Peripheral Nerve Crush in Drosophila Larvae.

The long length of axons makes them vulnerable to damage; hence, it is logical that nervous systems have evolved adaptive mechanisms for responding to axon damage. Studies in Drosophila melanogaster have identified evolutionarily conserved molecular pathways that enable axonal degeneration and regeneration of damaged axons and/or dendrites. This protocol describes a simple method for inducing nerve crush injury to motoneuron and sensory neuron axons in the peripheral (segmental) nerves in second- or early third-instar larvae. Small forceps are used to pinch the cuticle at a location that overlays the segmental nerves. Although the connective tissue of the nerves remains intact and the larva survives the injury, single motoneuron and sensory neuron axons incur a break in continuity at the damage site and then undergo Wallerian degeneration distal to the break. This degeneration includes the dismantling of neuromuscular junction (NMJ) synapses formed by the axons that incurred damage. With stereotyped anatomy and accessibility to structural and electrophysiological studies, the larval NMJ is a good model to characterize the cellular changes that occur in synapses undergoing degeneration and to identify conditions that can protect axons and synapses from degeneration.