Inhibition linearizes firing rate responses in human motor units: implications for the role of persistent inward currents.
Inhibition linearizes firing rate responses in human motor units: implications for the role of persistent inward currents.
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抑制使人类运动单位的放电率反应线性化：对持续内向电流作用的影响。
DOI：
10.1113/jp272823
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发表时间：
2017
期刊：
影响因子：
--
通讯作者：
Fuglevand,AndrewJ
中科院分区：
文献类型：
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作者：
Revill,AnnL;Fuglevand,AndrewJ
关键点运动神经元是中枢神经系统的输出神经元，负责控制肌肉收缩。当在随意收缩过程中最初被激活时，运动神经元的放电率急剧增加，但随后以适度的速率趋于平稳。在募集开始时，兴奋性电流的内在来源的激活可能是运动神经元放电率最初急剧增加的基础。我们试图禁用这种内在兴奋性电流。当记录运动神经元的活动，同时进行抑制反射时，放电率不再急剧增加，这表明内在的兴奋性电流可能是运动神经元放电率最初急剧上升的原因。运动单位（MU）放电率在恢复时急剧增加，但随后以适度的速率平稳，即使肌肉力量继续增加。这种放电行为的机制尚不清楚，但可能涉及持续内向电流（PIC）的激活。PIC是内在的电压依赖性电流，当运动神经元（MN）首次被招募时会强烈激活。这种激活可能会导致去极化电流急剧上升，并导致MU放电率的初始急剧上升。由于PICs可以通过突触抑制而被禁用，因此我们假设抑制性通路的人工激活可能会抑制放电率的这种初始急剧上升。为了测试这一点，人类受试者在不存在和存在通过腓肠神经刺激递送至胫骨前肌（TA）MN的强直性突触抑制的情况下进行踝背屈肌的缓慢三角斜坡收缩。在这些任务期间记录的TA MU的放电率曲线（表示为收缩力的函数）进行了比较，用于控制和刺激条件。在控制条件下，在三角形收缩的上升阶段，93%的射击率配置文件是最好的拟合上升指数函数。然而，在刺激下，放电率曲线最适合线性函数或不太陡升的指数。放电率曲线的下降阶段的收缩最适合与线性函数的控制和刺激条件。这些结果似乎与PIC在收缩的上升阶段而不是下降阶段有助于非线性放电率曲线的想法一致。
Key pointsMotor neurons are the output neurons of the central nervous system and are responsible for controlling muscle contraction.When initially activated during voluntary contraction, firing rates of motor neurons increase steeply but then level out at modest rates.Activation of an intrinsic source of excitatory current at recruitment onset may underlie the initial steep increase in firing rate in motor neurons.We attempted to disable this intrinsic excitatory current by artificially activating an inhibitory reflex.When motor neuron activity was recorded while the inhibitory reflex was engaged, firing rates no longer increased steeply, suggesting that the intrinsic excitatory current was probably responsible for the initial sharp rise in motor neuron firing rate.AbstractDuring graded isometric contractions, motor unit (MU) firing rates increase steeply upon recruitment but then level off at modest rates even though muscle force continues to increase. The mechanisms underlying such firing behaviour are not known although activation of persistent inward currents (PICs) might be involved. PICs are intrinsic, voltage‐dependent currents that activate strongly when motor neurons (MNs) are first recruited. Such activation might cause a sharp escalation in depolarizing current and underlie the steep initial rise in MU firing rate. Because PICs can be disabled with synaptic inhibition, we hypothesized that artificial activation of an inhibitory pathway might curb this initial steep rise in firing rate. To test this, human subjects performed slow triangular ramp contractions of the ankle dorsiflexors in the absence and presence of tonic synaptic inhibition delivered to tibialis anterior (TA) MNs by sural nerve stimulation. Firing rate profiles (expressed as a function of contraction force) of TA MUs recorded during these tasks were compared for control and stimulation conditions. Under control conditions, during the ascending phase of the triangular contractions, 93% of the firing rate profiles were best fitted by rising exponential functions. With stimulation, however, firing rate profiles were best fitted with linear functions or with less steeply rising exponentials. Firing rate profiles for the descending phases of the contractions were best fitted with linear functions for both control and stimulation conditions. These results seem consistent with the idea that PICs contribute to non‐linear firing rate profiles during ascending but not descending phases of contractions.