On the control of stridulation in the acridid grasshopper Omocestus viridulus L.

Summary

In tethered, minimally dissected grasshoppers spiking and non-spiking interneurons in the metathoracic ganglion complex were recorded, stimulated and stained during stridulation. The functional significance of the interneurons for the form of the stridulation movement was tested and quantitatively analysed. Local interneurons had hemiganglionic arborizations in the lateral dorsal neuropil. They did not show branching patterns typical for stridulation interneurons. An abdominal intersegmental interneuron had bilateral arborizations in the dorsal medial neuropil, similar to other stridulation interneurons. The interneurons exhibited rhythmic membrane potential oscillations in the stridulation rhythm. Intracellular stimulation modulated the form of the stridulation movement but did not change the stridulation cycle or the coordination of the hindlegs. Tonic stimulation changed either the amplitude of stridulation or the leg position. Phasic stimulation revealed phase-dependent increment or decrement of the upstroke or downstroke amplitude, respectively. The motor effects were reciprocal for the antagonistic movements in the metathoracic thoraco-coxal joint. Local interneurons elicited only ipsilateral motor effects. There is evidence for a functional separation of rhythm generation, coordination and movement shaping within the stridulation network.