Why Is alcohol addictive? Study offers clues

We know alcohol makes many people feel good, and that it affects the brain, but new research goes a step further by tightening the focus on areas of the brain most likely affected by alcohol.

The new brain imaging research may lead to a better understanding of alcohol addiction and possibly better treatments for people who abuse alcohol and other drugs.

Investigators say they have identified specific differences in how the so-called reward center of the brain responds to alcohol in heavy and light drinkers.

In both groups, drinking alcohol caused the release of naturally occurring feel-good opioids known as endorphins in two key brain regions associated with reward processing.

But heavy drinkers released more endorphins in response to alcohol, and they reported feeling more intoxicated than the lighter drinkers after drinking the same amount of alcohol.

The findings suggest that people whose brains release more natural opioids in response to alcohol may get more pleasure out of drinking and may be more likely to drink too much and become alcoholics, researcher Jennifer M. Mitchell, PhD, of the University of California, San Francisco, says.

"Greater endorphin release was associated with more hazardous drinking," Mitchell says. "We believe this is an important step in understanding where and how alcohol acts in the brain."

Alcoholism and the Brain

Mitchell says the findings could lead to better versions of the existing alcohol abuse drug naltrexone, which blocks the opioid response and blunts alcohol cravings in some, but not all people.

Mitchell says a better understanding of the specific endorphin receptors involved in the alcohol "high" could lead to treatments that better target these reward centers. Currently, naltrexone takes more of a buckshot approach, affecting multiple receptors. This research could lead to more focused medications.

The University of California study included 13 people who identified themselves as heavy drinkers and 12 people who did not.

Using PET imaging, the researchers were able to measure opioid release in the brain before and immediately after the study participants drank the same amount of alcohol.

Drinking alcohol was found to be associated with opioid release in the nucleus accumbens and orbitofrontal cortex -- two areas of the brain associated with reward processing.

The study appears in the Jan. 11 issue of the journal Science Translational Medicine.

Alcoholism 'Many Diseases'

Although the nucleus accumbens has been previously associated with opioid regulation and reward processing, the involvement of the orbitofrontal cortex was unexpected, Mitchell and colleagues write.

Raymond F. Anton, MD, who directs the Center for Drug and Alcohol Programs at the Medical University of South Carolina, says it is likely that there are other, as-yet-unidentified regions of the brain associated with addiction.

"It is also likely that alcohol dependence is not one disease, but many, with many systems involved," he says. "People drink for different reasons, so a treatment that works for one person may not work for another."

Anton is conducting genetic research in hopes of discovering why naltrexone blunts alcohol cravings in some people but not others.

"We may be able to say in a few years if genetic predisposition can predict who will and will not respond to this drug," Anton says.