Some Brains May Be Predisposed to Substance Abuse

Less dopamine encourages impulsivity and addiction, rat study suggests.

By E.J. Mundell
HealthDay Reporter
Thursday, March 1, 2007; 12:00 AM

Copyright © 2007 ScoutNews, LLC. All rights reserved.

THURSDAY, March 1 (HealthDay News) -- Do the brain changes noted in drug addicts help cause their addiction, or are they the result of drug abuse?

A new study might solve that chicken-and-egg puzzle -- pointing to new ways of preventing and treating addiction, researchers say.

The rat study suggests that "some individuals may be predisposed to the effects of cocaine on the brain," making them more likely to try the drug and become addicts, said lead researcher Dr. Jeffrey Dalley, of Cambridge University's Behavioural and Clinical Neuroscience Institute in the United Kingdom.

Specifically, rats that went on to compulsively self-administer cocaine intravenously were more likely to have fewer brain cell-surface receptors for the neurotransmitter dopamine in an area of the brain called the nucleus accumbens, compared to rodents that were less prone to addiction.

"The study is the first to conclusively demonstrate that changes in dopamine receptors in the nucleus accumbens pre-date cocaine use," Dalley said. That means that these brain changes are not caused by cocaine exposure but may encourage use of the drug.

The findings are published in the March 2 issue of Science.

Understanding the neurological changes that help trigger and sustain addiction is key to developing effective prevention and treatment. Numerous studies have noted a myriad of differences in the brain of drug addicts versus healthy individuals, but "it's been basically impossible to know which ones were there before they started to take the drug and which were a consequence of the exposure to the drug," said Dr. Nora Volkow, director of the U.S. National Institute on Drug Abuse.

One brain change noted in many addicts -- a paucity of dopamine receptors on cells in the nucleus accumbens -- has been especially intriguing.

"The nucleus accumbens forms part of the basal ganglia, a series of interconnected brain structures involved in movement and motivated behavior," Dalley explained. "The nucleus accumbens is considered by many to be the interface of motivation and behavior. It has been extensively implicated in drug reward/addiction."