A woman walks along the boardwalk while leaving the U.S. Open tennis tournament in New York September 4, 2007. REUTERS/Lucas Jackson  Mark Bear and colleagues at the Massachusetts Institute of  Technology studied the effects of a chemical that suppresses  appetite by blocking cannabinoid receptors in the brain, the  same brain mechanisms that make people hungry when they smoke  marijuana. “I think that the cautionary note is that these mechanisms  play an important role in ... brain development,” said Bear,  whose study appears in the journal Neuron. Sanofi-Aventis’ weight-loss pill rimonabant, also known as  Zimulti and sold under the brand name Acomplia in Europe, is  the first in this new class of drugs. A U.S. expert panel  rejected it last June because of fears it might trigger  suicidal thoughts. Other drugmakers, including Merck & Co Inc, are working on  similar drugs. Bear’s team at MIT was hoping to gain insight into how the  brain adapts and rewires itself through learned experiences. This so-called plasticity is central to the development of  neurons in the brain of children and young animals. Bear said these cannabinoid receptors are known to regulate  signals between neurons, and his team wanted to see if they  would have an effect on plasticity in these young mice. They were specifically testing learning in the visual  cortex of the mouse, a part of the brain that processes  information gathered from what they see. Their experiments tested how well the animals adapted if  one eye was closed. The researchers did not use rimonabant in the study. Instead, they used a chemical analog or copy — in this case a  drug available for laboratory use known as AM 251. When they gave the mice AM 251 to block their cannabinoid  receptors, the animals still behaved as if both eyes were open. This suggested the visual cortex was not adapting as it should. “Our finding of a profound disruption of cortical  plasticity in juvenile mice treated with AM 251 suggests  caution is advised in the use of such compounds in children,”  the researchers wrote. Bear said the finding is similar to the situation with many  drugs. “You have to weigh the benefits against the risks. If the  benefit is related more to vanity than morbidity, I don’t think  the risks are tolerable,” he said. Sanofi-Aventis spokeswoman Julissa Viana said rimonabant is  not approved for use in children. “At this point in time it is approved for use in adults who  are overweight and obese with cardiovascular risk factors,” she  said. “We don’t encourage its use in children and it has not  been studied nor is it indicated for use in children.”   A woman walks along the boardwalk while leaving the U.S. Open tennis tournament in New York September 4, 2007. REUTERS/Lucas Jackson  The finding is the latest blow for rimonabant, which once  was predicted to be a multibillion-dollar seller. A study last month of the drug in obese heart patients  found more than 40 percent of patients who took the drug  developed psychiatric problems. But last month the drugmaker Sanofi said it still believes  Acomplia can be a winner and reiterated plans to submit the  drug worldwide as a treatment for type 2 diabetes in 2009.
Weight-loss drugs may harm developing brain: study.