Control of the motor pattern generator in the VIIth abdominal ganglion of Locusta: Descending neural inhibition and coordination with the oviposition hole digging central pattern generator

Abstract

The control of a motor pattern generator in the VIIth abdominal ganglion of Locusta was examined. Sucrose gap block of ventral nerve cord neural activity in non-egg-laying locusts, anterior to the VIIth abdominal ganglion, initiated the rhythmic neural activity in the oviducal nerves which is produced by this motor pattern generator. Removal of the sucrose gap block resulted in the cessation of the pattern. Extracellular stimulation of the nerve cord caused the inhibition of the rhythmic neural activity in preparations in which the pattern was initiated by transection of the ventral nerve cord. Taken together, these results confirm that the main control of the central pattern generator in the VIIth abdominal ganglion is by descending neural inhibition. Using serial transections of the ventral nerve cord, the source of the inhibition was localized to the brain, suboesophageal ganglion and thoracic ganglia. In addition to being controlled by descending neural inhibition, the motor pattern generator in the VIIth abdominal ganglion was also found to be coordinated with the oviposition digging central pattern generator in the VIIIth abdominal ganglion. The data suggest that communication with the digging central pattern generator may be important in view of the fact that the outputs of these distinct pattern generators are highly coordinated.