Motor outputs of giant nerve fiber in Drosophila.

Abstract

The giant fiber of D. melnogaster was stimulated electrically in the brain and action potentials were recorded intracellularly from its axon. A single spike in the giant fiber drives short and constant-latency muscle potentials in the tergotrochanter muscle (TTM) and the dorsal longitudinal muscle (DLM). The giant fiber pathway is extremely stable in response to high-frequency stimuli. The pathway to the DLM follows stimuli at frequencies as high as 100 Hz. the pathway to the TTM follows stimuli at frequencies as high as 300 Hz. Motoneuron responses were described to time the events occurring between the giant fiber spikes and the TTM and DLM muscle potentials. Most of this time is due to motoneuron axon conduction and neuromuscular transmission. Relatively less time is due to transmission between the giant fiber and the motoneurons. Results are compared with giant fiber pathway neuroanatomy. The giant fiber may drive the TTM via a monosynaptic connection to the TTM motoneuron. The giant fiber drives the DLM motoneurons disynaptically via the peripherally synapsing interneuron (PSI) of King and Wyman. It is further suggested that: connections between the giant fiber and the TTM motoneuron transmit electrically, connections between the giant fiber and the PSI transmit electrically and connections between the PSI and the DLM motoneurons transmit chemically.