Human motor unit discharge patterns reveal differences in neuromodulatory and inhibitory drive to motoneurons across contraction levels.

IF 2.1 3区 医学 Q3 NEUROSCIENCES
Jakob Škarabot, James A Beauchamp, Gregory E P Pearcey
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引用次数: 0

Abstract

All motor commands converge onto motor units (MUs), which transduce the signals into mechanical actions of muscle fibres. This process is highly non-linear due to combinations of ionotropic (excitatory/inhibitory) and metabotropic (neuromodulatory) inputs. Neuromodulatory inputs facilitate dendritic persistent inward currents, which introduce non-linearities in MU discharge patterns and provide insights into the structure of motor commands. Here, we investigated the relative contribution of neuromodulation and the pattern of inhibition to modulate human MU discharge patterns with contraction forces up to 70% maximum. Leveraging MU discharge patterns identified from three human muscles (tibialis anterior - TA, and vastus lateralis and medialis), we show that with increased contraction force, the onset-offset discharge rate hysteresis (ΔF) increased whilst ascending MU discharge patterns become more linear, with lower slopes. In a follow-up experiment, we demonstrated that the observations of increased ΔF and more linear ascending MU discharge patterns with greater contraction force are maintained even when accounting for contraction duration and rate of force increase. We then reverse-engineered TA MU discharge patterns using highly realistic in silico motoneuron pools to substantiate the inferred physiological mechanisms from human recordings. We demonstrate a sharply restricted solution space, whereby the contraction force-induced changes in experimentally obtained MU discharge patterns can only be recreated with increased neuromodulation and a more reciprocal (i.e. push-pull) inhibitory pattern. In summary, our experimental and computational data suggest that neuromodulation and inhibitory patterns are uniquely shaped to generate discharge patterns that support force increases across a large proportion of the motor pool's recruitment range.

人类运动单元放电模式揭示了运动神经元在收缩水平上的神经调节和抑制性驱动的差异。
所有的运动指令都汇聚到运动单元(mu)上,运动单元将信号转化为肌肉纤维的机械动作。由于离子性(兴奋性/抑制性)和代谢性(神经调节性)输入的组合,该过程是高度非线性的。神经调节输入促进树突持续向内电流,这在MU放电模式中引入了非线性,并提供了对运动命令结构的见解。在这里,我们研究了神经调节和抑制模式对人类MU放电模式的相对贡献,收缩力最大可达70%。利用从人体三块肌肉(胫骨前肌- TA,股外侧肌和内侧肌)识别的MU放电模式,我们发现随着收缩力的增加,发作偏移放电率滞后(ΔF)增加,而上升的MU放电模式变得更线性,斜率更低。在后续的实验中,我们证明了即使考虑到收缩持续时间和力的增加速度,随着收缩力的增加,ΔF和更多线性上升的MU放电模式仍然保持不变。然后,我们使用高度逼真的硅运动神经元池对TA MU放电模式进行逆向工程,以证实从人类记录中推断的生理机制。我们证明了一个严格限制的溶液空间,在实验中获得的MU放电模式中,收缩力引起的变化只能通过增加的神经调节和更互惠的(即推拉)抑制模式来重现。总之,我们的实验和计算数据表明,神经调节和抑制模式是独特的,可以产生放电模式,支持在大部分机动池的招募范围内的力增加。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Journal of neurophysiology
Journal of neurophysiology 医学-神经科学
CiteScore
4.80
自引率
8.00%
发文量
255
审稿时长
2-3 weeks
期刊介绍: The Journal of Neurophysiology publishes original articles on the function of the nervous system. All levels of function are included, from the membrane and cell to systems and behavior. Experimental approaches include molecular neurobiology, cell culture and slice preparations, membrane physiology, developmental neurobiology, functional neuroanatomy, neurochemistry, neuropharmacology, systems electrophysiology, imaging and mapping techniques, and behavioral analysis. Experimental preparations may be invertebrate or vertebrate species, including humans. Theoretical studies are acceptable if they are tied closely to the interpretation of experimental data and elucidate principles of broad interest.
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