One in every 3,000 people worldwide will become blind due to degeneration of the photoreceptor cells in the retina, which convert light into electrical impulses and pass them on to the brain. Researchers have been working on a variety of ways to either restore these damaged cells or circumvent the problem. In the April 6, 2006 issue of Neuron, Anding Bi and colleagues at Wayne State University describe a new approach.
Some neurons remain in the retina after photoreceptors die, including neurons that would normally help transmit the signals from the photoreceptors to the visual cortex in the brain. These cells, however, lack the machinery necessary to respond to light.
In the current experiment, the scientists used a harmless virus to transfer a light-sensitive protein from green algae, called channelrhodopsin-2 (ChR2), to the retinal cells of mice that were blind from retinal degeneration. After infection with the virus, the residual neurons expressed ChR2 and incorporated it into their cell membranes.
When these mice were exposed to light, the algae protein opened a channel in the cell membrane allowing positive ions to flow into the neuron. That influx mimicked the response of normal photoreceptor cells to light and initiated an electric signal to the brain.
Zhuo-Hua Pan, the senior scientist on the project, cautions that much more work must be done before the new approach can even be tried in humans. A key experiment that remains is to test whether the animals interpret the signal from these neurons as visual cues.