Drainage for the brain

The lymphatic system was found in the brain

Kirill Stasevich, "Science and Life" based on the materials of The Scientist: Brain Drain

The lymphatic system has many functions, one of the most important is protective and "garbage collection": immune cells and lymph proteins neutralize bacteria and toxins. Lymph penetrates into all tissues of the body, with the exception of the brain. As you know, the brain is so well fenced off from everything else that even antibodies with immune cells cannot penetrate it. However, despite its "fortress walls", the brain is still not immune from the penetration of pathogens. But then the brain itself must have some kind of protection systems against the invasion of viruses and bacteria. On the other hand, in the course of metabolism, all kinds of molecular waste accumulate, which also need to be disposed of somehow - but how if the lymph does not penetrate into the brain, and there is a powerful blood-brain barrier in the blood vessels, through which not every molecule will get through?

Physiologists have been intrigued by this question for a long time. On the one hand, the brain itself can process harmful substances in special cells. On the other hand, there are also so–called glial, or auxiliary cells in it - some of them perform the same functions as ordinary immune cells, that is, they search for and destroy everything alien. Finally, over time, it was possible to find additional mechanisms to help get rid of unwanted substances. The ventricles of the brain secrete the so-called cerebrospinal fluid, which freely circulates between them and the spinal canal, the cells themselves also secrete something into the external space, resulting in a unified system of intercellular and cerebrospinal fluid. How is it cleaned of biochemical debris?

A few years ago, researchers at the University of Rochester discovered that the blood vessels in the brain are surrounded by "covers" of the processes of astrocytes – auxiliary, or glial cells. A double tube is obtained, and a "littered" intercellular fluid penetrates into the gap between its two walls, which filters debris into the blood vessel. Moreover, astrocytes create pressure in it, so the filtration here is not passive, but active. The system was called glymphatic: it functioned like a normal lymphatic system, only it was made of glial cells.

However, as it turned out, there is an ordinary lymphatic system in the brain after all - Jonathan Kipnis and colleagues from the University of Virginia found it; whose article has just appeared in Nature (Structural and functional features of central nervous system lymphatic vessels). Here you need to make a small excursion into anatomy. As you know, the brain and spinal cord are clothed with three shells: soft, spider and hard, the uppermost of the three. In some places, the hard shell is embedded in the cracks of the brain, forming channels – they are called sinuses. They collect venous blood from the vessels of the brain, the hardest shell and the bones of the skull, which then enters the jugular veins. (Although the sinuses in the drawings are very similar to blood vessels, they do not enter the circulatory system, they are separate formations.)

Old and new schemes of the lymphatic system (from the University of Virginia press release
Researchers Find Textbook-Altering Link Between Brain, Immune System) – VM.

It turned out that in the sinuses there are immune cells and molecular markers peculiar to lymphatic vessels. When the researchers injected the dye into the mice in the subarachnoid space – the cavity between the soft and arachnoid meninges filled with cerebrospinal fluid – the dye soon ended up in the sinuses. This means that the cerebrospinal fluid passes through the sinuses. Moreover, the dye turned out to be in the cervical lymph nodes. The authors of the work also managed to show that fluid from the lymph nodes can pass into the cerebral sinuses.

Recall that until recently it was believed that the lymphatic system does not contact the brain in any way. Now, this point of view will have to be largely revised, since it turned out that the sinuses of the dura perform the function of lymphatic vessels and serve as the residence of immune cells. Debris and toxins accumulating in the cerebrospinal fluid can be removed from it through the sinuses, although the details of the process have yet to be clarified. It is also worth adding that immune cells, despite any barriers, still penetrate into the brain, recently they have been found here more and more often. Although it was previously believed that their appearance in brain tissues is an unambiguous sign of pathology (for example, severe infection), however, apparently, they come to a healthy brain too. And, most likely, sinuses play an important role here. Of course, the new information will be of great interest to doctors – after all, the brain and immunity were more closely connected than they thought.

Portal "Eternal youth" http://vechnayamolodost.ru 03.06.2015