Dracula may have been onto something, after all. Humans have been searching for the fountain of youth since perhaps the beginning of time, and the answer may be in our very own bodies - or at least the bodies of someone younger than us. Researchers made the old brains of mice almost as good as new when the team transferred blood from young mice into old mice's bodies. The results may have positive implications for cognitive decline and even Alzheimer's disease in humans.

Saul Villeda, of Stanford University, led the work. Previous research by Villeda and a multinational team of researchers hailing from the United States, Austria, South Korea, and Switzerland published last year in Nature, found that the brains of young mice aged more quickly when the mice were injected with blood from old mice. Researchers gave 18-month-old mice blood from young mice, connecting the circulatory systems in mice pairs through a system called heterochronic parabiosis.

After the mice were given a few days to rest, researchers examined their brains, finding clear signs that the aging process had slowed down in older mice. Researchers found that the number of stem cells in the brain had increased. In addition, the brains of the old mice had 20 percent more neural connections, a huge coup because, as animals age, the brain's neural connections break, causing issues with memory and learning.

This more recent study, yet unpublished in a peer-reviewed journal but presented at the Society of Neuroscience conference in New Orleans, looked at just the opposite. Saul Villeda looked at two groups of mice. One group was four to six months old, while the other group was 18 months old. They took blood plasma from the young mice, 5 percent of the mice's total blood supply, and injected it into the old mice. These injections took place eight times over the course of a month.

The mice then needed to perform a water maze test, where they needed to locate a hidden platform. The older mice who had received the injections performed almost as well as the young mice, finding the platform on the first try in most cases. The older mice who had not received the injections made many errors, on the other hand.

Villeda believes that the young blood rejuvenated the brain by increasing key chemical components that decline as organisms age. Unfortunately, no one knows what those components are, since there are thousands of these in blood.

Villeda hopes that such a treatment could be used in humans to slow down the aging process. But Andrew Randall, a professor of applied neurophysiology at the Exeter and Bristol universities, was more measured in his response. "Although this [research] may suggest that Bram Stoker [the author of Dracula] had ideas way ahead of his time, temporarily plumbing teenagers' blood supplies into those of their great-grandparents does not seem a particularly feasible future therapy for cognitive decline in ageing. Instead this fascinating work suggests there may be significant benefit in working out what the 'good stuff' is in the high octane young blood, so that we can provide just those key components to the elderly," he said to the Guardian.

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