Evidence of a link between inflammation in the brain and major episodes of depression could have implications for possible new treatments for depression, Canadian researchers say.

Clinical depression has been found to be associated with a 30 percent increase of inflammation in the brain, which may account for some symptoms including reduced ability to sleep, low mood and loss of appetite, scientists at the Center for Addiction and Mental Health in Toronto say.

For their study, reported in JAMA Psychiatry, they scanned the brains of 20 people suffering from depression and 20 healthy participants as controls.

The scans showed evidence of significant inflammation in the brains of the patients with depression, the researchers say, and the level of inflammation was found to be the highest in the participants suffering the most severe depression.

"This finding provides the most compelling evidence to date of brain inflammation during a major depressive episode," says study senior author Dr. Jeffrey Meyer. "Previous studies have looked at markers of inflammation in blood, but this is the first definitive evidence found in the brain."

Inflammation is the immune system's natural response to infection or disease, and can be a way for the brain to protect itself, similar to the way a sprained ankle is inflamed during the healing process, but excessive inflammation can be damaging, the researchers suggest.

As to which might be the cause and which the effect, previous studies have suggested depression is more likely to add to inflammation as opposed to arising as a consequence of inflammation.

In other words, researchers say, inflammation occurring independently of physical illness may be highly associated with clinical depression.

"Depression is a complex illness and we know that it takes more than one biological change to tip someone into an episode," says Meyer. "But we now believe that inflammation in the brain is one of these changes and that's an important step forward."

Since current treatments for depression are not targeting inflammation, future studies should investigate whether anti-inflammatory drugs might have an impact on depression symptoms, he suggests.

"This discovery has important implications for developing new treatments for a significant group of people who suffer from depression," says Meyer, who studies the neurochemistry of major depression. "It provides a potential new target to either reverse the brain inflammation or shift to a more positive repair role, with the idea that it would alleviate symptoms."

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