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Have we found a brand new system in the human brain?

Human Brain

Scientists say they have found the first evidence that the human brain may be draining waste. Certainly, a startling finding that has been eluding discovery for two centuries.

A paper describing the research was published in eLife. The scientists behind it said they saw lymphatic vessels removing waste and fluid from the brain, a function that researchers were not sure the brain possessed.

Does the human brain drain waste?

This idea was actually first postulated in 1816 by Italian anatomist Paolo Mascagni. He claimed to have seen lymphatic vessels in cadavers he was dissecting. Since then however, nobody had been able to prove this claim.

However, in a recent experiment, a team led by Dr Daniel Reich from the National Institute of Health used an MRI and scanned the brains of five healthy volunteers. These people were injected with a magnetic dye called gadobutrol. This dye is made of molecules too big to actually enter the brain, but small enough to leak out of blood vessels into the dura. That’s the brain’s leathery outer coating.

Using MRI scans, the team saw that the dye had leaked out of the blood vessels. It then flowed through the dura and entered into neighboring lymphatic vessels, lighting up in the scans. The team then used a second dye with larger molecules. These were too big to leave the blood vessels and found the lymph vessels did not light up accordingly.

The key is in the lymphatic vessels

Lymphatic vessels transport immune cells and waste around the body. Blood vessels deliver white blood cells to organs, and the lymphatic system removes these and recirculates them. Therefore, this astounding discovery suggests the brain has a sort of drainage system to remove waste. Next, the team hopes to discover whether the lymphatic system works differently in cases of multiple sclerosis or other neuroinflammatory disorders.

I was completely surprised. In medical school, we were taught that the brain has no lymphatic system,” exclaimed Dr Reich.

Further on, he added: “For years we knew how fluid entered the brain. Now we may finally see that, like other organs in the body, brain fluid can drain out through the lymphatic system.

Findings of the research still needs to be verified of course. The study was fairly small, as MRI scans are expensive. But should it be confirmed, it could fundamentally change what we know about how the human brain and the immune system work together.