Researchers from the Wake Forest Baptist Medical Center are a step closer to completely understand what makes cocaine so addictive after uncovering clues in a study involving an animal model.

Published in the Journal of Neuroscience, the study showed one way cocaine users keep coming back to the drug. Earlier studies have established that cocaine has an effect on the dopamine system and dopamine transporters, that's why the current study was designed to focus on dopamine transporters, giving researchers an avenue to better understand how drug tolerance develops.

With an animal model, the researchers mimicked cocaine addiction in rats by allowing the subjects to consume as much cocaine as they wanted within six hours. Based on existing data, a six-hour period every day was enough to escalate intake and push animals into uncontrolled, binge-like behaviors.

Continuous access to cocaine was allowed for five days, then the rats were not allowed any of the drug for 14 or 60 days. After abstaining from cocaine, the animals had dopamine transporters that appeared normal, comparable to those who did not have one dose of the drug.

However, when just a single dose of cocaine was administered after 60 days of abstinence, the rats experienced tolerance levels for the effects of the drug as if they had been on a binge. When control animals that had never taken cocaine were given one dose of the drug, they did not manifest the same effect.

This told the researchers that cocaine leaves a lasting imprint on a user's dopamine system, which reactivates with renewed access to the drug. Possibly permanent, this "priming effect" may be what's contributing to persistent relapses in cocaine addicts.

The 60-day period of abstinence enforced on the rats is equivalent to about four human years. That many years may be enough to get someone on their feet, but just one dose of cocaine again can bring all recovery efforts down, increasing the likelihood of a binge.

"Currently, there isn't any effective treatment available for cocaine addiction so understanding the underlying mechanism is essential for targeting potential new treatments," said Sara R. Jones, Ph.D., the study's lead author.

However, several drugs that act like amphetamines are being tested in preclinical trials right now, so there is hope that more therapies against cocaine addiction are underway.

The study received funding support from the National Institutes of Health. Jones is joined by Steve C. Fordahl, Ph.D. and Cody A. Siciliano, Ph.D. as co-authors.

Photo: Valerie Everett | Flickr

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