The following news release is being issued today by the U.S.
Department of Energy's Brookhaven National Laboratory. The release and
accompanying images may also be viewed online at:
http://www.bnl.gov/bnlweb/pubaf/pr/PR_display.asp?prID=07-97
*********
NEWS RELEASE
Number: 07-97
For release on Thursday, October 25, 2007
Food Restriction Increases Dopamine Receptor Levels in Obese Rats
Evidence for interplay of brain's "reward" chemical with availability
of food in obesity
UPTON, NY -- A brain-imaging study of genetically obese rats conducted
at the U.S. Department of Energy's Brookhaven National Laboratory
provides more evidence that dopamine - a brain chemical associated
with reward, pleasure, movement, and motivation - plays a role in
obesity. The scientists found that genetically obese rats had lower
levels of dopamine D2 receptors than lean rats. They also demonstrated
that restricting food intake can increase the number of D2 receptors,
partially attenuating a normal decline associated with aging.
"This research corroborates brain-imaging studies conducted at
Brookhaven that found decreased levels of dopamine D2 receptors in
obese people compared with normal-weight people," said Brookhaven
neuroscientist Panayotis (Peter) Thanos, lead author of the current
study, which will be published in the journal Synapse and is now
available online.
It's not clear whether reduced receptor levels are a cause or
consequence of obesity: Overeating may chronically reduce receptor
levels, which, over the long term, could eventually contribute to
obesity. But having genetically low receptor levels may also lead to
obesity by predisposing the individual to overeating in an attempt to
stimulate a "blunted" reward system. Either way, revving up receptor
levels by restricting food intake could enhance the impact of this
common strategy for combating obesity.
"Consuming fewer calories is obviously important for people trying to
lose weight, plus improving the brain's ability to respond to rewards
other than food may help prevent overeating," Thanos said. Because
food intake can have such a dramatic effect on dopamine receptor
levels, "this study also provides further evidence for the interplay
of genetic factors with the environment in the development of obesity
in our society," he said.
The finding that food restriction can attenuate the effects of aging
on the brain's ability to respond to dopamine may also help explain
why food restriction slows down other changes associated with aging,
such as declines in locomotor activity and sensitivity to reward.
Study methods and main findings
The researchers measured dopamine D2 receptor levels in adolescent and
young adult genetically obese Zucker rats and lean rats. Between
measures, half of the rats in each group were given free access to
food while the other half were given 70 percent of the daily average
amount of food eaten by the unrestricted group.
The scientists measured D2 receptor levels using two different
techniques: micro-positron emission tomography (microPET) in living
animals, which uses a radioactively tagged molecule that competes with
the brain's natural dopamine for D2 receptor binding sites, and
autoradiography, which uses a tracer that binds more strongly than
natural dopamine but can only be used in tissue samples rather than in
living animals. Together these two methods indicate the absolute
number of D2 receptors found in the brain and how many are available
or free during day-to-day function, which might be relevant to further
elucidating the role of dopamine in obesity.
One main finding was that the overall number of D2 receptors was lower
in obese than in lean rats. Also D2 receptor levels decreased with
age, but this decline was significantly blunted in food-restricted
rats compared with those given free access to food. This attenuation
was most apparent in the obese rats.
Another main finding was that D2 receptor availability - that is, the
number of receptors available for binding dopamine - was greater at
adulthood in the obese rats compared to the lean rats. This suggests
that perhaps the release of dopamine had significantly decreased with
age in the obese unrestricted animals more than in the restricted ones
or the lean rats. The possibility of lower release of dopamine in
obese subjects is presently being examined, the researchers say.
This research was funded by the Office of Biological and Environmental
Research within the U.S. Department of Energy's Office of Science and
by the Intramural Research Program of the National Institute on
Alcohol Abuse and Alcoholism, which is part of the National Institutes
of Health.
For more information about Peter Thanos's research, see http://www.bnl.gov/thanoslab.
One of ten national laboratories overseen and primarily funded by the
Office of Science of the U.S. Department of Energy (DOE), Brookhaven
National Laboratory conducts research in the physical, biomedical, and
environmental sciences, as well as in energy technologies and national
security. Brookhaven Lab also builds and operates major scientific
facilities available to university, industry and government
researchers. Brookhaven is operated and managed for DOE's Office of
Science by Brookhaven Science Associates, a limited-liability company
founded by the Research Foundation of State University of New York on
behalf of Stony Brook University, the largest academic user of
Laboratory facilities, and Battelle, a nonprofit, applied science and
technology organization.
Visit Brookhaven Lab's electronic newsroom for links, news archives,
graphics, and more: http://www.bnl.gov/newsroom
--
Sheldon