Age-related changes in the association between serotonergic function and aggression in boys with ADHD.

The results of several studies have indicated an inverse relationship between central serotonergic (5-HT) mechanisms and aggression in animals and adults, but studies in children have yielded conflicting results. This study assessed 5-HT function, using a fenfluramine (FEN) challenge procedure, in an attempt to replicate a previously reported enhancement of the prolactin (PRL) response to FEN in aggressive relative to nonaggressive ADHD boys. The study failed to replicate the previous finding. Samples from both studies were then examined to reconcile the discrepant findings. The samples differed significantly in age. The entire group (n = 50) was then divided into older and younger subgroups and reanalyzed using a two-way (age-group x aggression) analysis of covariance (ANCOVA) controlling for plasma medication level. The ANCOVA generated a significant age-group x aggression interaction. Young aggressive boys had a significantly greater PRL response to FEN than young nonaggressive boys, but no such difference existed in the older age-group. These findings raise the possibility of different developmental trajectories in 5-HT function between aggressive and nonaggressive boys.