ORGANIZATION OF THE COMMISSURAL FIBERS IN THE ADULT BRAIN OF THE LOCUST

The brain (supraoesophageal ganglion) is the most complex of the segme ntal ganglia composing the nerve cord of the locusts Schistocerca greg aria and Locusta migratoria. In this paper, we describe the ground pla n of the commissures crossing the midline of the brain and propose a n omenclature with the aim of making a complex neuropil more understanda ble at the level of individual neurons. For developmental and comparat ive reasons the neuroarchitecture of the brain is related to the neura l axis, not to the body axis. We have identified 73 commissural fiber bundles belonging to the adult brain, and these are named according to their location (ventral, dorsal, anterior, posterior, medial) with re spect to the central complex as reference point. Reconstructions of id entified neurons from intracellular stainings, cobalt backfills, or im munohistochemical studies demonstrate the various configurations in wh ich fibers cross the brain.