A cephalothoracic command system controls stridulation in the acridid grasshopper Omocestus viridulus L.

1. In the acridid grasshopper Omocestus viridulus, I performed intracellular recording and stimulation of descending brain neurons simultaneously with the recording of the stridulatory hindleg movements in a minimally dissected preparation. The descending B-DC-3 interneurons were identified with intracellular staining techniques. In each half of the brain at least two sibling B-DC-3 interneurons exist. Main features of the neurons are a medial soma position and a pronounced dendritic arborization within the medial dorsal posterior protocerebrum. The axon descends contralaterally and occupies an extreme medial position in the cervical and thoracic connectives. 2. The occurrence of stridulatory behavior is strictly coupled with tonic spike activity in the B-DC-3 interneurons. During spontaneous stridulation these interneurons discharge action potentials at a rate of approximately 100 action potentials per second. 3. Individual B-DC-3 interneurons are sufficient to initiate and maintain the species-specific leg movements of courtship stridulation. During gradual depolarization stridulation is elicited at discharge rates of approximately 70 action potentials per second. On pulselike depolarization the neurons show a phasic-tonic discharge pattern. 4. The interneurons are necessary for the generation of stridulatory leg movements. Inhibition of an individual B-DC-3 interneuron can stop spontaneous stridulatory motor activity. 5. Depolarization of an individual B-DC-3 interneuron during ongoing spontaneous stridulation increases the repetition rate and amplitude of the stridulatory leg movements. Thus the B-DC-3 interneurons can also modulate the output of the stridulatory pattern generator. 6. Because of their number, structure, and properties, the B-DC-3 interneurons have to be regarded as the command system of stridulation in the acridid grasshopper O. viridulus.