Probing Neuronal Activity Using Genetically Encoded Red Fluorescent Calcium Indicators

Abstract

Understanding brain function requires experimental approaches that decipher the information coded by individual neurons. Calcium imaging with genetically encoded calcium indicators (GECIs) is a promising method that can visualize the spatiotemporal activity patterns of brain cells. Recent advances in protein engineering have greatly improved the properties of fluorescent GECIs, and they now have high flexibility for imaging defined cell populations over the course of months. The action spectra of single-wavelength GECIs have been extended by the development of color-shifted fluorescence probes, which increase the potential for multicolor imaging of different cell structures and, more importantly, can be integrated into optogenetics experiments with photoactivatable proteins. In particular, red-shifted GECIs are highly important for imaging deeper tissues because longer-wavelength light can reduce tissue scattering and background autofluorescence. This chapter mainly describes recent advances in the engineering of red GECIs, and highlights important neuroscience applications in optical monitoring and the manipulation of neuronal activity.