Effects of a novel method of acute tryptophan depletion on plasma tryptophan and cognitive performance in healthy volunteers.
BACKGROUND
Disorders associated with low levels of serotonin (5-HT) are characterized by mood and cognitive disturbances. Acute tryptophan depletion (ATD) is an established method for lowering 5-HT levels and an important tool to study the effects of reduced 5-HT on mood and cognition in human subjects. The traditional ATD method, i.e., administration of separate amino acids (AAs), has several disadvantages. The AA mixture is costly, unpalatable and associated with gastrointestinal discomfort.


OBJECTIVE
The University of Maastricht developed a new and inexpensive method for ATD: a natural collagen protein (CP) mixture with low tryptophan (TRP) content. The reductions in plasma TRP after taking this CP mixture were compared with the reductions achieved taking the traditional AA mixture, and effects on memory and reversal learning were studied.


METHODS
Fifteen healthy young volunteers participated in a double-blind, counterbalanced within-subject study. Reversal learning, verbal memory and pattern recognition were assessed at baseline and 3-4 h after taking the CP mixture.


RESULTS
The new ATD method significantly reduced plasma TRP by 74% and the ratio between TRP and the other large AAs (TRP/LNAA) by 82%. The placebo mixture did not change these measures. Delayed recognition reaction time on the verbal learning task was increased following ATD. No other cognitive effects were found.


CONCLUSIONS
The CP mixture was shown to be an efficient tool for lowering plasma TRP in humans. The validity of this method with regard to behavioral changes remains to be established in healthy, vulnerable and clinical populations.
Evers
E A T
EA
Department of Psychiatry and Neuropsychology (DRT10), Brain and Behavior Institute, Maastricht University, P.O. Box 616, Maastricht, 6200, The Netherlands. l.evers@np.unimaas.nl
Tillie
D E
DE
van der Veen
F M
FM
Lieben
C K
CK
Jolles
J
J
Deutz
N E P
NE
Schmitt
J A J
JA
D000328:Adult; D000339:Affect / Q000187:drug effects; D000596:Amino Acids / Q000097:blood; D003071:Cognition / Q000187:drug effects*; D018592:Cross-Over Studies; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D008297:Male; D008568:Memory / Q000187:drug effects; D010364:Pattern Recognition, Visual / Q000187:drug effects; D010455:Peptides / Q000378:metabolism / Q000494:pharmacology; D011930:Reaction Time; D012193:Reversal Learning / Q000187:drug effects; D014364:Tryptophan / Q000097:blood* / Q000172:deficiency*
D000596:Amino Acids; D010455:Peptides; D014364:Tryptophan