The spinal fluid from the young mice sharpened the memories of the older rodents

When it was successful, Dr. Iram said the result was about 10 microliters of cerebrospinal fluid, about one-fifth the size of a drop of water. To collect enough for the infusions, he had to perform the procedure on many hundreds of mice, questioning the technical challenges that Dr. Wyss-Coray had warned him with the sheer force of repetition.

“I enjoy doing these types of studies that require a lot of perseverance,” said Dr. Iram said. “I just set a goal and I don’t stop.”

To infuse young cerebrospinal fluid into old mice, Dr. Iram made a small hole in their skulls and implanted a pump under the skin in their upper back. For comparison, a separate group of old mice was infused with artificial cerebrospinal fluid.

A few weeks later, the mice were exposed to signals – a tone and a flashing light – that they had previously learned to associate with shaking their feet. Animals that received the infusion of young cerebrospinal fluid tended to freeze for longer, suggesting that they had retained stronger memories of the original foot shocks.

“This is a very interesting study that seems scientifically sound to me,” said Matt Kaeberlein, a biologist who studies aging at the University of Washington and was not involved in the research. “This adds to the growing body of evidence that it is possible, perhaps surprisingly easy, to restore function in aged tissues by targeting the mechanisms of biological aging.”

Dr Iram sought to determine how young CSF was helping to preserve memory by analyzing the hippocampus, a portion of the brain dedicated to memory formation and storage. Treating old mice with the fluid, she found, had a strong effect on cells acting as precursors to oligodendrocytes, which produce layers of fat known as myelin that insulate nerve fibers and ensure strong signal connections between neurons.

The study authors focused on a particular protein in the young CSF that appeared to be involved in triggering the chain of events that led to greater nerve isolation. Known as fibroblast growth factor 17, or FGF17, the protein could be infused into older CSF and could partially replicate the effects of young fluid, the study found.