Descending stridulatory interneurons in the suboesophageal ganglion of two grasshopper species

1. The activity of interneurons in the suboesophageal ganglion of the acridid grasshoppers Omocestus viridulus (L.) and Chorthippus mollis (Charp.), recorded intracellularly during stridulation, was found to conform to the rhythm of the singing movements. The arborizations of these neurons in this ganglion are largely bilaterally symmetrical; the axon descends contralaterally to the soma and passes at least into the metathoracic ganglion.
2. The anatomical and physiological characteristics of these neurons are similar in the two species and of four types. Three of them exhibit a tonic, spontaneous activity in the resting animal, which is modulated in the stridulatory rhythm as soon as singing begins. The fourth type has no resting activity and discharges only during the song, in a stridulation-specific pattern.
3. By transecting the connectives it was shown that the rhythmic activity of the neurons is not determined by input from the brain, nor is it generated in the suboesophageal ganglion itself. It is based on information about the song pattern that ascends from the thoracic ganglia.