Kannan, M. et al. Nat. Methods https://doi.org/10.1038/s41592-018-0188-7 (2018)

VARNAM is the Sanskrit word for ‘hue’ and also the acronym for a new genetically encoded voltage indicator recently developed by researchers at Yale and Stanford universities. Short for “voltage-activated red neuronal activity monitor,” the indicator fluoresces at the red end of the visual spectrum whenever it detects a voltage change, such as the firing of a neuron. VARNAM is faster, brighter, and more sensitive than previously engineered red fluorescent indicators.

The researchers describe the screening process to identify VARNAM and demonstrate its functionality in murine brain slices, Drosophila, and behaving adult mice in Nature Methods. The indicator can be used alone or alongside other colored optical tools to provide multispectral functional imaging in vivo.