Examining serotonin function: A modified technique for rapid tryptophan depletion

Lois E. Krahn, Peter Y. Lu, George Klee, Pedro R. Delgado, Slong Chi Lin, Ralf C. Zimmermann

Research output: Contribution to journalReview articlepeer-review

32 Scopus citations


Tryptophan (TRP) depletion was used to study serotonin because the ratio of TRP to large neutral amino acids (TRP/LNAA) determines the quantity of TRP that enters the brain. Because TRP is not universally available, a modified technique of TRP depletion was developed where a 1/4 strength preparation of an amino acid mixture (AAM) replaces TRP as the placebo. Seven healthy subjects could not differentiate between the preparations in this double-blind, placebo-controlled study. Urinary hydroxymelatonin sulfate (6-MS) was monitored as a biochemical marker of serotonin. The TRP/LNAA ratio (GG = 0.0001) and 6-MS secretion (GG = 0.024) were decreased, but placebo TRP levels (GG = 0.062) were not altered significantly. This modified technique facilitates the use of TRP depletion in clinical research.

Original languageEnglish (US)
Pages (from-to)325-328
Number of pages4
Issue number4
StatePublished - Oct 1996


  • Competing amino acids
  • Melatonin
  • Mood
  • Serotonin
  • Tryptophan

ASJC Scopus subject areas

  • Pharmacology
  • Psychiatry and Mental health


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