THE LARVAL OPTIC-NERVE IS REQUIRED FOR THE DEVELOPMENT OF AN IDENTIFIED SEROTONERGIC ARBORIZATION IN DROSOPHILA-MELANOGASTER

The larval visual system in the fruitfly Drosophila melanogaster consi sts of two bilateral clusters of 12 photoreceptor cells. These neurons send their axons in a fascicle, the Bolwig's nerve, toward the target area in the ventral lateral region of the brain hemispheres. We descr ibe the development of a serotonergic arborization originating in the central brain found in the larval optic center in association with the larval optic nerve. This arborization is formed by processes from lar val neurons born during embryogenesis. However, these neuronal process es do not reach their final destination, the larval optic center, unti l late in larval development. Using mutations that disrupt the connect ivity and/or development of the larval photoreceptor cells, as well as mosaic analysis, we demonstrate that the innervation of the larval op tic center by this serotonergic arborization depends upon contact with the larval optic nerve. (C) 1995 Academic Press, Inc.