Laser Ablation ofDrosophilaEmbryonic Motoneurons Causes Ectopic Innervation of Target Muscle Fibers

We have tested the effects of neuromuscular denervation inDrosophilaby laser-ablating the RP motoneurons in intact embryos before synaptogenesis. We examined the consequences of this ablation on local synaptic connectivity in both 1st and 3rd instar larvae. We find that the partial or complete loss of native innervation correlates with the appearance of alternate inputs from neighboring motor endings and axons. These collateral inputs are found at ectopic sites on the denervated target muscle fibers. The foreign motor endings are electrophysiologically functional and are observed on the denervated muscle fibers by the 1st instar larval stage. Our data are consistent with the existence of a local signal from the target environment, which is regulated by innervation and influences synaptic connectivity. Our results show that, despite the stereotypy ofDrosophilaneuromuscular connections, denervation can induce local changes in connectivity in wild-typeDrosophila, suggesting that mechanisms of synaptic plasticity may also be involved in normalDrosophilaneuromuscular development.