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(December 8, 2003) - Drugs given to children to treat attention deficit hyperactivity disorder could have long-term effects on their growing brains, studies on rats suggest.
Several studies published on Monday show that rats given a popular ADHD drug were less likely to want to use cocaine later in life, but also often acted clinically depressed and behaved differently from rats give dummy injections.
While rats are different from humans, the studies suggest that doctors should watch children for long-term effects, too.
In the United States between 3 percent and 5 percent of children arediagnosed with attention deficit disorder, marked by reduced ability to concentrate, difficulty in organizing and impulsive behavior.
Patients are commonly prescribed stimulants but the practice is sometimes controversial.
William Carlezon of McLean Hospital and Harvard Medical School in Boston and colleagues raised two groups of rats. One was given Ritalin, known generically as methylphenidate, during the rat equivalent of pre-adolescence, while the other was given a salt water injection.
When they matured, the rats were tested for "learned helplessness" -- how quickly they gave up on behavioral tasks under stress.
"Rats exposed to Ritalin as juveniles showed large increases in learned-helplessness behavior during adulthood, suggesting a tendency toward depression," Carlezon said in a statement.
But rats, which generally like cocaine, were less likely to eat it if they had been give Ritalin.
Carlezon said he did not believe the effects were specific to Ritalin, made by Swiss drug giant Novartis. It could instead be a general effect of stimulant drugs, many of which act by increasing the activity of a key message-carrying chemical called dopamine.
Higher dopamine levels could affect the way brain cells cement their connections during development, Carlezon wrote in the Dec. 15 issue of the journal Biological Psychiatry.
A team at the University of Texas Southwestern Medical Center at Dallas found that adult rats were less responsive to rewarding stimuli and reacted more to stress if they had been given methylphenidate as youngsters.
A third study done by a team at Finch University of Health Sciences/The Chicago Medical School found changes in how dopamine neurons responded to methylphenidate.
"These three studies remind us how limited our knowledge is of the neurochemical and functional characteristics of the human brain during childhood and adolescence and on the effects of psychotropic drugs on brain development," Dr. Thomas Insel, Director of the National Institute of Mental Health, wrote in a commentary.
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