Lack of seasonal rhythms in central serotonergic function in boys with ADHD.

This study examined seasonal variations in central 5-HT function in a relatively large sample of prepubertal boys with attention-deficit/hyperactivity disorder (ADHD). In addition, seasonal differences in central 5-HT function among aggressive and non-aggressive children in the sample were explored. Ninety-three boys with ADHD were divided into aggressive (n=54) and nonaggressive (n=39) groups based on parental responses to interviews and ratings of behavior. Central 5-HT function was assessed by measuring the prolactin response to a single 1 mg/kg oral dose of d,l-fenfluramine. The prolactin values were derived from different children over the course of eight years, but were collapsed across years and analyzed in terms of day of the year. Cosinor analysis revealed no annual, bi-annual, 3-monthly, 2-monthly, monthly, or bi-monthly rhythms in the prolactin response in the entire sample of boys with ADHD. Moreover, there was no evidence of seasonal differences in the prolactin response between the aggressive and non-aggressive subgroups. These results indicate that seasonality-related variance is not a threat to the validity of the neurochemical procedure and does not account for the inconsistencies in the studies of central 5-HT and aggression in children with ADHD.