OBJECTIVE To determine limb differences in motor axon excitability properties in stroke survivors and their relation to maximal electromyographic (EMG) activity. METHODS The median nerve was stimulated to record compound muscle action potentials (CMAP) from the abductor pollicis brevis (APB) in 28 stroke subjects (57.3 ± 7.5 y) and 24 controls (56.7 ± 9.3 y). RESULTS Paretic limb axons differed significantly from non-paretic limb axons including (1) smaller superexcitability and subexcitability, (2) higher threshold during subthreshold depolarizing currents, (3) greater accommodation (S3) to hyperpolarization, and (4) a larger stimulus-response slope. There were smaller differences between the paretic and control limbs. Responses in the paretic limb were reproduced in a model by a 5.6 mV hyperpolarizing shift in the activation voltage of Ih (the current activated by hyperpolarization), together with an 11.8% decrease in nodal Na+ conductance or a 0.9 mV depolarizing shift in the Na+ activation voltage. Subjects with larger deficits in APB maximal voluntary EMG had larger limb differences in excitability properties. CONCLUSIONS Stroke leads to altered modulation of Ih and altered Na+ channel properties that may be partially attributed to a reduction in neuromuscular activation. SIGNIFICANCE Plastic changes occur in the axon node and internode that likely influence axon excitability.

中文翻译：

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中风后神经兴奋性改变可能与神经肌肉激活减少有关

目的 确定中风幸存者肢体运动轴突兴奋特性的差异及其与最大肌电图 (EMG) 活动的关系。方法 刺激正中神经以记录 28 名中风受试者（57.3 ± 7.5 岁）和 24 名对照（56.7 ± 9.3 岁）的拇短外展肌 (APB) 的复合肌肉动作电位 (CMAP)。结果 瘫痪肢体轴突与非瘫痪肢体轴突显着不同，包括（1）更小的超兴奋性和亚兴奋性，（2）阈下去极化电流期间更高的阈值，（3）对超极化的更大适应（S3）和（4）更大的刺激 -响应斜率。麻痹肢体和控制肢体之间的差异较小。瘫痪肢体的反应在一个模型中由 5. Ih 的激活电压（由超极化激活的电流）发生 6 mV 超极化偏移，同时节点 Na+ 电导降低 11.8% 或 Na+ 激活电压去极化偏移 0.9 mV。APB 最大自愿 EMG 缺陷较大的受试者在兴奋性方面有较大的肢体差异。结论 中风导致 Ih 的调节改变和 Na+ 通道特性的改变，这可能部分归因于神经肌肉激活的减少。意义 轴突节和节间发生塑性变化，可能影响轴突兴奋性。APB 最大自愿 EMG 缺陷较大的受试者在兴奋性方面有较大的肢体差异。结论 中风导致 Ih 的调节改变和 Na+ 通道特性的改变，这可能部分归因于神经肌肉激活的减少。意义 轴突节和节间发生塑性变化，可能影响轴突兴奋性。APB 最大自愿 EMG 缺陷较大的受试者在兴奋性方面有较大的肢体差异。结论 中风导致 Ih 的调节改变和 Na+ 通道特性的改变，这可能部分归因于神经肌肉激活的减少。意义 轴突节和节间发生塑性变化，可能影响轴突兴奋性。