Optogenetics is most commonly perceived as a neuromodulation technique targeting the brain. Indeed, one of the first applications of an optogenetic tool, the expression of channelrhodopsin in neurons, allowed for the first time the precise control of neuronal activity solely with light. Channelrhodopsin is a light-gated ion channel that conducts cation influx upon illumination with blue light. Precisely, the introduction of this single-component optogenetic system into neuronal cells leads to light-induced depolarization of the cell membrane and hence the induction of action potentials.
Shortly after this discovery, a light-gated ion pump was added to the optogenetic toolbox. Upon green/yellow illumination, halorhodopsin pumps chloride ions into the cell, leading to hyperpolarization of the cell membrane. Artificial introduction of halorhodopsin into neurons can thus be used to optogenetically inhibit action potentials and thus silence neuronal activity of the brain.
Another more complex tool to inhibit neuronal activity is based on the light-sensitive receptor protein rhodopsin. This G protein coupled receptor (GPCR) acts through the recruitment of intracellular signaling components, ultimately silencing neuronal action potentials.
Optogenetic control of neuronal activity has thus far led to numerous new findings in the fields of neuroscience and neuropsychiatric disease. Among those neural circuits investigated so far are brain disorders such as Parkinson’s disease, schizophrenia, autism, drug abuse, depression and anxiety.