A single dose of morphine blocks nerve-cell connections in the brain and causes a spike in dopamine levels, possibly raising the risk of addiction, according to Brown University researchers.

WebMD reported April 25 that researcher Julie Kauer, Ph.D.., and colleagues said that studies of lab rats found that one dose of morphine altered the ventral tegmental area (VTA) of the brain.

"It's as if a brake were removed," Kauer said. "The brain may, in fact, be learning to crave drugs."

On the other hand, she said, the study showed that the VTA nerve-cell connections that limit dopamine levels could be good targets for future anti-addiction therapies.

The study appears in the April 26, 2007 issue of the journal Nature.