In tethered grasshoppers, Chorthippus mollis, stridulatory leg movements were elicited by d.c. brain stimulation. Stridulatory chirps comprise both slow up-and-down movements and rapid oscillations of the hindlegs. Intracellular recording, stimulation and staining of interneurones within the metathoracic ganglion complex were performed simultaneously with recordings of leg movement. Five interneurones were identified in the metathoracic ganglion complex. The branching patterns of these interneurones were typical of stridulatory interneurones. Three of these neurones had a structure very similar to stridulatory interneurones already characterized in the species Omocestus viridulus. During stridulation, the spike activity of all interneurones was phasically coupled to the chirp rhythm; two interneurones additionally exhibited coupling to the rapid leg oscillations. Intracellular stimulation of interneurones A1-AC-2 and A1-AI-1 prolonged the duration of the rapid leg oscillations and influenced the generation of the chirp rhythm. Interneurones T3-LI-2 and T3-LC-4 decreased the amplitude of the slow up-and-down movement. The data indicate that at least part of the metathoracic stridulatory network of C. mollis is organized in a structurally and functionally similar way to that of O. viridulus.

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