The light-producing gene inserted into the mice is taken from the water-dwelling microorganism Chlamydomonas reinhardtii, which, as a plant, needs sunlight for photosynthesis. Tiny hairlike structures along the outside of the algae propel it toward the light. These structures are controlled by channelrhodopsin-2, a so-called "ion channel," which reacts to light by stimulating movement toward it.
While researchers previously have used channelrhodopsin-2 in a variety of experiments in cell culture, the Duke experiments mark the first time the gene controlling its action has been inserted into the genetic makeup of a living mammal, the researchers said. The mice were created by Ehlers' colleague Guoping Feng, Ph.D., assistant professor of neurobiology.
The researchers decided to test the mice first on the sense of smell, since the olfactory system not only involves complex neural circuits but also has a behavioral component.
"The perception of smell is quite complex," Ehlers said. "The brain can decode thousands of smells that enter the nose, discriminating even the slightest scent and often conjuring up vivid memories. So we wanted to know how the brain decodes the presence of these chemicals in the air and turn them into a perception. It's still quite mysterious."
Ehlers said that even though these experiments shed new light on the inner workings of the olfactory system, their greatest significance is that they provided proof of principle that this new model can be used to study a wide variety of questions involving the brain.
"There are a lot of tools that work well in simpler systems or in isolated nerve cells, but the findings are often difficult to translate into an intact mammalian brain," Ehlers said. "This new model opens up whole new avenues for study. We may reach a future where brain injuries, spinal cord damage, neuron loss in Alzheime
Source:Duke University Medical Center