Cellular voltage imaging in behaving mice

What is cellular voltage imaging?

This novel fluorescence imaging technique uses genetically encoded voltage indicators (GEVIs) that are expressed in neurons. GEVI (e.g. Archon, ASAP3, JEDI-2P, ArcLight) are packaged in viruses such that GEVI sequence is integrated in the neuron’s genome. The fluorescent proteins are then produced and integrated in the neuron’s membrane and they have a key property: their fluorescence behavior is voltage-dependent. That means that photons the protein emits when excited depends, preferably linearly, on the membrane voltage. Therefore, the amount of recorded emitted photons by the GEVI provide information about the membrane voltage. This includes the subthreshold as well as suprathreshold (action potentials) part of the membrane potential, which were previously only accessible via patch-clamp electrophysiology.

Can cellular voltage imaging be used to study neural circuits in awake behaving animals?

While a few years ago most GEVI were largely limited for in-vitro applications, the development of novel and powerful GEVI has allowed their application in dense neural tissues of behaving animals. Critical for this achievement was the development of robotic-assisted evolutionary selection of potent GEVI, sparse-labeling techniques (e.g. soma-targeting) and development of fast (kilohertz) and sensitive optical 1photon and 2photon imaging techniques.

Contributions to voltage imaging techniques

Patterned voltage imaging using digital-mirror-device (DMD). By splitting the laser lights using the DMD into small ‚beamlets‘ targeting selectively neurons‘ somas, the number of neurons recorded and signal-to-noise ratio were remarkably improved.

Cellular voltage imaging of 76 CA1 neurons simultaneously through a patterned illumination technique. From Xiao, Lowet,Gritton et al., 2022, iScience

Ultra-fast voltage imaging. Using a high-performance sCMOS camera, I reccorded single and complex spikes of hippocampal CA1 neurons at 10kHz in awake mice.

Ultra-fast somArchon voltage imaging of CA1 neuron at 10kHz. (a) Single trial example. (b) Zoom-in view of the single trial shown in (a) as indicated by the blue box. (c-e). Action potential shapes at different sampling frequencies. Color (blue to red) indicate whether the Action potential occurred early or late during a complex burst spike event. It was expected that Action potential occurring late (red) have wider shapes. Adapted from Lowet et al.,(2023), Cell reports