Imaging the activity of neurons and muscles

Optical methods provide a noninvasive way to monitor the activity of neurons and muscles in C. elegans. Although optical techniques are of use in many experimental systems, they are of particular interest for C. elegans researchers. Worms are optically transparent, and thus can be imaged while fully intact, and a variety of genetically encoded indicators are available which can be targeted to cells of interest with appropriate promoters. Optical calcium indicators appear to provide a good indirect measure of the activity of neurons and muscles. This chapter reviews the principles of operation of some common genetically encoded indicators, describes the microscopy equipment and image analysis needed to optically measure activity, discusses general principles and pitfalls of applying optical methods in biological samples, and finally gives example protocols for imaging calcium in specific muscles and neurons.