Retina Works Best When Bathed in Vitamin C

Megan Brooks

July 20, 2011

July 20, 2011 — New research suggests that gamma-aminobutyric acid (GABA) receptors in the retina need ascorbic acid (vitamin C) to function properly, a finding that potentially has implications for diseases such as glaucoma and epilepsy.

The research was published in the June 29 issue of the Journal of Neuroscience.

GABA, the major inhibitory neurotransmitter in the retina and brain, "helps inhibit runaway excitation by neurons, and vitamin C, it seems, keeps the inhibition functioning," Henrique von Gersdorff, PhD, from the Vollum Institute at Oregon Health & Science University, Portland, and a coauthor of the study, explained in an interview with Medscape Medical News.

Dr. von Gersdorff

"Because the retina is part of the central nervous system...this suggests there is likely an important role for vitamin C throughout our brains, to a degree we had not realized before," he added in a prepared statement.

Vitamin C in the Central Nervous System

The scientists note in their paper that GABA-C receptors are highly expressed in the retina. Ascorbic acid is also highly concentrated in the retina and other regions of the central nervous system. Yet "there is actually very little known about how vitamin C works in the brain or in the retina," Dr. von Gersdorff said.

Dr. von Gersdorff and colleagues studied the effect of ascorbic acid in thin slices of retina from goldfish, which have the same overall biological structure as human retinas.

"We put microelectrodes on the neurons and recorded the response," he explained. They showed that ascorbic acid regulates the function of GABA-C and GABA-A receptors.

The function of native retinal and recombinant GABA-C receptors was significantly enhanced in the presence of ascorbic acid, the scientists report, whereas in the absence of ascorbic acid a significant decline in GABA-C receptor function was seen. Ascorbic acid had similar effects on retinal GABA-A receptor function.

"We found that if you don't have vitamin C inside or outside the cells in the retina, the cells and the receptors start to break down and don't function very well. But as soon as you add vitamin C, function is preserved perfectly well," Dr. von Gersdorff said.

"This was unexpected," he added, "because nobody had reported that ascorbic acid would be particularly important to keep the function of this particular type of GABA receptor in the brain."

Overall, the results suggest that ascorbic acid can be a "powerful endogenous modulator of GABAergic neurotransmission," the scientists write.

It is interesting to note, they say, that when the human body is deprived of ascorbic acid, vitamin C stores in the brain are the last to be depleted. "Perhaps the brain is the last place you want to lose vitamin C," Dr. von Gersdorff said.

"Maybe a vitamin C–rich diet could be neuroprotective for the retina," he added, especially for people who are prone to glaucoma or to epilepsy or other conditions involving overexcitation of the brain.

"This is speculative," he emphasized, "and there is much to learn. But this research provides some important insights and will lead to the generation of new hypotheses and potential treatment strategies."

The work was supported by the Consejo Nacional de Investigaciones Científicas y Tecnicas (Argentina), the Pew Foundation, the International Brain Research Organization, and the National Eye Institute of the National Institutes of Health. The authors have disclosed no relevant financial relationships.

J Neurosci. 2011;31:9672-9682. Abstract

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