Science tells us that a lot of good things happen in our brains while we sleep—learning and memories are consolidated and waste is removed, among other things.
In a new study, researchers found for the first time that important immune cells called microglia—which play an important role in reorganizing the connections between nerve cells, fighting infections, and repairing the damage—are also primarily active while we sleep.
The findings have implications for brain plasticity, diseases like autism, schizophrenia, and dementia, which arise when the brain’s networks are not maintained properly, and the ability of the brain to fight off infection and repair the damage following a stroke or other traumatic injury.
The research was conducted by a team from the University of Rochester Medical Center.
Microglia serve as the brain’s first responders, patrolling the brain and spinal cord and springing into action to stamp out infections or gobble up debris from dead cell tissue.
It is only recently that Majewska and others have shown that these cells also play an important role in plasticity, the ongoing process by which the complex networks and connections between neurons are wired and rewired during development and to support learning, memory, cognition, and motor function.
The microglia help maintain the health and function of the synapses and prune connections between nerve cells when they are no longer necessary for brain function.
The current study points to the role of norepinephrine, a neurotransmitter that signals arousal and stress in the central nervous system.
This chemical is present in low levels in the brain while we sleep, but when production ramps up it arouses our nerve cells, causing us to wake up and become alert.
The study showed that norepinephrine also acts on a specific receptor, the beta2 adrenergic receptor, which is expressed at high levels in microglia.
When this chemical is present in the brain, the microglia slip into a sort of hibernation.
The team says the enhanced remodeling of neural circuits and repair of lesions during sleep may be mediated in part by the ability of microglia to dynamically interact with the brain.
The research reinforces the important relationship between sleep and brain health and could help explain the established links between sleep disturbances and the onset of neurodegenerative conditions like Alzheimer’s and Parkinson’s.
One author of the study is Ania Majewska, Ph.D., a professor at the University of Rochester Medical Center.
The study is published in Nature Neuroscience.
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