Posted by SLS on February 5, 2001, at 18:28:23
In reply to A summary of a study on obesity which may link..., posted by dj on February 5, 2001, at 13:21:01
On the same subject:
EMBARGOED FOR RELEASE: 1 FEBRUARY 2001 AT 18:30 ET US Brookhaven NationalScientists find link between dopamine and obesity
Upton, NY -- Dopamine, a brain chemical associated with addiction to
cocaine, alcohol, and other drugs, may also play an important role in
obesity. According to a study by scientists at the U.S. Department of
Energy's Brookhaven National Laboratory, obese people have fewer receptors
for dopamine, a neurotransmitter that helps produce feelings of
satisfaction and pleasure. The findings, which will appear in the February
3, 2001 issue of The Lancet, imply that obese people 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 at improving
dopamine function might be beneficial in the treatment of obese
individuals," says physician Gene-Jack Wang, the lead scientist on the
study.Brookhaven scientists have done extensive research showing that dopamine
plays an important role in drug addiction. Among other things, they've
found that addictive drugs increase the level of dopamine in the brain,
and that addicts have fewer dopamine receptors than normal subjects."Since eating, like the use of addictive drugs, is a highly reinforcing
behavior, inducing feelings of gratification and pleasure, we suspected
that obese people might have abnormalities in brain dopamine activity as
well," says psychiatrist Nora Volkow, who was also involved in the study.To test this hypothesis, the scientists measured the number of dopamine
receptors in the brains of ten severely obese individuals and ten normal
controls. Their method consisted of giving each volunteer subject an
injection containing a radiotracer, a radioactive chemical "tag" designed
to bind to dopamine receptors in the brain. Then, the researchers scanned
the subjects' brains using a positron emission tomography (PET ) camera.
The PET camera picks up the radioactive signal of the tracer and shows
where it is bound to dopamine receptors in the brain. The strength of the
signal indicates the number of receptors.Obese individuals, the scientists found, had fewer dopamine receptors than
normal-weight subjects. And within the obese group, the number of dopamine
receptors decreased as the subjects' body mass index, an indicator of
obesity, increased. That is, the more obese the individual, the lower the
number of receptors."It's possible that obese people have fewer dopamine receptors because
their brains are trying to compensate for having chronically high dopamine
levels, which are triggered by chronic overeating," says Wang. "However,
it's also possible that these people have low numbers of dopamine
receptors to begin with, making them more vulnerable to addictive
behaviors including compulsive food intake."The researchers note that, based on this study alone, they cannot conclude
whether the brain changes they've detected are a consequence or a cause of
obesity. They also acknowledge that the regulation of body weight is
extremely complex, involving many physiological mechanisms and
neurotransmitters. But they do suggest that addressing the dopamine
receptor deficiency or finding other ways to regulate dopamine in obese
people might help reduce their tendency to overeat.Unfortunately, many of the drugs that have been shown to alter dopamine
levels are highly addictive. But exercise, which has other obvious
benefits in weight control, is another way obese subjects might be able to
stimulate their dopamine pleasure and satisfaction circuits, the
researchers suggest. "In animal studies conducted elsewhere, exercise has
been found to increase dopamine release and to raise the number of
dopamine receptors," Volkow says. This suggests that obese people might be
able to boost their dopamine response through exercise instead of eating -
just one more reason to exercise if you're trying to lose weight.
poster:SLS
thread:4438
URL: http://www.dr-bob.org/babble/social/20010105/msgs/4443.html