It's better to fall on your side 19.08.2015

For a long time, no one knew how the brain gets rid of biochemical debris: metabolic products, damaged molecules that have served their purpose, etc. Usually the circulatory and lymphatic systems serve as a "sewerage", but between the nervous tissue and the blood vessels in the brain there is a powerful blood-brain barrier , which passes little through itself.

However, a few years ago, Maiken Nedergaard and his colleagues at the University of Rochester found their own garbage collection system in the brain. Blood vessels in the brain are surrounded by sheaths of processes of astrocytes - auxiliary, or glial cells. It turns out a double tube, and "littered" intercellular fluid penetrates into the gap between its two walls, which filters the debris into the blood vessel. Moreover, astrocytes create pressure in it, so that 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.

The work of the garbage collection system depends on the actions of the membrane channels of astrocytes, which require quite a lot of energy. This led to the idea that the glymphatic system of the brain remains functional during sleep: no energy is spent on the work of neurons, on the perception and analysis of external signals, on analytics, etc., so it can be directed to garbage collection.

Further experiments confirmed the hypothesis: active pumping of the intercellular fluid through the glial filter was turned on precisely in sleep. Moreover, during sleep, the distance between nerve cells increased by 60%, which, as it were, shrank to expand the channels for the circulation of cerebrospinal fluid and facilitate its access to the glymphatic system. As for the control over it, here the researchers give the main role to the neurotransmitter norepinephrine, the level of which drops sharply during sleep and increases upon awakening.

But if the glymphatic system turns on during sleep, does it mean that its work depends on how we sleep? Indeed, as Miken Nedergaard and the staff of the University of Rochester and the researchers who joined them at the State University of New York at Stony Brook found out, the efficiency of garbage collection processes in the brain is affected by body position during sleep. Experiments were carried out on animals: laboratory rodents were given a special label that could be used to monitor how efficiently spoiled proteins were removed from the brain, and the animals were put to sleep. As the authors of the work write in the Journal of Neuroscience, brain "sewerage" worked best if the animals slept on their side. It is worth mentioning here that both animals and humans most often sleep on their side, which may be due to the work of the glymphatic channels (although the results will still need to be confirmed in studies involving humans).

The tainted molecules that were monitored in the experiments were tau proteins and beta-amyloid - accumulating in neurons, they cause Alzheimer's syndrome. It is known that many neurological diseases, including neurodegenerative syndromes, are associated with sleep disorders. Perhaps the disruption of the garbage collection system, which is activated during sleep, just contributes to the development of such diseases. So proper sleep helps the brain not only restore mental functions, but also effectively get rid of dangerous substances.