Samara Ramsey F, Currie Scott N
Department of Cell Biology and Neuroscience, University of California-Riverside, Riverside, CA 92521, USA.
J Neurophysiol. 2008 Apr;99(4):1953-68. doi: 10.1152/jn.01087.2007. Epub 2008 Feb 13.
We performed mechanical lesions of the midbody (D2-D3; second to third postcervical spinal segments) spinal cord in otherwise intact turtles to locate spinal cord pathways that 1) activate and control the amplitude of voluntary hindlimb swimming movements and 2) coordinate hindlimb swimming with the movement of other limbs. Pre- and postlesion turtles were held by a band clamp around the carapace just beneath the water surface in a clear Plexiglas tank and videotaped from below so that kinematic measurements could be made of voluntary forward swimming with motion analysis software. Movements of the forelimbs (wrists) and hindlimbs (knees and ankles) were tracked relative to stationary reference points on the plastron to obtain bilateral measurements of hip and forelimb angles as functions of time along with foot trajectories. We measured changes in limb movement amplitude, cycle period, and interlimb phase before and after spinal lesions. Our results indicate that locomotor command signals that activate and regulate the amplitude of voluntary hindlimb swimming travel primarily in the dorsolateral funiculus (DLF) at the D2-D3 level and cross over to drive contralateral hindlimb movements. This suggests that electrical stimulation of the D3 DLF, which was previously shown to evoke swimming movements in the contralateral hindlimb of low-spinal turtles, activated the same locomotor command pathways that the animal uses during voluntary behavior. We also show that forelimb-hindlimb coordination is maintained by longitudinal spinal pathways that are largely confined to the ventrolateral funiculus (VLF) and mediate phase coupling of ipsilateral limbs, presumably by interenlargement propriospinal fibers.
我们对原本完好无损的乌龟中体（D2 - D3；颈后脊髓第二至第三节段）脊髓进行机械损伤，以定位脊髓通路，这些通路能够：1）激活并控制自主后肢游泳运动的幅度；2）使后肢游泳与其他肢体的运动相协调。损伤前后的乌龟被用一个束带夹固定在透明有机玻璃水箱水面下方的背甲周围，并从下方进行录像，以便使用运动分析软件对自主向前游泳进行运动学测量。相对于腹甲上的固定参考点，追踪前肢（手腕）和后肢（膝盖和脚踝）的运动，以获取髋部和前肢角度随时间变化的双侧测量值以及足部轨迹。我们测量了脊髓损伤前后肢体运动幅度、周期和肢体间相位的变化。我们的结果表明，激活并调节自主后肢游泳幅度的运动指令信号主要在D2 - D3水平的背外侧索（DLF）中传导，并交叉驱动对侧后肢运动。这表明，先前已证明电刺激D3 DLF可在低位脊髓乌龟的对侧后肢诱发游泳运动，激活了动物在自主行为中使用的相同运动指令通路。我们还表明，前肢 - 后肢协调由纵向脊髓通路维持，这些通路主要局限于腹外侧索（VLF），并可能通过节段间脊髓固有纤维介导同侧肢体的相位耦合。
