The need for sleep goes far beyond simply replenishing our energy levels every 12 hours. Our brains actually change states when we sleep to remove the toxic byproducts of neural activity during the day.
Strangely enough, research on mice has revealed that the same process is beginning to occur in brains that are also chronically sleepy – except that it is trapped in hyperthyroidism.
Researchers have found that persistent poor sleep causes the brain to significantly deplete neurons and synaptic connections, and regaining sleep may not reverse the damage.
In 2017, a team led by neuroscientist Michele Bellesi of Marche Polytechnic University in Italy investigated mammals’ response to poor sleeping habits, and found a bizarre similarity between the well-rested and sleeping mice.
Like the cells elsewhere in your body, the neurons in your brain are constantly being replenished by two different types of glial cells – supporting cells that are often called the glue of the nervous system.
The microglial cells are responsible for clearing out old and worn cells through a process called phagocytosis – which means “in the mind”.
The job of astrocytes is to cut unnecessary synapses (connections) in the brain to refresh and shape its wiring.
We knew this process happens when we sleep to take away the neurological wear and tear of the day, but now it seems that the same thing happens when we start sleeping.
But instead of being a good thing, the brain goes overboard with the distraction, and begins to harm itself instead.
Think of it when the trash is wiped while you are asleep, against someone who comes into your house after several sleepless nights and throws your television, refrigerator and family dog unspoiled.
“We are showing for the first time that parts of synapses are literally being eaten by astrocytes due to sleep deprivation,” Bellesi told Andy Coghlan at New scientist.
To find out, the researchers imaged the brains of four groups of mice:
- one group slept 6 to 8 hours (good rest)
- another was periodically awakened from sleep (spontaneous awakening)
- a third group was kept awake for 8 hours (sleepy)
- and a final group was kept awake for five days (chronically sleep-deprived).
When the researchers compared the activity of the astrocytes in the four groups, they identified it in 5.7 percent of the synapses in the well-rested mouse brain, and 7.3 of the spontaneously awakened mouse brain.
In the sleepy and chronic sleepy mice, they noticed something different: the astrocytes had increased their activity after actually eating parts of the synapses such as microglial cells eating waste – a process known as astrocytic phagocytosis.
In the sleepy mouse brains, the astrocytes were found to be active in about 8.4 percent of the synapses, and in the chronic sleepy mice, a whopping 13.5 percent of their synapses showed astrocyte activity.
As Bellesi told me New scientist, most of the synapses eaten in the two groups of dormant mice were the largest, which are the oldest and most commonly used – “like old furniture” – which is probably a good thing.
However, when the team monitored the activity of the microglial cells in the four groups, they found that it had also increased in the group with chronic sleep.
And that’s a concern, because unbridled microglial activity has been linked to brain disease such as Alzheimer’s and other forms of neurodegeneration.
“We find that astrocytic phagocytosis, especially of presynaptic elements in large synapses, occurs after both acute and chronic sleep loss, but not after spontaneous awakening, suggesting that it may promote the recovery and recovery of worn parts from heavily used, strong synapses,” tell the researchers.
“In contrast, only chronic sleep loss activates microglia cells and promotes their phagocytic activity … suggesting that extended sleep disorder may primrogly microglia and perhaps predispose the brain to other forms of insult.”
Many questions remain, such as whether this process is replicated in human brains, and whether inhaling sleep can reverse the damage.
But the fact that Alzheimer’s death has increased by an incredible 50 percent since 1999, coupled with the struggle many of us have to get a good night’s rest, means that this is something we need to get to the bottom of – and fast .
The study is published in the Journal of Neuroscience.
A version of this article was first published in May 2017.
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