Atsuta Y, Garcia-Rill E, Skinner R D
Department of Anatomy, University of Arkansas for Medical Sciences, Little Rock 72205-7199.
Somatosens Mot Res. 1991;8(1):45-53. doi: 10.3109/08990229109144728.
We previously described the ability to induce adult-like, coordinated airstepping following electrical stimulation of the brainstem in the hindlimb-attached, in vitro brainstem-spinal cord preparation. These findings suggest the presence at birth of supraspinal systems capable of activating and modulating spinal locomotor mechanisms, which presumably also are present at birth. The current study employed the hindlimb-attached in vitro brainstem-spinal cord preparation from 0- to 4-day-old rats maintained in oxygenated artificial cerebrospinal fluid. After the control threshold-frequency relationship for eliciting airstepping was established, the dorsal roots to the attached limbs were severed and the procedure was repeated. No changes in electrical threshold or major differences in the elicited locomotor pattern were observed after deafferentation, although the amplitude of the electromyograms decreased. The mean frequency of alternation at threshold before deafferentation was similar to that after deafferentation. However, the maximum mean frequency induced by suprathreshold stimulation was significantly higher after deafferentation than that before deafferentation. These results suggest that (1) the supraspinal modulation of spinal locomotor mechanisms is not entirely dependent on afferent input; (2) intrinsic spinal locomotor mechanisms are present in the spinal cord at birth; and (3) afferent input may limit the maximum frequency of alternation of the limbs early in development.
我们之前描述过，在体外将脑干与后肢相连的脑干脊髓标本中，通过电刺激脑干可诱导出类似成年动物的协调性空中踏步。这些发现表明，出生时即存在能够激活和调节脊髓运动机制的脊髓上系统，推测这些系统在出生时也已存在。本研究采用0至4日龄大鼠的体外脑干脊髓标本，将其与后肢相连，并置于充氧的人工脑脊液中。在建立了引发空中踏步的对照阈值-频率关系后，切断与相连肢体的背根神经，然后重复该过程。去传入神经后，未观察到电阈值的变化或所诱发运动模式的主要差异，尽管肌电图的幅度有所下降。去传入神经前阈值时的平均交替频率与去传入神经后相似。然而，阈上刺激诱发的最大平均频率在去传入神经后显著高于去传入神经前。这些结果表明：（1）脊髓运动机制的脊髓上调节并不完全依赖于传入输入；（2）出生时脊髓中即存在内在的脊髓运动机制；（3）传入输入可能在发育早期限制了肢体交替的最大频率。
