REMODELING OF THE PERIPHERAL PROCESSES AND PRESYNAPTIC TERMINALS OF LEG MOTONEURONS DURING METAMORPHOSIS OF THE HAWKMOTH, MANDUCA-SEXTA

During metamorphosis of the hawkmoth, Manduca sexta, the muscles, cuti cular structures, and most sensory neurons of the larval thoracic legs are replaced by new elements in the adult legs. The thoracic leg moto neurons, however, survive the loss of the larval muscles and persist t o innervate new targets in the imaginal legs. Here we have used biocyt in staining, immunocytochemistry, and confocal microscopy to follow th e fates of the peripheral processes and presynaptic terminals of the l eg motoneurons. Although the most distal processes of the motor nerves retract following the degeneration of larval leg muscles, the axon te rminals always retain close association with the muscle remnants and t he anlagen of the new adult muscles. As the imaginal muscles different iate and enlarge, the motor terminals expand to form adult presynaptic terminals. An antibody to the presynaptic protein, synaptotagmin, rev ealed its localization to the terminal varicosities in both larval and adult stages but distribution within pre-terminal branches during adu lt development. Electrophysiological methods revealed that functional neuromuscular transmission first occurs quite early during metamorphos is, before the differentiation of contractile elements in the muscle f ibers. (C) 1996 Wiley-Liss, Inc.