ADHD and the dopamine reward pathway

This paper published not long ago in the Journal of the American Medical Association provides more evidence for the association of deficiencies of dopamine function with ADHD. The authors first note:

"Attention-deficit/hyperactivity disorder (ADHD)—characterized by symptoms of inattention and hyperactivity-impulsivity—is the most prevalent childhood psychiatric disorder that frequently persists into adulthood, and there is increasing evidence of reward-motivation deficits in this disorder."

The authors used positron emission tomography (PET) to image the brain dopamine reward pathway. Specifically they measured dopamine synaptic markers (transporters and receptors). What did their data show?

"A reduction in dopamine synaptic markers associated with symptoms of inattention was shown in the dopamine reward pathway of participants with ADHD."

This has great practical significance when we consider that physiological precursor therapy naturally and without side-effects provides the resources for the body to increase its own dopamine levels and up-regulate the reward pathways.