ADHD Associated With Depressed Dopamine Activity In The Brain

A report in the ScienceDaily suggests that dopamine dysfunction may be involved with attention-deficit/hyperactivity disorder (ADHD) symptoms and may contribute to substance abuse that often occurs simultaneously. Adults with (ADHD) show a blunted response to the drug methylphenidate, which increases brain dopamine levels, according to a report in the August issue of Archives of General Psychiatry, one of the JAMA/Archives journals.

Nora D. Volkow, M.D., of the National Institute on Drug Abuse, Bethesda, Md., and colleagues studied 19 adults with ADHD (average age 32) who had never received medication and 24 healthy controls (average age 30). Brain scans were performed using positron emission tomography (PET) and a drug known as raclopride labeled with carbon 11 ([11C]raclopride), which binds with dopamine receptors. Scans were performed twice, after injections of placebo and of methylphenidate.

The participants unknown of which drug they had received, were asked to report the severity of their ADHD symptoms, whether they could detect the drug, if they liked or disliked it, and if it made them feel "high," tired, alert, anxious or restless.

In individuals with ADHD, methylphenidate caused less of a decrease in the amount of [11C]raclopride that bound to dopamine receptors in areas of the brain associated with attention than it did in those without ADHD. Since levels of methylphenidate in the blood were the same in both groups, this suggests that those with ADHD released less dopamine in response to the drug than controls. This blunted response was associated with symptoms of inattention.

The findings of reduced dopamine release in subjects with ADHD are consistent with the notion that the ability of stimulant medications to enhance extracellular dopamine underlies their therapeutic effects in ADHD. Individuals with ADHD also reported liking methylphenidate more than individuals without ADHD.

The reinforcing responses to methylphenidate were negatively correlated with the dopamine increases, suggesting that decreased dopaminergic activity may also be involved in modulating the magnitude of the reinforcing effects of methylphenidate. This suggests that dopamine dysfunction is involved with symptoms of inattention but may also contribute to substance abuse comorbidity in ADHD."

Source: http://www.sciencedaily.com/releases/2007/08/070806164505.htm

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