During the 20th century, several bacteria were discovered that behaved in a peculiar fashion when exposed to specific wavelengths of light. In the 1970s, Oesterhelt and Stoeckenius discovered a species of halobacteria whose membrane changed color depending on whether it was in the dark or the light. Through several experiments they discovered a special protein-based channel in the membrane that could absorb light, causing the shape to change and ions to be let in or out of the bacterial cell. Subsequent research conducted by several other scientists led to the discovery of two bacterial ion channels that would one day change the course of scientific research, halorhodopsin and channelrhodopsin (Friedman, 2021).
Halorhodopsin is an ion pump that lets chloride ions into a cell when it is exposed to yellow light. Channelrhodopsin is an ion channel that lets hydrogen, sodium, potassium, and calcium ions into a cell when it is exposed to blue light (Deisseroth, 2010). So why do either of these proteins matter? Well, chloride ions cause neurons to inactivate, while hydrogen, sodium, potassium, and calcium ions cause neurons to activate. Scientists at Stanford and MIT realized that if we could make animal cells express these channels, we could activate or deactivate populations of neurons using light (Boyden, 2011)!
Today, a significant amount of neuroscience research hinges on this work. Optogenetics, the use of advanced gene manipulation techniques to create animals whose neuronal activity can be manipulated with light, has allowed researchers to better understand the function of neuronal populations (Ferenczi et al., 2019; Joshi et al., 2020). There is no doubt the explosion of optogenetic research today will lead to better treatments for neurological and psychiatric diseases tomorrow!
