Akay Turgay, Acharya Hernish J, Fouad Karim, Pearson Keir G
Department of Physiology, University of Alberta, Edmonton, Alberta, Canada.
J Neurophysiol. 2006 Aug;96(2):642-51. doi: 10.1152/jn.00174.2006. Epub 2006 Apr 26.
EphA4 receptors play an important role in axon guidance during development. Disrupting the expression of these receptors in mice has been shown to modify neuronal connections in the spinal cord and results in the production of a characteristic hopping gait. The EphA4-null mouse has been used in numerous investigations aimed at establishing mechanisms responsible for patterning motor activity during walking. However, there have been no detailed behavioral or electrophysiological studies on adult EphA4-null mice. We used high-speed video recordings to determine the coordination of leg movements during locomotion in adult EphA4-null mice. Our data show that the hopping movements of the hind legs are not always associated with synchronous movements of forelegs. The coupling between the forelegs is weak, resulting in changes in their phase relationship from step to step. The synchronous coordination of the hind legs can switch to an alternating pattern for a short period of time during recovery from isoflurane anesthesia. Comparison of the kinematics of hind leg movements in EphA4-null mice and wild-type animals shows that besides the synchronous coordination in EphA4-null mice, the swing durations and the swing amplitude are shorter. Electromyographic recordings from a knee extensor muscle show double bursting in the EphA4-null animals but single bursts in wild types. This double burst changes to single-burst activity during swimming and when hind legs are stepping in alternation. These observations suggest an influence of sensory feedback in shaping the pattern of muscle activity during locomotion in the mutant animals. Our data give the first detailed description of the locomotor behavior of an adult mouse with genetically manipulated spinal networks.
EphA4受体在发育过程中的轴突导向中起重要作用。研究表明，破坏小鼠体内这些受体的表达会改变脊髓中的神经元连接，并导致特征性跳跃步态的产生。EphA4基因敲除小鼠已被用于众多旨在确定步行过程中运动模式形成机制的研究中。然而，尚未对成年EphA4基因敲除小鼠进行详细的行为或电生理研究。我们使用高速视频记录来确定成年EphA4基因敲除小鼠运动过程中腿部运动的协调性。我们的数据表明，后腿的跳跃运动并不总是与前腿的同步运动相关。前腿之间的耦合较弱，导致它们的相位关系在步与步之间发生变化。在从异氟烷麻醉中恢复的短时间内，后腿的同步协调可以切换为交替模式。对EphA4基因敲除小鼠和野生型动物后腿运动学的比较表明，除了EphA4基因敲除小鼠中的同步协调外，摆动持续时间和摆动幅度较短。来自膝伸肌的肌电图记录显示，EphA4基因敲除动物出现双爆发，但野生型动物出现单爆发。这种双爆发在游泳时以及后腿交替迈步时会转变为单爆发活动。这些观察结果表明，感觉反馈对突变动物运动过程中肌肉活动模式的形成有影响。我们的数据首次详细描述了具有基因操纵脊髓网络的成年小鼠的运动行为。
