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Chronic stress, inflammation and depression

An estimated 12% of Canadians experience depressive episodes. But in patients with chronic illnesses involving inflammation—such as obesity, diabetes, Alzheimer disease and heart disease—this figure more than doubles to 25 to 50%. In response to these statistics, Caroline Ménard, professor in the Department of Psychiatry and Neuroscience at Université Laval and researcher at the CERVO research centre, sought to determine whether inflammation and chronic stress were perhaps the cause of the increased risk of depression.

This discovery paves the way for new means to diagnose and possibly treat depression.

To test her hypothesis, her team delved into the impacts of social stress on the immune and vascular systems of animal models. The findings showed that while a majority of rats showed signs of depression, some remained resilient in their responses to stress. When she took a closer look at the rodents' brains using MRI, Caroline Ménard noted that chronic stress and the resulting immune response led the brain to open the blood-brain barrier: the filter that stops contaminants and hormones in the blood from entering the brain. In the mice that were more resilient to stress, this barrier remained unaffected.

Intrigued, she further explored these observations in brains from the Douglas-Bell Canada Brain Bank. Her studies confirmed that the integrity of the barrier is diminished in depressive subjects. She was even able to see how certain molecules produced in the blood of depressed mice in response to stress cross the blood-brain barrier and impact the nervous system.

This discovery paves the way for new means to diagnose and possibly treat depression. For example, people suffering from a chronic disease could undergo an MRI to learn more about their blood-brain barrier. The team is also looking for blood biomarkers: chemical molecules from the brain that enter the blood through the open barrier. Medication to relieve inflammation, such as arthritis treatments, are currently being tested. Caroline Ménard believes that it may be possible shut the barrier and provide more effective treatment for depression in some sufferers.