Drosophila In Vivo Calcium Imaging: A Method for Functional Imaging of Neuronal Activity

- To perform in vivo calcium imaging in the Drosophila nervous system, target the expression of a genetically encoded calcium indicator, such as GCaMP, to the neurons of interest. When neurons fire an action potential, rapid depolarization of the membrane causes voltage-gated calcium channels to open, leading to an influx of extracellular calcium into the cell.

GCaMP is a fusion protein in which enhanced green fluorescent protein, or EGFP, is modified and fused to the M13 fragment of the myosin light chain at the N-terminus, and to the calcium-binding protein, calmodulin, at the C-terminus. Calcium binds to calmodulin, triggers conformation changes in GCaMP, causing an increase in the protein's fluorescence.

To image changes in GCaMP fluorescence as a proxy for neuronal activity in vivo, expose the region of the nervous system with anticipated activity. Then, use a fluorescent microscope that can capture GCaMP dynamics and is equipped with a stimulus delivery setup. Deliver the stimulus, for example, an odor, while recording GCaMP fluorescence in responding neurons.

In the example protocol, we will see GCaMP functional imaging being used to visualize responses in the brain's mushro