Aion and BREXIT, two novel optogenetic tools for long-lasting and bidirectional control of neuronal activity

Silvia Rodriguez-Rozada1, Federico Tenedini2, Johannes Vierock3, Joachim Ahlbeck4, Florian Pieper4, Andreas K. Engel4, Peter Hegemann3, Peter Soba2, Simon Wiegert1

1 Research Group Synaptic Wiring and Information Processing, Center for Molecular Neurobiology Hamburg, University Medical Center Hamburg-Eppendorf, 20251 Hamburg, Germany
2 Research Group Neuronal Patterning and Connectivity, Center for Molecular Neurobiology Hamburg, University Medical Center Hamburg-Eppendorf, 20251 Hamburg, Germany
3 Institute for Biology, Experimental Biophysics, Humboldt University Berlin, D-10115 Berlin Germany
4 Institute of Neurophysiology and Pathophysiology, University Medical Center Hamburg-Eppendorf, 20251 Hamburg, Germany

Despite enormous progress in the development of optogenetic tools for manipulation of neuronal networks, most of the available silencing tools allow inhibition of neural activity for a restricted amount of time that is bound to the duration of the illumination period. We developed a new anion conducting channelrhodopsin, Aion, with a long-lasting conducting state that permits faithful silencing of neurons over many hours with short light pulses spaced many minutes apart. Notably, Aion can be brought back to its closed state with light of a longer wavelength, granting precisely timed termination of silencing. To determine the role of defined neuronal populations for circuit function it is often advantageous not only to inhibit but also to activate that same population of cells. Here, we present BREXIT, a Blue-Red EXcitation-Inhibition Tool, consisting of a cation conducting and an anion conducting channelrhodopsin with spectrally distinct activation spectra, allowing bidirectional control of the same set of neurons using light of different wavelengths. Since both opsins are coupled in a single tandem construct, each transduced cell exhibits the same excitation-inhibition ratio, a feature that is often challenging to achieve, especially when AAV-transduction of multiple tools is required in vivo.

In summary, our new optogenetic tools expand the possibilities for optical manipulation of neuronal networks. Aion broadens the available toolkit of silencers in the temporal domain, while BREXIT allows for faithful dual-color bidirectional control of neurons as demonstrated in organotypic hippocampal slices, as well as different in vivo systems such as fruit fly and ferret.