Juvin Laurent, Simmers John, Morin Didier
Université Bordeaux 1, UMR CNRS 5227, Laboratoire Mouvement-Adaptation-Cognition bâtiment 2A, 146 rue Léo Saignat, 33076 Bordeaux, France.
J Physiol. 2007 Aug 15;583(Pt 1):115-28. doi: 10.1113/jphysiol.2007.133413. Epub 2007 Jun 14.
The temporal properties of limb motoneuron bursting underlying quadrupedal locomotion were investigated in isolated spinal cord preparations (without or with brainstem attached) taken from 0 to 4-day-old rats. When activated either with differing combinations of N-methyl-D,L-aspartate, serotonin and dopamine, or by electrical stimulation of the brainstem, the spinal cord generated episodes of fictive locomotion with a constant phase relationship between cervical and lumbar ventral root bursts. Alternation occurred between ipsi- and contra-lateral flexor and extensor motor root bursts, and the cervical and lumbar locomotor networks were always active in a diagonal coordination pattern that corresponded to fictive walking. However, unlike typical locomotion in adult animals in which extensor motoneuron bursts vary more with cycle period than flexor bursts, in the isolated neonatal cord, an increase in fictive locomotor speed was associated with a decrease in the durations of both extensor and flexor bursts, at cervical and lumbar levels. To determine whether this symmetry in flexor/extensor phase durations derived from the absence of sensory feedback that is normally provided from the limbs during intact animal locomotion, EMG recordings were made from hindlimb-attached spinal cords during drug-induced locomotor-like movements. Under these conditions, the duration of extensor muscle bursts increased with cycle period, while flexor burst durations now tended to remain constant. Moreover, after a complete dorsal rhizotomy, this extensor dominant pattern was replaced by flexor and extensor muscle bursts of similar duration. In vivo and in vitro experiments were also conducted on older postnatal (P10-12) rats at an age when body-supported adult-like locomotion occurs. Here again, characteristic extensor-dominated burst patterns observed during intact treadmill locomotion were replaced by symmetrical patterns during fictive locomotion expressed by the chemically activated isolated spinal cord, further indicating that sensory inputs are normally responsible for imposing extensor biasing on otherwise symmetrically alternating extensor/flexor oscillators.
在取自0至4日龄大鼠的离体脊髓标本（不带或带有附着的脑干）中，研究了四足动物运动过程中肢体运动神经元爆发的时间特性。当用N-甲基-D，L-天冬氨酸、血清素和多巴胺的不同组合激活，或通过脑干的电刺激激活时，脊髓会产生虚构运动发作，颈腹根和腰腹根爆发之间具有恒定的相位关系。同侧和对侧的屈肌和伸肌运动根爆发交替出现，颈和腰运动网络总是以与虚构行走相对应的对角协调模式活动。然而，与成年动物的典型运动不同，成年动物中伸肌运动神经元爆发随周期变化比屈肌爆发更多，在离体新生脊髓中，虚构运动速度的增加与颈和腰水平伸肌和屈肌爆发持续时间的减少有关。为了确定这种屈肌/伸肌相位持续时间的对称性是否源于完整动物运动过程中肢体通常提供的感觉反馈缺失，在药物诱导的类似运动的运动过程中，对附着后肢的脊髓进行了肌电图记录。在这些条件下，伸肌爆发的持续时间随周期增加，而屈肌爆发的持续时间现在趋于保持恒定。此外，在完全切断背根后，这种伸肌占主导的模式被持续时间相似的屈肌和伸肌爆发所取代。还对出生后较大（P10 - 12）的大鼠进行了体内和体外实验，这个年龄段会出现类似成年动物依靠身体支撑的运动。同样，在完整跑步机运动过程中观察到的特征性伸肌主导的爆发模式，在化学激活的离体脊髓所表现出的虚构运动过程中被对称模式所取代，这进一步表明感觉输入通常负责对原本对称交替的伸肌/屈肌振荡器施加伸肌偏向。
