17 January 2011
Colored light used to control brains of GM animals
by Kate Melville
Optogenetics researchers at the Georgia Institute of Technology have achieved unparalleled control over the brain circuits in laboratory animals by exciting and inhibiting their genetically modified mechano-sensory and locomotion neurons with colored light. The researchers, reporting on their work in Nature Methods, used red, green and blue lights from a projector to activate light-sensitive microbial proteins that are genetically engineered into the worms (Caenorhabditis elegans), allowing the researchers to switch neurons on and off like light bulbs and turn muscles on and off like engines. Previously, such control could only be achieved by placement of an optical fiber into the animal's brain.
"This illumination instrument significantly enhances our ability to control, alter, observe and investigate how neurons, muscles and circuits ultimately produce behavior in animals," said Hang Lu, from Georgia Tech's School of Chemical & Biomolecular Engineering.
The illumination system includes a modified off-the-shelf LCD projector, which is used to cast a multi-color pattern of light onto an animal. The independent red, green and blue channels allow researchers to activate excitable cells sensitive to specific colors, while simultaneously silencing others. "Because the central component of the illumination system is a commercially available projector, the system's cost and complexity are dramatically reduced, which we hope will enable wider adoption of this tool by the research community," explained Lu.
In one experiment, the researchers illuminated the head of a worm at regular intervals while the animal moved forward. This produced a coiling effect in the head and caused the worm to crawl in a triangular pattern. In another experiment, the team scanned light along the bodies of worms from head to tail, which resulted in backward movement when neurons near the head were stimulated and forward movement when neurons near the tail were stimulated.
Additional experiments showed that the intensity of the light affected a worm's behavior and that several optogenetic reagents excited at different wavelengths could be combined to control a variety of functions. "This instrument allowed us to control defined events in defined locations at defined times in an intact biological system, allowing us to dissect animal functional circuits with greater precision and nuance," said Lu.
Source: Georgia Institute of Technology Research News