Rodent of the Week: Why cocaine becomes addictive

A clue to explain how cocaine becomes addictive has emerged and may lead to new ways to treat the addiction.

Research funded by the National Institute on Drug Abuse shows that an epigenetic mechanism in the brain helps explain cocaine's addictiveness. Epigenetics is a hot, new branch of science that focuses on changes to gene expression even though a gene's sequence remains unchanged. Epigenetic changes are thought to be largely triggered by environmental factors, such as diet, substance abuse and toxic exposures.

In a study using mice, researchers led by Dr. Eric J. Nestler of Mount Sinai School of Medicine gave one group of mice repeated doses of cocaine and another group repeated doses of saline with a final dose of cocaine to determine how the effects of repeated cocaine exposure differ from one-time exposure. They found that one mechanism by which cocaine alters the pleasure circuits in the brain is by repressing an enzyme called G9A that plays an important role in epigenetic control of gene expression. When the researchers reversed the cocaine-induce repression of G9A, they found they could block changes in gene expression and prevent the preference for cocaine.

"This fundamental discovery advances our understanding of how cocaine addiction works," Dr. Nora D. Volkow, director of the National Institute on Drug Abuse, said in a news release. "Although more research will be required, these findings have identified a key new player in the molecular cascade triggered by repeated cocaine exposure, and thus a potential novel target for the development of addiction medications."

The study was published this month in the journal Science.

-- Shari Roan

Photo credit: Advanced Cell Technology Inc.