Interspike interval relationship among flight muscle fibres in Drosophila

Simultaneous intracellular recordings were made from the 10 motor units (12 fibres) comprising the bilateral pair of dorsal longitudinal flight muscles in Drosophila melanogaster while in stationary flight. The neural input which commonly drives these units was characterized by observing the influence which this input has on the interspike intervals of the various units. It was observed that the intervals of these units (both ipsilateral and contralateral), when considered collectively (that is, as a series of successively occurring intervals without regard for which unit represents which interval), fluctuate in a serially correlated manner. These interval fluctuations collectively define a fluctuation of complex waveform. The characteristics of this waveform suggest that two (or more) oscillating inputs are involved in commonly driving these units. In addition, a coupling in frequency and timing was observed between certain pairs of ipsilateral units, as well as between the units of one side relative to those of the other side. This coupling suggests that the neural pathway leading from the oscillating driving source might diverge, first to left and right sides, and then at a more peripheral level into three separate pathways, one leading to units 1 and 2, another to units 3 and 4, and a third to unit 5/6.