Frigon Alain, Desrochers Étienne, Thibaudier Yann, Hurteau Marie-France, Dambreville Charline
Department of Pharmacology-Physiology, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Sherbrooke, Quebec, Canada, J1H 5N4.
J Physiol. 2017 Jan 1;595(1):341-361. doi: 10.1113/JP272740. Epub 2016 Aug 13.
Coordination between the left and right sides is essential for dynamic stability during locomotion. The immature or neonatal mammalian spinal cord can adjust to differences in speed between the left and right sides during split-belt locomotion by taking more steps on the fast side. We show that the adult mammalian spinal cord can also adjust its output so that the fast side can take more steps. During split-belt locomotion, only certain parts of the cycle are modified to adjust left-right coordination, primarily those associated with swing onset. When the fast limb takes more steps than the slow limb, strong left-right interactions persist. Therefore, the adult mammalian spinal cord has a remarkable adaptive capacity for left-right coordination, from simple to extreme conditions.
Although left-right coordination is essential for locomotion, its control is poorly understood, particularly in adult mammals. To investigate the spinal control of left-right coordination, a spinal transection was performed in six adult cats that were then trained to recover hindlimb locomotion. Spinal cats performed tied-belt locomotion from 0.1 to 1.0 m s and split-belt locomotion with low to high (1:1.25-10) slow/fast speed ratios. With the left hindlimb stepping at 0.1 m s and the right hindlimb stepping from 0.2 to 1.0 m s , 1:1, 1:2, 1:3, 1:4 and 1:5 left-right step relationships could appear. The appearance of 1:2+ relationships was not linearly dependent on the difference in speed between the slow and fast belts. The last step taken by the fast hindlimb displayed longer cycle, stance and swing durations and increased extensor activity, as the slow limb transitioned to swing. During split-belt locomotion with 1:1, 1:2 and 1:3 relationships, the timing of stance onset of the fast limb relative to the slow limb and placement of both limbs at contact were invariant with increasing slow/fast speed ratios. In contrast, the timing of stance onset of the slow limb relative to the fast limb and the placement of both limbs at swing onset were modulated with slow/fast speed ratios. Thus, left-right coordination is adjusted by modifying specific parts of the cycle. Results highlight the remarkable adaptive capacity of the adult mammalian spinal cord, providing insight into spinal mechanisms and sensory signals regulating left-right coordination.
左右两侧之间的协调对于运动过程中的动态稳定性至关重要。未成熟或新生哺乳动物的脊髓可以通过在较快一侧采取更多步幅，来适应分带运动时左右两侧速度的差异。我们发现成年哺乳动物的脊髓也能够调整其输出，以便较快一侧能够采取更多步幅。在分带运动期间，仅周期的某些部分会被修改以调整左右协调，主要是那些与摆动起始相关的部分。当较快肢体比较慢肢体采取更多步幅时，强烈的左右相互作用持续存在。因此，成年哺乳动物的脊髓在从简单到极端的条件下，对左右协调具有显著的适应能力。
尽管左右协调对于运动至关重要，但其控制机制却知之甚少，尤其是在成年哺乳动物中。为了研究左右协调的脊髓控制，对六只成年猫进行了脊髓横断手术，然后训练它们恢复后肢运动。脊髓猫以0.1至1.0米/秒的速度进行系绳带运动，并以低至高（1:1.25 - 10）的慢/快速度比进行分带运动。当左后肢以0.1米/秒的速度迈步且右后肢以0.2至1.0米/秒的速度迈步时，会出现1:1、1:2、1:3、1:4和1:5的左右步幅关系。1:2+关系的出现并非线性依赖于慢带和快带之间的速度差异。随着慢肢体过渡到摆动，快后肢迈出的最后一步显示出更长的周期、站立期和摆动期，并且伸肌活动增加。在具有1:1、1:2和1:3关系的分带运动中，快肢体相对于慢肢体的站立起始时间以及两肢体在接触时的位置，随着慢/快速度比的增加而不变。相反，慢肢体相对于快肢体的站立起始时间以及两肢体在摆动起始时的位置会随着慢/快速度比而调节。因此，通过修改周期的特定部分来调整左右协调。结果突出了成年哺乳动物脊髓显著的适应能力，为调节左右协调的脊髓机制和感觉信号提供了见解。
