具有 也被发现在磁刺激中具有不同的敏感性。AIM 1.2将调查 神经元的生物物理性质和类型对状态依赖刺激的影响。 计算模型提供了对潜在的细胞和离子通道机制的见解 状态依赖抑制。我们将检验高频磁刺激的假设 导致钠通道电导显著降低，从而导致状态依赖 抑制神经元活性。AIM 2.1试图直接观察还原的钠通道 电导与电压钳制实验。AIM 2.2将使用药理学工具直接 激活钠通道，观察其对状态依赖性磁刺激的影响。 单个神经元是神经系统的构建单位。状态依赖的抑制作用 磁场可能会对TMS的机械设计产生重大影响 在临床环境中实践。微线圈技术是全新的，只有少数几个实验室能够 将下一代微线圈器件的制造与对 技术在分子水平上的影响。了解细胞和分子机制 微线圈刺激将为这一尖端技术的发展提供指导。

Neural modulation with repetitive transcranial magnetic stimulation (rTMS) is widely used for the treatment of many neurological diseases. Output of magnetic stimulation is largely dependent on the stimulation parameters, such as the duration, frequency, and intensity of the magnetic field, because they affect the excitation of individual neurons, synaptic transmission, and ion channel dynamics. Recent clinical evidence suggests that the excitation state of the nervous system plays a significant role in the outcome of magnetic stimulation (termed “state-dependent”). For example, magnetic stimulation produces different perceptual or behavioral outcomes that are dependent on the excitability levels of the brain. The instantaneous brain state has been used to promote efficacious induction of plasticity by TMS. In comparison to the clinical success, the neural mechanisms underlying state-dependent magnetic stimulation is largely unknown. Previously, this question has been difficult to address at the cellular and ion channel levels because the large sized TMS coil could not provide highly specific stimulation. Recent development of the micro-coil technology improved the cellular specificity of coil stimulation. These sub-millimeter sized coils allow the study of single cell responses to the magnetic stimulation, and the observation of its state-dependency. Preliminary data report an interesting “state-dependent” phenomena at the single cell level – neurons in a low active state are easier to be completely inhibited by the same magnetic stimulation than the neurons in a high active state. This advocates for monitoring the dynamics of the brain’s excitation states for the optimal design, practice, and analysis of magnetic stimulation on the brain. In this proposal, we will use combined tools of electrophysiology, pharmacology, and computer simulation to investigate the cellular and molecular mechanisms underlying state-dependent neural inhibition by magnetic stimulation with the novel micro-coil technology. Since the level of neural activity is essential in the neuronal response to magnetic inhibition, Aim 1.1 will investigate the state-dependent magnetic stimulation under a spectrum of in vitro physiological/pathological conditions. The biophysics properties of single neurons, such as the size, shape, and membrane conductivity of the neuron, play important roles in magnetic stimulation. Cells of different types have also been found to have different sensitivities in magnetic stimulation. Aim 1.2 will investigate the impact of biophysics properties and types of neurons on state-dependent stimulation. Computational modeling provides insights on the cellular and ion channel mechanisms underlying state-dependent inhibition. We will test the hypothesis that high frequency magnetic stimulation causes a significant reduction in sodium channel conductance, which leads to the state-dependent suppression of neuron activity. Aim 2.1 seeks to directly observe the reduced sodium channel conductance with voltage clamp experiments. Aim 2.2 will use pharmacological tools to directly activate the sodium channels and observe its impact on state-dependent magnetic stimulation. Individual neurons are the building units of the nervous system. The state-dependent inhibition by the magnetic field could have significant implications to the mechanistically-based design of TMS practice in clinical settings. Micro-coil technology is brand new, and only a few labs are able to combine fabrication of the next generation micro-coil devices with an understanding of the technique's effects at a molecular level. Understanding the cellular and molecular mechanisms of micro-coil stimulation will provide guidelines for the development of this cutting-edge technology.