Scientists have found that a single use of cocaine can modify neural connections in the brain, and this may help explain at the cellular level how occasional drug use can progress into a compulsion.

The researchers from the University of California in San Francisco report in the May 31 issue of "Nature" that a single injection of cocaine induced a long-lasting (between 5 and 10 days) increase in excitatory synaptic transmission in the ventral tegmental area of the brain in rats and mice. The increase in synaptic currents that were activated by cocaine had many similarities to the changes in neural activity involved in learning and memory processes in many areas of the brain.

"These findings on the impact of cocaine on the memory and learning circuits of the brain may help explain the switch from occasional drug use to addiction. This study emphasizes the dangers of even experimenting with cocaine and other illicit drugs," says Alan I. Leshner, Ph.D., Director of the National Institute on Drug Abuse (NIDA).

"The significance of this finding," says lead investigator Dr. Antonello Bonci, "is that the single dose of cocaine 'usurped' a cellular mechanism involved in a normally adaptive learning process, which may help to explain cocaine's ability to take control of incentive-motivational systems in the brain and produce compulsive drug-seeking behavior."

In addition, the researchers said that the changes that were observed in the brains of the rats and mice may be important not just for the early stages of addiction, but also may help explain the neural basis for relapse, where a single exposure to cocaine after a period of abstinence can induce renewed drug-seeking behavior.