One of the main tools in the fight against depression is the use of selective serotonin re-uptake inhibitors (SSRI) drugs such as Prozac. SSRI medication has the effect of increasing the neurotransmitter serotonin in some parts of the brain, so it has always been assumed that depression must result from low serotonin levels. However, recent research has revealed that the brain chemistry of a depressed person is far more complex, and that too much serotonin in parts of the brain could actually cause depression.
Christopher A. Lowry Ph.D., of the Department of Integrative Physiology
University of Colorado, is reported in the journal New Scientist as saying the discovery of multiple types of serotonin-releasing neurons in the brain, along with high levels of serotonin recorded in people with depression is prompting a rethink as to the cause of depression.
Lowry feels that it is far more likely that there are subgroups of serotonin neurons that are overactive during depression, rather than under-active as many people have assumed. The piecing together of evidence started over three years ago when researchers at the Baker Heart Institute in Australia discovered up to four times the normal level of serotonin in the brains of people panic disorder. In depressed people not receiving treatment it was two times higher. Another interesting finding was that long-term use of SSRIs in people with depression and panic disorder actually seems to decrease serotonin levels - although it isn't clear why.
It now seems that there are multiple types of serotonin neurons that can be independently regulated. According to Dr. Lowry the increased levels of anxiety felt in the short term by people taking SSRIs is almost inevitably due to the activation of a particular group of serotonin neurons. Suicidal ideation reported by some users of SSRIs could be due to the boost in serotonin affecting "impulsivity circuits in the brain".
The report, by Linda Geddes, goes on to suggest that Lowry's findings correspond with separate research that points to why high levels of serotonin in certain regions of the brain can lead to improved mood, while in other regions it could have negative effects.
These new findings are likely to have implications for the drugs industry. It is recognized that SSRI medications have a calming effect in the long-term, but nobody actually knows why. The revelation that serotonin neurons may be regulated independently points to the possibility of designing drugs that can turn on or off specific groups of neurons responsible for anxiety or depression.
Geddes, Linda. "Rethink needed for cause of depression." New Scientist. 207.2770 (2010): 12. Print.