Division of Biological Sciences, University of Missouri, Columbia, MO, United States.
Interdisciplinary Neuroscience Program, University of Missouri, Columbia, MO, United States.
Front Neural Circuits. 2017 Nov 24;11:89. doi: 10.3389/fncir.2017.00089. eCollection 2017.
The contribution of left-right reciprocal coupling between spinal locomotor networks to the generation of locomotor activity was tested in adult lampreys. Muscle recordings were made from normal animals as well as from experimental animals with rostral midline (ML) spinal lesions (~13%→35% body length, BL), before and after spinal transections (T) at 35% BL. Importantly, in the present study actual locomotor movements and muscle burst activity, as well as other motor activity, were initiated in whole animals by descending brain-spinal pathways in response to sensory stimulation of the anterior head. For experimental animals with ML spinal lesions, sensory stimulation could elicit well-coordinated locomotor muscle burst activity, but with some significant differences in the parameters of locomotor activity compared to those for normal animals. Computer models representing normal animals or experimental animals with ML spinal lesions could mimic many of the differences in locomotor activity. For experimental animals with ML and T spinal lesions, right and left rostral hemi-spinal cords, disconnected from intact caudal cord, usually produced tonic or unpatterned muscle activity. Hemi-spinal cords sometimes generated spontaneous or sensory-evoked relatively high frequency "burstlet" activity that probably is analogous to the previously described "fast rhythm", which is thought to represent lamprey locomotor activity. However, "burstlet" activity in the present study had parameters and features that were very different than those for lamprey locomotor activity: average frequencies were ~25 Hz, but individual frequencies could be >50 Hz; burst proportions (BPs) often varied with cycled time; "burstlet" activity usually was not accompanied by a rostrocaudal phase lag; and following ML spinal lesions alone, "burstlet" activity could occur in the presence or absence of swimming burst activity, suggesting the two were generated by different mechanisms. In summary, for adult lampreys, left and right hemi-spinal cords did not generate rhythmic locomotor activity in response to descending inputs from the brain, suggesting that left-right reciprocal coupling of spinal locomotor networks contributes to both phase control and rhythmogenesis. In addition, the present study indicates that extreme caution should be exercised when testing the operation of spinal locomotor networks using artificial activation of isolated or reduced nervous system preparations.
左侧和右侧脊髓运动网络之间的交互耦合对运动活动的产生的贡献在成体七鳃鳗中进行了测试。在进行脊髓横切（T）之前和之后，从正常动物以及中线（ML）脊髓损伤（~13%→35%体长，BL）的实验动物的肌肉记录中进行了记录，T 在 35%BL 处进行。重要的是，在本研究中，通过对头部前部的感觉刺激，通过下行脑脊髓通路在整个动物中引发了实际的运动运动和肌肉爆发活动以及其他运动活动。对于具有 ML 脊髓损伤的实验动物，感觉刺激可以引发协调良好的运动肌肉爆发活动，但与正常动物相比，运动活动的参数存在一些显著差异。代表正常动物或具有 ML 脊髓损伤的实验动物的计算机模型可以模拟运动活动的许多差异。对于具有 ML 和 T 脊髓损伤的实验动物，与完整的尾段分离的左右头侧半脊髓通常会产生紧张或无模式的肌肉活动。半脊髓有时会自发或感觉诱发相对较高频率的“爆发样”活动，这可能类似于先前描述的“快速节律”，该节律被认为代表七鳃鳗的运动活动。然而，本研究中的“爆发样”活动的参数和特征与七鳃鳗的运动活动非常不同：平均频率约为 25Hz，但单个频率可能>50Hz；爆发比例（BP）经常随循环时间而变化；“爆发样”活动通常不伴有头尾相位滞后；并且单独进行 ML 脊髓损伤后，“爆发样”活动可以在存在或不存在游泳爆发活动的情况下发生，这表明两者是由不同的机制产生的。总之，对于成体七鳃鳗，左右半脊髓在没有来自大脑的下行输入的情况下不会产生节律性运动活动，这表明脊髓运动网络的左右交互耦合有助于相位控制和节律发生。此外，本研究表明，在使用分离或简化的神经系统制剂的人工激活来测试脊髓运动网络的运行时，应格外小心。
