THE SPATIAL-DISTRIBUTION OF EXCITABILITY AND MEMBRANE CURRENT IN NORMAL AND DEMYELINATED MAMMALIAN NERVE-FIBERS
THE SPATIAL-DISTRIBUTION OF EXCITABILITY AND MEMBRANE CURRENT IN NORMAL AND DEMYELINATED MAMMALIAN NERVE-FIBERS
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DOI：
10.1113/jphysiol.1983.sp014791
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发表时间：
1983-01-01
影响因子：
5.5
通讯作者：
SHERRATT, RM
中科院分区：
文献类型：
--
作者：
BOSTOCK, H;SEARS, TA;SHERRATT, RM
电刺激的阈值与传导脉冲的膜电流同时被记录在大鼠脊髓根沿未解剖的单纤维的许多位置。在正常有髓纤维中，明显的阈值最小值总是与向内电流产生的部位一致，因此被确定为Ranvier淋巴结。在节点之间，阈值上升了一个数量级。在正常节点，电荷阈值与刺激持续时间呈线性关系，这是由计算机模拟模型髓鞘纤维所预测的（Bostock, 1983）。强度-持续时间常数平均为64.9 +-。8.3 .mu。S（平均值）+-。SD)在37度。Q10为1/1.39。它们对电极间距离的变化或河豚毒素部分麻醉相对不敏感。在6-8天前用白喉毒素处理的纤维中，为了诱导淋巴结旁或节段脱髓鞘，在淋巴结和节间区域都发现了最小阈值，产生向内膜电流。在这些纤维中，强度-持续时间曲线的一般形式与正常节点相同，但在加宽节点（高达350 .mu）时强度-持续时间常数有所增加。S)和可激节间（600-725 μ S）。与计算机模型的比较表明，这些变化很可能是由于轴突膜暴露的时间常数比正常淋巴结膜暴露的时间常数长得多。在检查的脱髓鞘纤维中没有发现任何高兴奋性的证据。
Thresholds to electrical stimulation were recorded, concurrently with the membrane currents of conducted impulses, at many positions along undissected single fibers in rat spinal roots. In normal myelinated fibers, distinct threshold minima invariably coincided with sites of inward current generation, and were therefore identified as nodes of Ranvier. Between nodes, the thresholds rose by an order of magnitude. At normal nodes, the charge thresholds were linearly related to stimulus duration, as predicted by computer simulations of a model myelinated fiber (Bostock, 1983). The strength-duration time constants averaged 64.9 .+-. 8.3 .mu.s (mean .+-. SD) at 37.degree. C, and had a Q10 of 1/1.39. They were relatively insensitive to changes in inter-electrode distance, or to partial anesthetization with tetrodotoxin. In fibers treated with diphtheria toxin 6-8 days previously, to induce paranodal or segmental demyelination, threshold minima were found both at nodes and in internodal regions generating inward membrane current. In these fibers strength-duration curves were of the same general form as at normal nodes, but with strength-duration time constants increased at widened nodes (up to 350 .mu.s) and at excitable internodes (600-725 .mu.s). Comparison with the computer model indicated that these changes were most likely due to exposure of axon membrane with a time constant much longer than that of the normal nodal membrane. In none of the demyelinated fibers examined was any evidence of hyperexcitability found.