STANFORD, Calif., July 11 (UPI) -- By stimulating the optic nerves in blind mice, researchers were able to re-establish links between the eye and the brain to return partial sight, according to a new study.
Researchers at Stanford University coaxed optic nerve cables stretching from a blind eye to the brain to regrow, allowing the mice to regain sight for the first time.
Photoreceptor cells in the back of the retina react to light, sending information through ganglion cells that reach from the optic nerve through electric-wire-like axons to regions of the brain, connecting to nerve cells that are translated into sight.
When axons in the brain or spinal cord are damaged, they do not regenerate, unlike axons in the other parts of the body. Anything from an injury to a progressive condition like glaucoma can damage the retina, causing vision to be damaged without hope of being restored -- or so the researchers thought.
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"More than a third of the human brain is dedicated to the processing of visual information," Dr. Andrew Huberman, an associate professor of neurobiology at Stanford University, said in a press release. "Over two dozen brain areas get direct signals from retinal ganglion cells. These areas are involved in not only what we typically think of as vision, but also circadian rhythms and mood. When those cells' axons are severed, it's like pulling the vision plug right out of the outlet."
For the study, published in the journal Nature Neuroscience, researchers treated adult mice with one optic nerve crushed with either a regimen of high-contrast visual stimulation, biochemical manipulations reactivating a retinal pathway or both.
In groups of mice receiving either treatment, modest axonal regrowth was seen, with even greater growth in mice receiving both treatments. The researchers were surprised to see axons regrew to the proper places in the brain.
To test their vision, researchers showed the mice projections such as an expanding dark circle mimicking the approach of a bird. Even with their good eye obstructed, the mice moved to a "safety zone" out of the way of the shadow -- suggesting some portion of their vision had been restored. The researchers note, however, some mice that succeeded at simple tests such as the fake bird shadow failed tests requiring more detailed vision.
Future research will focus on increasing the quantity of retinal ganglion cell axons that reach their target location in the brain, which Huberman said also must be established for greater understanding of how the mice regained any part of their sight.
