Swadlow H A
J Neurophysiol. 1985 Nov;54(5):1346-62. doi: 10.1152/jn.1985.54.5.1346.
The long-term stability of conduction velocity and recovery processes were studied in a fast-conducting (corticotectal) and in a more slowly conducting (visual callosal) axonal system. Chronic microelectrode recording methods were used in conjunction with antidromic activation via electrical stimulation at one or more axonal site. These methods enabled 54 axons to be studied for greater than 20 days and seven of these cells to be studied for 101-448 days. The conduction velocities of corticotectal axons were characteristic of myelinated axons and were very stable over time. The conduction velocities of most callosal axons were characteristic of nonmyelinated axons, and 68% of callosal axons had conduction velocities that were stable over long periods of time. Of the remaining callosal axons, approximately one third showed an increase in conduction velocity (8-14%), whereas two thirds showed a progressive and systematic decrease in conduction velocity (6-81%). These changes in conduction velocity were distributed along the callosal axon, rather than limited to a single segment of axon. Although the refractory period of callosal and corticotectal axons showed considerable variability over time, the minimal interval between two conducted impulses was stable. The stability of this property was remarkable because the minimal interspike intervals of different axons with similar conduction velocities often differed greatly. Callosal axons show a supernormal period of increased conduction velocity following the relative refractory period and a subsequent subnormal period of decreased conduction velocity following a burst of prior impulses. In different callosal axons the magnitude of the velocity changes (percent change) differs greatly, even among axons of the same conduction velocity. For a given axon, however, these properties are very stable over time. These results on axonal properties may be useful in studies requiring the examination of extracellular responses of individual neurons over long periods of time. Antidromic latency provides a useful means of identifying a cell, particularly when conduction times are long. The stability of the minimal interspike interval and the supernormal period within individual axons make them suitable as ancillary criteria in identifying individual neurons. These three measures are independent of spike amplitude and waveform, and together they provide a "signature" by which individual cortical neurons can be identified over periods that represent a significant portion of the lifespan of adult mammals.
在快速传导（皮质-顶盖）和传导速度较慢（视胼胝体）的轴突系统中，研究了传导速度的长期稳定性和恢复过程。慢性微电极记录方法与通过在一个或多个轴突部位进行电刺激的逆向激活相结合使用。这些方法使得能够对54条轴突进行超过20天的研究，其中7个细胞进行了101 - 448天的研究。皮质-顶盖轴突的传导速度具有有髓轴突的特征，并且随时间非常稳定。大多数胼胝体轴突的传导速度具有无髓轴突的特征，并且68%的胼胝体轴突的传导速度在长时间内是稳定的。在其余的胼胝体轴突中，大约三分之一的轴突传导速度增加（8 - 14%），而三分之二的轴突传导速度呈渐进性和系统性下降（6 - 81%）。这些传导速度的变化沿胼胝体轴突分布，而不是局限于轴突的单个节段。尽管胼胝体和皮质-顶盖轴突的不应期随时间显示出相当大的变异性，但两个传导冲动之间的最小间隔是稳定的。这一特性的稳定性很显著，因为传导速度相似的不同轴突的最小峰间间隔往往差异很大。胼胝体轴突在相对不应期后显示出传导速度增加的超常期，以及在先前冲动爆发后随后传导速度降低的低常期。在不同的胼胝体轴突中，速度变化的幅度（百分比变化）差异很大，即使在传导速度相同的轴突之间也是如此。然而，对于给定的轴突，这些特性随时间非常稳定。这些关于轴突特性的结果可能在需要长时间检查单个神经元细胞外反应的研究中有用。逆向潜伏期提供了一种识别细胞的有用方法，特别是当传导时间较长时。单个轴突内最小峰间间隔和超常期的稳定性使它们适合作为识别单个神经元的辅助标准。这三种测量方法与峰幅和波形无关，它们共同提供了一个“特征”，通过这个特征可以在代表成年哺乳动物寿命很大一部分的时间段内识别单个皮质神经元。
