APA Aug. 7, 2013

There is only a limited so-called "critical period" in patients with amblyopia, during which "lazy eye" and other serious visual problems can be corrected until they become permanent. But US researchers have now discovered a gene that may change that. In experiments with animals where the gene was not present, there was no critical period. Therefore, they concluded in "Neuron", a treatment of amblyopia may be possible at any age.

"The generally accepted view has been that as the inhibitory neurons develop, synaptic plasticity declines, which was thought to occur at about five weeks of age in rodents," roughly equivalent to five years of age in humans," said Elizabeth M. Quinlan from the University of Maryland, who led the project with Alfredo Kirkwood from Johns Hopkins University. But in earlier experiments, Quinlan and Kirkwood found no correlation between the development of these inhibitory neurons and the loss of plasticity.

The team therefore looked "one synapse upstream from these inhibitory neurons," studying the control of that synapse by a protein called NARP (Neuronal Activity-Regulated Pentraxin). Working with mice lacking the NARP gene as well as a control group, the researchers covered one eye in each animal to simulate conditions that produce amblyopia.

The mice in the control group developed amblyopia, but the mice that lacked NARP did not. Without NARP, the mice simply had no critical period in which the brain circuitry was weakened in response to the impaired blocking vision in one eye. Except for the lack of this plasticity, their vision was normal. "It's remarkable how specific the deficit is," Quinlan said. "We can completely turn off the critical period for plasticity by knocking out this protein." The discovery raises hope that a treatment could allow correction of amblyopia late in life.