PROJECTIONS OF SUBESOPHAGEAL DESCENDING INTERNEURONS IN THORACIC GANGLIA OF THE GRASSHOPPER OMOCESTUS-VIRIDULUS L (ORTHOPTERA, ACRIDIDAE)

Descending interneurons (DINs) from the suboesophageal ganglion (SOG) and some from the brain of the grasshopper Omocestus viridulus L. (Ort hoptera: Acrididae) were stained intracellularly with Lucifer Yellow, and the details of their projections in SOG, prothoracic, and, where p ossible, mesothoracic ganglion were examined. DINs could be followed t hrough the prothoracic ganglion in only c.10% of the preparations. Sev eral SOG DINs terminated in the prothoracic ganglion, while some termi nated in the mesothoracic ganglion. The few DINs, which could be follo wed through the mesothoracic ganglion, had the same projections in bot h thoracic ganglia. Three major thoracic projection forms were found: lateral, mediolateral and medial. Most DINs, both from the brain and S OG, branch dorsally in thoracic motor integration neuropiles, although not necessarily exclusively. Two DINs with branches only in the ventr al sensory integration areas were found. The arborisation or depth pro file of the DINs in the SOG does not correlate with the projection in the thoracic ganglia. The functional consequences for the role of the SOG in suprasegmental motor control are discussed.