Division of Biotechnology, Convergence Research Institute, DGIST, Daegu 42988, Korea
eNeuro. 2020 Apr 27;7(2). doi: 10.1523/ENEURO.0014-20.2020. Print 2020 Mar/Apr.
The goal of this study is to investigate how the activation location of persistent inward current (PIC) over motoneuron dendrites is linked to motor output in the closed-loop motor unit. Here, a physiologically realistic model of a motor unit including afferent inputs from muscle spindles was comprehensively analyzed under intracellular stimulation at the soma and synaptic inputs over the dendrites during isometric contractions over a full physiological range of muscle lengths. The motor output of the motor unit model was operationally assessed by evaluating the rate of force development, the degree of force potentiation and the capability of self-sustaining force production. Simulations of the model motor unit demonstrated a tendency for a faster rate of force development, a greater degree of force potentiation, and greater capacity for self-sustaining force production under both somatic and dendritic stimulation of the motoneuron as the PIC channels were positioned farther from the soma along the path of motoneuron dendrites. Interestingly, these effects of PIC activation location on force generation significantly differed among different states of muscle length. The rate of force development and the degree of force potentiation were systematically modulated by the variation of PIC channel location for shorter-than-optimal muscles but not for optimal and longer-than-optimal muscles. Similarly, the warm-up behavior of the motor unit depended on the interplay between PIC channel location and muscle length variation. These results suggest that the location of PIC activation over motoneuron dendrites may be distinctively reflected in the motor performance during shortening muscle contractions.
本研究旨在探讨持久内向电流（PIC）在运动神经元树突上的激活位置与闭环运动单位的运动输出之间的关系。在此，我们综合分析了一个包括来自肌梭传入输入的运动单位的生理现实模型，在等长收缩期间，在整个生理肌肉长度范围内，在体部和树突上的突触输入下，对体部刺激进行了全面分析。通过评估力发展速率、力增强程度和自维持力产生能力，对运动单位模型的运动输出进行了操作评估。模型运动单位的模拟表明，随着 PIC 通道沿着运动神经元树突的路径更远离体部，运动神经元的体部和树突刺激都会导致更快的力发展速率、更大的力增强程度和更大的自维持力产生能力。有趣的是，这些 PIC 激活位置对力产生的影响在不同的肌肉长度状态下显著不同。对于短于最佳长度的肌肉，力发展速率和力增强程度会被 PIC 通道位置的变化系统地调节，但对于最佳和长于最佳长度的肌肉则不会。同样，运动单位的预热行为取决于 PIC 通道位置和肌肉长度变化之间的相互作用。这些结果表明，PIC 在运动神经元树突上的激活位置可能会在缩短肌肉收缩期间的运动表现中得到明显反映。
