Dynamic Analysis of Larval Locomotion in Drosophila Chordotonal Organ Mutants. J.C. Caldwell , M.M. Miller , S. Wing , D.R. Soll , D.F. Eberl. Biological Sciences, University of Iowa, Iowa City, IA.

   Rhythmic movements, such as peristaltic contraction, are initiated by output from central pattern generator (CPG) neurons in the central nervous system. These oscillatory neurons elicit locomotion in the absence of external sensory or descending inputs, but CPG circuits produce more directed and behaviorally relevant movement via PNS input. Normal locomotion of foraging Drosophila melanogaster larvae results from patterned muscle contractions that move stereotypically along the larval body segments, but without feedback from the nervous system, contraction of body segments is uncoordinated. We have dissected the role of a subset of mechanosensory neurons in the larval PNS, the chordotonal organs (cho), in providing sensory feedback to the locomotor CPG circuit with the DIAS (Dynamic Image Analysis System) software. We have used an array of mutants carrying chordotonal organ mutations including atonal, a cho proneural gene, beethoven, a cho cilia class mutant, smetana and touch insensitive larva B, two axonemal mutants and 5D10, a cho partial mutant.
   Using DIAS, we found defects in gross path morphology of all cho mutants as compared to wild type. These mutants exhibit increased frequency and duration of turning (decision-making) and reduced duration of linear locomotion. Furthermore, we found defects in locomotor parameters including reduced average speed, direction change and persistence. DIAS analysis of peristaltic waves indicates that mutants exhibit reduced average speed and reduced positive and negative flow. A differential plot of body length over time indicates that cho mutants have increased stride period during each peristaltic wave. Thus, chordotonal sensillae are major proprioceptive components that underlie touch sensitivity, locomotion and peristaltic contraction by providing sensory feedback to the locomotor CPG circuit in larvae.