Methylphenidate (Ritalin) elevates norepinephrine levels in the brains of rats to help focus attention while suppressing nerve signal transmissions in the sensory pathways to make it easier to block out extraneous stimuli, a Philadelphia research team has found.
Their report in the Journal of Neurophysiology helps explain how a stimulant aids people with attention deficit and hyperactivity disorders to improve their focus without increasing their motor activity. Methylphenidate, prescribed under the brand name Ritalin, has been used for more than 20 years, mostly in children, to treat attention deficit hyperactivity disorder (ADHD) and attention deficit disorder (ADD). The drug can also help people who dont suffer either disorder to attend better to a cognitive task.
Despite its wide use, little is known about how the drug, a chemical cousin of amphetamines, produces its therapeutic effects. Researchers want to unlock the mystery of why the drug has the paradoxical effect of decreasing hyperactive behavior and increasing the ability to focus, even though it is a stimulant, said Barry Waterhouse, the studys senior author.
In addition, the researchers found that the higher dose caused the rats to increase motor activity, while the lower dose did not.
Scientists still have much to learn about methylphenidate, which has an impact on neural circuits throughout the entire brain, not just the sensory pathway studied in this paper, Waterhouse noted. The changes that occur in this sensory pathway may affect other areas of the brain and changes in other areas of the brain may affect this pathway. In addition to sensory pathways, other scientists are studying how the drug affects cognitive and emotional areas of brain.
"This experiment adds to our knowledge of what the drug is doing at the cellular level and gives us a springboard to other studies," Waterhouse said. "One question now is, how does the individuals perception of what is an important stimulus factor into the equation?"
Researchers in this area keep in touch and share their results, Waterhouse said. One group, for example, is looking at the drugs effects on dopamine and norepinephrine in the prefrontal cortex, he noted. These results will eventually have to be combined, as changes in one area of the brain are likely to affect other areas.
"Weve been thinking about this for a long time," Waterhouse said of his research. "We hope to have a good idea of the drugs action when we put it all together."
One broad question that intrigues researchers is whether ADHD traces back to the same area of the brain as attention deficit disorder, a similar condition but one in which hyperactivity isnt a symptom.
They also want to know whether Ritalin has any toxic or long-lasting effects, not only for ADHD patients, but also for individuals taking the drug who do not suffer from ADHD or ADD. Methylphenidate use is on the rise among college students who solicit prescriptions from friends or siblings diagnosed with ADHD and use the drug to postpone fatigue and stay alert and focused while studying for exams or completing projects, Waterhouse said.
Christine Guilfoy | EurekAlert!
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