ADHD drug 'harmonizes' with body's dopamine system, gives hint to effect on children, adults
Preliminary basic science study provides direct evidence of beneficial effect of methylphenidate, says report presented by German researchers at SNM's 53rd Annual Meeting June 37 in San DiegoSAN DIEGO, Calif.--The brain's dopamine system, which has long been associated with reward learning and reward-related behavior, works differently in treated and untreated attention deficit hyperactivity disorder (ADHD) individuals, according to a study presented by German researchers at SNM's 53rd Annual Meeting June 37 in San Diego.
"The significant difference we found between treated and untreated ADHD patients provides an important hint on the effect of the most commonly prescribed drug for this disease, which has long baffled and frustrated parents and physicians," noted Felix M Mottaghy, research fellow at University Ulm in Germany. Until this study, there has been no direct evidence pointing to the beneficial effect of methylphenidate (drugs like Ritalin) on the body's dopamine system, added the co-author of "Midbrain, Striatal and Amygdalar Dopaminergic Dysfunction in Attention Deficit Hyperactivity Disorder (ADHD)." For years, researchers have speculated that methylphenidate calms people with ADHD by amplifying the release of the neurotransmitter dopamine, improving attention and focus in those who have weak dopamine signals. "This is a very preliminary basic science study, initiated by Andrea G. Ludolph from the child and youth psychiatry department of the University Ulm; however, future studies of the dopamine system could aid differential diagnosis in hyperactive children," said Mottaghy.
The principal characteristics of ADHD are inattention, hyperactivity and impulsivity, and this condition can become apparent early in a child's life--sometimes as soon as preschool. Estimates indicate that there are as many as 2 million ADHD children (or 1 in every classroom of about 25 students) in the United States. With ADHD, there is an imbalance of several neurotransmitter systems, said Mottaghy. "The most affected seemed to be the dopaminergic system. Until now most studies focused on the so-called postsynaptic or receiving part of this system," he explained. "Our study shows that the beneficial effect of methylphenidate is received via 'normalization' of the dopamine system," he added. "We demonstrated that the brain's dopamine system--including midbrain, the striatum and the amygdala--is differentially modulated in treated and untreated ADHD patients with respect to healthy normal controls," noted Mottaghy. "Methylphenidate leads to a harmonization of the presynaptic dopaminergic neurons that could explain in part the beneficial effects of this central nervous system stimulant," he indicated.
The researchers used positron emission tomography (PET), a noninvasive brain scan, with 18F-DOPA, an imaging drug that is a precursor of dopamine. The University Ulm researchers also used statistic parametric mapping to obtain the statistical comparison of normalized and reoriented brain images, said Mottaghy. "It gives an impression of the distribution of differences within the brain comparing groups of patients or different conditions within one subject," he explained. Additional studies with more subjects need to be undertaken, said Mottaghy, including direct comparison of presynaptic and postsynaptic alterations in an age-matched patients group.
Abstract: F.M. Mottaghy, C. Glaser, B. Neumaier, S. Thees, A.K. Buck, B.J. Krause and S.N. Reske, all nuclear medicine, University Ulm, Ulm, Germany, and A.G. Ludolph, K. Schmeck and J.M. Fegert, child and youth psychiatry, University Ulm, Ulm, Germany, "Midbrain, Striatal and Amygdalar Dopaminergic Dysfunction in Attention Deficit Hyperactivity Disorder (ADHD)," SNM's 53rd Annual Meeting, June 37, 2006, Scientific Poster 1240.
SNM is holding its 53rd Annual Meeting June 37 at the San Diego Convention Center. Research topics for the 2006 meeting include molecular imaging in clinical practice in the fight against cancer; the role of diagnostic imaging in the management of metastatic bone disease, metabolic imaging for heart disease, neuroendocrine and brain imaging, new agents for imaging infection and inflammation, and an examination of dementia, neurodegeneration, movement disorders and thyroid cancer.
SNM is an international scientific and professional organization of more than 16,000 members dedicated to promoting the science, technology and practical applications of molecular and nuclear imaging to diagnose, manage and treat diseases in women, men and children. Founded more than 50 years ago, SNM continues to provide essential resources for health care practitioners and patients; publish the most prominent peer-reviewed journal in the field; host the premier annual meeting for medical imaging; sponsor research grants, fellowships and awards; and train physicians, technologists, scientists, physicists, chemists and radiopharmacists in state-of-the-art imaging procedures and advances. SNM members have introduced--and continue to explore--biological and technological innovations in medicine that noninvasively investigate the molecular basis of diseases, benefiting countless generations of patients. SNM is based in Reston, Va.; additional information can be found online at http://www.snm.org.
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