In the current study, first author Vijay A. Ramchandani, Ph.D., an investigator in NIAAA's Laboratory of Clinical and Translational Studies, Dr. Heilig, and their colleagues explored whether the 118G mu-opioid receptor variant influences dopamine release from a forebrain region called the ventral striatum in response to alcohol.
Using human positron emission tomography (PET), an imaging technique that allowed the researchers to analyze dopamine activity in the brain, they compared dopamine release in two groups of people that had been given a dose of alcohol. The groups consisted of those who carried a copy of the gene for the 118G mu-opioid receptor variant, and those who carried only genes for the more common 118A variant. They found that only people with the 118G variant had a dopamine response to alcohol no such response happened in subjects with the 118A receptor variant.
In a separate experiment, they inserted genes for the human 118G or 118A mu-opioid receptor variants into mice and then directly measured the animals' dopamine response to a dose of alcohol. Mice with the 118G variant showed a fourfold higher peak dopamine response to the alcohol challenge compared to mice with the 118A variant.
"Taken together, our data strongly support a causal role of the 118G variant of the mu-opioid receptor to confer a more vigorous dopamine response to alcohol in the ventral striatum," says Dr. Ramchandani. "The findings add further support to the notion that individuals who possess this receptor variant may experience enhanced pleasurable effects from alcohol that could increase their risk for developing alcohol abuse and dependence. It may also explain why these individuals, once addicted, benefit more from treatment with blockers of endogenous opioids."
|Contact: John Bowersox|
NIH/National Institute on Alcohol Abuse and Alcoholism