Axonal site of spike initiation enhances auditory coincidence detection
Axonal site of spike initiation enhances auditory coincidence detection
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DOI：
10.1038/nature05347
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发表时间：
2006-12-21
期刊：
影响因子：
64.8
通讯作者：
Ohmori, Harunori
中科院分区：
文献类型：
--
作者：
Kuba, Hiroshi;Ishii, Takahiro M.;Ohmori, Harunori
神经元在轴突初始段或轴突第一个节点启动尖峰（1-4）。然而，目前尚不清楚刺突起始位置如何影响神经元的活动和功能。在鸟类的层状核中，神经元充当声源定位的巧合检测器，并在每个特征频率（CF）下分别编码耳间时差（ITDs）（5-7）。我们发现，在雏鸡的层状核中，轴突的尖刺起始位点与体细胞有一定距离，从而在每个CF处获得最高的ITD灵敏度。高CF （2.5-3.3 kHz）和中CF （1.0-2.5 kHz）神经元的体细胞中没有Na+通道，而是聚集在轴突与体细胞相隔20-50 μ m的短段内；在低cf （0.4-1.0 kHz）的神经元中，它们聚集在靠近体细胞的轴突较长的一段。因此，随着神经元CF的增加，神经元在一个更遥远的位置启动峰值。结果表明，在高cf和中cf神经元中，正峰和反峰的体细胞振幅都较小，而在低cf神经元中则较大。计算机模拟表明，优化了起始点的几何形状，降低了峰值产生的阈值，提高了每个CF处的ITD灵敏度。特别是在高CF神经元中，由于起始点与体细胞和树突的电隔离，使得spike起始点的远定位提高了ITD灵敏度。并通过沿轴突的低通滤波减弱突触电位的时间总和，从而减少Na+通道失活。
Neurons initiate spikes in the axon initial segment or at the first node in the axon(1-4). However, it is not yet understood how the site of spike initiation affects neuronal activity and function. In nucleus laminaris of birds, neurons behave as coincidence detectors for sound source localization and encode interaural time differences (ITDs) separately at each characteristic frequency (CF)(5-7). Here we show, in nucleus laminaris of the chick, that the site of spike initiation in the axon is arranged at a distance from the soma, so as to achieve the highest ITD sensitivity at each CF. Na+ channels were not found in the soma of high-CF (2.5-3.3 kHz) and middle-CF (1.0-2.5 kHz) neurons but were clustered within a short segment of the axon separated by 20-50 mu m from the soma; in low-CF (0.4-1.0 kHz) neurons they were clustered in a longer stretch of the axon closer to the soma. Thus, neurons initiate spikes at a more remote site as the CF of neurons increases. Consequently, the somatic amplitudes of both orthodromic and antidromic spikes were small in high-CF and middle-CF neurons and were large in low-CF neurons. Computer simulation showed that the geometry of the initiation site was optimized to reduce the threshold of spike generation and to increase the ITD sensitivity at each CF. Especially in high-CF neurons, a distant localization of the spike initiation site improved the ITD sensitivity because of electrical isolation of the initiation site from the soma and dendrites, and because of reduction of Na+-channel inactivation by attenuating the temporal summation of synaptic potentials through the low-pass filtering along the axon.