Differential behavioral effects of plasma tryptophan depletion and loadingin aggressive and nonaggressive men

Preliminary findings indicate that men with high trait hostility may be pro ne to aggression increases following plasma tryptophan (Trp) depletion. We measured laboratory aggression in men selected for presence (n = 12) or abs ence (n = 12) of aggressive histories. Testing occurred before and after pl asma Trp depletion, Trp loading, and under a food-restricted control condit ion. Subjects were provoked by subtractions of money, and aggression was me asured as the responses the subject made to ostensibly subtract money from the instigator of the subtractions. When subjects were highly provoked, the re was a significant Trp condition x aggression history interaction effect on aggressive responding. In particular, laboratory aggression in aggressiv e men was elevated under Trp-depleted conditions relative to Trp-loaded con ditions, whereas the opposite occurred in nonaggressive men. Moreover, plas ma total Trp levels after Trp loading were significantly higher in nonaggre ssive men, and plasma free (but not total) Trp levels after Trp loading cor related negatively with aggressive responses in the aggressive men may be m ore prone to aggression induced by reductions in plasma Trp. (C) 2000 Ameri can College of Neuropsychopharmacology. Published by Elsevier Science Inc.