Tools, methods, and applications for optophysiology in neuroscience

Abstract

The advent of optogenetics and genetically encoded photosensors has provided neuroscience researchers with a wealth of new tools and methods for examining and manipulating neuronal function in vivo. There exists now a wide range of experimentally validated protein tools capable of modifying cellular function, including light-gated ion channels, recombinant light-gated G protein-coupled receptors, and even neurotransmitter receptors modified with tethered photo-switchable ligands. A large number of genetically encoded protein sensors have also been developed to optically track cellular activity in real time, including membrane-voltage-sensitive fluorophores and fluorescent calcium and pH indicators. The development of techniques for controlled expression of these proteins has also increased their utility by allowing the study of specific populations of cells. Additionally, recent advances in optics technology have enabled both activation and observation of target proteins with high spatiotemporal fidelity. In combination, these methods have great potential in the study of neural circuits and networks, behavior, animal models of disease, as well as in high-throughput ex vivo studies. This review collects some of these new tools and methods and surveys several current and future applications of the evolving field of optophysiology.

Keywords: ChR2; channelrhodopsin; genetically encoded sensors; halorhodopsins; optical reporter; optogenetics; photoactuators; photosensors.

FIGURE 1

Diagram of DIO transgenic system in mice. The double-floxed inverse open reading frame (DIO) construct comprises inverted terminal repeats (ITR), the EF1α promoter, an eYFP-ChR2 fusion gene surrounded by a pair of LoxP sites and a pair of Lox2722 sites oriented inward, a woodchuck hepatitis virus post-transcriptional regulatory element (WPRE) and a human growth hormone polyadenylation signal (hGH polyA). The eYFP-ChR2 gene starts in an inverted, inactive orientation. Expression of Cre recombinase will cause serial recombination resulting in the active, fixed orientation of the transgene (bottom; figure adapted from Sohal et al., 2009).