Interviewees: Brian Large and Tricia Gooden, smokers;
Strength of Addiction
Tricia Gooden wants to quit smoking.
“I keep seeing all those commercials on TV about people who are like dying, who have holes in their throats,” says the 24-year old office manager who has smoked on and off for six years. But a previous effort to kick her nicotine addiction with patches failed.
“Once you start it’s really hard to stop,” she laments.
Nicotine addiction has even been compared to narcotics like heroin or morphine, also known as opiates. Neuroscientist Dan McGehee, of University of Chicago says the relapse rates are much higher for tobacco users than the users of other drugs, citing approximately 40 percent relapse on average for all drugs of abuse compared to 80 to 90 percent for tobacco.
“Many factors contribute to this difference, and one of these is the addictive effects of these drugs,” he says.
McGehee’s recent study gives more evidence that nicotine and heroin have similar effects in the brain. He measured these effects in individual rat brain cells in lab dishes using a sophisticated technique to record electrical activity. He also measured the release of the pleasure chemical dopamine.
Nicotine and opiates increase dopamine release in the pleasure center of the brain. This center is also involved in the addictive properties of both types of drugs. Dopamine is also released in large quantities in response to experiences such as sex and running.
McGehee and his team applied nicotine and a heroin-like substance called endomorphin to brain cells. Because the two drugs work in completely different ways, the researchers did not expect to find that the cells in a particular area, called the nucleus accumbens, responded in an identical way to both drugs.
“We were a little surprised to see an effect that was so similar between these two different classes of drugs,” says McGehee.
Dopamine-releasing brain cells release only small amounts of dopamine until they are prompted by a stimulus to release large bursts of dopamine. The researchers knew from prior studies that nicotine caused the low level release of dopamine to be suppressed. This results in hypersensitivity in that brain area to dopamine, which can greatly enhance feelings of reward. In this study the scientists found that in the presence of the heroin-like substance, the neurons responded in the same way.
“And so when the sensitivity of those cells is enhanced, we believe that’s going to contribute in a big way to reward and motivation. So people that are exposed to drugs will go out and seek them again because it’s something that makes them feel particularly good,” explains McGehee.
But McGehee points out that this study only looked at first time exposure to both drugs, not at addicted individuals. In the future he would like to study what happens to the brain after long-term exposure to nicotine and drugs like heroin. He hopes that further research will lead to treatments to help people beat addiction to many different types of drugs. In the meantime people like Gooden, who says she smokes to cope with stress, will have to keep trying to break the habit in other ways.
“I guess it’s a matter of focusing on other things or hobbies that I could do to get my mind off it whenever I am stressed,” says Gooden.
This research by Jonathan Britt and Daniel S. McGehee was published the February 13, 2008 issue of the Journal of Neuroscience, and was funded by the National Institutes of Health.
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