Effects of oral 5-hydroxytryptophan on a standardized planning task: insight into possible dopamine/serotonin interactions in the forebrain

Objective Several studies have suggested that exogenous administration of the serotonin precursor 5-hydroxytryptophan (5-HTP) can result in the ectopic production of serotonin in dopaminergic neurons and a concomitant reduction in dopamine release. This study tested this hypothesis using the Tower of London (TOL), a test of planning and executive control that is sensitive to changes in forebrain dopamine activity, but insensitive to alterations in serotonin. Methods A sample of 68 undergraduates participated, and each received either three 50-mg 5-HTP capsules or placebos, and completed the TOL following a set absorption period. Results 5-HTP significantly lengthened the average time needed to complete each of the 10 trials of the TOL. 5-HTP did not affect accuracy on this task. Conclusions Oral exogenous 5-HTP disrupts dopaminergic function in the human forebrain. Copyright (c) 2013 John Wiley & Sons, Ltd.