Laboratory of Cellular Neurobiology, School of Life Sciences, Tokyo University of Pharmacy and Life Sciences, 1432-1 Horinouchi, Hachioji,Tokyo 192-0392, Japan.
Brain Res. 2011 Apr 6;1383:22-35. doi: 10.1016/j.brainres.2011.01.097. Epub 2011 Feb 3.
Non-synaptic interactions among neurons via extracellular electric fields may play functional roles in the CNS. Previously in a study using voltage-sensitive dye imaging, we reported characteristic membrane polarization profiles in the CA1 region of hippocampal slices during exposure to extracellular DC fields: slow monophasic polarization in somatic region and biphasic polarization (fast polarization and following slow repolarization) in mid-dendritic region. Here, using optical imaging and patch-clamp recordings, we showed that CA1 pyramidal neurons indeed show the characteristic polarization in response to DC fields, and investigated the mechanism underlying the profiles. Both the monophasic and biphasic polarization could be fitted with a double exponential function. The τs (ms) were 12.6±2.5 and 56.0±4.7 for the monophasic polarization, and 14.2±1.2 and 42.2±2.8 for the biphasic polarization. Based on our previous theoretical studies, we hypothesized that lower resistivity in the distal apical dendrites is responsible for generating the characteristic polarization profiles. We tested this hypothesis by removing the distal apical dendrites or by blocking ion channel-mediated conductance. Removal of distal dendrites caused drastic changes in the polarization profiles, e.g. biphasic polarization was damped. However, none of the blockers tested had a marked effect on the biphasic polarization. Our results demonstrate the importance of the apical dendrite for generating the characteristic polarization profiles, and suggest that voltage-activated conductance, including HCN channel-mediated conductance, had only minor contributions to these profiles. These findings provide a better understanding of how neurons in the CNS respond to extracellular electric fields.
神经元之间通过细胞外电场的非突触相互作用可能在中枢神经系统中发挥功能作用。以前，在一项使用电压敏感染料成像的研究中，我们报告了海马切片 CA1 区在暴露于细胞外直流场时特征性的膜极化谱：在体细胞区为缓慢的单相极化，在中间树突区为双相极化（快速极化和随后的缓慢复极化）。在这里，我们使用光学成像和膜片钳记录，显示 CA1 锥体神经元确实对直流场表现出特征性的极化，并研究了其机制。单相和双相极化都可以用双指数函数拟合。单相极化的 τs（ms）为 12.6±2.5 和 56.0±4.7，双相极化的 τs（ms）为 14.2±1.2 和 42.2±2.8。基于我们以前的理论研究，我们假设远端顶树突的低电阻率是产生特征性极化谱的原因。我们通过去除远端顶树突或阻断离子通道介导的电导来测试这个假设。去除远端树突会导致极化谱的剧烈变化，例如双相极化减弱。然而，测试的阻断剂都没有对双相极化产生明显的影响。我们的结果表明顶树突对产生特征性极化谱的重要性，并表明电压激活的电导，包括 HCN 通道介导的电导，对这些谱只有较小的贡献。这些发现为理解中枢神经系统中的神经元如何对细胞外电场做出反应提供了更好的认识。
