20 July 2007
ADHD Drug Affects Developing Brain
by Kate Melville
Ritalin - used to treat attention deficit/hyperactivity disorder - may cause long-term changes in children's brains, suggests a new study from the Weill Cornell Medical College. While figures are vague, up to 18 percent of American children are thought to be affected by ADHD and Ritalin, a stimulant similar to amphetamine, is one of the most prescribed drugs for the disorder. Reported in the Journal of Neuroscience, the study suggest that doctors should exercise care in their diagnosis of ADHD before prescribing Ritalin.
"The changes we saw in the brains of treated rats occurred in areas strongly linked to higher executive functioning, addiction and appetite, social relationships and stress. These alterations gradually disappeared over time once the rats no longer received the drug," said the study's senior author Dr. Teresa Milner.
In the study, week-old male rat pups were given Ritalin twice a day during their more physically active nighttime phase. The rats continued receiving the drug intravenously up until they were 35 days old. "Relative to human lifespan, this would correspond to very early stages of brain development," explained co-researcher Jason Gray. "That's earlier than the age at which most children now receive Ritalin, although there are clinical studies underway that are testing the drug in 2- and 3-year olds."
The researchers then tracked changes in both the chemical neuroanatomy and structure of the treated rats' brains at postnatal day 35, which is roughly equivalent to the adolescent period. "These revealed Ritalin-associated changes in four main areas," Dr. Milner said. "First, we noticed alterations in brain chemicals such as catecholamines and norepinephrine in the rats' prefrontal cortex - a part of the mammalian brain responsible for higher executive thinking and decision-making. There were also significant changes in catecholamine function in the hippocampus, a center for memory and learning."
Alterations were also noted in the striatum - a brain region known to be key to motor function - and in the hypothalamus, a center for appetite, arousal and addictive behaviors.
Dr. Milner cautioned that it was too early to say whether the changes could be extrapolated to humans, or, if the changes might be harmful. "One thing to remember is that these young animals had normal, healthy brains," she said. "In ADHD-affected brains - where the neurochemistry is already somewhat awry or the brain might be developing too fast - these changes might help 'reset' that balance in a healthy way. On the other hand, in brains without ADHD, Ritalin might have a more negative effect. We just don't know yet."
The study also found that 3 months after the rats stopped receiving Ritalin, the animals' brain chemistry largely had resolved back to the pre-treatment state. "That's encouraging," noted Dr. Milner, adding that the team's concerns were more to do with long-term use. "It's unclear from this study whether Ritalin might leave more lasting changes, especially if treatment were to continue for years. In that case, it is possible that chronic use of the drug would alter brain chemistry and behavior well into adulthood," she concluded.
Source: Weill Cornell Medical College