title: Intensity dependence of auditory evoked potentials (AEPs) as biological marker for cerebral serotonin levels: effects of tryptophan depletion in healthy subjects.
abstract: BACKGROUND
  The intensity dependence of the auditory evoked potentials (AEP) has been suggested to be a specific biological marker of central serotonergic activity.
  
  
  OBJECTIVE
  While previous studies used circumstantial evidence to support this hypothesis, we manipulated (decreased) cerebral levels of serotonin directly by using tryptophan depletion.
  
  
  METHODS
  Twelve healthy young subjects were investigated using placebo and two different amino acid mixtures in a double blind cross over design on three different occasions. AEPs recorded during tryptophan depletion were analyzed by dipole analysis and regional sources using methods published in the literature.
  
  
  RESULTS
  For none of the mixtures a significant effect of tryptophan depletion was found. There was a trend towards reduced intensity dependency after tryptophan depletion, especially in the right hemisphere. This reduction correlated with the amount of reduced tryptophan in plasma.
  
  
  CONCLUSIONS
  The results indicate, in contrast to earlier indirect studies, that the intensity dependence of AEPs is not a specific marker of central serotonergic activity.
authors.affiliation: Division of Clinical Neurophysiology, University of Frankfurt, Frankfurt, Germany. dierks@puk.unibe.ch
authors.forename: T
authors.initials: T
authors.lastname: Dierks
authors.forename: S
authors.initials: S
authors.lastname: Barta
authors.forename: L
authors.initials: L
authors.lastname: Demisch
authors.forename: K
authors.initials: K
authors.lastname: Schmeck
authors.forename: E
authors.initials: E
authors.lastname: Englert
authors.forename: A
authors.initials: A
authors.lastname: Kewitz
authors.forename: K
authors.initials: K
authors.lastname: Maurer
authors.forename: F
authors.initials: F
authors.lastname: Poustka
mesh_terms: D000328:Adult; D015415:Biomarkers; D001923:Brain Chemistry; D018592:Cross-Over Studies; D004311:Double-Blind Method; D005072:Evoked Potentials, Auditory; D005260:Female; D006801:Humans; D008297:Male; D012701:Serotonin / Q000032:analysis*; D014364:Tryptophan / Q000032:analysis* / Q000097:blood
chemical_list: D015415:Biomarkers; D012701:Serotonin; D014364:Tryptophan