Department of Neuroscience, University of Copenhagen, Blegdamsvej 3, 2200, Copenhagen N, Denmark.
Center for Health, Safety and Environmental Management, Shinshu University, Matsumoto, Japan.
Exp Brain Res. 2019 Nov;237(11):2897-2909. doi: 10.1007/s00221-019-05628-6. Epub 2019 Sep 6.
The output from a motor nucleus is determined by the synaptic input to the motor neurons and their intrinsic properties. Here, we explore whether the source of synaptic inputs to the motor neurons (cats) and the age or post-stroke conditions (humans) may change the recruitment gain of the motor neuron pool. In cats, the size of Ia EPSPs in triceps surae motor neurons (input) and monosynaptic reflexes (MSRs; output) was recorded in the soleus and medial gastrocnemius motor nerves following graded stimulation of dorsal roots. The MSR was plotted against the EPSP thereby obtaining a measure of the recruitment gain. Conditioning stimulation of sural and peroneal cutaneous afferents caused significant increase in the recruitment gain of the medial gastrocnemius, but not the soleus motor neuron pool. In humans, the discharge probability of individual soleus motor units (input) and soleus H-reflexes (output) was performed. With graded stimulation of the tibial nerve, the gain of the motor neuron pool was assessed as the slope of the relation between probability of firing and the reflex size. The gain in young subjects was higher than in elderly subjects. The gain in post-stroke survivors was higher than in age-matched neurologically intact subjects. These findings provide experimental evidence that recruitment gain of a motor neuron pool contributes to the regulation of movement at the final output stage from the spinal cord and should be considered when interpreting changes in reflex excitability in relation to movement or injuries of the nervous system.
运动核的输出由运动神经元的突触输入及其固有特性决定。在这里，我们探讨了运动神经元（猫）的突触输入来源以及年龄或中风后状况（人）是否可能改变运动神经元池的募集增益。在猫中，在背根分级刺激后，在比目鱼肌和内侧胫骨神经中记录了三头肌运动神经元（输入）和单突触反射（输出）中 Ia EPSP 的大小。将 MSR 绘制为 EPSP，从而获得募集增益的度量。对腓肠和腓浅皮传入纤维的条件刺激导致内侧胫骨神经运动神经元池的募集增益显着增加，但比目鱼肌运动神经元池则没有。在人类中，进行了个体比目鱼肌运动单位（输入）和比目鱼肌 H 反射（输出）的放电概率。随着胫骨神经的分级刺激，运动神经元池的增益评估为发射概率与反射大小之间关系的斜率。年轻受试者的增益高于老年受试者。中风幸存者的增益高于年龄匹配的神经完整受试者。这些发现提供了实验证据，即运动神经元池的募集增益有助于调节脊髓的最终输出阶段的运动，并且在解释与运动或神经系统损伤有关的反射兴奋性变化时应予以考虑。
