Rusty memories rejuvenated in elderly mice

Forgetfulness that accompanies the march of time may be reversible ? in mice at least. Elderly mice have had their faltering memories restored after receiving extra amounts of an enzyme that switches genes on or off in the brain.

"We found they performed just like young animals," says Hilmar Bading of the University of Heidelberg in Germany.

He and his colleagues injected a virus directly into the brain's hippocampus ? an area responsible for memory. The virus contained extra copies of a gene that makes an enzyme called DNA methyltransferase (Dnmt3a2). This enzyme alters gene activity through methylation, the addition of chemical methyl groups to DNA.

The team then gave the mice a series of memory tasks. They were presented with a pair of objects, then a day later they were presented with the same set-up but with one object moved to a new position. Because young mice remember the original positions of the objects, they spent more time investigating the one that had been moved. Elderly mice generally spent the same amount of time on each.

When elderly mice were given the virus, they matched the young mice in the task, spending 70 per cent of their time investigating the moved object.

When the researchers used similar techniques to halve the amount of Dnmt3a2 that young mice produce, their performance deteriorated to that of non-treated elderly mice. "Clearly, if you have too little of the enzyme, your memory works less well," says Bading.

As yet, there is no drug that could boost levels of Dnmt3a2 in the human brain, but Bading says that more of it gets made naturally when the brain is active.

So while his team intend to investigate possible memory-enhancing treatments, his advice to people as they age is to keep their brains and bodies as active as possible.

Journal reference: Nature Neuroscience, DOI: 10.1038/nn.3151

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