Attention deficit hyperactivity disorder (ADHD) affects up to 10% of school-aged children and half as many adults. The core features of impulsivity, hyperactivity, and inattentiveness commonly give rise to academic underachievement, poor social relationships, and increased risk for mood and anxiety disorders. Although the relevant neurobiological mechanisms remain poorly understood, altered mesocorticolimbic dopamine (DA) transmission has been proposed. The aim of the present study was to compare striatal DA function in treatment-naive adults with ADHD vs. age- and IQ-matched controls. Two PET/[11C]raclopride scans, one with placebo and one with d-amphetamine (d-AMP; 0.3 mg/kg, p.o.), were administered to five men with ADHD and five healthy male volunteers. The ADHD group differed from controls in demonstrating significant d-AMP-induced reductions in posterior caudate (p<0.05). These results may support a proposed model of reduced DA tone leading to increased phasic signaling in ADHD.

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