Too little sleep causes the brain to destroy itself

Many people think that little sleep has no major consequences, beyond the fact that it causes a feeling of fatigue that can be quite bearable for some people. Nevertheless, lack of sleep causes alterations in the functioning of the brain which are not always easy to detect but are associated with serious long-term problems.

A recent study carried out at the Marche Polytechnic University in Italy provides relevant information on this fact. According to the authors, little sleep can make a substance called glia “eat up” healthy neural connections (so-called "synapses"), affecting neuronal connectivity and increasing the risk of developing neurological disorders such as dementia. Glia are made up of nervous system cells called glial cells which normally make sure everything works as it should, but certain alterations seem to modify their behavior.

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Glial cells: astrocytes and microglia

In order to understand the discoveries made by this research, it is necessary to be clear about the functions of glial cells in the nervous system. The study focuses specifically on the role of two of them: astrocytes and the 

microglia.

glial cells or neuroglia are specialized in providing support to neurons, which are very efficient in neural transmission but highly limited in other ways. Different types of glia provide a solid structure to cells. neurons, accelerate synaptic connections and maintain the balance of the extracellular environment of the nervous system.

astrocytes They are a type of glia that is located in the central nervous system, that is, in the brain and spinal cord. In addition to being part of the blood-brain barrier that nourishes and protects neurons, astroglia remove unnecessary synapses to promote the regeneration of damaged tissues.

Microglial cells or microglia are also located in the central nervous system. They are considered part of the immune system because of their ability to phagocytose (“eat”) waste products and damaged cells, which is very important to protect the body from pathogens, infections and other threats.

The study by Bellesi et al.

The research team from the Marche Polytechnic University, headed by Michele Bellesi, studied the effects of sleep deprivation in mice comparing the brains of three sets of experimental subjects using three-dimensional representation and measurement techniques.

Rodents from one of the groups were able to sleep freely. Those in the second had been kept awake for 8 hours when they needed to sleep, while those in the third were sleep deprived for a period of 5 days. This latter group had the goal of simulating chronic sleep deprivation.

The study focused on analyzing the differences in glial cell activity depending on the degree of sleep deprivation, particularly that of astrocytes and microglia, that the Bellesi's team and other research groups had previously linked degeneration with cerebral.

The researchers found that the intensity of phagocytosis increased with that of sleep deficit. Thus, while astrocytes were active in 6% of the synapses of the mice that had been able to sleep, they were 7% in the mildly deprived mice and 13.5% in the sleep deprived group chronic.

On the other hand, Bellesi and his collaborators also identified an increase in the activity of microglia. This may be even more relevant than phagocytosis carried out by astrocytes, since the excess in the function of microglia is related to the development of neurodegenerative diseases, as we will explain later.

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Background of this research

Previously, Bellesi's team had found that the genes that drive astrocytes to initiate the process of phagocytosis are more intensely expressed under conditions of deprivation of dream. However, until now they had not been able to demonstrate a direct connection between the activity of this glial cell and lack of sleep.

Studies had also been published, both with rodents and with humans, suggesting a causal relationship between little sleep and increased inflammation of the nervous system. The research by Bellesi's team provides the important information that this inflammation is due to an increase in the activity of microglia.

This type of glia has received a lot of attention from the scientific community because of the role of the chronic inflammation in various neurodegenerative diseases, particularly Alzheimer's and Parkinson. The functions of microglia they become destructive instead of regenerative when the amount of brain damage is excessive.

Implications of the findings

Synthetically, the results of this study suggest that the activity of certain glial cells is intensified under conditions of sleep deprivation. These data are in turn connected with the known fact that if astrocytes or microglia act excessively can cause long-term brain damage.

In the case of astrocytes, Bellesi's team found that little sleep can cause them to engulf portions of healthy synapses as well as irrelevant connections and waste products. This leads to a deterioration in neuronal transmission that would become more marked the longer the sleep deficit is maintained.

Excessive activity of microglia has been linked to neurodegenerative diseases such as Alzheimer's dementia. This seems to be because the inflammatory responses elicited by this glial cell predispose to further damage if sustained for too long.

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Bibliographic references:

• Bellesi, M.; de Vivo, L.; Chini, M.; Gilli, F.; Tononi, G. & Cirelli, C. (2017). Sleep loss promotes astrocytic phagocytosis and microglial activation in mouse cerebral cortex. Journal of Neuroscience, 37(21): 5263-73.