Hu Xiaogang, Suresh Nina L, Rymer William Z
Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, Illinois; and
Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, Illinois; and.
J Neurophysiol. 2015 Mar 15;113(6):1952-7. doi: 10.1152/jn.00946.2014. Epub 2014 Dec 24.
Hyperexcitable motoneurons are likely to contribute to muscle hypertonia after a stroke injury; however, the origins of this hyperexcitability are not clear. One possibility is that the effective duration of the Ia excitatory postsynaptic potential (EPSP) is prolonged, increasing the potential for temporal summation of EPSPs, making action potential initiation easier. Accordingly, the purpose of this study was to quantify the time course of EPSPs in motoneurons of stroke survivors. The experimental protocol, which was based on parameters derived from simulation, involved sequential subthreshold electrical stimuli delivered to the median nerve of hemispheric stroke survivors. The resulting H-reflex responses were recorded in the flexor carpi radialis muscle. H-reflex response probability was then used to quantify the time course of the underlying EPSPs in the motoneuron pool. A population EPSP was estimated based on the probability of evoking an H reflex from the second electrical stimulus in the absence of a reflex response to the first stimulus. The accuracy of this time-course estimate was quantified using a computer simulation that explored a range of feasible EPSP parameters. Our experimental results showed that in all five hemispheric stroke survivors the rate of decay of the population EPSP was consistently slower in spastic compared with the contralateral motoneuron pools. We propose that one potential mechanism for hyperexcitability of motoneurons in spastic stroke survivors may be linked to this prolongation of the Ia EPSP time course. Our subthreshold double-stimulation approach also provides a noninvasive tool for quantifying the time course of EPSPs in both healthy and pathological conditions.
中风损伤后，运动神经元的过度兴奋可能导致肌肉张力亢进；然而，这种过度兴奋的起源尚不清楚。一种可能性是，Ia兴奋性突触后电位（EPSP）的有效持续时间延长，增加了EPSP时间总和的可能性，使动作电位的起始更容易。因此，本研究的目的是量化中风幸存者运动神经元中EPSP的时间进程。实验方案基于模拟得出的参数，包括对半球性中风幸存者的正中神经进行连续阈下电刺激。在桡侧腕屈肌中记录由此产生的H反射反应。然后，使用H反射反应概率来量化运动神经元池中潜在EPSP的时间进程。基于在对第一个刺激无反射反应的情况下，从第二个电刺激诱发H反射的概率，估计群体EPSP。使用探索一系列可行EPSP参数的计算机模拟来量化这种时间进程估计的准确性。我们的实验结果表明，在所有五名半球性中风幸存者中，与对侧运动神经元池相比，痉挛侧群体EPSP的衰减速率始终较慢。我们提出，痉挛性中风幸存者运动神经元过度兴奋的一种潜在机制可能与Ia EPSP时间进程的这种延长有关。我们的阈下双刺激方法还提供了一种非侵入性工具，用于量化健康和病理状态下EPSP的时间进程。
