Live imaging of axonal transport in Drosophila pupal brain explants.

Axonal transport is essential for the initial growth, maintenance and synaptic plasticity of axons, and altered axonal transport has been observed in different models of neurodegenerative pathologies. Dissecting the mechanisms underlying axonal transport in developing or degenerating brains requires dynamic imaging of axonal cargo movement in living samples. Whereas methods exist to image axonal transport in Drosophila larval neurons, they are not suitable to follow this process during metamorphosis, when brains undergo extensive remodeling. Here we present a simple method that enables confocal imaging of both fast and slow axonal transport in Drosophila pupal brain explants. We describe how to prepare chambers adapted for live imaging, how to maintain brain explants under physiological conditions and how to monitor and quantitatively analyze the movement of fluorescently labeled cargoes. This protocol requires minimal equipment and is ideally suited for experiments that combine genetics, optogenetics and pharmacological approaches. The brains can be prepared for image acquisition in 1.5 h, and the protocol can be performed easily in any fly laboratory.