Old blood carries risks for brain

Harmful factors circulating in old blood may be partly responsible for the mental decline that can come with age, a small study in mice suggests. 

Irina Conboy of the University of California, Berkeley and colleagues devised a new way to mingle blood in two mice that didn’t involve stitching their bodies together, as in previous experiments (SN: 5/31/14, p. 8). Instead, researchers used a microfluidic device to shuttle blood, a process that precisely controlled the timing and amount of blood transferred between the mice. The method, reported online November 22 in Nature Communications, allows more precise tests of blood’s influence on aging, the researchers believe.

Old mice benefited in some ways from infusions of young blood, experiments with four young-old pairs of mice revealed. With young blood around, old muscles were better able to recover after an injury. And young blood seemed to improve old livers in some tests.

But young blood didn’t seem to help one measure of brain health. After transfusions of young blood, old mice still had lower numbers of newborn nerve cells in the hippocampus, a brain structure important for learning and memory. What’s more, old blood reduced the number of newborn nerve cells in young mice. This damage happened quickly, after just one blood exchange, the researchers found. The results suggest that old blood contains components that harm brain cells, an insight that makes scientists eager to identify those factors.