Just before the brain scans, the women also had their blood tested to measure levels of two hormones that are released in response to stress. The depressed women were then prescribed an antidepressant drug and reported regularly about their depression symptoms for the next ten weeks. Those whose depression hadn't eased by the end of the first month received a prescription for an increased dose of antidepressant.
"Women who had more pronounced responses in their stress response mechanisms during brain imaging also showed alterations in hormones, like cortisol, that are sometimes over-secreted in depression," Zubieta explains. "In addition, these women responded poorly to treatment with medication."
The research builds on previous studies that found differences in the body's and brain's stress-response system among people with depression. But this is the first time that specific differences in the mu-opioid system have been shown between people with depression and those without.
Zubieta performed the work with former doctoral student, Susan Kennedy, Ph.D., who is first author on the new paper. They used a brain-imaging technique that the U-M team has previously used to see how the brain responds to pain ?and to placebo pain treatment.
The technique uses a form of a drug called carfentanil, which binds to the same receptors on the surface of brain cells that brain chemicals called mu-opioids bind to. Mu-opioids, sometimes also called endorphins, reduce or block the spread of messages related to pain, stress and emotional distress between the body and the brain. They have been called the body's "natural painkillers." The drug is modified to allow it to be "seen" by the PET scanner, so that the researchers can create maps of the specific brain areas where the natural mu-opioids are more or less active at any given time.
In the new study, the researchers also found that the mu-opioid system was overactive in women
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Source:University of Michigan Health System
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