Scientists at the University of Wisconsin-Madison (UoW) have discovered another reason why sleep is great! Resting boosts the growth of special cells — called oligodendrocytes — that repair the brain when it is injured, according to new findings reported in the Journal of Neuroscience.           

"For a long time, sleep researchers focused on how the activity of nerve cells differs when animals are awake versus when they are asleep," said lead author Dr. Chiara Cirelli, a sleep neuroscientist at UoW. "Now it is clear that the way other supporting cells in the nervous system operate also changes significantly depending on whether the animal is asleep or awake."

Oligodendrocytes are one brand of support cells found in the brain. They produce a substance called myelin, which coats the ‘wiring’ that connects different neurons together and accelerates the rate at which they can send messages back and forth to each other. If normal neuron chatter is like “e-mail,” then cognition without myelin is like using smoke signals. When the brain is injured, oligodendrocytes kick into gear to produce extra myelin that helps to repair the brain and restore regular neurotransmission.

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This explains why multiple sclerosis, an autoimmune disease that destroys myelin and kills oligodendrocytes, is so devastating. Hardened scars in the brain are the classic feature in the more than two million victims of the disease, which typically strikes between the ages of 20 and 40. These brain injuries yield a variety of symptoms, including muscle spasms, difficulties with coordination, and chronic back pain.

Cirelli’s team found that sleep helped oligodendrocytes make myelin in mouse brains. Genes responsible for making myelin were more active in well-rested mice compared those who were sleep-deprived. In contrast, losing sleep triggered the activity of genes implicated in cell death and stress responses. 

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In addition, the number of oligodendrocyte precursor cells (OPCs) — cells that become oligodendrocytes — doubled during sleep, which occurred particularly during the rapid eye movement (REM) stage of sleep that is associated with dreaming. This phenomena, according to the authors, is possibly due to the neurotransmitter glutamate, which is known to block the reproduction of these precursor cells and is higher while awake than during sleep.

According to the authors, the findings suggest that chronic sleep loss could possibly aggravate some symptoms of multiple sclerosis.

"These findings hint at how sleep or lack of sleep might repair or damage the brain," said Dr. Mehdi Tafti, Ph.D., a sleep researcher at the University of Lausanne in Switzerland who was not involved with the study.

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Source: Bellesi M, Pfister-Genskow M, Maret S, Keles S, Tononi G, Cirelli C. Effects of Sleep and Wake on Oligodendrocytes and Their Precursors. Journal of Neuroscience. 2013.