A neural traffic light
To selectively take control of neurons, the researchers used a virus to insert genes for producing light-sensitive proteins into cells of interest. The gene ChR2 is derived from an algae that makes affected neurons more active when exposed to blue light. Deisseroth and collaborators first showed this in a paper in Nature Neuroscience in 2005. In this week's paper, they demonstrate that another gene, NpHR, which is borrowed from a microbe called an archaebacterium, can make neurons less active in the presence of yellow light. Combined, the two genes can now make neurons obey pulses of light like drivers obey a traffic signal: Blue means "go" (emit a signal), and yellow means "stop" (don't emit).
In the new paper, the group shows this technique can have immediately observable effects in living creatures. The Stanford team's collaborators in Germany were able to cause tiny worms called C. elegans to stop swimming while their genetically altered motor neurons were exposed to pulses of yellow light focused through a microscope. In some experiments, exposure to blue light caused the worms to wiggle in ways they weren't moving while unperturbed. When the lights were turned off, the worms resumed their normal behavior.
Meanwhile, in experiments in living brain tissues extracted from mice at Stanford, the researchers were able to use the technique to cause neurons to signal or stop on the millisecond timescale, just as they do naturally. Other experiments showed that cells appear to suffer no ill effects from exposure to the light. They resume their normal function once the expo
Contact: David Orenstein