Cellular Mechanisms Underlying State-Dependent Neural Inhibition with Magnetic Stimulation

利用重复经颅磁刺激（rTMS）的神经调制被广泛用于 治疗多种神经系统疾病。磁刺激的输出在很大程度上取决于 刺激参数，例如磁场的持续时间、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起着 在磁刺激的结果中起重要作用（称为“状态依赖性”）。 例如，磁刺激产生不同的感知或行为结果， 取决于大脑的兴奋程度瞬时大脑状态已经被用来 促进TMS对可塑性的有效诱导。与临床成功相比， 状态依赖性磁刺激的潜在机制在很大程度上是未知的。 以前，这个问题在细胞和离子通道水平上很难解决，因为 大尺寸的TMS线圈不能提供高度特异性的刺激。新发展 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 线圈允许研究单细胞对磁刺激的反应，并观察其 国家依赖初步数据报告了一个有趣的“状态依赖”现象， 单细胞水平-处于低活性状态的神经元更容易被相同的 磁刺激比处于高活跃状态的神经元。这一倡议主张监测 大脑的最佳设计，实践和分析磁激励状态的动力学 刺激大脑。 在这个建议中，我们将使用电生理学，药理学和计算机的组合工具 模拟研究状态依赖性神经元的细胞和分子机制 通过新型微线圈技术的磁刺激抑制。由于神经水平 活动是必不可少的神经元反应磁抑制，目的1.1将探讨 体外生理/病理谱下状态依赖性磁刺激 条件单个神经元的生物物理特性，如大小，形状和膜 神经元的电导率，在磁刺激中起重要作用。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。目标1.2将调查 生物物理性质和神经元类型对状态依赖性刺激的影响。 计算建模提供了对细胞和离子通道机制的见解， 状态依赖性抑制我们将检验高频磁刺激 导致钠通道电导显著降低，这导致状态依赖性 抑制神经元活动。目的2.1旨在直接观察还原钠通道 电导与电压钳实验。目标2.2将使用药理学工具直接 激活钠通道并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。状态依赖性抑制 磁场可能对TMS的机械设计产生重大影响 在临床环境中实践。微弹簧圈技术是全新的，只有少数实验室能够 联合收割机制造下一代微弹簧圈装置， 技术在分子水平上的影响。了解细胞和分子机制， 微线圈刺激将为这项尖端技术的发展提供指导方针。

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.