What makes alcohol so addictive

Drinking alcohol leads to the release of endorphins in areas of the brain that produce feelings of pleasure and reward, a new study has claimed.

The findings of the study led by researchers at the Ernest Gallo Clinic and Research Center at the University of California, San Francisco marks the first time that endorphin release in the nucleus accumbens and orbitofrontal cortex in response to alcohol consumption has been directly observed in humans.  Endorphins are small proteins with opiate-like effects that are produced naturally in the brain.

“This is something that we’ve speculated about for 30 years, based on animal studies, but haven’t observed in humans until now,” Jennifer Mitchell, the lead author, said.

“It provides the first direct evidence of how alcohol makes people feel good,” she said. According to Howard L. Fields, senior author of the study, the discovery of the precise locations in the brain where endorphins are released provides a possible target for the development of more effective drugs for the treatment of alcohol abuse.

For the study, the researchers used positron emission tomography, or PET imaging, to observe the immediate effects of alcohol in the brains of 13 heavy drinkers and 12 matched “control” subjects who were not heavy drinkers.

They found that in all of the subjects, alcohol intake led to a release of endorphins. And, in all of the subjects, the more endorphins released in the nucleus accumbens, the greater the feelings of pleasure reported by each drinker.

In addition, the more endorphins released in the orbitofrontal cortex, the greater the feelings of intoxication in the heavy drinkers, but not in the control subjects.

“This indicates that the brains of heavy or problem drinkers are changed in a way that makes them more likely to find alcohol pleasant, and may be a clue to how problem drinking develops in the first place,” Mitchell said.

“That greater feeling of reward might cause them to drink too much,” hse said.

Before drinking, the subjects were given injections of radioactively tagged carfentanil, an opiate-like drug that selectively binds to sites in the brain called opioid receptors, where endorphins also bind. As the radioactive carfentanil was bound and emitted radiation, the receptor sites “lit up” on PET imaging, allowing the researchers to map their exact locations.

The subjects were then each given a drink of alcohol, followed by a second injection of radioactive carfentanil, and scanned again with PET imaging. As the natural endorphins released by drinking were bound to the opioid receptor sites, they prevented the carfentanil from being bound.

By comparing areas of radioactivity in the first and second PET images, the researchers were able to map the exact locations, areas of lower radioactivity, where endorphins were released in response to drinking.

They found that endorphins released in response to drinking bind to a specific type of opioid receptor, the Mu receptor.