Steffens H, Hoheisel U, Eek B, Mense S
Institut für Anatomie und Zellbiologie, Universität Heidelberg, Im Neuenheimer Feld 307, D-69120, Heidelberg, Germany.
Neurosci Res. 2001 Apr;39(4):413-9. doi: 10.1016/s0168-0102(01)00198-5.
The effect of the sodium channel blocking agent tetrodotoxin (TTX) on signal processing in afferent fibres of dorsal roots was tested in Sprague-Dawley rats. TTX applied to the dorsal roots L4-L6 blocked the fast afferent volleys from the sural nerve, which was stimulated electrically with supramaximal strength for A-fibres. Afferent C-fibre compound action potentials (CAPs) elicited by electrical stimulation of the dorsal root L5 peripherally from the TTX block or by electrical stimulation of the sural nerve likewise disappeared from the recording. Cord dorsum potentials (CDPs) recorded at the dorsal root entry zone of L4 were blocked completely if elicited by A-fibre volleys. In contrast, CDPs elicited by C-fibre stimulation persisted with longer latency and reduced amplitude in the first part of the CDP. During TTX block, C-fibre potentials could also be recorded from dorsal root filaments after stimulation of the sural nerve or the dorsal root L5 peripherally of the TTX-block. The results suggest that in the axonal membrane of cutaneous C-afferents, both TTX sensitive and TTX-resistant voltage gated sodium channels exist, the latter being responsible for the propagation of signals in a portion of C-fibres after TTX application. The TTX-resistant portion of the afferent potential does not seem to contribute much to the afferent C-fibre CAP before TTX application, but its central effects seem to be overproportionally strong.
在Sprague-Dawley大鼠中测试了钠通道阻滞剂河豚毒素（TTX）对背根传入纤维信号处理的影响。将TTX应用于L4-L6背根，可阻断来自腓肠神经的快速传入冲动，该神经以最大强度电刺激A纤维。由L5背根外周TTX阻断处的电刺激或腓肠神经的电刺激所引发的传入C纤维复合动作电位（CAPs）同样从记录中消失。如果由A纤维冲动引发，在L4背根进入区记录的脊髓背电位（CDPs）会被完全阻断。相反，由C纤维刺激引发的CDPs在CDP的第一部分中持续存在，潜伏期延长且幅度减小。在TTX阻断期间，在刺激腓肠神经或TTX阻断外周的L5背根后，也可从背根细丝记录到C纤维电位。结果表明，在皮肤C传入纤维的轴突膜中，存在对TTX敏感和对TTX耐药的电压门控钠通道，后者负责在应用TTX后一部分C纤维中信号的传播。在应用TTX之前，传入电位的TTX耐药部分似乎对传入C纤维CAP的贡献不大，但其中枢效应似乎异常强烈。
