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首页> 外文期刊>Journal of Neurophysiology >Nerve excitability differences in slow and fast motor axons of the rat: more than just I-h
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Nerve excitability differences in slow and fast motor axons of the rat: more than just I-h

机译：大鼠慢速和快速运动轴突的神经兴奋性差异：不仅仅是i-h

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The objective was to determine biophysical differences between fast and slow motor axons using threshold tracking and demonstrate confounds related to anesthetic. Nerve excitability of motor axons innervating the slow-twitch soleus (SOL) and fast-twitch tibialis anterior (TA) muscles was tested. The experiments were conducted with pentobarbital sodium (SP) anesthetic and compared with previous results that used ketamine-xylazine (KX). Nerve excitability indices measured with SP show definitive differences between TA and SOL motor axons that extend beyond previous reports. Nerve excitability indices sensitive to changes in I-h indicated an increase in SOL axons compared with TA axons [e.g., S3 t = 7.949 (df = 10), P < 0.001; hyperpolarizing threshold electrotonus (90-100 ms), t = 2.659 (df = 20); P = 0.01; hyperpolarizing I/V slope, t = 4.308 (df = 19); P < 0.001]. SOL axons also had a longer strength-duration time constant [t = 3.35 (df = 20); P = 0.003] and a longer and larger magnitude relative refractory period [RRP (ms) t = 3.53 (df = 12); P = 0.004; Refractoriness at 2 ms, t = 0.0055 (df = 9); P = 0.006]. Anesthetic choice affected many measures of peripheral nerve excitability with differences most apparent in tests of threshold electrotonus and recovery cycle. For example, recovery cycle with KX lacked a clear superexcitable and late subexcitable period. We conclude that KX had a confounding effect on nerve excitability results consistent with ischemic depolarization. Results using SP revealed the full extent of differences in nerve excitability measures between putative slow and fast motor axons of the rat. These results provide empirical evidence, beyond conduction velocity, that the biophysical properties of motor axons vary with the type of muscle fiber innervated. These differences suggest that fast axons may be predisposed to dysfunction during hyperpolarizing stresses, e.g., electrogenic sodium pumping following sustained impulse conduction.
机译：目的是使用阈值跟踪来确定快速和慢动作轴突之间的生物物理差异，并展示与麻醉有关的混淆。测试了慢速抽搐肠（溶胶）和快速抽搐胫骨前（TA）肌肉的电动机轴突的神经兴奋。实验用戊巴比妥钠（SP）麻醉进行，与使用氯胺酮 - 木嗪（KX）的先前结果进行比较。用SP测量的神经兴奋性指数显示TA和溶胶电机轴突之间的明确差异，延伸到以前的报告之外。与I-H的变化敏感的神经兴奋性指数表明，与TA轴突相比，溶胶轴突的增加[例如，S3 T = 7.949（DF = 10），P <0.001;超极化阈值电气（90-100ms），T = 2.659（DF = 20）; p = 0.01;超极化I / V斜率，T = 4.308（DF = 19）; P <0.001]。溶胶轴突也具有更长的强度持续时间常数[t = 3.35（df = 20）; p = 0.003]和更长且较大的幅度相对耐火周期[RRP（MS）T = 3.53（DF = 12）; p = 0.004; 2ms，T = 0.0055（DF = 9）的耐火材料; p = 0.006]。麻醉选择影响了阈值电气和恢复循环的测试中最明显的差异的周围神经兴奋性。例如，具有KX的恢复周期缺乏明确的超脆性和迟到的子表征。我们得出结论，KX对神经兴奋性导致缺血性去极化的结果具有混杂影响。结果采用SP揭示了大鼠推定慢速运动轴突之间神经兴奋性措施的全部差异。这些结果提供了超越传导速度的经验证据，即电动机轴突的生物物理性质随着肌肉纤维的类型而变化。这些差异表明，在超积极应力期间，例如，在持续脉冲传导之后，可以在超积极应力期间能够倾向于功能障碍。

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