Low and moderate but not high doses of alcohol trigger 'feel good' brain chemicals called beta-endorphins shows a new study.
Beta-endorphin release produces a general feeling of well-being that reinforces the desire to drink.
Scientists know that alcohol affects the brain, but the specifics remain unclear. One possibility is that alcohol may increase or decrease the release and the synthesis of endogenous opioid peptides, endorphins, enkephalins and dynorphins, in distinct brain regions important for drug addiction.
For the first time, a rodent study has confirmed that low to moderate levels of alcohol alter beta-endorphin release in the midbrain/Ventral Tegmental Area (VTA) region, producing the pleasant effects that likely reinforce alcohol consumption.
"Some of the functions of opioid peptides are similar to those of the opiate morphine," said Christina Gianoulakis, a professor in the departments of psychiatry and physiology at McGill University, and the study's corresponding author.
"Like morphine, endogenous opioid peptides can induce analgesia and a mild euphoric effect, reduce anxiety, and may lead to a general feeling of well being.
"Therefore, increased release of endogenous opioid peptides in response to drinking could be partially responsible for the mild euphoric and anxiolytic effects associated with low to moderate amounts of alcoholic beverages," Gianoulakis added.
Researchers injected male Sprague-Dawley rats with either saline or alcohol. Using an in vivo microdialysis technique, study authors tracked the response of endorphins, enkephalins, and dynorphins at the level of the midbrain, including the VTA.
"We found that low to moderate but not high doses of alcohol increase the release of beta-endorphin in the VTA, one of the brain regions shown to be important for mediating the rewarding effect of alcohol," said Gianoulakis.
"This supports a role of beta-endorphin in mediating some of the rewarding effects of alcohol. However, the same doses of alcohol that increase beta-endorphin release in the VTA have no significant effect on the release of enkephalins and dynorphins, the other two families of endogenous opioid peptides we examined," Gianoulakis added.
Results will be published in the June issue of Alcoholism: Clinical and Experimental Research and are currently available at Early View.