Action potential initiation and propagation in CA3 pyramidal axons
Action potential initiation and propagation in CA3 pyramidal axons
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DOI：
10.1152/jn.01288.2006
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发表时间：
2007-05-01
影响因子：
2.5
通讯作者：
Mennerick, Steven
中科院分区：
文献类型：
--
作者：
Meeks, Julian P.;Mennerick, Steven
薄薄的、无髓鞘的轴突密集地分布在哺乳动物的海马体和皮层。然而，在细轴突中，突状突起发生的位置和动力学尚不清楚。我们研究了幼年大鼠海马CA3神经元的spike起始和增殖的基本特性。钠通道α亚基分布和河豚毒素的局部应用表明，CA3神经元中第一个阈值跨越的位置与体细胞远端35 μ m相似，比我们之前的估计更近一些。这种差异可以通过同时进行全细胞体细胞和细胞外轴突记录的发现来解释，轴突延伸到体细胞远端约100 μ m的区域，由于钠从高密度通道流入，几乎同时达到最大的去极化速率。结合观察到的钠通道染色分布的近端轴突模型再现了躯体和轴突尖峰波形的显著特征，包括预测的起始区、特征尖峰潜伏期和传导速度。刺激强度和重复尖峰均未改变首选起始区，但重复尖峰使阈值升高，并显著减慢了初始节段募集时间和传导速度。我们的工作定义了海马主细胞轴突的起始和繁殖动力学，并可能有助于调和最近关于其他轴突起始位点的争议。
Thin, unmyelinated axons densely populate the mammalian hippocampus and cortex. However, the location and dynamics of spike initiation in thin axons remain unclear. We investigated basic properties of spike initiation and propagation in CA3 neurons of juvenile rat hippocampus. Sodium channel alpha subunit distribution and local applications of tetrodotoxin demonstrate that the site of first threshold crossing in CA3 neurons is similar to 35 mu m distal to the soma, somewhat more proximal than our previous estimates. This discrepancy can be explained by the finding, obtained with simultaneous whole cell somatic and extracellular axonal recordings, that a zone of axon stretching to similar to 100 mu m distal to the soma reaches a maximum rate of depolarization nearly synchronously by the influx of sodium from the high-density channels. Models of the proximal axon incorporating observed distributions of sodium channel staining recapitulated salient features of somatic and axonal spike waveforms, including the predicted initiation zone, characteristic spike latencies, and conduction velocity. The preferred initiation zone was unaltered by stimulus strength or repetitive spiking, but repetitive spiking increased threshold and significantly slowed initial segment recruitment time and conduction velocity. Our work defines the dynamics of initiation and propagation in hippocampal principal cell axons and may help reconcile recent controversies over initiation site in other axons.