Plasticity of human motoneurone properties

利用动物模型进行运动控制研究，有助于建立运动神经元的特性与受其支配的肌纤维之间的关系。在人类中，Matthews（1996）开发了一个模型来估计运动神经元的一种特性（超极化后（AHP）时间过程）。这个模型是观察人类运动神经元特性的唯一窗口之一。AHP的时间过程影响运动神经元释放动作电位的能力，从而影响肌肉产生的力。AHP的适应性还没有在动物模型中得到彻底的研究，在人类中也几乎没有被探索过。提出的研究将确定突触输入的能力，以修改人类运动神经元AHP的时间过程。我们将在单独的实验中研究三种突触输入：皮肤输入、肌纺锤体输入和由肌肉疲劳激活的III-IV组传入。踝关节背屈肌（胫骨前肌）的低强度收缩将保持30分钟：在增加突触输入之前、期间和之后各10分钟，通过细丝电极收集的运动单元电位序列计算每个阶段的运动神经元AHP。在缺血条件下，对胫骨前肌上覆的皮肤施加无痛的皮肤刺激，或对胫骨前肌肌腱施加振动，或使肌肉因进行低力收缩而疲劳。健康的成年志愿者和中风后单侧运动性麻痹的志愿者将参与这项研究。这个研究项目将推进我们对人类运动神经元特性的理解，当它们被下行指令和感觉输入自动激活时。这项研究将对迄今为止尚未研究的运动控制机制产生深远的影响，主要是因为相应的动物实验不涉及自愿收缩。获得的知识将有助于我们对运动控制障碍的理解，以及感觉输入是否有助于在神经损伤（如中风）后改变运动神经元的特性。

Motor control research using animal models has helped establish relations between properties of the motoneurone and the muscle fibers that it innervates.  In humans, Matthews (1996) developed a model for estimating one of the motoneurone properties (afterhyperpolarization (AHP) time-course).  This model represents one of the only windows to view the properties of motoneurones in humans.  The time-course of the AHP influences the capacity of the motoneurone to discharge action potentials and, thereby, the force produced by the muscle.  The adaptability of the AHP has not been thoroughly investigated in animal models and is virtually unexplored in humans.  The proposed research will determine the capacity of synaptic input to modify the time-course of the motoneurone AHP in humans.  We will study three synaptic inputs in separate experiments: cutaneous (skin) input, muscle spindle input, and input from group III-IV afferents activated by muscle fatigue.  Low-force contractions with the ankle dorsiflexor muscles (tibialis anterior) will be held for 30 min: 10 min before, during, and after the addition of synaptic input, with the motoneurone AHP being calculated in each phase from a train of motor unit potentials collected with a fine wire electrode.  Either a non- painful cutaneous stimulus will be applied to the skin overlying tibialis anterior, or vibration will be applied to the tibialis anterior tendon, or the muscle will be fatigued by performing a low-force contraction under ischemic conditions.  Healthy adult volunteers and volunteers with unilateral motor paresis after stroke will participate in the study.  This research program will advance our understanding of human motoneurone properties when they are activated voluntarily with both descending commands and sensory inputs.  This research will have far-reaching implications for motor control mechanisms that have not been investigated to date, primarily because the corresponding animal experiments do not involve voluntary contractions.  The acquired knowledge will contribute to our understanding of motor control disorders and whether sensory inputs may be useful in modifying motoneurone properties after a neurological insult, such as a stroke.