Young blood reversed brain aging in old mice

Researchers at UCSF and Stanford University surgically joined the circulatory systems of young and old mice, a technique called parabiosis, then separately injected aged mice with plasma drawn only from young mice to isolate what the blood itself was doing.

Old mice exposed to young blood grew more dendritic spines, the connection points between neurons, in the hippocampus, and showed improved performance on both fear-based and spatial memory tasks compared with old mice that received blood from other old mice. The team traced part of the effect to increased activation of a gene-regulating protein called Creb in the aged hippocampus.

The result suggested something circulating in young blood, not just the absence of old-blood factors, could partially rejuvenate an aged brain's structure and function. It was a mouse study using plasma injections and surgical blood-sharing rather than a therapy tested in people, and later work spent years trying to identify the exact molecules responsible, with mixed and still-debated results.

A transfusion, not a drug, rebuilt memory.