Medical XPress examines a link between major depression and immune-system cells in the brain called “microglia”:
In a groundbreaking theoretical review paper published in the peer-reviewed journal, Trends in Neurosciences, researchers from the Hebrew University of Jerusalem suggest that “progress in the understanding of the biology of depression has been slow,” requiring expanding beyond the “abnormalities in the functioning of neurons.” The contribution of other brain cells—often neglected by researchers—may be more relevant in causing depression, according to psychobiology Prof. Raz Yirmiya, director of the Hebrew University’s Laboratory for PsychoNeuroImmunology, and senior author of the journal’s paper, titled “Depression as a microglial disease.”
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In Trends in Neuroscience, the Hebrew University researchers claim that diseased microglia can cause depression and drugs that restore the normal functioning of these cells can be effective as fast-acting anti-depressants.
Microglia, which comprise 10% of all brain cells, are the brain’s immune cells. They fight infectious bacteria and viruses in the brain. They also promote repairing and healing processes of damages caused by brain injury and trauma.
“Our views on microglia have dramatically changed over the last decade,” Prof. Yirmiya says. “We now know that these cells play a role in the formation and fine-tuning of the connections between neurons (synapses) during brain development, as well as in changes of these connections throughout life. These roles are important for normal brain and behavioral functions, including pain, mood and cognitive abilities.”
“Studies in humans, using post-mortem brain tissues or special imaging techniques, as well as studies in animal models of depression, demonstrated that when the structure and function of microglia change, these cells can no longer regulate normal brain and behavior processes and this can lead to depression,” Prof. Yirmiya says.
Indeed, changes in microglia occur during many conditions associated with high incidence of depression, including infection, injury, trauma, aging, autoimmune diseases such as multiple sclerosis and neurodegenerative diseases such as Alzheimer’s disease. In these conditions, microglia assume an “activated” state in which they become big and round, and secrete compounds that orchestrate an inflammatory response in the brain.