Microfluidic Chips for <i>In Vivo</i> Imaging of Cellular Responses to Neural Injury in <i>Drosophila</i> Larvae

<div><p>With powerful genetics and a translucent cuticle, the <i>Drosophila</i> larva is an ideal model system for live imaging studies of neuronal cell biology and function. Here, we present an easy-to-use approach for high resolution live imaging in <i>Drosophila</i> using microfluidic chips. Two different designs allow for non-invasive and chemical-free immobilization of 3^rd instar larvae over short (up to 1 hour) and long (up to 10 hours) time periods. We utilized these ‘larva chips’ to characterize several sub-cellular responses to axotomy which occur over a range of time scales in intact, unanaesthetized animals. These include waves of calcium which are induced within seconds of axotomy, and the intracellular transport of vesicles whose rate and flux within axons changes dramatically within 3 hours of axotomy. Axonal transport halts throughout the entire distal stump, but increases in the proximal stump. These responses precede the degeneration of the distal stump and regenerative sprouting of the proximal stump, which is initiated after a 7 hour period of dormancy and is associated with a dramatic increase in F-actin dynamics. In addition to allowing for the study of axonal regeneration <i>in vivo</i>, the larva chips can be utilized for a wide variety of <i>in vivo</i> imaging applications in <i>Drosophila</i>.</p>