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Nicotine Addiction Leads to Long-term Changes in Brain Chemistry


Scientists have suspected for years that nicotine is as addictive as cocaine and heroin. But they haven't known exactly why. Now researchers from the U.S. National Institute of Drug Abuse have identified chemical changes in the brains of smokers and found they're similar to the kinds of chemical changes seen in laboratory animals exposed to cocaine, heroin and other addictive drugs.

Roy Wise and his colleagues obtained tissue samples from a brain bank with complete health histories of people who agreed to donate their brains after death. They were able to compare the tissue of smokers and non-smokers.

They looked for the presence of certain chemicals called peptides. Wise explains that peptides are made by brain cells. "[They] serve as chemical messengers and serve as receptors for the communication between brain cells and for the sensitivity of brain cells to drugs."

Then the researchers compared the human brains to those of rats exposed to addictive drugs. Wise says they found that changes in brain peptides produced by smokers paralleled the changes in the brain chemistry of drug-addicted rats. "The changes that we found were changes that reflect alterations in the sensitivity of the brains cells to drugs, and alterations in the functioning of those cells so that the drugs were more effective that they'd otherwise be."

But what Wise says was disturbing was how persistent the changes in the smokers' brains were. "We're talking about smokers who in some cases hadn't smoked for perhaps years," he points out, "and so we were a little surprised to see that the changes lasted that long, that the brain hadn't fully recovered from the experience in the sense of going back to the way it was before the person started smoking."

Wise says these findings indicate that once a person becomes addicted to a drug, their brain structure actually changes. And they remain more vulnerable to the effects of that drug for many years, even after they stop taking it. Their results are published in The Journal of Neuroscience.

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