Abstract
Optogenetics is an extremely powerful tool for selective neuronal activation/inhibition and dissection of neural circuits. However, a limitation of in vivo optogenetics is that an animal must be tethered to an optical fiber for delivery of light. Here, we describe a new method for in vivo, optogenetic inhibition of neural activity using an internal, animal-generated light source based on firefly luciferase. Two adeno-associated viruses encoding luciferase were tested and both produced concentration-dependent light after administration of the substrate, luciferin. Mice were co-infected with halorhodopsin- and luciferase-expressing viruses in the striatum, and luciferin administration significantly reduced Fos activity compared to control animals infected with halorhodopsin only. Recordings of neuronal activity in behaving animals confirmed that firing was greatly reduced after luciferin administration. Finally, amphetamine-induced locomotor activity was reduced in halorhodopsin/luciferase mice pre-injected with luciferin compared to controls. This demonstrates that virally encoded luciferase is able to generate sufficient light to activate halorhodopsin and suppress neural activity and change behavior. This approach could be used to generate inhibition in response to activation of specific molecular pathways.
Highlights
The use of optogenetics has increased dramatically in the last several years, largely due to its applicability to studies spanning from single-cell electrophysiology to whole-animal behavior
One restriction to in vivo optogenetics is the necessity of an external light source that must be connected to the animal via indwelling cannula
Animals were kept on a 12 h light/dark cycle and provided standard chow and water ad libitum, and all animal procedures were performed in accordance with the protocol approved by the Institutional Animal Care and Use Committee (IACUC)
Summary
The use of optogenetics has increased dramatically in the last several years, largely due to its applicability to studies spanning from single-cell electrophysiology to whole-animal behavior. In vivo techniques are powerful as they allow for control of behavior with manipulation of a single neuron subtype (Witten et al, 2010; Narayanan et al, 2012). Two groups have introduced wireless optogenetics approaches, where the signal/power is sent to a headstage containing indwelling LEDs (Wentz et al, 2011; Kim et al, 2013). While this solves the problem of tethering, specialized equipment is needed to both send the signal and to receive it, which could add a significant cost to the setup and may require significant expertise to implement
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