This noninvasive approach could pave the way to using optogenetics in human patients to treat epilepsy and other neurological disorders, the researchers say, although much more testing and development is needed. Led by
Optogenetics, a technique developed over the past 15 years, has become a common laboratory tool for shutting off or stimulating specific types of neurons in the brain, allowing neuroscientists to learn much more about their functions.
The neurons to be studied must be genetically engineered to produce light-sensitive proteins known as opsins, which are channels or pumps that influence electrical activity by controlling the flow of ions in or out of cells. Researchers then insert a light source, such as an optical fiber, into the brain to control the selected neurons.
Such implants can be difficult to insert, however, and can be incompatible with many kinds of experiments, such as studies of development, during which the brain changes size, or of neurodegenerative disorders, during which the implant can interact with brain physiology. In addition, it is difficult to perform long-term studies of chronic diseases with these implants.
Mining nature's diversity
To find a better alternative, Boyden, graduate student
Boyden's team had previously identified two light-sensitive chloride ion pumps that respond to red light, which can penetrate deeper into living tissue. However, these molecules, found in the bacteria Haloarcula marismortui and Haloarcula vallismortis, did not induce a strong enough photocurrent - an electric current in response to light - to be useful in controlling neuron activity.
Chuong set out to improve the photocurrent by looking for relatives of these proteins and testing their electrical activity. She then engineered one of these relatives by making many different mutants. The result of this screen, Jaws, retained its red-light sensitivity but had a much stronger photocurrent - enough to shut down neural activity.
"This exemplifies how the genomic diversity of the natural world can yield powerful reagents that can be of use in biology and neuroscience," says Boyden, who is a member of
Using this opsin, the researchers were able to shut down neuronal activity in the mouse brain with a light source outside the animal's head. The suppression occurred as deep as 3 millimeters in the brain, and was just as effective as that of existing silencers that rely on other colors of light delivered via conventional invasive illumination.
Working with researchers at the
This type of noninvasive approach to optogenetics could also represent a step toward developing optogenetic treatments for diseases such as epilepsy, which could be controlled by shutting off misfiring neurons that cause seizures, Boyden says. "Since these molecules come from species other than humans, many studies must be done to evaluate their safety and efficacy in the context of treatment," he says.
Boyden's lab is working with many other research groups to further test the Jaws opsin for other applications. The team is also seeking new light-sensitive proteins and is working on high-throughput screening approaches that could speed up the development of such proteins.
Keywords for this news article include: Cells, Opsins, Neurons, Engineering, Eye Proteins, Retinal Pigments,
Our reports deliver fact-based news of research and discoveries from around the world. Copyright 2014, NewsRx LLC
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