Fluorescent sensors of membrane potential that are genetically encoded

Imaging activity of neurons in intact brain tissue was conceived several decades ago, and, after many years of development, voltage-sensitive dyes now offer the highest spatial and temporal resolution for imaging neuronal functions in the living brain. Further progress in this field is expected from the emergent development of genetically encoded fluorescent sensors of membrane potential. These fluorescent protein voltage sensors overcome some drawbacks of organic voltage-sensitive dyes, such as nonspecificity of cell staining and the low accessibility of the dye to some cell types. In a transgenic animal, a genetically encoded sensor could, in principle, be expressed specifically in any cell type and would have the advantage of staining only the cell population determined by the specificity of the promoter used to drive expression. Here we, critically review the current status of these developments.