Optogenetics is a biological technique to control the activity of neurons or other cell types with light. This is achieved by expression of light-sensitive ion channels, pumps or enzymes specifically in the target cells. On the level of individual cells, light-activated enzymes and transcription factors allow precise control of biochemical signaling pathways. In systems neuroscience, the ability to control the activity of a genetically defined set of neurons has been used to understand their contribution to decision making, learning, fear memory, mating, addiction, feeding, and locomotion. In a first medical application of optogenetic technology, vision was partially restored in a blind patient with Retinitis pigmentosa.
Fig 1. Channelrhodopsin-2 (ChR2) induces temporally precise blue light-driven activity in rat prelimbic prefrontal cortical neurons. a) In vitro schematic (left) showing blue light delivery and whole-cell patch-clamp recording of light-evoked activity from a fluorescent CaMKllα::ChR2-EYFP expressing pyramidal neuron (right) in an acute brain slice. b) In vivo schematic (left) showing blue light (473 nm) delivery and single-unit recording. (bottom left) Coronal brain slice showing expression of CaMKllα::ChR2-EYFP in the prelimbic region. Light blue arrow shows tip of the optical fiber; black arrow shows tip of the recording electrode (left). White bar, 100
Fig 2. Halorhodopsin (NpHR) rapidly and reversibly silences spontaneous activity in vivo in rat prelimbic prefrontal cortex. (Top left) Schematic showing in vivo green (532 nm) light delivery and single- unit recording of a spontaneously active CaMKllα::eNpHR3.0- EYFP expressing pyramidal neuron. (Right) Example trace showing that continuous 532 nm illumination inhibits single-unit activity in vivo. Inset, representative single unit event; Green bar, 10 seconds.
Cages for rat equipped with optogenetic LED commutators which permit in vivo study of animal behavior during optogenetic stimulations
Halorhodopsin is a seven-transmembrane retinylidene protein from microbial rhodopsin family. It is a chloride-specific light-activated ion pump found in archaea known as halobacteria. It is activated by green light wavelengths of approximately 578nm. Halorhodopsin also shares sequence similarity to channelrhodopsin, a light-gated ion channel.
Halorhodopsin Cartoon Visualization by Jawahar Swaminathan and MSD staff at the European Bioinformatics Institute