Abstract
We have established a preparation in larval Drosophila to monitor fictive locomotion simultaneously across abdominal and thoracic segments of the isolated CNS with genetically encoded Ca2+ indicators. The Ca2+ signals closely followed spiking activity measured electrophysiologically in nerve roots. Three motor patterns are analyzed. Two comprise waves of Ca2+ signals that progress along the longitudinal body axis in a posterior-to-anterior or anterior-to-posterior direction. These waves had statistically indistinguishable intersegmental phase delays compared with segmental contractions during forward and backward crawling behavior, despite being ∼10 times slower. During these waves, motor neurons of the dorsal longitudinal and transverse muscles were active in the same order as the muscle groups are recruited during crawling behavior. A third fictive motor pattern exhibits a left-right asymmetry across segments and bears similarities with turning behavior in intact larvae, occurring equally frequently and involving asymmetry in the same segments. Ablation of the segments in which forward and backward waves of Ca2+ signals were normally initiated did not eliminate production of Ca2+ waves. When the brain and subesophageal ganglion (SOG) were removed, the remaining ganglia retained the ability to produce both forward and backward waves of motor activity, although the speed and frequency of waves changed. Bilateral asymmetry of activity was reduced when the brain was removed and abolished when the SOG was removed. This work paves the way to studying the neural and genetic underpinnings of segmentally coordinated motor pattern generation in Drosophila with imaging techniques.
Highlights
CENTRAL PATTERN GENERATING (CPG) networks produce coordinated motor output without sensory feedback and underlie many behaviors, such as walking, flying, singing, and eating
We have used a genetically encoded Ca2ϩ indicator (GCaMP3; Tian et al 2009) to image motor activity simultaneously across thoracic and abdominal ganglia in the larval central nervous system (CNS). We combine this with electrophysiology and behavioral analysis to demonstrate that the isolated larval CNS produces a range of motor patterns that are quantifiably similar to crawling behavior in intact larvae
For all dissections and experiments, the CNS was covered with physiological saline containing 135 NaCl, 5 KCl, 2 CaCl2, 4 MgCl2, 5 TES, and 36 sucrose
Summary
CENTRAL PATTERN GENERATING (CPG) networks produce coordinated motor output without sensory feedback and underlie many behaviors, such as walking, flying, singing, and eating (for reviews see Delcomyn 1980; Marder and Calabrese 1996; Mulloney and Smarandache 2010). A fundamental aspect of many behaviors, such as swimming (Hocker et al 2000), crawling (Puhl and Mesce 2008), and ventilation (Lewis et al 1973; Ramirez and Pearson 1989), is the coordination between multiple body segments, and in many species studying these networks with imaging techniques is difficult because of the large distances between the neurons involved To overcome these limitations, we have studied the larval locomotor system of Drosophila. We have used a genetically encoded Ca2ϩ indicator (GCaMP3; Tian et al 2009) to image motor activity simultaneously across thoracic and abdominal ganglia in the larval CNS We combine this with electrophysiology and behavioral analysis to demonstrate that the isolated larval CNS produces a range of motor patterns that are quantifiably similar to crawling behavior in intact larvae. This work provides a foundation for future work on the neural basis of crawling in Drosophila larvae using imaging techniques and opens up new possibilities for the study of intersegmental coordination in a genetically manipulable organism
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