By studying human brain samples, the research team of Naguib Mechawar, PhD, Director of the Douglas-Bell Canada Brain Bank and Bell Senior Fellow in Mental Health, found strong evidence that depression and suicide are related to inflammation in the brain.

Astrocytes are the most abundant cells of the human brain and are essential for efficient communication between neurons. Previous studies had shown that astrocyte networks are disturbed in depressed people who commit suicide. However, the exact mechanism was unknown. 

Using tissue samples from the Brain Bank, Dr. Mechawar’s team studied astrocytes in the anterior cingulate cortex (ACC) of the brain – a region implicated in impulse control and emotion, and consistently implicated in mood disorders.

They showed that the astrocytes in the ACC of depressed people who committed suicide were much larger than those of the control group.

It is well known that astrocytes are activated in response to inflammation – in order to fight it. Therefore, Dr. Mechawar’s team hypothesized that the increased size and complexity of these astrocytes is a sign of inflammation in the brains of depressed people who committed suicide. 

This finding supports the popular hypothesis that depression and suicide are related to neuro-inflammation. In fact, the blood work of depressed patients generally shows higher levels of some of the main pro-inflammatory molecules (cytokines), which are lowered once they starts taking antidepressants. This neuroinflammation is thought to reflect an immune system response to chronic stress and other factors.

Studying tissue samples has allowed this team to better understand the microscopic changes that occur in the brain regions involved in suicide and depression. Only by understanding these changes can we develop more effective and better targeted treatments.

Dr. Mechawar’s team has since investigated other types of cells in the ACC, namely microglia, which act as the immune cells of the brain. They have found evidence of increased microglial activation in the ACC of depressed people who committed suicide, thus further supporting the notion that the brain is fighting inflammation. Taken together, these findings indicate that, at least in certain cases, depression is linked to inflammation and that treatments for depression could be targeted to reduce this inflammation.

Photo 1: Astrocytes, among the most abundant cells of the human brain

Photo 2: Astrocyte size in the brain tissue of people who were depressed and committed suicide is larger than that of the control group.