Impulsiveness and the prolactin response to d-fenfluramine

Rationale: A number of studies have reported abnormalities of serotonin function in aggressive and impulsive behaviours in psychiatric and forensic populations. It is unknown whether this is because serotonin function plays a part in determining the dimension of trait impulsiveness in the general population or whether this is restricted to these behaviourally extreme groups. Method: The prolactin response to d-fenfluramine was measured in subjects scoring high and low on a scale of impulsiveness selected from a panel of healthy volunteers screened for impulsiveness. Measures included the I7 impulsiveness scale, State Trait Anger Expression Inventory (STAngXI) and the Tridimensional Personality Questionnaire (TPQ). Plasma cortisol was also determined along with fenfluramine and its metabolite norfenfluramine. Results: The high impulsive group had reduced AUC (PRL) compared with the low impulsive group; this remained significant after adjusting for baseline prolactin, cortisol and drug levels. There was no significant association between impulsiveness, the harm avoidance subscale of the TPQ or trait anger (STAngXI) and prolactin rise. Repeated serum prolactin measures were not significantly different between the two groups. Conclusions: This study provides some support to the hypothesis that reduced serotonin function contributes to high trait impulsiveness and is not restricted to behaviourally extreme populations.