Optogenetic inhibition of neurons by internal light production

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.

Illuminating odors: when optogenetics brings to light unexpected olfactory abilities

“…With the exception of the two last articles cited above (Chuong et al 2014;Land et al 2014), one may notice that none of the studies reviewed here use inhibitory opsins. The reason is simple: while activating 5%-10% of a given neuronal population could provide behavioral changes (through a gain of function), it is more difficult to detect behavioral alterations when reducing (or inhibiting) a small fraction of a given population.…”

“…Recently, a team coexpressed luciferase and an inhibitory opsin in the mouse striatum. They were able to show that luciferin injection into the striatum could activate the opsins and reduce the striatum activity (Land et al 2014).…”

Beyond the brain: Optogenetic control in the spinal cord and peripheral nervous system

“…From a translational perspective, the development of magnetic (137), acoustic (138), or thermal stimuli for neuromodulation through the use of genetically encoded effectors may have particular advantages, potentially allowing for control of deep neural structures without the use of light-emitting implants while retaining temporal specificity. Similarly, in applications where temporal specificity is not important, such as long-term inhibition of neural structures, optogenetic approaches may be most effective when combined with internal light-generating systems (105,106). The complementary DREADD (designer receptors exclusively activated by designer drugs) technology that uses chemical ligand-activated synthetic G protein (heterotrimeric guanine nucleotide-binding protein)-coupled receptors may also be an alternative that avoids the challenges of light delivery (139)(140)(141).…”

“…In the future, light may be delivered using light-emitting fabrics (top right). (D) For internal organs, wirelessly powered devices could be implanted next to the organs (top right), flexible light-emitting meshes could be developed that would wrap around opsin-expressing organs (top left), or intrinsic lightemission systems such as luciferin/luciferase expressed within the organ could be used to activate opsins (bottom)(106).…”

Evolution of optogenetic microdevices

“…A rotary connector can be used to ensure free-moving behavior and uninterrupted optical connection within an open-topped behavioral apparatus, but they restrict experiments that require an enclosed home-cage top. 56 Although a rotary connector seems to be an ideal solution for tethered experiments, it causes continuous pulling forces on the animal due to retraction of the cord, and frictional torques during animal rotations. Careful consideration of the animal species is important when using a rotary connector, as mice are able to withstand torques of up to 150 μN · m, while rats can exceed torque tolerations of >300 μN · m. 57 Therefore, optimization of pulling forces by the rotary connector is necessary to keep the cord taunt without causing unnecessary cord retracting stress to the animal.…”