Coordination and Modulation of Locomotion Pattern Generators inDrosophila Larvae: Effects of Altered Biogenic Amine Levels by theTyramine β Hydroxlyase Mutation

摘要

Forward locomotion of Drosophila melanogaster larvae is composed of rhythmic waves of contractions that are thought to be produced by segmentally organized central pattern generators. We present a systematic description of spike activity patterns during locomotive contraction waves in semi-intact wild-type and mutant larval preparations. We have shown previously that Tβh^nM18 mutants, with altered levels of octopamine and tyramine, have a locomotion deficit. By recording en passant from the segmental nerves, we investigated the coordination of the neuronal activity driving contraction waves of the abdominal body-wall muscles. Rhythmic bursts of activity that occurred concurrently with locomotive waves were frequently observed in wild-type larvae but were rarely seen in Tβh^nM18 mutants. These centrally generated patterned activities were eliminated in the distal stumps of both wild-type and Tβh^nM18 larvae after severing the segmental nerve from the CNS. Patterned activities persisted in the proximal stumps deprived of sensory feedback from the periphery. Simultaneous recordings demonstrated a delay in the bursting activity between different segments, with greater delay for segments that were farther apart. In contrast, bilateral recordings within a single segment revealed a wellsynchronized activity pattern in nerves innervating each hemisegment in both wild-type andTβh^nM18 larvae. Significantly, rhythmic patterns ofbursts and waves could be evoked in Tβh^nM18 mutants byhead or tail stimulation despite their highly irregular spontaneous activities. Theseobservations suggest a role of the biogenic amines in the initiation and modulation ofmotor pattern generation. The technique presented here can be readily extended to examinethe locomotion motor program of other mutants.