Effects of imaging conditions on mitochondrial transport and length in larval motor axons of Drosophila

The distribution of mitochondria is sensitive to physiological stresses and changes in metabolic demands. Consequently, it is important to carefully define the conditions facilitating live imaging of mitochondrial transport in dissected animal preparations. In this study, we examined Schneider's and the haemolymph-like solutions HL3 and HL6 for their suitability to image mitochondrial transport in motor axons of dissected Drosophila melanogaster larvae. Overall, mitochondrial transport kinetics in larval motor axons appeared similar among all three solutions. Unexpectedly, HL3 solution selectively increased the length of mitochondria in the context of the net-direction of transport. We also found that mitochondrial transport is sensitive to the extracellular Ca²⁺ but not glutamate concentration. High concentrations of extracellular glutamate affected only the ratio between motile and stationary mitochondria. Our study offers a valuable overview of mitochondrial transport kinetics in larval motor axons of Drosophila under various conditions, guiding future studies genetically dissecting mechanisms of mitochondrial transport.