Depressive disorder is one of the main causes of disability (and interest in life). Other diseases, for example, the cardiovascular system, affect this much less.
However, progress in understanding the biological mechanisms of depression has been slow. Researchers at the Hebrew University of Jerusalem believe that “abnormal neuronal function” is not a sufficient explanation for depression. Other brain cells that are not usually taken into account in studies of depression may also play an important role.
Recent data obtained by scientists show that the cause of the development of some forms of depression may be a malfunction of brain cells called microglial cells. Approximately 10% of the total number of brain cells are of this type. They play a critical role in the immune defense of the central nervous system, helping the brain fight dangerous bacteria and viruses. They also contribute to the recovery of the brain after injury or damage.
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“Our understanding of how microglial cells work has changed dramatically over the past 10 years. We now know that they play an important role in the formation and tuning of connections between neurons (synapses) during brain development, as well as in the changes that occur with these connections throughout life. They are important for the normal functioning of the brain and can affect areas such as pain, mood, cognitive abilities. Post-mortem studies of brain cells and scanning technologies that allow studying the living brain, as well as animal studies, have shown that with certain structural and functional changes in microglial cells, these cells no longer regulate brain function normally, which can lead to depression. At the same time, one should not assume that all types of depression and other mental disorders are caused solely by problems with microglial cells, ”says Raz Yirmiya, director of the laboratory of psychoneuroimmunology at the Hebrew University of Jerusalem. Her research may lead to the creation of a new generation of fast-acting antidepressants that will restore the normal functioning of microglial cells.
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Remarkably, many of the conditions known to increase the risk of depression involve changes in microglial cells—in infections, injuries, injuries, aging, autoimmune (like multiple sclerosis) and neurodegenerative (like Alzheimer’s) diseases. Under these conditions, microglial cells become unusually active, increase in size, and begin to secrete substances that contribute to the development of inflammatory processes.
Changes in microglial cells can also occur due to chronic and unpredictable psychological stress, one of the most common causes of depression. Recent studies of the laboratory, which is run by Raz Yirmia, have shown that under the influence of such stress, some microglial cells die, while the rest decrease and degrade.
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It turns out that depression can be caused by both excessive activation and degradation of microglial cells. Because of this, most likely, it will not be possible to create one universal drug for the treatment of these conditions, each of them may require special drugs.
Since Yirmia hopes that in the future the treatment of patients with depression will begin with an examination of the state of the microglial cells in his brain. Based on the information received, it will be possible to choose a drug that will either reduce the excessive activity of these cells, or, on the contrary, will stimulate degraded cells.
Подробнее см. R. Yirmiya et al. «Depression as a Microglial Disease», Trends in Neurosciences, October 2015.