14 DAY TRIAL // "A brain sensitive to light" has got a new meaning.
Researchers at Duke University Medical Center and the Howard Hughes Medical Institute have engineered a breed of mice whose brain olfactory cells respond to a light flash.
They introduced into the cells a gene from green algae that enables them to detect light and head towards it.
The water-dwelling Chlamydomonas algae need sunlight to make photosynthesis.
When the olfactory brain areas were exposed to light, the researchers could observe in real time which brain zones were turned on by comparing electrical zones that pointed the presence of the algae gene.
"This work provides a new method in live animals that will define the experimental approach for studying of mammalian neural circuitry in the coming decade," said Dr. Michael Ehlers, a Duke neurobiologist and Howard Hughes Medical Institute investigator.
"This mouse model and its future variants mark the first use of genetically produced light activation in the study of the intact mammalian brain, and we believe this advance in nerve circuit mapping will be to neurobiology what microarray technology has been to genomic science -- a fundamental breakthrough," Ehlers said.
"This mouse model is the first to be able to provide real-time mapping of brain circuitry in a living, intact mammal," said the team.
The green algae possess hairlike structures called flagella that propel them toward the light.
The flagella are controlled by channelrhodopsin-2 which is sensitive to light heading toward it.
The team tested first on the olfaction because the olfactory system has a behavioral component.
"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." said Ehlers.
"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," he 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 Alzheimer's disease, or even depression are treated by fiber optics delivering light to genetically defined populations of nerve cells."