• V J Knott, A L Howson, M Perugini, A V Ravindran, and S N Young.
• Department of Psychiatry, University of Ottawa, Ontario, Canada.
• Biol. Psychiatry. 1999 Jul 15; 46 (2): 229-38.

BackgroundEfforts to model putative serotonergic deficits associated with affective disorders have frequently involved acute tryptophan depletion (ATD) as a manipulation strategy aimed at lowering brain serotonin synthesis. In an attempt to widen the scope of the measurement probes used in these investigations, the central actions of ATD and a subsequent dose of fenfluramine were examined via utilization of quantitative electroencephalography (EEG) and mood ratings.MethodsElectroencephalograms (EEG) and subjective mood ratings were assessed in 28 healthy men before and after double-blind ingestion of a tryptophan-depleting (T-) amino acid mixture, or a nutritionally balanced (B) amino acid mixture containing tryptophan, and again after a single-blind oral dose of D,L-fenfluramine hydrochloride (60 mg).ResultsCompared to the B mixture, the T- mixture reduced total plasma tryptophan by more than 75% 5 hours after ingestion. Tryptophan depletion was associated with a modest lowering of mood and a slowing of EEG as indicated by increases in delta amplitude. Fenfluramine caused no change in mood but increased fast wave (beta) activity in anterior recordings when administered after the T-, but not after the B mixture.ConclusionsQuantitative EEG measurements may be a promising method for studying the central mechanisms underlying serotonin-mediated changes in mood and behavior.

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