Plasticity of human motoneurone properties

使用动物模型进行的运动控制研究帮助建立了运动神经元的特性和它所支配的肌肉纤维之间的关系。在人类中，Matthews(1996)开发了一个用于估计运动神经元特性之一的模型(后超极化(AHP)时间过程)。该模型代表了观察人类运动神经元特性的仅有的窗口之一。AHP的时间过程影响运动神经元放电动作电位的能力，从而，由肌肉产生的力。AHP的适应性还没有在动物模型中得到彻底的研究，在人类身上也几乎没有被探索过。这项拟议的研究将确定突触输入改变人类运动神经元AHP的时间过程的能力。我们将在不同的实验中研究三种突触输入：皮肤(皮肤)输入，肌梭输入，以及由肌肉疲劳激活的III-IV组传入的输入。与脚踝背屈肌肉(胫骨前肌)的低力收缩将保持30分钟：在增加突触输入之前、期间和之后，根据用细丝电极收集的一系列运动单位电位，在每个阶段计算运动神经元AHP。或者对胫骨前肌上的皮肤施加非痛性皮肤刺激，或者对胫骨前肌腱施加振动，这些健康的成年志愿者和中风后患有单侧运动瘫痪的志愿者将参与这项研究。这项研究计划将促进我们对人类运动神经元属性的理解，当它们被下行命令和感觉输入自愿激活时。这项研究将对迄今尚未被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。所获得的知识将有助于我们理解运动控制障碍，以及感觉输入是否有助于在神经损伤后改变运动神经元属性，例如中风。

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.