The work, conducted in rats, strongly suggests that the same thing occurs in humans, the scientists say. It offers what could be important new clues in the fight against alcohol and drug addiction.
A report on the findings appears as a rapid communication in the newest issue of the Journal of Neuroscience.
Authors of the paper include Drs. M. Foster Olive of the University of California at San Francisco and Clyde W. Hodge of the University of North Carolina at Chapel Hill.
"This is the first demonstration that drugs of abuse increase beta endorphin levels in a key part of the brain that influences addiction," said senior author Hodge, associate professor of psychiatry at the UNC School of Medicine. "The name of this important forebrain region is the nucleus accumbens. We and others had suspected this response, but it had never been proven until now because methods were not available to test it.
"In this latest work, Dr. Olive adapted a technique for quantifying endorphins and used it to measure how one of the brains natural painkillers responds to addicting drugs."
For at least four decades, biomedical researchers have known based on animal studies that certain regions of the brain, when stimulated, produced pleasurable effects, said Hodge, also a member of UNCs Bowles Center for Alcohol Studies. Those "rewards" promote substance use initially, and eventually, habitual users find it hard to function without them.
About 15 or so years ago, scientists discovered that in those brain regions drugs of abuse caused an elevation in the neurotransmitter compound dopamine, he said. Such knowledge helps them pin down how abused substances affect humans and narrows the sea
Contact: David Williamson
University of North Carolina at Chapel Hill