Depressed Brains Are Different, Say Researchers

Researchers at the University of Michigan Depression Center say that depressed people have fewer receptors for the brain's "feel good" chemicals than non-depressed people.

The researchers also say that, even among depressed people, the number of receptors varies and can be correlated to the severity of their depression and the chances that they'll feel better after taking medication.

Their preliminary findings were presented last week at the American Psychiatric Association's annual meeting in Washington, D.C.

At the meeting, lead researcher, Jon-Kar Zubieta, presented data from positron emission tomography (PET) scans of patients with major depression who had not yet been treated. These scans were compared with scans from non-depressed volunteers.

One group of depressed and non-depressed volunteers were scanned using a tracer that can show the location and concentration of a type of receptor called the 5HT1a receptor. This receptor allows the brain to receive signals from the neurotransmitter serotonin. Low levels of serotonin have been associated with depression so a shortage of receptor sites could theoretically lead to depression.

Among those given the tracer for the 5HT1a receptor, it was found that the concentrations of receptor sites was markedly lower in depressed patients. Among depressed volunteers, the number of receptors sites varied and lower concentrations of receptor sites were associated with lower scores on assessments of daily function. Volunteers with lower numbers of receptors were also less likely to respond when prescribed an antidepressant.

Another group of depressed and non-depressed volunteers were scanned using a tracer which allowed the researchers to see the mu-opioid receptors in the brain. These receptors receive signals sent by the brain's natural painkillers, called endogenous opioids or endorphins. These chemicals are involved in the stress response and are responsible for the so-called "runner's high" that athletes get. These same "feel good" receptor sites are also involved in drug addiction.

The researchers looked at both the distribution of these receptors and how active they were when volunteers were asked to summon up a sad memory.

Depressed volunteers had lower concentrations of mu-opioid receptors, however, their receptors were more active than in non-depressed volunteers. Also, the fewer the receptors they had, the worse they responded to medication.

This results of this study have not yet been published, but you can learn more about the work being done by Zubieta and colleagues at http://www.depressioncenter.org/.