Kudina L P, Alexeeva N L
Institute for Problems of Information Transmission, Russian Academy of Sciences, Moscow.
Electroencephalogr Clin Neurophysiol. 1992 Aug;85(4):243-7. doi: 10.1016/0168-5597(92)90112-o.
In order to study the probable mechanisms of repetitive doublets in human motoneurones, the firing patterns of single motor units (MUs) of the trapezius were analysed during a weak voluntary muscle contraction. The mean frequencies of MUs were 9.4-21.7 imp/sec (the mean interspike interval ranged from 46.0 to 106.7 msec). Repetitive doublets (up to 28 in succession) were recorded in 21 out of 120 MUs, mostly at the onset of a slow recruitment. These were followed by single discharges. Intradoublet intervals ranged between 2.5 and 20.0 msec. A significant difference between single spike firing and doublet firing was revealed by plotting interspike interval histograms, showing that two distinct mechanisms were involved. The analysis of interspike interval successions belonging to several MUs firing simultaneously showed that one of the MUs could start with doublets while the others went on firing single spikes with the regular mean frequency and interspike interval scatter. The results lead us to suggest that the intrinsic properties of motoneurones can be regarded as the main factor in the origin of repetitive doublets. It seems that a descending synaptic drive also contributes to the control of double firing since in a number of cases no doublets were produced at the beginning of MU activity. The findings are discussed with regard to the problems of regulating repetitive firing of human motoneurones by after-potentials. Steady delayed depolarization is assumed to be a possible mechanism of repetitive doublets.
为了研究人类运动神经元中重复双脉冲的可能机制，在轻度随意肌肉收缩期间分析了斜方肌单个运动单位（MU）的放电模式。运动单位的平均频率为9.4 - 21.7次/秒（平均峰间间隔为46.0至106.7毫秒）。在120个运动单位中的21个中记录到了重复双脉冲（连续多达28个），大多出现在缓慢募集开始时。随后是单个放电。双脉冲内间隔在2.5至20.0毫秒之间。通过绘制峰间间隔直方图揭示了单个峰放电和双脉冲放电之间的显著差异，表明涉及两种不同的机制。对同时放电的几个运动单位的峰间间隔序列分析表明，其中一个运动单位可能以双脉冲开始，而其他运动单位则以规则的平均频率和峰间间隔离散继续发放单个峰。结果使我们认为运动神经元的内在特性可被视为重复双脉冲起源的主要因素。似乎下行突触驱动也有助于双脉冲发放的控制，因为在许多情况下，运动单位活动开始时没有产生双脉冲。结合通过后电位调节人类运动神经元重复放电的问题对这些发现进行了讨论。稳态延迟去极化被认为是重复双脉冲的一种可能机制。
