Localization of Motor Neurons and Central Pattern Generators for Motor Patterns Underlying Feeding Behavior in <i>Drosophila</i> Larvae

Motor systems can be functionally organized into effector organs (muscles and glands), the motor neurons, central pattern generators (CPG) and higher control centers of the brain. Using genetic and electrophysiological methods, we have begun to deconstruct the motor system driving Drosophila larval feeding behavior into its component parts. In this paper, we identify distinct clusters of motor neurons that execute head tilting, mouth hook movements, and pharyngeal pumping during larval feeding. This basic anatomical scaffold enabled the use of calcium-imaging to monitor the neural activity of motor neurons within the central nervous system (CNS) that drive food intake. Simultaneous nerve- and muscle-recordings demonstrate that the motor neurons innervate the cibarial dilator musculature (CDM) ipsi- and contra-laterally. By classical lesion experiments we localize a set of CPGs generating the neuronal pattern underlying feeding movements to the subesophageal zone (SEZ). Lesioning of higher brain centers decelerated all feeding-related motor patterns, whereas lesioning of ventral nerve cord (VNC) only affected the motor rhythm underlying pharyngeal pumping. These findings provide a basis for progressing upstream of the motor neurons to identify higher regulatory components of the feeding motor system.运动系统可按功能划分为效应器（effector organs，即肌肉与腺体）、运动神经元、中枢模式发生器（central pattern generators，CPG）以及大脑的高级控制中枢。本研究借助遗传学与电生理方法，已将驱动果蝇幼虫取食行为的运动系统拆解为各个组成部分。本文中，我们鉴定出在幼虫取食阶段介导头部倾斜、口钩运动及咽泵活动的不同运动神经元集群。这一基础解剖框架使得我们可利用钙成像技术，监测驱动食物摄取的中枢神经系统（central nervous system，CNS）内运动神经元的神经活动。同步神经与肌肉记录实验证实，运动神经元可同侧及对侧支配食窦扩张肌（cibarial dilator musculature，CDM）。通过经典的损伤实验，我们将一组介导取食运动神经元活动模式的中枢模式发生器定位于食管下区（subesophageal zone，SEZ）。对大脑高级中枢的损伤会减慢所有取食相关的运动模式，而对腹神经索（ventral nerve cord，VNC）的损伤仅影响咽泵活动相关的运动节律。上述研究结果为从运动神经元上游进一步鉴定取食运动系统的高级调控组分提供了基础。