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New theories emerge about predisposition for alcoholism: are dopamine receptors protective?

NEW ORLEANS -- Two new theories have emerged about how genetic predisposition for alcoholism works in the brain, on the basis of research presented at the annual meeting of the Society of Nuclear Medicine.

Lowered activity in the orbitofrontal cortex, which has been associated with alcoholism, may play a role in predisposing people at high risk of developing the addiction, said Dr. Nora D. Volkow, formerly of the Brookhaven National Laboratory, Upton, N.Y. In addition, increased availability of dopamine D2 receptors--implicated in the effects of alcohol--may have a protective effect against alcoholism in the same group of patients.

Eight high-risk patients--who each had an alcoholic biologic father and at least two other first--or second-degree relatives who were alcoholics--and eight low-risk patients were evaluated using positron emission tomography with (18)fluorodeoxyglucose (FDG) and (11)C raclopride.

Contrary to expectations, high-risk patients had higher levels of dopamine D2 receptors according to the raclopride scan data, particularly in the caudate and the putamen. Another surprise was that there was less evidence of glucose metabolism in the orbitofrontal cortex in the high-risk patients than in the low-risk patients, according to the FDG scans.

Interpreting those results led to the two new theories of the neurobiologic mechanisms involved in the genetic predisposition for alcoholism. Previous research has shown that increasing dopamine D2 receptors reduced alcohol intake in rats, noted Dr. Volkow, who is now director of the National Institute on Drug Abuse, Bethesda, Md. In addition, although the patients in this study were at a high risk for alcoholism, most were in their 20s and had no history of alcoholism. "Maybe these guys' dopamine D2 receptors have protected them from alcoholism."

The results in the orbitofrontal cortex were surprising because there are reductions in the activity in this region of the brain in alcoholics, and these have been interpreted as the effects of chronic drug administration. "Here we were faced with decreases in individuals who are not alcoholics that are similar to those that we have seen in alcoholics," Dr. Volkow said. The researchers speculate that this decreased activity is one of the factors that lead to vulnerability.
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Title Annotation:Addiction Psychiatry
Author:Wachter, Kerri
Publication:Clinical Psychiatry News
Date:Oct 1, 2003
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