Nicotine linked to pleasurable feelings

By ADAM NAGOURNEY
Why is it so hard to quit smoking cigarettes? One reason may be that nicotine acts on the same brain system in humans as heroin and morphine, a new study has found.

Earlier studies in animals had found that that nicotine could set off the release of brain chemicals called opioids, which play a role in suppressing pain and causing pleasurable feelings. The new study is the first to establish that the same process occurs in people, the researchers said.

To prove that opioids were involved, the researchers first had to figure out a way to use positron emission tomography or PET scanners to measure opioid brain activity. They also had to persuade officials at the University of Michigan to waive the no-smoking rules and allow their volunteers to smoke in the hospital's scanner. (They solved the problem by figuring out a way to vent the smoke outside.)

The study, led by David J. Scott, a graduate student, found that smokers appeared to have an increased flow of opioids in the brain all the time. After they smoked a cigarette, there was even more opioid activity in the parts of the brain involved in emotion and desire. The findings were presented recently at a meeting of the Society for Neuroscience.

Scott said that he had expected to confirm the nicotine-opioid link, but that it was more pronounced that he had thought. He also said there was no question that the nicotine was responsible, since the volunteers were given both regular cigarettes and nicotine-free ones.

"What we're seeing is purely the pharmacological action of the nicotine," he said.

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