title: Tryptophan depletion and depressive vulnerability.
abstract: BACKGROUND
  Rapid and transient depletion of tryptophan (TRP) causes a brief depressive relapse in most patients successfully treated with and taking selective serotonin reuptake inhibitors, but little change in drug-free, symptomatic depressed patients. This study investigates the effects of TRP depletion in drug-free subjects in clinical remission from a prior major depressive episode (MDE).
  
  
  METHODS
  Twelve subjects with a prior MDE, currently in clinical remission and drug-free for at least 3 months (patients), and 12 healthy subjects without personal or family history of Axis I disorder (controls), received TRP depletion. The study was conducted in a double-blind, controlled [full (102-g) and quarter-strength (25 g) 15-amino acid drinks], crossover fashion. Behavioral ratings and plasma TRP levels were obtained prior to, during, and after testing.
  
  
  RESULTS
  All subjects experienced significant depletion of plasma TRP on both test-drinks, showing a significant dose-response relation. Healthy control subjects had minimal mood changes, but patients had a depressive response of greater magnitude.
  
  
  CONCLUSIONS
  In the context of prior TRP depletion studies with antidepressant-treated, and drug-free symptomatic depressed patients, these results suggest that depression may be caused not by an abnormality of 5-HT function, but by dysfunction of other systems or brain regions modulated by 5-HT.
authors.affiliation: Department of Psychiatry, College of Medicine, University of Arizona Health Science Center, Tucson 85724, USA.
authors.forename: F A
authors.initials: FA
authors.lastname: Moreno
authors.forename: A J
authors.initials: AJ
authors.lastname: Gelenberg
authors.forename: G R
authors.initials: GR
authors.lastname: Heninger
authors.forename: R L
authors.initials: RL
authors.lastname: Potter
authors.forename: K M
authors.initials: KM
authors.lastname: McKnight
authors.forename: J
authors.initials: J
authors.lastname: Allen
authors.forename: A P
authors.initials: AP
authors.lastname: Phillips
authors.forename: P L
authors.initials: PL
authors.lastname: Delgado
mesh_terms: D000328:Adult; D000368:Aged; D015415:Biomarkers; D018592:Cross-Over Studies; D003863:Depression / Q000097:blood*; D004311:Double-Blind Method; D005260:Female; D020022:Genetic Predisposition to Disease; D006801:Humans; D008297:Male; D019964:Mood Disorders / Q000097:blood; D011569:Psychiatric Status Rating Scales; D012008:Recurrence; D012701:Serotonin / Q000097:blood*; D012727:Sex Characteristics; D014364:Tryptophan / Q000172:deficiency*
chemical_list: D015415:Biomarkers; D012701:Serotonin; D014364:Tryptophan