Scientists from Invicro and Imperial College London have found direct evidence that serotonin release is impaired in the brains of people with depression, supporting the “serotonin” hypothesis of depression. Research published in the journal Biological Psychiatry.
Since the 1960s, researchers have believed that major depressive disorder is caused by disturbances in the serotonin transmission system, but the evidence for this idea was circumstantial, although plentiful. A recent comprehensive review of studies concluded that there is no strong evidence to support the “serotonin hypothesis”. Despite this, drugs used in the treatment of depression mainly aim to increase the levels of extracellular serotonin, also known as 5-hydroxytryptamine (5-HT).
The new study used a new imaging technique to directly assess the levels of serotonin released from neurons in response to drugs. The researchers used this technique to compare serotonin release in 17 depressed patients and 20 healthy controls.
The results of the scans led to the conclusion that participants with depression had impaired release of serotonin in key areas of the brain. The study found no relationship between the severity of depression and the degree of deficiency in the ability to release serotonin.
The authors noted that low serotonin releasing capacity was a sign of depression, not a consequence of antidepressant treatment, as 11 of 17 patients had never taken antidepressants.
Impairment of serotonin transmission cannot explain all the symptoms and differences between different types of depression. However, this study shows that serotonin deficiency is present in people with depression who are not taking medication.