Study suggests why alcohol is addictive
By Liz Lockhart
The consumption of alcohol causes the release of endorphins in the brain that produce feelings of reward and 
pleasure, a new study suggests.
The study is led by researchers at the Ernest Gallo Clinic and Research Centre at the University of California (UCSF) and appears in the current edition of Science, Translational Medicine.
This study’s findings mark the first time that endorphin release in the nucleus accumbens and orbitofrontal cortex as a result of alcohol consumption has been observed in humans. Endorphins are opiate-like proteins which are naturally produced in the brain.
Lead author, Jennifer Mitchell Ph.D., said ‘This is something that we’ve speculated about for 30 years, based on animal studies, but haven’t observed in humans until now. It provides the first direct evidence of how alcohol makes people feel good.’
A possible target for the development of treatment of alcohol abuse could be the outcome of the discovery of the precise locations in the brain where the endorphins are released, said senior author Howard L. Fields MD, Ph.D.
In this study, the researchers utilised positron emission tomography (PET) imaging to observe the immediate effects that alcohol has on the brain. Thirteen heavy drinkers and 12 people who were not heavy drinkers were used as ‘control’ subjects for the study.
All of the participants were found to release endorphins when consuming alcohol. They all reported greater feelings of pleasure as more endorphins were released in the nucleus accumbens. The more endorphins released in the orbitofrontal cortex, the greater the feeling of intoxication was experienced in the heavy drinking participants only.
Mitchell said ‘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. That greater feeling of reward might cause them to drink too much.’
All the participants were given injections of an opiate-like drug called carfentanil which selectively binds to sites in the brain called opioid receptors, where endorphins also bind. This was done before drinking any alcohol. As this injected drug bound and emitted radiation, the receptor sites ‘lit up’ on the PET imaging, thus allowing the researchers to pinpoint their locations.
Each participant was then given an alcoholic drink followed by a second injection of carfentanil. They were then scanned again using the PET imaging method. The carfentanil was prevented from being bound as the natural endorphins were released by drinking as these were bound to the opioid receptor sites.
The comparison of radioactivity in the two PET images enabled the researchers to map the exact locations where endorphins were released as a response to drinking alcohol.
The researchers now hope that it will now be possible to improve the efficacy of treatment for alcohol abuse through the design of better medications.
