title: Effects of selective and combined serotonin and dopamine depletion on the loudness dependence of the auditory evoked potential (LDAEP) in humans.
abstract: BACKGROUND
  The loudness dependence of the auditory evoked potential (LDAEP) has been suggested as a possible in vivo measure of central serotonin function. However, more recent studies suggest that the LDAEP may be modulated by multiple neuromodulatory systems in addition to the serotonergic system. Accordingly we further examined the effects of selective serotonin, dopamine and simultaneous serotonin and dopamine depletion on the LDAEP in healthy subjects.
  
  
  METHODS
  The study employed a placebo-controlled, double-blind, cross over design. Fourteen subjects were tested under four acute treatment conditions: placebo (balanced amino acid drink), tryptophan (serotonin) depletion (ATD), tyrosine/phenylalanine (dopamine) depletion (ATPD) and combined tryptophan/tyrosine/phenylalanine (serotonin and dopamine) depletion (CMD). Testing was conducted 5.5 h post-depletion and changes in the amplitude of the N1/P2 at varying intensities (60, 70, 80, 90, 100 dB) were examined at C(Z).
  
  
  RESULTS
  Greater than 80% plasma precursor depletion was achieved across all conditions. Despite significant depletion of monoamine precursors, ATD, (p = 0.318), ATPD (p = 0.061) and CMD (p = 0.104) had no effects on the LDAEP (60-100 dB).
  
  
  CONCLUSIONS
  Acute serotonin and dopamine depletion did not modulate the LDAEP. This finding adds support to growing evidence that the LDAEP is insensitive to acute changes in serotonin and dopamine neurotransmission.
authors.affiliation: Biological Psychiatry Research Unit, Brain Sciences Institute, Swinburne University of Technology, Melbourne, Australia. boneill@groupwise.swin.edu.au
authors.forename: Barry V
authors.initials: BV
authors.lastname: O'Neill
authors.forename: Valérie
authors.initials: V
authors.lastname: Guille
authors.forename: Rodney J
authors.initials: RJ
authors.lastname: Croft
authors.forename: Sumie
authors.initials: S
authors.lastname: Leung
authors.forename: Kirsty E
authors.initials: KE
authors.lastname: Scholes
authors.forename: K Luan
authors.initials: KL
authors.lastname: Phan
authors.forename: Pradeep J
authors.initials: PJ
authors.lastname: Nathan
mesh_terms: D000161:Acoustic Stimulation; D000328:Adult; D018592:Cross-Over Studies; D004298:Dopamine / Q000172:deficiency*; D004311:Double-Blind Method; D004569:Electroencephalography; D004576:Electromyography; D005072:Evoked Potentials, Auditory; D006801:Humans; D008144:Loudness Perception / Q000502:physiology*; D008297:Male; D010649:Phenylalanine / Q000097:blood / Q000172:deficiency; D012701:Serotonin / Q000172:deficiency*; D014364:Tryptophan / Q000097:blood / Q000172:deficiency; D014443:Tyrosine / Q000097:blood / Q000172:deficiency
chemical_list: D012701:Serotonin; D014443:Tyrosine; D010649:Phenylalanine; D014364:Tryptophan; D004298:Dopamine