Effect of tryptophan depletion on impulsive behavior in men with or without a family history of alcoholism.

This study investigated the effects of acute serotonin depletion on two measures of impulsive behavior in healthy men with a family history of alcoholism. Serotonin has been implicated in several forms of impulsive behavior, as well as in the etiology of Type II alcoholism. The present study was designed to determine if an acute disturbance of serotonin function would increase impulsive responding on two behavioral indices of impulsivity, and whether this effect would be greater in individuals with a genetic predisposition to alcoholism. Forty healthy men, half of whom had an alcoholic father, participated in a two-session study. Subjects ingested a tryptophan-depleting diet on one session and a balanced diet on the other session, and completed tasks measuring behavioral inhibition and delay discounting. Tryptophan depletion impaired performance on the behavioral inhibition task in the males with a positive family history, relative to the males without alcoholic relatives, whereas it improved behavioral inhibition in the family history negative group. Tryptophan depletion had negligible effects on mood, and it did not alter performance on the delay discounting task. The results provide partial support for the hypothesis that impulsive behavior is related to low serotonin function, and further suggests that the role of serotonin depends on genetic factors related to alcoholism. The results complement the results of a parallel study investigating the effects of serotonin depletion on a similar behavioral inhibition procedure in rats. Parallel studies in rats and humans are important to validate the large body of neurobiological research with non-human species to humans.