Vol. 4, No. 4, 1998 Page 5

New study expands on findings about serotonin's
link to hostility, impulsivity

Studies link aggression, impulsiveness, antisocial behavior, depression, alcoholism, suicide, and even fire-setting to low levels of the neurotransmitter serotonin. Now a large-scale study indicates that even among mentally healthy individuals, reduced serotonin system responsiveness is linked to aggression and impulsivity.

Stephen Manuck and colleagues studied 119 men and women between the ages of 30 and 60, all participants in a study on cardiovascular risk factor modification. As part of this study, the subjects' serotonin function was measured using a test called a fenfluramine challenge. (The amount of increase in plasma prolactin when the drug fenfluramine is administered is one measure of the responsiveness of the serotonin system.)

In men, the researchers say, "heightened aggression and impulsivity were associated with low prolactin responses to fenfluramine (i.e., reduced serotonergic activity)." No correlations were seen in women until the data from post-menopausal women were analyzed separately. In this subgroup of women, in whom menstrual cycle variations could not influence findings, prolactin response correlated inversely with impulsiveness and directly with conscientiousness. In addition, post-menopausal women with low prolactin responses tended to show increased "attitudinal hostility." The researchers say this suggests that the hostility associated with reduced serotonin activity "may relate more to hostile attributions among women and to overt expressions of hostile intent in men."

These findings from a general-population sample are significant, Manuck et al. say, because they indicate that serotonin levels are associated with individual differences in aggression and impulsive behavior. Their data support earlier research by Terrie Moffit and colleagues (see related article, Crime Times, 1998, Vol. 4, No. 2, Page 1), who studied 781 young men and women selected from the general population, and found a strong relationship between altered serotonin functioning and violence in men.


"Aggression, impulsivity, and central nervous system serotonergic responsivity in a nonpatient sample," Stephen B. Manuck, Janine D. Flory, Jeanne M. McCaffery, Karen A. Matthews, J. John Mann, and Matthew F. Muldoon, Neuropsychopharmacology, Vol. 19, No. 4, 1998, pp. 287-299. Address: Stephen B. Manuck, Behavioral Physiology Laboratory, 506 EH, 4015 O'Hara Street, University of Pittsburgh, Pittsburgh, PA 15260.

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