Study identifies chemical messenger as key to visual acuity

Source:Xinhua Published: 2017/9/7 11:35:28

A new study indicates that gamma-aminobutyric acid, or GABA, a chemical messenger responsible for communication between cells, especially those in the brain, is key to visual acuity.

The study, conducted in rabbits and published this week in the journal Current Biology, can help explain why during the Aug. 21 total solar eclipse in the United States people and objects were easier to see than on a typical moonless night.

"It has been known for decades that there is a mechanism in the retina in the eye that helps us see small objects and detect edges on bright days, and that this mechanism gradually turns off when it is dark," noted lead researcher Stuart Mangel. "However, what this mechanism is and how it is controlled has been a mystery."

The GABA receptor, a protein, is in abundance on certain cells in the retina on sunny days, and enhances the ability to see details and edges of objects. At night, it disappears.

The normally gradual process involves assembling and moving the GABA receptor to a specific site in the retina during bright daytime, and disassembling the same protein and moving it away from the synapse as dusk sets in.

When people are outdoors, it takes hours for the background light to decrease from bright to dark as the Earth rotates on its axis. When it becomes dark at dusk, a person's ability to see small details is much lower than during the middle of the day.

But Mangel, a professor of neuroscience at the Ohio State University College of Medicine, said he and others experienced an unusual clarity of vision during the minutes when the moon shut out the sun's rays more than two weeks ago.

"Several people I was with commented that they could see as well during totality as they could when it had been bright, and that their acuity was much better than it usually is when it is dark at dusk."

A possible explanation is that when the total eclipse took viewers from brightness to darkness in minutes, the GABA receptor would have still been present on those cells in their eyes. "The reason our acuity stayed high during the total eclipse is that there wasn't enough time for protein disassembly to take place," Mangel said.

In addition, Mangel and his colleagues found that the neurotransmitter dopamine regulates whether the GABA receptor is working. "On bright days, dopamine levels are high and signaling is strong, enhancing the detection of spatial details and edges," he was quoted as saying in a news release. "On moonless nights, however, dopamine levels are low and the GABA signal is minimal, decreasing our ability to see those details."

Posted in: PHYSICS

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