ROLE OF NEURAL ACTIVITY DURING SYNAPTOGENESIS IN DROSOPHILA

This article reveals a novel aspect in the regulation of synaptic conn ectivity in Drosophila. Reducing neural activity genetically or pharma cologically disrupts the normally precise embryonic and larval neuromu scular connections. In third instar larvae with mutations that affect sodium channel function or expression such as no action potential, tem perature-induced paralysis E, or seizure, foreign neuromuscular synaps es, arising from inappropriate nerve sources, are observed on muscle f ibers throughout the abdominal body wall. Their frequencies increase a s neural activity is further reduced in double mutant combinations. Th ese foreign connections are first observed during late embryogenesis a s filopodial-like contacts, but critical period analysis suggests that neural activity must be reduced during both late embryogenesis and th e first larval instar to promote the differentiation of these embryoni c contacts into foreign motor synapses. In addition, the loss of elect rical activity in the motoneuron, as opposed to the loss of postsynapt ic potentials in the muscle fibers, appears to be responsible for thes e changes in connectivity. Our experiments suggest that neural activit y may function during development by preventing inappropriate connecti ons and thereby maintaining the precise connectivity achieved during n erve outgrowth and target selection.