ABSTRACT
Walking is a complex rhythmic locomotor behaviour generated by sequential and periodical contraction of muscles essential for coordinated control of movements of legs and leg joints. Studies of walking in vertebrates and invertebrates have revealed that premotor neural circuitry generates a basic rhythmic pattern that is sculpted by sensory feedback and ultimately controls the amplitude and phase of the motor output to leg muscles. However, the identity and functional roles of the premotor interneurons that directly control leg motoneuron activity are poorly understood. Here we take advantage of the powerful genetic methodology available in Drosophila to investigate the role of premotor inhibition in walking by genetically suppressing inhibitory input to leg motoneurons. For this, we have developed a novel algorithm for automated analysis of leg motion to characterize the walking parameters of wildtype flies from high speed video recordings. Further, we use genetic reagents for targeted RNAi knockdown of inhibitory neurotransmitter receptors in leg motoneurons together with quantitative analysis of resulting changes in leg movement parameters in freely walking Drosophila. Our findings indicate that targeted down regulation of GABAA receptor Rdl in leg motoneurons results in a dramatic reduction of walking speed and step-length without the loss of general leg coordination during locomotion. Genetically restricting the knockdown to the adult stage and subsets of motoneurons yields qualitatively identical results. Taken together, these findings identify GABAergic premotor inhibition of motoneurons as an important determinant of correctly coordinated leg movements and speed of walking in freely behaving Drosophila.
SIGNIFICANCE STATEMENT Inhibition is an important feature of neuronal circuit and in walking it aids in controlling coordinated movement of legs, leg segments and leg joints. Recent studies in Drosophila reports the role of premotor inhibitory interneurons in regulation of larval locomotion. However, in adult walking the identity and functional role of premotor interneurons is less understood. Here, we use genetic methods for targeted knockdown of inhibitory neurotransmitter receptor in leg motoneurons that results in slower walking speed and defects in walking parameters combined with novel method we have developed for quantitative analysis of the fly leg movement and the observed changes in walking parameters. Our results indicate that GABAergic pre-motor inhibition to leg motoneurons is required to control the normal walking behaviour in adult Drosophila.
