Scientists have found a completely new aspect of human anatomy, but providing exactly that, describing a previously unknown network of tunnels located between the skull and the brain. The study was published this week in Nature Neuroscience.
In mice, the newly discovered tunnels, or vascular channels, allow for the quick transport of immune cells to brain injuries brought on by stroke or other brain disorders. Matthias Nahrendorf discovered the tunnels, studying the way bone marrow produces and distributes immune cells throughout the body.
Importantly, the same anatomical features were also found to exist in humans. It’s quite likely that these vascular channels facilitate the same healing function in humans as they do in mice, but future research will be needed to prove it.
A Spongy Tissue
Red blood cells and other immune cells are produced within our bone marrow, a spongy tissue located within our bones. These immune cells help us to fend off infections and heal injuries, whether these injuries happen in our legs, hands, torso, or even the brain.
Immune cells produced within our arms and legs can travel via the bloodstream to damaged tissue in the brain. Scientists have wondered if these immune cells are produced and disseminated throughout the bone marrow of the entire body, or in select areas.
In particular, they wanted to know if, after a stroke, immune cells that rush to the brain came from bone marrow in the skull, or if they came from the tibia, a large leg bone known to produce immune cells.
Using high-resolution scanners and microscopes, the scientists observed neutrophils moving through previously undetected tunnels in the skulls of mice. These tiny channels connected the marrow directly with the outer lining of the brain, known as the meninges.
Before this discovery, scientists had observed larger veins traversing the skull, but not these small channels linking the bone marrow cavities to the meninges. Perhaps the channels were missed by other scientists because they are small. They have to look for them with high-resolution CT or microscopy to find them. Microscopy is rarely done on the bone because it is technically challenging.
Normally, blood flows through these channels from the inner portions of the skull to the bone marrow. After a stroke, however, the neutrophils were seen moving in the opposite direction, traveling towards the damaged tissue.
The channels seen in human skulls were five times larger in diameter than the ones seen in mice. Regarding function, the action of the immune cells moving through the vascular channels were only observed in mice. Proving that it works the same way in humans as it does in mice, however, might be difficult.
In addition to this challenge, Nahrendorf’s team is hoping to identify other types of cells that might travel through these channels, and how these structures might contribute to healthy function or disease.