PET reveals increased dopamine levels in ADHD patients

June 23, 2003

An estimated 5% of elementary school-aged children have been diagnosed with Attention Deficit Hyperactivity Disorder (ADHD), a common behavioral disorder that can adversely affect performance in school and emotional development, continuing into adulthood. Using evaluation techniques such as PET, scientists are striving to understand how to most effectively treat ADHD.

One therapeutic approach to treating ADHD is the use of methylphenidate (MP). ADHD has been linked to low levels of the neurotransmitter dopamine (DA) and MP blocks the dopamine transporters that are the primary mechanism for the removal of extracellular dopamine.

Nora D. Volkow, MD and colleagues from the Medical and Chemistry Departments at Brookhaven National Laboratory, the Psychiatry Department of the State University of New York, Stony Brook, and the Department of Pediatrics at the University of California, Irvine, conducted a study using PET technology to gauge extracellular dopamine levels induced by MP in relation to different stimuli. The research involved 14 normal individuals ranging from 26 to 44 years old. PET scans were performed on the patients using the radiopharmaceutical [11C]raclopride. The study compared changes in extracellular DA after the use of either MP or a placebo in response to both a behaviorally salient stimulus (math problems displayed on cards with monetary reward) and a neutral stimulus (pictures of scenery with no monetary reward).

The results, presented at the Society of Nuclear Medicine's 50th Annual Meeting, demonstrated that neither MP coupled with the neutral stimulus nor the placebo combined with the behavioral stimulus led to increased levels of extracellular dopamine. Only the combination of MP and the behavioral stimulus resulted in more extracellular dopamine. Moreover, the increases in DA were associated with increases of perception of the behavioral task as interesting and motivating.

Volkow and her colleagues believe this result "suggests that MP's therapeutic effects may be secondary to its ability to enhance the ability of environmental stimuli to increase DA, thus making them more interesting, exciting, and motivating to the subject." They also believe the findings, "support the development of educational strategies that make schoolwork more interesting as non-pharmacological interventions to treat ADHD."
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Society of Nuclear Medicine

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