MIGRATION OF NEURONS BETWEEN GANGLIA IN THE METAMORPHOSING INSECT NERVOUS-SYSTEM

Migration of neurons over long distances occurs during the development of the adult central nervous system of the sphinx moth Manduca sexta, and the turnip moth Agrotis segetum. From each of the suboesophageal and three thoracic ganglia, bilaterally-paired clusters of immature ne urons and associated glial cells migrate posteriorly along the interga nglionic connectives, to enter the next posterior ganglion. The first sign of mio gration is observed at the onset of metamorphosis, when po sterio-lateral cell clusters gradually separate from the cortex of neu ronal cell bodies and enter the connectives. Cell clusters migrate pos teriorly along the connective to reach the next ganglion over the firs t three days (approximately 15%) of pupal development. During migratio n, each cell cluster is completely enveloped by a single giant glial c ell spanning the entire length of the connective between two adjacent ganglia. Intracellular cobalt staining reveals that each migrating neu ron has an ovoid cell body and an extremely long leading process which extends as far as the next posterior ganglion; this is not a common m orphology for migrating neurons that have been described in vertebrate s. Once the cells arrive at the anterior cortex of the next ganglion, they rapidly intermingle with the surrounding neurons and so we were u nable to determine the fate of the migrating neurons at their final lo cation.