Bradley N S, Smith J L
Department of Kinesiology, University of California, Los Angeles 90024.
Brain Res. 1988 Jan 1;466(1):37-52. doi: 10.1016/0165-3806(88)90084-3.
Neuromuscular patterns associated with the development of hindlimb stepping behaviors were studied from birth to postnatal day 60 in normal kittens. Hindlimb muscles were chronically implanted with EMG electrodes at birth to characterize interlimb coordination and intralimb synergies during development of overground and treadmill stepping. Airstepping was also examined but seldom occurred after the second postnatal week. All kittens performed stepping under each condition, including weight-supported stepping, by postnatal day 3. The number of sequential steps on the treadmill and overground increased with age and cycle periods decreased. At onset, stepping behaviors were characterized by adult-like EMG patterns. Interlimb coordination was typified by alternating extensor bursts of similar duration. Extensors at the knee and ankle were coactive during the stance phase, and extensor burst durations were strongly correlated with the cycle periods over a wide range of stepping frequency. Ankle flexor and extensor muscles were reciprocally active during postural tremor, bouts of airstepping, and weight-supported steps on the treadmill and overground. The duration of the reciprocal flexor bust did not vary with cycle period or age. Observations of stepping behaviors and adult-like EMG patterns during initial postnatal development were contingent on optimal testing conditions. Taken together, the data suggest that pattern-generating circuits for regulating interlimb coordination and intralimb muscle synergies are potentially functional prior to the normal ontogenetic onset of locomotion. Perhaps the prolonged postnatal development of locomotion reflects the time required to establish adaptive mechanisms, such as postural control and agility, rather than spinal pattern-generating circuits for locomotion.
在正常小猫中，研究了从出生到出生后60天与后肢迈步行为发育相关的神经肌肉模式。出生时在后肢肌肉中长期植入肌电图电极，以表征在地面行走和跑步机行走发育过程中的肢体间协调和肢体内协同作用。还检查了空中踏步，但在出生后第二周后很少发生。到出生后第3天，所有小猫在每种条件下都能进行踏步，包括负重踏步。跑步机和地面上连续踏步的次数随年龄增加，周期缩短。开始时，踏步行为以类似成年动物的肌电图模式为特征。肢体间协调的典型表现是持续时间相似的伸肌交替爆发。在站立阶段，膝关节和踝关节的伸肌共同活动，伸肌爆发持续时间在很宽的踏步频率范围内与周期密切相关。在姿势性震颤、空中踏步发作以及跑步机和地面上的负重踏步过程中，踝关节屈肌和伸肌相互活动。屈肌爆发的持续时间不随周期或年龄而变化。出生后早期发育过程中对踏步行为和类似成年动物肌电图模式的观察取决于最佳测试条件。综合来看，数据表明调节肢体间协调和肢体内肌肉协同作用的模式产生回路在正常运动发育开始之前可能就已经发挥作用。也许出生后运动发育的延长反映了建立适应性机制（如姿势控制和敏捷性）所需的时间，而不是用于运动的脊髓模式产生回路所需的时间。
