Calcium Imaging: A Method to Visualize Neural Activity in Live C. elegans

- Place one transgenic worm expressing GCaMP-- a calcium sensing protein-- in an imaging chamber along with bacterial food for the worm. Then seal the dish with the lid and laboratory film to prevent evaporation. View it under a compound microscope equipped for wide field epifluorescence. Record time lapse images of the worms to track their behavior and capture fluorescence using imaging software.

Transgenic worms express a GCaMP sensor protein under the control of a promoter that drives GCaMP expression in a specific neuron. When that neuron is activated, it fires an action potential, which depolarizes the plasma membrane. Upon de-polarization, voltage-gated calcium channels open in the plasma membrane. This causes an influx of calcium ions into the cell, resulting in neuronal excitation.

GCaMP in the excited neuron binds the calcium ions. This causes GCaMP to fluoresce when the worms are imaged with a low intensity fluorescence excitation light. In the example protocol, we will use calcium imaging to visualize AVA interneuron activity in transgenic C. elegans in agarose microchambers.

- Calcium imaging is performed on a compound microscope equipped for wide field epifluorescence.