Contact: Kara Villamil, or Mona S. Rowe
Brain scan image associated with this release
UPTON, NY - In a discovery that strikes at the very heart of cocaine addiction, scientists from the U.S. Department of Energy's Brookhaven National Laboratory may have found a clue to why addicts crave the drug so strongly and use it repeatedly.
Their study, published in this month's issue of The American Journal of Psychiatry, describes signs of damage to the very chemical pathways that send signals between the cells in cocaine addicts' brains.
"While we do not yet know if this is damage caused by the cocaine use or is already present in the addicts' brain chemistry, this is an important step in understanding why people use cocaine repeatedly, feeding an addiction that is destructive both physically and socially," said team leader and BNL Medical Department chair Nora Volkow.
Volkow and her colleagues found the signs of brain-chemistry damage using a brain-scanning technique known as positron emission tomography, or PET. They scanned the brains of 27 volunteers - 13 cocaine addicts and 14 non-drug users - twice, then looked for differences.
The first scan was performed after the volunteers were given a placebo, the second after they had been given the drug lorazepam, known commercially as Ativan and used to treat anxiety.
"We used lorazepam because it stimulates the same chemical pathways that transfer signals between brain cells when a person uses cocaine," Volkow explained. "These pathways let our brains receive the message sent by the neurotransmitter chemical dopamine - the message that tells us that what we're doing is pleasurable and we should do it again."
Volkow and others have shown that cocaine and other drugs affect the brain's dopamine system, causing the "pleasure message" to be repeated and reinforcing the desire to take the drug.
The PET scans showed drastic differences between lorazepam's effect on cocaine addicts' brains and the effects in the comparison volunteers. The difference, said Volkow, indicates that addicts are more sensitive to lorazepam because of damage to a crucial chemical pathway called GABA. As the brain's main inhibitory neurotransmitter, GABA tells neurons to stop firing.
Cocaine addicts' abnormal response to lorazepam, which stimulates GABA pathways, may also explain their increased propensity to seizures and the sleep abnormalities seen in such subjects.
Said Secretary of Energy Federico Peña, "Dr. Volkow and BNL have made important contributions to our understanding of addiction, which can have lasting impacts on how our society copes with this public health problem. I congratulate her team for this progress." The research was sponsored by DOE's Office of Energy Research and the National Institute on Drug Abuse.
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Side-by-side comparison of two PET
scans from two subjects. The top two scans show
a non-drug user's brain before and after taking a dose of lorazepam; the bottom two are
from a cocaine addict. Note the difference in activity between the two scans in the
right-hand column; these differences indicate an altered response to stimulation of the
GABA pathways that transmit dopamine "pleasure signals" in the brain.