A group of Israeli biologists have discovered that the barrier between the blood and the brain tissue is not as durable and impervious to a major substances, as previously thought. They noticed that neuronal stem cells their processes are directly in contact with cells of the vascular wall. Furthermore, stem cells, apparently, make the blood vessels to capture and transfer the substances from the blood. Such transportation was also indiscriminate: inside the nervous tissue in the experiment was not only harmless dyes and carbohydrates, but and the drug for chemotherapy. Work published in the journal eLife.
In the brain of the adult mammal, there are two zones in which concentrated precursors of nerve cells: the olfactory bulb and dentate gyrus of the hippocampus. To understand the extent to which they share during the life of the body, uneasy, but, apparently, most of the time they spend in rest, although in some experiments, scientists have found that neurogenesis in the hippocampus may increase or, conversely, hampered by — for example, after transfusion, mice blood from young or old counterparts, respectively.
How exactly are neural stem cells in the hippocampus respond to the composition of the blood, is unclear. Theoretically, they should be separated from the blood by the blood-brain barrier — a barrier which consists of a wall of the vessel and intercellular substance. So perhaps only two ways in which blood can act on stem cells. Either they break the barrier, reaching for the vessel directly, or the blood acts on cells in the vessel wall, and they already emit their signal substances in the cerebral tissue.
Tamar Licht (Licht Tamar), together with colleagues from the Hebrew University in Jerusalem have used a line of genetically modified mice in which red fluorescent protein is produced only neural stem cells. These cells resemble a tree: the body is in a single cell layer (“crown”), and the long arm (“trunk”) goes in another layer, where it produces many small processes whose functions remain unclear. The researchers examined slices of mouse hippocampus in an electron microscope and found that these small processes surround blood vessels.