Optogenetics, a new science of embedding genes into animals that code for light sensitive proteins, has the potential to help us study and one day treat a variety of conditions through selective activation of cell activity. Though the principles have been established, optogenetics has been limited by the challenge of delivering light in a controlled way to a very small volume of tissue that researchers are trying to focus on. Until now, fiberoptics have been used in laboratory animals with the actual light source being an external device, requiring tethering that limits the experiments that can be conducted.
Now researchers from Washington University in St. Louis and University of Illinois at Urbana-Champaign have developed devices thinner than a human hair that contain tiny LEDs at the tip that are the size of neurons. By injecting these devices into the brains of mice with genetically engineered light sensitive cells, they showed that these wireless optoelectronics can be used reliably to trigger individual brain cells. In the latest study in Science, the team showed that the mice were made to produce dopamine through selective triggering of specific brain cells using the new technique.
Using light from the cellular-scale LEDs to stimulate dopamine-producing cells in the brain, the investigators taught the mice to poke their noses through a specific hole in a maze. Each time a mouse would poke its nose through the hole, that would trigger the system to wirelessly activate the LEDs in the implanted device, which then would emit light, causing neurons to release dopamine, a chemical related to the brain’s natural reward system.
“We used the LED devices to activate networks of brain cells that are influenced by the things you would find rewarding in life, like sex or chocolate,” says co-first author Jordan G. McCall, a neuroscience graduate student in Washington University’s Division of Biology and Biomedical Sciences. “When the brain cells were activated to release dopamine, the mice quickly learned to poke their noses through the hole even though they didn’t receive any food as a reward. They also developed an associated preference for the area near the hole, and they tended to hang around that part of the maze.”
The researchers believe the LED implants may be useful in other types of neuroscience studies or may even be applied to different organs. Related devices already are being used to stimulate peripheral nerves for pain management. Other devices with LEDs of multiple colors may be able to activate and control several neural circuits at once. In addition to the tiny LEDs, the devices also carry miniaturized sensors for detecting temperature and electrical activity within the brain.
Washington University press release: Tiny wireless device shines light on mouse brain, generating reward…