Serotonin function and vulnerability to depression

Acute dietary depletion of tryptophan (ATD), an essential amino acid precursor to serotonin, has been used as a method to explore the role of serotonin in patients vulnerable to depression. ATD has been reported to lead to a depressive relapse in patients maintained on serotonin reuptake inhibitors, and to cause depressive symptoms in healthy subjects with a family history of depression. This study used ATD to explore the role of serotonin in subjects with a prior personal history of depression, in remission at the time of testing. 4 subjects with a history of major depression received ATD and control testing. All subjects had a Hamilton Depression Rating Scale (HDRS) score < 10 at the time of testing, and were not taking any psychotropic medications. ATD was accomplished by giving a low tryptophan diet for 24 hours, followed by a administration of a concentrated amino acid drink (100 am.) deficient in tryptophan. Control testing used an identical method, but with a 25% strength amino acid drink. Preliminary data are that one of the four patients experienced an exacerbation of depressive symptoms, measured by HDRS, during ATD but not control testing. A larger sample size will be presented at the meeting.