Depression can affect individuals in different ways, and new research from the University of Michigan indicates that the biological changes associated with depression may also vary from person to person. Using positron emission tomography (PET) scans of depressed subjects and controls, the researchers examined brain receptors, the proteins that bind to neurotransmitters allowing brain cells to receive important signals. Their results, which were presented last week at the American Psychiatric Association's annual meeting, indicate that the concentration of certain receptors may correlate to the severity of a depressive episode.
In order to observe brain receptors unaffected by antidepressants, the researchers included subjects who had been diagnosed with major depressive disorder but had not yet been treated with medication. In the first part of their study, the researchers compared the brain scans of 17 depressed subjects and 19 matched controls. Those with depression had significantly fewer 5HT1a receptors, which bind to the neurotransmitter serotonin. Researchers have long investigated a connection between low serotonin levels and mood disorders, and this study's results supported this relationship, finding not only an association between depression and fewer serotonin receptors, but also that the concentration of serotonin receptors varied among depressed individuals in ways that corresponded with the severity of their depression. Those with the smallest number of receptors experienced greater impairments in their lives at home and at work, and they were also less likely to benefit from commonly prescribed antidepressants.
The researchers achieved similar results in a second experiment involving a separate sample of 18 depressed subjects and 19 matched controls. This time, they focused on mu-opioid receptors, which bind to endorphins, the painkillers made naturally by the body. Once again, subjects with depression had fewer receptors compared with controls, and the amount of receptors present in their brains indicated the severity of their depression as well as their likely response to treatment with a common antidepressant. Additionally, the researchers found that mu-opioid receptors acted differently in depressed subjects. When asked to recall a sad memory, these individuals experienced greater activity in mu-opioid receptors compared to controls.
Depression is a complex disorder fueled by various and interrelated factors, and the researchers did not discuss whether these receptor variations might have been a contributing factor in depressive symptoms or were a consequence of depression. Their study was also small, and further research would be beneficial in determining the true role of these neurotransmitter systems in depression. By continuing to investigate this subject, we may gain a better understanding of the different ways in which depression can affect the brain, and this may allow researchers to learn why antidepressants work for some individuals but not for others. Researchers may be able to identify those who will not respond to the most common treatments by examining the concentration of certain brain receptors, and this may lead to new treatments tailored specifically for these individuals.
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