Researchers at the U.S. Department of Energy's Brookhaven National Laboratory have shown that increasing the brain level of receptors for dopamine, a pleasure-related chemical, can reduce use of cocaine by 75 percent in rats trained to self-administer it.
Earlier research by this team had similar findings for alcohol intake. Treatments that increase levels of these chemicals - dopamine D2 receptors -- may prove useful in treating addiction, according to the authors. The study will be published online April 16 and will appear in the July 2008 issue of Synapse.
"By increasing dopamine D2 receptor levels, we saw a dramatic drop in these rats' interest in cocaine," said lead author Panayotis (Peter) Thanos, a neuroscientist with Brookhaven Lab and the National Institute on Alcohol Abuse and Alcoholism (NIAAA) Laboratory of Neuroimaging. "This provides new evidence that low levels of dopamine D2 receptors may play an important role in not just alcoholism but in cocaine abuse as well. It also shows a potential direction for addiction therapies."
The D2 receptor receives signals in the brain triggered by dopamine, a neurotransmitter needed to experience feelings of pleasure and reward. Without receptors for dopamine, these signals get "jammed" and the pleasure response is blunted. Previous studies at Brookhaven Lab have shown that chronic abuse of alcohol and other addictive drugs increases the brain's production of dopamine. Over time, however, these drugs deplete the brain's D2 receptors and rewire the brain so that normal pleasurable activities that stimulate these pathways no longer do - leaving the addictive drug as the only way to achieve this stimulation.
The current study suggests that cocaine-dependent individuals may have their need for cocaine decreased if their D2 levels are boosted. Thanos' lab previously demonstrated dramatic reductions in alcohol use in alcohol-preferring rats infused with dopamine D2 receptors (see: http://www.bnl.gov/discover/Winter_06/alcohol_1.asp). Thanos hypothesized that the same would hold true with other addictive drugs.
The researchers tested this hypothesis by injecting a virus that had been rendered harmless and altered to carry the D2 receptor gene directly into the brains of experimental rats that were trained to self-administer cocaine -- the same technique used in the earlier alcohol study. The virus acted as a mechanism to deliver the gene to the nucleus accumbens, the brain's pleasure center, enabling the cells in this brain region to make receptor proteins themselves.
The scientists examined how the injected genes affected the rats' cocaine-using behavior after they had been taking cocaine for two weeks. After receiving the D2 receptor treatment, the rats showed a 75 percent decrease in self-administration of the drug. This effect lasted six days before their cocaine self-administration returned to previous levels.
"This adds another piece to the puzzle of the complex role of dopamine D2 receptors in addiction," said Thanos.
This research was funded by The National Institute on Alcohol Abuse and Alcoholism Intramural Research Program at the National Institutes of Health and by the Office of Biological and Environmental Research within the U.S. Department of Energy's (DOE) Office of Science. DOE has a long-standing interest in research on brain chemistry gained through brain-imaging studies. Brain-imaging techniques such as positron emission tomography (PET) and magnetic resonance imaging (MRI) are a direct outgrowth of DOE's support of basic physics and chemistry research.
All research involving laboratory animals at Brookhaven National Laboratory is conducted under the jurisdiction of the Lab's Institutional Animal Care and Use Committee in compliance with the Public Heath Service (PHS) Policy on Humane Care and Use of Laboratory Animals, the U.S. Department of Agriculture's Animal Welfare Act, and the National Academy of Sciences' Guide for the Care and Use of Laboratory Animals. This research has enhanced understanding of a wide array of human medical conditions including cancer, drug addiction, Alzheimer's and Parkinson's diseases, and normal aging and has led to the development of several promising treatment strategies.
For further information on Peter Thanos' lab and research visit http://www.bnl.gov/thanoslab. For more on Brookhaven National Laboratory's addiction research go to http://www.bnl.gov/CTN/addiction.asp.
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.
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