Craving Boosts Dopamine Levels in Brain’s Habit Centers; Cocaine Addiction May Hijack Mechanism Evolved for Food
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CRAVING BOOSTS DOPAMINE LEVELS IN BRAIN’S HABIT CENTERS; COCAINE ADDICTION MAY HIJACK MECHANISM EVOLVED FOR FOOD
WASHINGTON, DC June 15, 2006 - The mere sight of a person taking drugs can knock an addict off the path to recovery. Now, scientists have revealed how such visual cues act in the brain to spur an addict's often uncontrollable desire for more.
The findings, published in the June 14 issue of The Journal of Neuroscience, show that craving inspired by drug cues, even in the absence of the drug itself, causes a rise in levels of dopamine in the dorsal striatum -- an area of the brain associated with forming habits and initiating action. Dopamine is a key neurotransmitter, a chemical that relays information from one neuron to another, and acts in the brain's reward system.
"The study helps explain why addicts repeatedly relapse, sometimes after years of abstinence, and why treatment is so difficult," says Charles O'Brien, MD, PhD, of the University of Pennsylvania, who has studied craving for 35 years.
In the study, first author Nora Volkow, MD, director of the National Institute on Drug Abuse, and colleagues from Brookhaven National Laboratory and the University of Pennsylvania School of Medicine used positron emission tomography (PET) to scan the brains of 18 people addicted to cocaine. They measured changes in dopamine levels while the subjects of the study were watching a video simulating cocaine use and a video of nature scenes.
Besides pinpointing where the neurotransmitter was released, the team showed a correlation between the degree of addiction and the rise in dopamine: The more severe a subject's addiction, the higher dopamine levels rose in the brain, and the stronger the craving was felt.
Such increases, the study's authors noted, could be a target for addiction treatment. O'Brien likens the rising neurotransmitter levels to "a priming dose of a drug that makes the addict want it more."
Based on their own previous research showing dopamine increases in food-deprived subjects shown food, the authors speculate that addiction results when basic mechanisms that evolved to ensure survival are turned to another purpose. "The similarity in the neurochemical responses to food cues in food-deprived subjects and cocaine-cues in the addicted subjects suggests that drugs may hijack the neurocircuitry that underlies the motivation to procure food," Volkow says.
The Journal of Neuroscience is published by the Society for Neuroscience, an organization of more than 37,500 basic scientists and clinicians who study the brain and nervous system. Volkow can be reached at nvolkow@nida.nih.gov.
