The Serotonin Theory of Depression

In its simplest form, the serotonin deficiency theory of depression postulates that there is a net reduction in serotonin transmission in depressive illness. The pathophysiological change may result from two different mechanisms. The first involves a decrease in serotonin (5-HT) availability which has the consequential effect of compensatory receptor up-regulation or super sensitivity. The second mechanism implies a primary defect in receptor activity and/or signal transduction. The objective of this review is to analyze the serotonin system in depression as it relates to the above two postulates.