Patterned synaptic drive to locust flight motoneurons after hemisection of thoracic ganglia

Intracellular recordings were carried out on locust flight motoneurons after hemisection of individual thoracic ganglia. With the exception of minimal surgical manipulations, the animals were intact and able to perform tethered flight. Analysis of the synaptic drive recorded in the motoneurons during flight motor activity revealed the extent to which ganglion hemisection influenced the premotor rhythm generating network.

1.	Hemisection of the mesothoracic ganglion (Fig. 2) as well as hemisection of both the mesothoracic and the prothoracic ganglia (Fig. 3) had no significant effects on the pattern of synaptic input to the flight motoneurons. Thus the rhythm generating premotor network does not depend on commissural information transfer in the mesothoracic and the prothoracic ganglia. This conclusion was supported by experiments in which more extensive surgical isolations of thoracic ganglia were carried out (Fig. 5).
2.	Removal of input from wing receptors (deafferentation) in addition to hemisection of the mesothoracic ganglion (Fig. 4) resulted in rhythmic and coordinated oscillations of the motoneuron membrane potential which were indistinguishable from those observed in deafferented animals with all ganglia intact.
3.	Hemisection of the metathoracic ganglion had more pronounced effects on the patterns of synaptic drive to the flight motoneurons and their spike discharge. Rhythmic activity which was often subthreshold could, however, still be recorded following a metathoracic split (Fig. 6).
4.	No rhythmic synaptic input was observed after hemisection of both mesothoracic and metathoracic ganglia (Fig. 7).