waste drainage system in the human brain
Researchers at the National Institutes of Health got an evidence that our brains may drain some waste out through lymphatic vessels. To scan the brains of healthy volunteers, the results said the vessels could act as a pipeline between the brain and the immune system.
We literally watched people’s brains drain fluid into these vessels, said, Daniel S. Reich, senior author of the study. We hope that our results provide new insights to a variety of neurological disorders.
Lymphatic vessels are part of the body’s circulatory system. In most of the body they run alongside blood vessels. They transport lymph, a colorless fluid containing immune cells and waste, to the lymph nodes. Blood vessels deliver white blood cells to an organ and the lymphatic system removes the cells and recirculates them through the body. The process helps the immune system detect whether an organ is under attack from bacteria or viruses or injure.
In 2015, two studies of mice found evidence of the brain’s lymphatic system in the dura, the leathery outer coating of the brain.
“I was completely surprised. In medical school, we were taught that the brain has no lymphatic system,” said, Dr. Reich. To look for the vessels, Dr. Reich’s team scan the brains of five healthy volunteers who injected with gadobutrol, a magnetic dye typically used to visualize brain blood vessels damaged by diseases.
The dye molecules are small enough to leak out of blood vessels in the dura. But, too big to pass through the blood-brain barrier and enter other parts of the brain.
At first, when the researchers scan to see blood vessels, the dura lit up brightly, and they could not see any signs of the lymphatic system. However, when they tuned the scanner differently the blood vessels disappeared.
Also, the researchers saw that dura contained smaller, but almost equally bright spots and lines which they suspected lymph vessels. The results suggested that the dye leaked out of the blood vessels flowed through the dura into neighboring lymphatic vessels.
However, the researchers performed another round of scans on two subjects after first injecting them with a second dye made up of larger molecules that leak much less out of blood vessels. Contrast with the first round of scans, the researchers saw blood vessels in the dura, but no lymph vessels regardless of how they tuned the scanner, confirming their suspicions.
They also found evidence for blood and lymph vessels in the dura of autopsied human brain tissue. Moreover, brain scans and autopsy studies of the brains of non-human primates confirmed the results seen in humans. Also, suggesting the lymphatic system is a common feature of mammalian brains.
“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,” said, Dr. Reich.
More information: [eLIFE]