Monitoring calcium levels with genetically encoded indicators

Calcium indicators are widely used to monitor activity in living neuronal tissue because of the tight relation between action potential firing and increases in the intracellular calcium concentration. Here, we describe the use of genetically encoded calcium indicators (GECIs) of the latest generation for monitoring calcium levels in the mammalian brain. We discuss how to choose the sensor for a given experiment, how to introduce the sensor into the cells of interest and how to estimate the sensitivity of the sensor in situ and in vivo. Finally, we illustrate the application of these sensors for high resolution in vivo imaging of sensory-driven neuronal activity