Nearly a decade ago, the era of optogenetics was ushered in with the development of channelrhodopsins, light-activated ion channels that can, with the flick of a switch, instantaneously turn on neurons in which they are genetically expressed. What has lagged behind, however, is the ability to use light to inactivate neurons with an equal level of reliability and efficiency. Now, Howard Hughes Medical Institute (HHMI) scientists have used an analysis of channelrhodopsin’s molecular structure to guide a series of genetic mutations to the ion channel that grant the power to silence neurons with an unprecedented level of control.
The new structurally engineered channel at last gives neuroscientists the tools to both activate and inactivate neurons in deep brain structures using dim pulses of externally projected light. Deisseroth and his colleagues published their findings April 25, 2014 in the journal Science. “We’re excited about this increased light sensitivity of inhibition in part because we think it will greatly enhance work in large-brained organisms like rats and primates,” he says.
First discovered in unicellular green algae in 2002, channelrhodopsins function as photoreceptors that guide the microorganisms’ movements in response to light. In a landmark 2005 study, Deisseroth and his colleagues described a method for expressing the light-sensitive proteins in mouse neurons. By shining a pulse of blue light on those neurons, the researchers showed they could reliably induce the ion channel at channelrhodopsin’s core to open up, allowing positively charged ions to rush into the cell and trigger action potentials. Channelrhodopsins have since been used in hundreds of research projects investigating the neurobiology of everything from cell dynamics to cognitive functions.