In vivo neuroreceptor Imaging in attention-deficit/hyperactivity disorder: A focus on the dopamine transporter

There is converging evidence of the role of catecholamine dysregulation in the underlying pathophysiology of attention-deficit/ hyperactivity disorder (ADHD). The dopamine tansporter (DAT) is known to be a key regulator of dopamine, and recent genetic, treatment. and imaging stadies have highlighted the role of DAT in ADHD. There is an emerging literature on in vivo neuroreceptor, imaging of DAT in ADHD and control subjects reported by a number of groups internationally. A comprehensive review of existing imaging studies of DAT binding in ADHD shows that six of eight independent studies by six diffierent groups have reported increased DAT binding in (mostly) treatment-naive children and adults with ADHD. Althogh there is fair agreement regarding the presence and direction of abnorma DAT binding, there remains disagreement as to The magnitude of the finding and the importance of many potentially confounding variables, including clinical charcteristics and imaging methodologies, Three studies by three different groups have reported decreased DAT binding after methylphenidate treatment, Interpretation of the latter finding awaits clarificalion of the issue of timing of drug administration and imaging to disentangle receptor occupancy from downregulation.