Research ArticleAlcohol

Alcohol Consumption Induces Endogenous Opioid Release in the Human Orbitofrontal Cortex and Nucleus Accumbens

Science Translational Medicine  11 Jan 2012:
Vol. 4, Issue 116, pp. 116ra6
DOI: 10.1126/scitranslmed.3002902

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Alcohol, Legal Drug of Choice

The brain is agnostic to the law and responds similarly to legal and illegal drugs of abuse. Like cocaine and amphetamine, alcohol causes release of endogenous opioids (the small peptides endorphins, enkephalins, and dynorphins) in the so-called reward centers of the brain. To start to understand what might cause some people to drink more than others, Mitchell et al. measured the endogenous opioids released by one drink in groups of light and heavy drinkers. The single drink was able to release more opioid in the reward centers of the heavy drinkers, suggesting that individual differences in this region might contribute to excessive drinking.

The authors determined the release of transmitters deep within the brain indirectly by monitoring displacement of a radioactive μ opioid receptor agonist by PET scanning. The more opioid that was released, the lower the radioactive signal, as it was diluted in the area of the receptor. Alcohol triggered release in two brain areas, the orbitofrontal cortex and the nucleus accumbens, both of which have been implicated in registering reward stimuli in rodents and humans. In addition to being larger in the heavy drinkers, the amount of ligand released in the orbitofrontal cortex was correlated with the subjects’ feelings of being intoxicated. From this relationship, the authors concluded that these endogenous opioids are closely tied to the effects of alcohol that could lead to abuse. People with orbitofrontal cortices or nucleus accumbens that are particularly responsive to alcohol—releasing large amounts of opioids—may get more pleasure out of each drink, possibly leading to more frequent consumption of this legal drug of abuse.