Output pattern generation by Drosophila flight motoneurons

Abstract

Twenty-six singly innervated muscle fibers provide power for flight in D. melanogaster. Spikes were recorded from individual motoneurons. The different motoneurons to each muscle fire in a repeating sequence, and this cycle in each muscle runs independently of the cycles in other muscles. The 4 ventral motor units of each dorsal longitudinal muscle fire preferentially in 2 sequences. A single antidromically stimulated spike in a motoneuron causes a complete re-setting of that motoneuron''s firing cycle and changes its position in the firing sequence. Firing time is not determined by periodic bursts from interneurons. Antidromic stimulation showed that the motoneurons to a single muscle inhibit each other. A mechanism is proposed in which the output pattern is generated essentially by interactions between the motoneurons. Quantitative measurements of the commonality of excitation, the re-setting of each motoneuron and inhibition between motoneurons show that these properties are of the magnitude required for pattern generation by this mechanism.