University of Tokyo, Bunkyo-ku, Tokyo, Japan.
J Neurosci. 2012 Feb 22;32(8):2868-76. doi: 10.1523/JNEUROSCI.5365-11.2012.
Depolarization of the neuronal soma augments synaptic output onto postsynaptic neurons via long-range, axonal cable properties. Here, we report that the range of this somatic influence is spatially restricted by not only axonal path length but also a branching-dependent decrease in axon diameter. Cell-attached recordings of action potentials (APs) from multiple axon branches of a rat hippocampal CA3 pyramidal cell revealed that an AP was broadened following a 20 mV depolarization of the soma and reverted to a normal width during propagation down the axon. The narrowing of the AP depended on the distance traveled by the AP and on the number of axon branch points through which the AP passed. These findings were confirmed by optical imaging of AP-induced calcium elevations in presynaptic boutons, suggesting that the somatic membrane potential modifies synaptic outputs near the soma but not long-projection outputs. Consistent with this prediction, whole-cell recordings from synaptically connected neurons revealed that depolarization of presynaptic CA3 pyramidal cells facilitated synaptic transmission to nearby CA3 pyramidal cells, but not to distant pyramidal cells in CA3 or CA1. Therefore, axonal geometry enables the differential modulation of synaptic output depending on target location.
神经元胞体去极化通过长程、轴突电缆性质增强突触后神经元的突触输出。在这里，我们报告说，这种胞体影响的范围不仅受到轴突路径长度的限制，还受到分支依赖性的轴突直径减小的限制。从大鼠海马 CA3 锥体神经元的多个轴突分支进行细胞贴附记录动作电位 (AP) 显示，胞体去极化 20 mV 后 AP 变宽，并在轴突向下传播过程中恢复正常宽度。AP 的变窄取决于 AP 行进的距离以及 AP 通过的轴突分支点的数量。这些发现通过光学成像 AP 诱导的突触前末梢钙升高得到证实，这表明胞体膜电位改变了靠近胞体的突触输出，但不改变长投射输出。与这一预测一致，从突触连接的神经元进行全细胞记录显示，CA3 锥体神经元的去极化促进了与附近 CA3 锥体神经元的突触传递，但不能促进 CA3 或 CA1 中的远距离锥体神经元的传递。因此，轴突几何形状使得根据目标位置对突触输出进行差异调节成为可能。
