Berendes Volker, Zill Sasha N, Büschges Ansgar, Bockemühl Till
Department of Animal Physiology, Zoological Institute, University of Cologne, Cologne 50674, Germany.
Department of Anatomy and Pathology, Joan C. Edwards School of Medicine, Marshall University, Huntington, WV 25704, USA.
J Exp Biol. 2016 Dec 1;219(Pt 23):3781-3793. doi: 10.1242/jeb.146720. Epub 2016 Sep 29.
In insects, the coordinated motor output required for walking is based on the interaction between local pattern-generating networks providing basic rhythmicity and leg sensory signals, which modulate this output on a cycle-to-cycle basis. How this interplay changes speed-dependently and thereby gives rise to the different coordination patterns observed at different speeds is not sufficiently understood. Here, we used amputation to reduce sensory signals in single legs and decouple them mechanically during walking in Drosophila. This allowed for the dissociation between locally generated motor output in the stump and coordinating influences from intact legs. Leg stumps were still rhythmically active during walking. Although the oscillatory frequency in intact legs was dependent on walking speed, stumps showed a high and relatively constant oscillation frequency at all walking speeds. At low walking speeds we found no strict cycle-to-cycle coupling between stumps and intact legs. In contrast, at high walking speeds stump oscillations were strongly coupled to the movement of intact legs on a one-to-one basis. Although during slow walking there was no preferred phase between stumps and intact legs, we nevertheless found a preferred time interval between touch-down or lift-off events in intact legs and levation or depression of stumps. Based on these findings, we hypothesize that, as in other insects, walking speed in Drosophila is predominantly controlled by indirect mechanisms and that direct modulation of basic pattern-generating circuits plays a subsidiary role. Furthermore, inter-leg coordination strength seems to be speed-dependent and greater coordination is evident at higher walking speeds.
在昆虫中，行走所需的协调运动输出基于提供基本节律性的局部模式生成网络与腿部感觉信号之间的相互作用，这些感觉信号在逐个周期的基础上调节这种输出。目前尚不完全清楚这种相互作用如何随速度变化，从而产生在不同速度下观察到的不同协调模式。在这里，我们通过截肢减少单个腿部的感觉信号，并在果蝇行走过程中使其机械解耦。这使得残肢中局部产生的运动输出与完整腿部的协调影响得以分离。在行走过程中，腿部残肢仍有节律地活动。尽管完整腿部的振荡频率取决于行走速度，但残肢在所有行走速度下都表现出较高且相对恒定的振荡频率。在低行走速度下，我们发现残肢与完整腿部之间不存在严格的逐个周期耦合。相反，在高行走速度下，残肢振荡与完整腿部的运动以一对一的方式强烈耦合。尽管在慢走时残肢与完整腿部之间没有优先相位，但我们仍然发现完整腿部的触地或离地事件与残肢的抬起或下降之间存在优先时间间隔。基于这些发现，我们假设，与其他昆虫一样，果蝇的行走速度主要由间接机制控制，而基本模式生成电路的直接调制起辅助作用。此外，腿部间的协调强度似乎取决于速度，在较高行走速度下更明显的协调作用显而易见。
