Optogenetic voltage imaging in slices and living mice using VSFP-Butterfly

In a recent paper published in the Journal of Neurophysiology, the Knöpfel lab (Riken, Japan) introduced a new design variant of FRET-based voltage sensitive fluorescent proteins, termed VSFP-Butterflies, along with an extensive series of application examples in brain slices and living mice. VSFP-Butterfly 1.2 uses red shifted FP, allowing excitation at 488 to 510 nm with acceptor emission > 600 nm. While the sensitivity of VSFP-Butterfly 1.2 is similar to that of VSFP2.3 (around 22% ΔF/F at half maximal activation, V1/2), its fluorescence to voltage relationship is left shifted, resulting in a more sensitive detection of subthreshold potentials as well as of action potentials (fig. 1). VSFP-Butterfly imaging of voltage signals over the cortex of living mice revealed traveling waves generated by the activity of layer 2/3 pyramidal cells (fig 2). The application examples in this report demonstrate that cell class-specific voltage imaging is practical with VSFP-Butterflies. The authors discuss how VSFP-based voltage imaging will opening new avenues towards a better understanding of the neuronal computations reflected in the dynamics of cortical circuits.

Fig. 1. VSFP-Butterfly 1.2 report of action potentials of a pyramidal cell in a mouse cortical slice (single trace). Modified from fig 3 of Akemann et al. (2012)

Fig. 2. Optogenetic imaging of slow brain oscillations, including traveling waves recorded over the somato-sensory cortex of a mouse under shallow pentobarbital anesthesia. A: depolarizing wave traveling. Images were obtained at 5-ms intervals with each fifth image shown. The whole sequence is available as Movie. B: spontaneous oscillatory activity sampled over the whole field of view shown in A. Asterisk marks the event illustrated in A. C: time course of the traveling wave observed over regions indicated by yellow and greener rectangles in A. Colored dots correspond to images shown in A.

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