Microglia: The Little Cells Connecting Our Brains and Bodies

If you’ve never heard of microglia, you’re not alone. These tiny brain cells make up to 10 percent of our human brains, but most people don’t even know that they exist, let alone how they function.

Microglia are a “type of neuronal support cell (neuroglia) occurring in the central nervous system of invertebrates and vertebrates that functions primarily as an immune cell.” Discovered in the 1920s, we now know that these cells clear out debris and dead neurons from nervous system tissue—by eating them. This is called cell phagocytosis, and is perfectly normal, despite sounding like a zombie movie playing out in your own skull.

Today, scientists are trying to find out whether microglia could be harnessed to fight degenerative neurological disorders, such as Alzheimer’s.

Microglia explained

Microglia aren’t limited to one area of the brain. They’re actually everywhere in the nervous tissue, and they move around to check on the health of other nerve cells. Researchers noticed that microglia were echoing a cell phagocytosis behavior pattern when they realized microglia would come into contact with the dead or damaged cell. They surround the dead or damaged cells—and then the cells would disappear.

Moderating the immune response

In other parts of the body, dead cells are consumed by “macrophages” (Greek for “big eaters”). Microglia appeared to be playing the part of macrophages within the brain tissue—which led to the question, “could microglia ever get mixed up and attack healthy cells?”

This question led to further research, which could help us understand the cause of degenerative neurological disorders. Despite what you’ve heard about humans using only a small portion of our brain power, there are hundreds of processes going on every moment of your life, which you’re not aware of as they happen.

The brain is made of millions of neurons (nerve cells) which need to communicate with each other. These cells are able to transfer information via synapses, so if that communication breaks down, or if you have an excess of synapses, the delicate balance in your brain could be thrown off.

That’s what has scientists excited about microglia: they could be responsible for or contribute to neurodegenerative disorders. That is, if the brain gets confused and starts tagging healthy cells for cell phagocytosis, it could destroy healthy brain tissue.

It turns out that this hypothesis was correct. When brain chemistry is thrown off, even a little, the microglia tried to root out a cause and destroy it—which sometimes led to overdoing it and killing healthy synapses and cells.

Scientists have found that microglia send signals to the brain that allow for their survival, called Colony-Stimulating Factor 1 receptor (CSF1R). If CSF1R is inhibited, the microglia cannot survive within the brain—meaning they can’t destroy healthy tissue accidentally. By the 21st day of CSF1R, 95% of all microglia were removed from the brain.

The empress cells of the brain

Donna Jackson Nakazawa, author of The Angel and the Assassin: The Tiny Brain Cell That Changed the Course of Medicine, refers to microglia as “empress cells,” which constantly roam around the brain and look for inconsistencies or threats to the environment. Not only does tissue and nerve health rely on healthy microglia, it’s proof that our emotions and physical bodies are inextricably linked.

Studying these tiny cells could have a big impact on our understanding of mental health and mental illness!

What can we learn from microglia?

There’s still much to learn from microglia, but researchers are looking forward to learning more about their potential role in mental illness. Microglia may be the key to understanding why mental illness can present mild symptoms in one person, yet completely devastate another. Could it have something to do with malfunctioning microglia destroying healthy synapses?

The hypothesis is intriguing, given that we know more microglia are present in people with major depressive episodes, OCD and Parkinson’s. Where psychiatry’s healing powers end, understanding the role of microglia could be a way to enhance and boost them.

Our current understanding of brain chemistry is limited—which is evident when you look at the slow recovery rates from mental illnesses—so scientists are hopeful that further research could illuminate new treatment possibilities.

While a “cure” might seem far off to anyone suffering from Alzheimer’s, mental illness or other neurodegenerative conditions, researchers seem confident that the study of microglia is a major puzzle piece, for which they’ve been searching for decades.

Abhishek Chauhan

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