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Vulnerability to alcoholism linked to the brain’s reward system

(McGill Tribune)While long-term alcohol use has been known to have various effects on the brain, including memory impairment and nerve damage, a more recent study suggests there might be another effect to add to that long list. Those who are vulnerable to alcoholism also experience a larger dopamine (reward system) response when consuming a large drink, as found in a study conducted by Marco Leyton, a researcher at the Mental Illness and Addiction axis at the Research Institute of the McGill University Health Centre (RI-MUHC).

“Dopamine is a chemical made in the brain. When released in the part of the brain called the striatum, it activates a circuit that fosters interest in natural rewards,” explained Leyton. “We need a system like this to survive both as individuals and as a species. Dopamine activation stimulates our interest in food, the opportunity to have sex, and plays an important role in motivation.”

According to Leyton, a sip of alcohol activates the brain’s dopamine system in two ways. Alcohol acts pharmacologically in the dopamine cell-body region, where it removes the inhibitory input on the cells— similar to releasing a brake— causing an influx of dopamine. Once people have some experience with alcohol, environmental cues associated with drinking can also fire-up the dopamine system, suggesting that this system has conditioning effects. “Some people might be especially sensitive to developing these [conditioned] effects,” added Leyton.

For the study, researchers recruited 26 social drinkers aged 18 to 30 in the Montreal area. The subjects at higher risk of alcoholism were then identified based on personality traits and having a lower intoxication response to alcohol—they did not feel as drunk, despite drinking the same amount as the other subjects.

Each participant then underwent two positron emission tomography (PET) brain scan exams after drinking a fairly large serving of either juice or alcohol (about three to four drinks in 15 minutes).

“The PET scans are to compare the brain scan signals obtained when people drink juice versus alcohol,” Leyton explained. The difference between the two scans is the change in dopamine release.”

The analysis indicated that people categorized as “high-risk” for alcohol-use problems experienced a large dopamine response after drinking the alcoholic beverage; this effect did not occur in the people categorized as “low-risk” for alcohol-use problems. Since dopamine triggers the brain’s reward system, subjects who experienced a higher release were positively reinforced for drinking and therefore were at a higher risk for alcoholism. These findings were subsequently published this January in the journal Alcoholism: Clinical & Experimental Research.

“Still, there are a number of issues that need following up,” said Leyton. He explained that, since this study is the first report of an altered dopamine response to alcohol consumption in people at risk, the study will need to be replicated.

“While both of these are well-established indices, it will be important to learn whether the brain dopamine response also predicts which individuals will go on to develop an alcohol-use disorder,” Leyton explained.

He believes it is likely that many pathways in the brain lead to alcoholism and looks to further investigate whether this dopamine response to alcohol contributes to one specific pathway or many.

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