UPTON, NY -- Dopamine, a brain chemical associated with addiction to cocaine, alcohol, and other drugs, may also play an important role inobesity. According to a study by scientists at the U.S. Department ofEnergy's Brookhaven National Laboratory, obese people have fewerreceptors for dopamine, a neurotransmitter that helps producefeelings of satisfaction and pleasure. The findings, which willappear in the February 3, 2001 issue of The Lancet, imply that obesepeople may eat more to try to stimulate the dopamine "pleasure"circuits in their brains, just as addicts do by taking drugs. "The results from this study suggest that strategies aimed atimproving dopamine function might be beneficial in the treatment ofobese individuals," says physician Gene-Jack Wang, the lead scientiston the study.
Brookhaven scientists have done extensive research showing thatdopamine plays an important role in drug addiction. Among otherthings, theyΉve found that addictive drugs increase the level ofdopamine in the brain, and that addicts have fewer dopamine receptorsthan normal subjects.
"Since eating, like the use of addictive drugs, is a highlyreinforcing behavior, inducing feelings of gratification andpleasure, we suspected that obese people might have abnormalities inbrain dopamine activity as well," says psychiatrist Nora Volkow, whowas also involved in the study.
To test this hypothesis, the scientists measured the number ofdopamine receptors in the brains of ten severely obese individualsand ten normal controls. Their method consisted ofgiving each volunteer subject an injection containing a radiotracer,a radioactive chemical "tag" designed to bind to dopamine receptorsin the brain. Then, the researchers scanned the subjects' brainsusing a positron emission tomography (PET ) camera. The PET camerapicks up the radioactive signal of the tracer and shows where it isbound to dopamine receptors in the brain. The strength of the signalindicates the number of receptors.
Obese individuals, the scientists found, had fewer dopamine receptorsthan normal-weight subjects. And within the obese group, the numberof dopamine receptors decreased as the subjects' body mass index, anindicator of obesity, increased. That is, the more obese theindividual, the lower the number of receptors.
"It's possible that obese people have fewer dopamine receptorsbecause their brains are trying to compensate for having chronicallyhigh dopamine levels, which are triggered by chronic overeating,"says Wang. "However, it's also possible that these people have lownumbers of dopamine receptors to begin with, making them morevulnerable to addictive behaviors including compulsive food intake."
The researchers note that, based on this study alone, they cannotconclude whether the brain changes they've detected are a consequenceor a cause of obesity. They also acknowledge that the regulation ofbody weight is extremely complex, involving many physiologicalmechanisms and neurotransmitters. But they do suggest that addressingthe dopamine receptor deficiency or finding other ways to regulatedopamine in obese people might help reduce their tendency to overeat.
Unfortunately, many of the drugs that have been shown to alterdopamine levels are highly addictive. But exercise, which has otherobvious benefits in weight control, is another way obese subjectsmight be able to stimulate their dopamine pleasure and satisfactioncircuits, the researchers suggest. "In animal studies conductedelsewhere, exercise has been found to increase dopamine release andto raise the number of dopamine receptors," Volkow says. Thissuggests that obese people might be able to boost their dopamineresponse through exercise instead of eating - just one more reason toexercise if you're trying to lose weight.
This study was funded by the U.S. Department of Energy and the National Institute on Drug Abuse, part of the National Institutes of Health.
The U.S. Department of Energy's Brookhaven National Laboratorycreates and operates major facilities available to university,industrial and government personnel for basic and applied research inthe physical, biomedical and environmental sciences and in selectedenergy technologies. The Laboratory is operated by BrookhavenScience Associates, a not-for-profit research management company,under contract with the U.S. Department of Energy.
Note to local editors: Gene-Jack Wang lives in Port Jefferson andNora Volkow lives in Shoreham, both in New York.
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