Kurtzer Isaac, Bouyer Laurent J, Bouffard J, Jin A, Christiansen L, Nielsen J B, Scott S H
Department of Biomedical Science, New York Institute of Technology-College of Osteopathic Medicine, Old Westbury, USA.
Department of Rehabilitation, Université Laval, Quebec, Canada.
Exp Brain Res. 2018 Mar;236(3):665-677. doi: 10.1007/s00221-017-5162-6. Epub 2018 Jan 3.
Sudden limb displacement evokes a complex sequence of compensatory muscle activity. Following the short-latency reflex and preceding voluntary reactions is an epoch termed the medium-latency reflex (MLR) that could reflect spinal processing of group II muscle afferents. One way to test this possibility is oral ingestion of tizanidine, an alpha-2 adrenergic agonist that inhibits the interneurons transmitting group II signals onto spinal motor neurons. We examined whether group II afferents contribute to MLR activity throughout the major muscles that span the elbow and shoulder. MLRs of ankle muscles were also tested during walking on the same day, in the same participants as well as during sitting in a different group of subjects. In contrast to previous reports, the ingestion of tizanidine had minimal impact on MLRs of arm or leg muscles during motor actions. A significant decrease in magnitude was observed for 2/16 contrasts in arm muscles and 0/4 contrasts in leg muscles. This discrepancy with previous studies could indicate that tizanidine's efficacy is altered by subtle changes in protocol or that group II afferents do not substantially contribute to MLRs.
肢体突然移位会引发一系列复杂的代偿性肌肉活动。在短潜伏期反射之后且在自主反应之前，有一个时期被称为中潜伏期反射（MLR），它可能反映脊髓对Ⅱ类肌肉传入神经的处理。检验这种可能性的一种方法是口服替扎尼定，它是一种α-2肾上腺素能激动剂，可抑制将Ⅱ类信号传递到脊髓运动神经元的中间神经元。我们研究了Ⅱ类传入神经是否在跨越肘部和肩部的主要肌肉中对MLR活动有贡献。在同一天，对相同参与者在行走过程中以及对另一组不同的受试者在坐着时，也测试了踝部肌肉的MLR。与先前的报告相反，在运动过程中，口服替扎尼定对臂部或腿部肌肉的MLR影响极小。在臂部肌肉的16次对比中有2次观察到幅度显著下降，在腿部肌肉的4次对比中则为0次。与先前研究的这种差异可能表明，替扎尼定的疗效会因方案中的细微变化而改变，或者Ⅱ类传入神经对MLR的贡献不大。
