Dopamine-serotonin interactions in attentiondeficit hyperactivity disorder

Poor control of attention-related and motor processes, often associated with behavioral or cognitive impulsivity, are typical features of numbers of children and adults with attention-deficit hyperactivity disorder (ADHD). Until recently clinicians have seen little need to improve on or add to the catecholaminergic model for explaining the features of ADHD. Recent genetic and neuroimaging studies however provide evidence for separate contributions of altered dopamine (DA) and serotonin (5-HT) function in this disorder. Genetic studies imply that for both DA and 5-HT systems variants may frequently occur in ADHD for neurotransmitter uptake, synthesis and breakdown functions. The separate distributions in the brain of mesolimbic DA transporter and mesocortical DA D4 binding sites, both strongly implicated in ADHD, draws attention to potentially differential contributions from the 5-HT system. However, the evidence here points less towards an anatomical differentiation, as towards one in terms inhibitory/facilitatory pre/postsynaptic location of receptors in the 5-HT1 and 5-HT2 families. While the monoamine metabolite levels excreted in ADHD are often correlated, this may well flow from a starting point where 5-HT activity is anomalously higher or lower than the generally lower than normal levels for DA. It appear