In popular conception, blood is the life force. We say that “young blood” can rejuvenate an aging culture or company; Dracula refreshes himself with the blood of young victims. But it turns out, this idea might have more scientific basis than we thought: a new study has found that an infusion of young blood can reverse some of the effects of aging in the brains of mice. These results could mean a new paradigm for recharging our aging brains, including techniques to treat Alzheimer's disease and other forms of dementia.

Mouse Melding

Tony Wyss-Coray at Stanford University and his team began by performing a bizarre-sounding experiment: They stitched together pairs of live laboratory mice, making sure that each pair’s circulatory systems were connected, so both mice would share the same blood. The conjoined pairs of mice, known as parabionts, fell into two groups: A group in which both the mice in each parabiont had already aged to a ripe old 18 months; and a second group in which only one mouse from each parabiont was aged, while the other was only a few months old. After the parabiont mouse pairs had spent five weeks sharing blood, the experimenters examined the genes in each mouse’s hippocampus – a brain structure crucial for learning and memory. They found that older mice which had gotten young blood displayed altered gene activity and more flexible signaling pathways in their hippocampus. Though the older animals' brains didn't transform all the way back into their younger selves, the flexibility of their connections was still well above the baseline of other mice their age. Youthfulness Injections This led the researchers to wonder if such brain changes would translate into better learning and memory for the old mice. The team gathered a new sample group of aged mice (not parabionts) and put them through three weeks of maze training. The mice got injections of blood plasma (the clear part of the blood made up of water, proteins and hormones) three times per week: Half got plasma from old mice, and half from young. The results were striking: Aged mice injected with young plasma learned much more quickly, and remembered their mistakes much more consistently, than their counterparts. After a day of training, their maze-navigation error rates averaged about 25 percent lower than those of mice injected with aged plasma. The findings are reported this week in Nature Medicine. But if brain aging can be reversed with something as simple as young blood, why hasn’t anyone tested this idea before? “This could’ve been done 20 years ago,” Wyss-Coray says. “You don’t need to know anything about how the brain works. You just give an old mouse young blood and see if the animal is smarter than before. I don't know why no one tried it before – but until now, nobody did.” Now that they’ve tried it and been proven right, though, Wyss-Coray and his team are eager to explore young blood’s potential regenerative effects beyond the hippocampus. “I believe the rejuvenating effects are widespread – even going beyond the brain,” Wyss-Coray says. “We don't know yet where the young factors come from, how they reach the brain, and which cells or receptors they target. I think there’ll turn out to be multiple rejuvenating factors, and we’re trying to isolate them now.” If researchers are able to isolate those factors, physicians may be able to use those specific chemicals to treat diseases that come with brain aging, such as Alzheimer's. And since blood and plasma transfusions are standard in medicine, the technique should be easy to adapt to trials in humans. The researchers hope to embark on human clinical trials in coming years.