Atlanta, GA--Georgia Institute of Technology researchers are using inexpensive components from ordinary liquid-crystal-display (LCD) projectors to control the brain and muscles of small organisms, including the much-studied worm Caenorhabditis elegans (C. elegans).1 Red, green, and blue pixels from a projector activate light-sensitive microbial proteins genetically engineered into the worms, allowing the researchers to switch neurons on and off and activate and deactivate muscles.
By connecting the illumination system to a microscope and combining it with video tracking, the researchers can track and record the behavior of freely moving animals, while maintaining the lighting in the intended anatomical position. When the animal moves, changes to the light's location, intensity, and color can be updated in less than 40 ms.
"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, the lead researcher. "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."
Maneuvered by light
Once Lu and her team built the prototype system, they used it to explore the "touch" circuit of C. elegans by exciting and inhibiting its mechano-sensory and locomotion neurons. For their first 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 in one experiment to understand circuit functions. The researchers were able to examine a large number of animals under a variety of conditions, demonstrating that the technique's results were both robust and repeatable.
"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.
While these proof-of-concept studies investigated the response of C. elegans to mechanical stimulation, the illumination system can also be used to evaluate responses to chemical, thermal, and visual stimuli. Researchers can also use it to study a variety of neurons and muscles in other small animals, such as the zebrafish and fruit-fly larvae.
"Experiments with this illumination system yield quantitative behavior data that cannot be obtained by manual touch assays, laser cell ablation, or genetic manipulation of neurotransmitters," said Lu.
1. Andrew M. Leifer et al., Nature Methods (2011) DOI:doi:10.1038/nmeth.1554