Researchers at the Georgia Institute of Technology have announced that, using inexpensive components from ordinary liquid crystal display (LCD) projectors, they're able to control both the brains and the muscles of tiny organisms such as worms.
Until now, the field of optogenetics (combining optical and genetic techniques) had been limited to larger animals, with manipulation achieved only by placing optical fibers into animals' brains or illuminating an animal's entire body.
The experiments out of Georgia Tech, however, demonstrate that it's also possible to control brain circuitry using the red, green, and blue lights from a projector. By using these lights to activate light-sensitive microbrial proteins genetically engineered into the organisms, the researchers can switch neurons and muscles on and off.
"This illumination instrument significantly enhances our ability to control, alter, observe, and investigate how neurons, muscles, and circuits ultimately produce behavior in animals," Hang Lu, an associate professor in the School of Chemical and Biomolecular Engineering at the Georgia Institute of Technology, said in a news release.
Described in the Jan. 16 edition of the journal Nature Methods, the system uses a modified LCD projector to cast a multicolor light pattern onto the organisms, with independent red, green, and blue channels activating specific color-sensitive cells and silencing others.
Researchers at the Johann Wolfgang Goethe-University Frankfurt Institute of Biochemistry in Germany provided the light-sensitive optogenetic reagents for the Georgia Tech experiments, while Lu and her team (including graduate students Jeffrey Stirman and Matthew Crane) built the prototype system--with support from the National Institutes of Health and the Alfred P. Sloan Foundation--to explore the "touch" circuit of the worm Caenorhabditis elegans.
To track and record the behavior of the organisms, the team connected the illumination system to a microscope with video tracking; when an organism moved, any changes to light location, intensity, and color could be updated in less than 40 milliseconds.
At first, the team illuminated the head of a worm at regular intervals as it moved in one direction, which produced a coiling effect in the head that resulted in a triangular pattern of movement. The team then scanned light along the bodies of worms, which guided the worms forward when neurons near the tail were stimulated first and backward when starting with neurons in the head.
"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," Lu said.
While this initial research only explores mechanical stimulation, the illumination system might also be used to investigate various small animal responses to chemical, thermal, and visual stimuli. Whether such a system can be used to manipulate the brains and muscles of more complex animals remains to be seen.
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