January 15, 1999 -- Much concern has been raised over prescribing Ritalin® or other stimulants to control hyperactivity disorders in children. Relatively little is known about the long-term effects of these stimulants or how they alter brain chemistry.

Now researchers at the Howard Hughes Medical Institute at Duke University have discovered that Ritalin® and other stimulants exert their paradoxical calming effects by boosting serotonin levels in the brain. Elevating serotonin appears to restore the delicate balance between the brain chemicals dopamine and serotonin and calms hyperactivity, says HHMI investigator http://www.hhmi.org/science/cellbio/caron.htm at Duke University Medical Center. Caron is an author of the study published in the January 15, 1999, issue of the journal Science.

Attention deficit hyperactivity disorder (ADHD) affects three to six percent of school-aged children. Symptoms include restlessness, impulsiveness, and difficulty concentrating. Stimulants commonly used to treat ADHD are so effective that "researchers haven't really taken the time to investigate how they work," says Caron.

Previous dogma, says Caron, held that the calming action of Ritalin® works through the neurotransmitter dopamine. Specifically, researchers believed that Ritalin® and other stimulants interact with the dopamine transporter protein (DAT), a housekeeper of sorts for nerve pathways. After a nerve impulse moves from one neuron to another, DAT removes residual dopamine from the synaptic cleft-the space between two neurons-and repackages it for future use.

Caron's team suspected that dopamine wasn't the only key to understanding ADHD, so they turned to mice in which they had "knocked out" the gene that codes for DAT. Since there is no DAT to "mop up" dopamine from the synaptic cleft, the brains of the mice are flooded with dopamine. The excess dopamine cau
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Contact: Jim Keeley
keeleyj@hhmi.org
301-215-8858
Howard Hughes Medical Institute
14-Jan-1999