Ultrafast optogenetic control

Abstract

Channelrhodopsins such as channelrhodopsin-2 (ChR2) can drive spiking with millisecond precision in a wide variety of cells, tissues and animal species. However, several properties of this protein have limited the precision of optogenetic control. First, when ChR2 is expressed at high levels, extra spikes (for example, doublets) can occur in response to a single light pulse, with potential implications as doublets may be important for neural coding. Second, many cells cannot follow ChR2-driven spiking above the gamma (approximately 40 Hz) range in sustained trains, preventing temporally stationary optogenetic access to a broad and important neural signaling band. Finally, rapid optically driven spike trains can result in plateau potentials of 10 mV or more, causing incidental upstates with information-processing implications. We designed and validated an engineered opsin gene (ChETA) that addresses all of these limitations (profoundly reducing extra spikes, eliminating plateau potentials and allowing temporally stationary, sustained spike trains up to at least 200 Hz).

Ultra light-sensitive and fast neuronal activation with the Ca2+-permeable channelrhodopsin CatCh

“…We focused on the third transmembrane domain as several mutated residues within this domain alter the photocycle and the gating of the channel (Fig. 1) [5][6][7]12 . Each residue from Arg 115 to Thr 139 was individually replaced by cysteine and 4 screened for functional changes in Xenopus laevis oocytes.…”

“…Here, we can consider CatCh as a light-gated membrane In comparison to already available optogenetic tools, CatCh induces in neurons an increased light-sensitivity similar to the slow-mutants 13 or SFO's 6 but with much accelerated response kinetics owing to its increased Ca ++ -permeability and the consequences on neuronal excitability. This makes CatCh superior to available ChR2 variants, where a high light-sensitivity had to be established at cost of fast kinetics and vice versa with respect to the fast channelrhodopsins 7,12 (see table 1). …”

Light induced stimulation and delay of cardiac activity

“…Influx of sodium via the gap junctions that connect the cells causes no change of the ionic composition of the cleft, but changes the ionic distribution in the cleft. This is coupled 45 to the electrode capacitively as a positive peak. Once the cell is depolarized above threshold, ion channels open and th e sodium influx from the cleft changes the ionic composition above the electrode.…”

“…This combination is seldom found together in other commercially available monitoring techniques, and allows the 40 analysis of the origin and propagation of cellular signals, the amount of action potentials fired, or even changes in signal shape. Custom made or prototype CMOS-MEAs achieve higher point to point resolution, but require slower sampling rates or use of only a fraction of the channels to monitor an 45 area as large as the conventional MEA [12]. To stimulate action potentials in the cell network, electrical stimulation via micro electrodes is the most common technique used.…”

“…Despite behavioral studies using ChR2 in vivo, quantitation of cellular responses has relied largely on patch clamp or calcium imaging techniques. These methods limit the number of cells that can be investigated at one time 45 or have slow response times, respectively. Extracellular recording using chip technology, including MEAs, overcomes these limitations.…”