Bradley N S, Smith J L
Department of Kinesiology, University of California, Los Angeles 90024.
Brain Res. 1988 Jan 1;466(1):53-67. doi: 10.1016/0165-3806(88)90085-5.
From birth to postnatal day 60, neuromuscular patterns for airstepping and treadmill stepping were assessed in kittens spinalized (T12) at birth (Day-1) or at the end of the second postnatal week (Day-14). Within 72 h after spinalization, all kittens displayed stepping motions, but exteroceptive facilitation (e.g. tail pinch) was required to initiate and sustain both behaviors. In Day-14 spinal kittens, the hindlimbs spontaneously and alternately airstepped, but in Day-1 spinal kittens exteroceptive stimulation was usually necessary to evoke airstepping, and the hindlimbs stepped synchronously. Kittens in both groups developed atypical neuromuscular patterns; flexor bursts were nearly twice as long in duration as extensor bursts. Development of bipedal treadmill stepping was similar for Day-1 and Day-14 spinal kittens, but differed from that for normal kittens. Tested at the same belt speeds, stepping was more easily elicited in spinal kittens, bouts of repetitive stepping were longer, and cycle periods were shorter than in normal kittens until postnatal week 6. Spinal kittens, however, seldom exhibited adequate weight support during hindlimbs stepping, and the neuromuscular patterns associated with bipedal stepping were atypical. For spinal kittens, the relationship between the extensor burst duration and the cycle period was reduced substantially, and flexor activity was initiated earlier in the step cycle and was longer in duration than that for normal kittens. These atypical intralimb synergies may have been the consequence of altered lumbosacral circuits produced by the spinal transection. It is also possible that these spinal circuits, lacking rostral input, were particularly susceptible to abnormal motion-dependent feedback resulting from reduced hindlimb weight support.
从出生到出生后第60天，对出生时（第-1天）或出生后第二周结束时（第14天）进行脊髓横断（T12）的小猫的空中踏步和跑步机踏步的神经肌肉模式进行了评估。在脊髓横断后72小时内，所有小猫都表现出踏步动作，但需要外感受性促进（如捏尾巴）来启动和维持这两种行为。在第14天脊髓横断的小猫中，后肢自发且交替地进行空中踏步，但在第1天脊髓横断的小猫中，通常需要外感受性刺激来诱发空中踏步，且后肢同步踏步。两组小猫都形成了非典型的神经肌肉模式；屈肌爆发的持续时间几乎是伸肌爆发的两倍。第1天和第14天脊髓横断的小猫双足跑步机踏步的发育情况相似，但与正常小猫不同。在相同的传送带速度下进行测试时，脊髓横断的小猫更容易引发踏步，重复踏步的次数更多，并且直到出生后第6周，其周期时间都比正常小猫短。然而，脊髓横断的小猫在后肢踏步时很少表现出足够的体重支撑，并且与双足踏步相关的神经肌肉模式是非典型的。对于脊髓横断的小猫，伸肌爆发持续时间与周期时间之间的关系大幅降低，并且屈肌活动在步周期中启动得更早，持续时间比正常小猫更长。这些非典型的肢体内部协同作用可能是脊髓横断导致腰骶回路改变的结果。也有可能这些缺乏延髓输入的脊髓回路特别容易受到后肢体重支撑减少导致的异常运动依赖性反馈的影响。
