Antidepressant drugs are common in the developed world and are among the most prescribed medications in North America. Though antidepressants are effective for some, there is a lot of variability in how individuals respond to antidepressant treatment.  

A recent study found that levels of a small molecule found only in primates are lower in the brains of depressed individuals, a discovery that may hold a key to improving treatment options for those who suffer from depression.

Depression is a common cause of disability, and while viable medications exist to treat it, finding the right medication for individual patients is often trial and error.

In a new Nature Medicine study, Dr. Gustavo Turecki, a professor in the Department of Psychiatry at McGill, and colleagues discovered that the levels of a small molecule, miR-1202, may provide a marker for depression and help detect individuals who are likely to respond to antidepressant treatment.

This is a sample from the Douglas-Bell Canada Brain. Credit: Douglas Institute

"Using samples from the Douglas Bell-Canada Brain Bank, we examined brain tissues from individuals who were depressed and compared them with brain tissues from psychiatrically healthy individuals, says Tureck. "We identified this molecule, a microRNA known as miR-1202, only found in humans and primates and discovered that it regulates an important receptor of the neurotransmitter glutamate."

The team conducted a number of experiments that showed that antidepressants change the levels of this microRNA. "In our clinical trials with living depressed individuals treated with citalopram, a commonly prescribed antidepressant, we found lower levels in depressed individuals compared to the non-depressed individuals before treatment," says Turecki. "Clearly, microRNA miR-1202 increased as the treatment worked and individuals no longer felt depressed.  
"We found that miR-1202 is different in individuals with depression and particularly, among those patients who eventually will respond to antidepressant treatment."

The discovery may provide "a potential target for the development of new and more effective antidepressant treatments," he adds.