TUESDAY, Sept. 8 (HealthDay News) -- Rewards-motivation deficits reported in people with attention-deficit/hyperactivity disorder (ADHD) may be associated with a disruption in the mesoaccumbens dopamine reward pathway evidenced by reduced dopamine synaptic markers seen in positron emission tomography (PET) imaging of the brain, according to a study in the Sept. 9 issue of the Journal of the American Medical Association.

Nora D. Volkow, M.D., of the National Institute on Drug Abuse in Bethesda, Md., and colleagues performed PET imaging on 53 subjects with ADHD who were not on medication, along with 44 healthy subjects, to study activity in the brain's mesoaccumbens dopamine reward pathway, which is believed to be involved in rewards-motivation behavior. Specific binding of positron emission tomographic radioligands for dopamine transporters (DAT) were measured using [¹¹C]cocaine and for D₂/D₃ receptors.

The researchers found lowered specific binding for both ligands in the left-side brain regions involved in the dopamine reward pathway in the subjects with ADHD. The mean for DAT in the nucleus accumbens was 0.63 for the ADHD subjects and 0.71 for controls, and in the midbrain was 0.09 for the ADHD subjects and 0.16 for controls. For the D₂/D₃ receptors, the median in the accumbens for the ADHD subjects was 2.68 and 2.85 for controls, and in the midbrain was 0.18 for the ADHD subjects and 0.28 for controls.

"In conclusion, these findings show a reduction in dopamine synaptic markers in the dopamine reward pathway midbrain and accumbens region of participants with ADHD that were associated with measures of attention," the authors write.

Several of the study authors reported receiving research support and consulting fees from pharmaceutical companies.

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