Pot-Like Brain Compounds Affect Drinking Desires

By Merritt McKinney

SOURCE: Proceedings of the National Academy of Sciences 2003;10.1073/pnas.0336351100. Journal of Neurochemistry 2003;24.

NEW YORK (Reuters Health) - Molecules in the brain that are similar to the active ingredient in marijuana may be involved in controlling how much alcohol a person drinks, researchers report.

Mice that lacked the brain receptors for these molecules or that had been treated with a drug that blocked them were much less likely to drink than normal mice.

Besides providing more information on how the brain controls the desire to drink, the research suggests that blocking these receptors, known as CB1 receptors, may be a promising way to help people with drinking problems, according to Dr. George Kunos.

"The CB1-receptor-blocking drug used in the study may be effective in reducing the rewarding effects of drinking and thus the desire to drink in alcoholics and heavy drinkers," Kunos, who is at the National Institute on Alcohol Abuse and Alcoholism in Bethesda, Maryland, told Reuters Health.

Kunos said that the National Institutes of Health (news - web sites), in collaboration with the French pharmaceutical company Sanofi-Synthelabo, is in the process of setting up a clinical trial to study the effect of the CB1-blocking drug. Sanofi-Synthelabo makes the drug, which is known as Rimonabant.

Marijuana produces a high as chemicals in the drug latch on to receptors in the body, including CB1 receptors in the brain. In the early 1990s, scientists discovered that the body has molecules of its own that attach to these receptors. The molecules, known as endocannabinoids, seem to be involved in controlling several different processes in the body, including appetite and how much we eat.

Now, two sets of researchers report that endocannabinoids appear to be involved in controlling alcohol consumption, too. Kunos and his colleagues report their findings in the online edition of the journal Proceedings of the National Academy of Sciences (news - web sites). Another team, led by Dr. Basalingappa L. Hungund of the New York State Psychiatric Institute in Orangeburg, has a report on the CB1 receptor-alcohol relationship in the Journal of Neurochemistry.

The research provides "unequivocal evidence" that endocannabinoids and CB1 play a role in alcohol drinking, Kunos and his colleagues conclude.

Young mice that were genetically engineered to lack CB1 receptors were much less likely to drink than normal young mice. Similarly, the CB1-blocking drug reduced drinking in normal mice but not in animals without the receptors.

The other set of researchers found that the lack of CB1 receptors did more than only make mice drink less. The absence of the receptor kept mice from releasing the pleasure-related brain chemical dopamine after they drank alcohol.

In a related finding, Kunos and his colleagues observed that in older mice, CB1 signaling was diminished in the part of the brain that releases dopamine in response to alcohol consumption.

This could explain why mice's appetites for not only food but also alcohol declined with age, according to Kunos.