THE MOTOR-NEURONS INNERVATING THE DIRECT FLIGHT MUSCLES OF DROSOPHILA-MELANOGASTER ARE MORPHOLOGICALLY SPECIALIZED

The anatomy of the motor neurons innervating six direct flight muscles in Drosophila melanogaster has been investigated by using a horseradi sh peroxidase backfilling technique. The somata of these motor neurons are arranged in two distinct clusters ipsilateral to the muscle they innervate. One cluster of cell bodies is located in the ventrolateral region between the prothoracic neuromere and the mesothoracic leg-rela ted neuropil and the other is situated dorsally and posteriorly to the mesothoracic leg-related neuropil. Axons from somata in the ventrolat eral cluster run in the anterior dorsal mesothoracic nerve, while axon s from somata in the other cluster run in the mesothoracic accessory n erve. This distribution of somata and axons is discussed in the light of the morphological similarity and proximity of these functionally re lated muscles. On the basis of the branching patterns of their neurite s, direct flight muscle motor neurons can be classified as stubbly, fi brous or tufted. The terminal arborizations of the motor neurons over the direct flight muscles are also morphologically specialized. Both t he central and the peripheral morphological specializations of the dir ect flight muscle motor neurons correlate with the activity patterns e xhibited by their associated muscles during flight and courtship song. (C) 1994 Wiley-Liss, Inc.