What has serotonin to do with depression?

The “serotonin hypothesis” of clinical depression is almost 50 years old. At its simplest, the hypothesis proposes that diminished activity of serotonin pathways plays a causal role in the pathophysiology of depression. This notion was based on the depressogenic effects of amine depleting agents such as reserpine, as well as the actions of antidepressant drugs such as monoamine oxidase inhibitors and tricyclic antidepressants, discovered by...