Imaging neural circuit dynamics with a voltage-sensitive fluorescent protein

Akemann W, Mutoh H, Perron A, Park YK, Iwamoto Y, Knpfel T. Imaging neural circuit dynamics with a voltage-sensitive fluorescent protein. J Neurophysiol 108: 2323-2337, 2012. First published July 18, 2012; doi:10.1152/jn.00452.2012.-Population signals from neuronal ensembles in cortex during behavior are commonly measured with EEG, local field potential (LFP), and voltagesensitive dyes. A genetically encoded voltage indicator would be useful for detection of such signals in specific cell types. Here we describe how this goal can be achieved with Butterfly, a voltagesensitive fluorescent protein (VSFP) with a subthreshold detection range and enhancements designed for voltage imaging from single neurons to brain in vivo. VSFP-Butterfly showed reliable membrane targeting, maximum response gain around standard neuronal resting membrane potential, fast kinetics for single-cell synaptic responses, and a high signal-to-noise ratio. Butterfly reports excitatory postsynaptic potentials (EPSPs) in cortical neurons, whisker-evoked responses in barrel cortex, 25-Hz gamma oscillations in hippocampal slices, and 2- to 12-Hz slow waves during brain state modulation in vivo. Our findings demonstrate that cell class-specific voltage imaging is practical with VSFP-Butterfly, and expand the genetic toolbox for the detection of neuronal population dynamics.