Study: Injecting Young Blood Rejuvenates Old Brains

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It sounds like something out of a vampire tale, but introducing young blood to old brains triggers the growth of new brain cells, at least in mice, researchers reported last fall.

The research, which was published in Nature in September (apologies, Healthland missed this the first time around, but thought it was cool enough to come back to) was inspired by the observation that when old mice are given young blood, it improves their immune systems and muscle function. So researchers wondered whether it would also work in the brain. Further, the researchers noted, stem cells in the brain, which give rise to new neurons, are physically closer than other cells to blood vessels, suggesting potential interaction.

In a series of experiments, researchers surgically connected pairs of mice, so that they shared a blood supply (which is perhaps creepier than the finding itself). When 3-month-old mice were connected to 2-year-old mice, researchers found, the development of new brain cells accelerated in the older mice — going from fewer than 400 cells to nearly 1,000 in the one area of the hippocampus, the brain region related to memory — and fell by a quarter in the younger ones. Researchers found that the shared circulatory system had no effect in pairings of mice the same age.

When researchers injected young mice with old blood, they found that neurogenesis — the creation of new brain cells — decreased and so did the animals’ performance on learning and memory tests like water mazes.

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Obviously, there was something different about young blood. Researchers searched for the factor that mattered. They looked at 66 plasma proteins, but couldn’t find the relevant compound in the young animals’ blood. They did, however, isolate 17 that increased as the mice aged.

Among them was a substance called CCL11, which is an immune system protein called a chemokine. Previous research has connected CCL11 to inflammation in asthma and allergies. So what does that have to do with brain function? Oddly enough, recent research also shows that inflammatory immune cells are involved in learning and memory, in a delicate balance that may go awry in aging.

Indeed, when the researchers injected CCL11 alone into young animals, it reduced neurogenesis, while blocking CCL11 with antibodies prevented this decline.

The researchers, led by Tony Wyss-Coray of Stanford University, are also looking for the compounds in younger blood that may stimulate enhanced neurogenesis. The fact that older cells responded well to the young blood was an encouraging sign that they exist — and suggests that older cells may not be irreparably damaged. So, could such a compound be used to prevent or reverse the memory loss and cognitive deficits that often accompany aging? Might it help treat Alzheimer’s disease? It remains to be seen whether these effects can be replicated in humans.

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Fortunately, we already know one method that increases neurogenesis in humans that’s free, has few side effects and is easily available to virtually everyone right now.

It’s called exercise and while it may not always be fun, at least it doesn’t (usually) involve bloodshed. As Dr. Richard Ransohoff, director of the Neuroinflammation Research Center at the Cleveland Clinic put it in a commentary that accompanied the Nature study, “this information is encouraging and should inspire increased activity in both joggers and neuroscientists.”

Maia Szalavitz is a health writer at TIME.com. Find her on Twitter at @maiasz. You can also continue the discussion on TIME Healthland’s Facebook page and on Twitter at @TIMEHealthland.

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