Institute for Information Transmission Problems, Kharkevich Institute, Russian Academy of Sciences, 19, Bol'shoi Karetnyi pereulok, 127051, Moscow, Russia.
Exp Brain Res. 2021 Mar;239(3):719-730. doi: 10.1007/s00221-020-05998-2. Epub 2021 Jan 3.
Neurone firing behaviour is a result of complex interaction between synaptic inputs and cellular intrinsic properties. Intriguing firing behaviour, delayed spiking, was shown in some neurones, in particular, in cat neocortical neurones and rat pyramidal hippocampal neurones. In contrast, the similar spiking mode was not reported for animal spinal motoneurones. In the present study, an attempt was made to look for possible evidence of delayed spiking in human motoneurones firing within the low-frequency, sub-primary range, characteristic for voluntary muscle contractions and postural tasks. Forty-seven firing motor units (MUs) were analyzed in ten experiments on three muscles (the flexor carpi ulnaris, the tibialis anterior, and the abductor pollicis brevis) in four healthy humans. Single MUs were activated by gentle voluntary muscle contractions. MU peri-stimulus time histograms, durations of inter-spike intervals, and motoneurone excitability changes within a target interspike interval were analyzed. It was found that during testing the firing motoneurone excitability by small, transient excitatory Ia afferent volley, depending firstly on volley timing within a target interspike interval and excitatory volley strength, the same motoneurone displayed either the direct short-latency response (the H-reflex) or the delayed response (with prolonged and variable latency). Thus, the findings, for the first time, provide evidence for a possibility of two modes of spiking in firing motoneurones. Methods of the estimation of delayed responses and their possible functional significance are discussed. It is emphasized that, for understanding of this issue, the integration of data from studies on experimental animals and humans is desirable.
神经元的发放行为是突触输入和细胞内在特性之间复杂相互作用的结果。在一些神经元中，特别是在猫大脑皮层神经元和大鼠海马锥体细胞中，表现出了有趣的发放行为，即延迟发放。相比之下，动物脊髓运动神经元中并没有报道类似的发放模式。在本研究中，我们试图寻找人类运动神经元在低频、亚主要范围内发放的可能证据，这种发放模式是自愿肌肉收缩和姿势任务的特征。在四项健康人类的三项肌肉（尺侧腕屈肌、胫骨前肌和拇指短展肌）的十项实验中，分析了 47 个发放运动单位（MUs）。单个 MUs 由温和的自愿肌肉收缩激活。分析了 MU 发放前时间直方图、发放间隔的持续时间以及在目标发放间隔内的运动神经元兴奋性变化。结果发现，在测试中，通过短暂的 Ia 传入兴奋传入来调节运动神经元的兴奋性，这取决于兴奋传入在目标发放间隔内的时间和兴奋传入的强度，同一个运动神经元会表现出直接的短潜伏期反应（H 反射）或延迟反应（潜伏期延长且可变）。因此，这些发现首次为运动神经元发放的两种模式提供了可能性的证据。讨论了延迟反应的估计方法及其可能的功能意义。强调了为了理解这个问题，整合来自实验动物和人类研究的数据是可取的。
