All-Optical Electrophysiology in Mammalian Neurons Using Engineered Microbial Rhodopsins
Optopatch enables high-fidelity optical stimulation and recording in cultured neurons: Parallel optical recording under increasingly strong 0.5-s optical step stimuli. Asterisk indicates a cell that showed periodic bursts of three or four APs under weak stimulation. Scale bar, 500 μm. Image is of EGFP fluorescence. [Figure reprinted by permission from Macmillan Publishers Ltd: see D.R. Hochbaum, Y. Zhao, S.L. Farhi, N. Klapoetke... et al., "All-optical electrophysiology in mammalian neurons using engineered microbial rhodopsins," Nature Methods (2014) doi:10.1038/nmeth.3000.]
All-optical electrophysiology—spatially resolved simultaneous optical perturbation and measurement of membrane voltage—would open new vistas in neuroscience research. Professor Adam Cohen and colleagues from Harvard, MIT, University of Alberta, Canada, and Beijing Genomics Institute–Shenzhen, China, evolved two archaerhodopsin-based voltage indicators, QuasAr1 and QuasAr2, which show improved brightness and voltage sensitivity, have microsecond response times and produce no photocurrent. They engineered a channelrhodopsin actuator, CheRiff, which shows high light sensitivity and rapid kinetics and is spectrally orthogonal to the QuasArs. A coexpression vector, Optopatch, enabled cross-talk–free genetically targeted all-optical electrophysiology. In cultured rat neurons, the researchers combined Optopatch with patterned optical excitation to probe back-propagating action potentials (APs) in dendritic spines, synaptic transmission, subcellular microsecond-timescale details of AP propagation, and simultaneous firing of many neurons in a network. Optopatch measurements revealed homeostatic tuning of intrinsic excitability in human stem cell–derived neurons. In rat brain slices, Optopatch induced and reported APs and subthreshold events with high signal-to-noise ratios. The Optopatch platform enables high-throughput, spatially resolved electrophysiology without the use of conventional electrodes.
(Also see the Gazette article.)