The spatio-temporal characteristics of action potential initiation in layer 5 pyramidal neurons: a voltage imaging study
The spatio-temporal characteristics of action potential initiation in layer 5 pyramidal neurons: a voltage imaging study
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DOI：
10.1113/jphysiol.2011.209015
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发表时间：
2011-09-01
影响因子：
5.5
通讯作者：
Zecevic, Dejan
中科院分区：
文献类型：
--
作者：
Popovic, Marko A.;Foust, Amanda J.;Zecevic, Dejan
轴突初始段 (AIS) 中 Na+ 通道聚类的空间模式在调整神经元计算中起着至关重要的作用，并且 Na+ 通道分布的变化已被证明可以介导轴突中神经元可塑性的新形式。然而，通道分布的免疫细胞化学数据可能无法直接预测动作电位启动的时空特征，并且先前的电生理测量要么是间接的（细胞外），要么缺乏足够的空间分辨率（细胞内）来直接表征尖峰触发区（TZ）。我们利用高灵敏度膜电位成像（V-m 成像）技术的关键方法改进来直接确定功能术语中定义的尖峰 TZ 的位置和长度。结果表明，在小鼠皮质第 5 层锥体细胞的成熟轴突中，动作电位在距体细胞 20 至 40 μm 中心、长度约为 20 μm 的区域中起始。从该区域，AP 去极化波在不到一毫秒的时间内侵入朗飞的初始节点，并以跳跃方式传播到轴突侧枝，在所有生理相关频率下都不会失败。我们进一步证明，与成熟轴突中的跳跃式传导相比，AP 传播在髓鞘形成之前在未成熟轴突中是非跳跃式（单调的）。
The spatial pattern of Na+ channel clustering in the axon initial segment (AIS) plays a critical role in tuning neuronal computations, and changes in Na+ channel distribution have been shown to mediate novel forms of neuronal plasticity in the axon. However, immunocytochemical data on channel distribution may not directly predict spatio-temporal characteristics of action potential initiation, and prior electrophysiological measures are either indirect (extracellular) or lack sufficient spatial resolution (intracellular) to directly characterize the spike trigger zone (TZ). We took advantage of a critical methodological improvement in the high sensitivity membrane potential imaging (V-m imaging) technique to directly determine the location and length of the spike TZ as defined in functional terms. The results show that in mature axons of mouse cortical layer 5 pyramidal cells, action potentials initiate in a region similar to 20 mu m in length centred between 20 and 40 mu m from the soma. From this region, the AP depolarizing wave invades initial nodes of Ranvier within a fraction of a millisecond and propagates in a saltatory fashion into axonal collaterals without failure at all physiologically relevant frequencies. We further demonstrate that, in contrast to the saltatory conduction in mature axons, AP propagation is non-saltatory (monotonic) in immature axons prior to myelination.