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THURSDAY, Aug. 24 (HealthScout) -- The nicotine in a single cigarette seems to be enough to start a smoker down the road to addiction, brain scientists say.
That amount of nicotine causes the same changes in the brain's pleasure center as heroin, cocaine and other addictive drugs, Huibert Mansvelder and Daniel McGehee of the University of Chicago report in the journal Neuron.
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Exactly how nicotine does that is different from that of other addictive drugs, says McGehee, who is an assistant professor in the university's department of anesthesia and critical care. The new study has identified the receptor on nerve cells that receives the input from nicotine and passes it on to the pleasure center.
The finding could help develop drugs to help smokers give up the habit, he says: "I'm hoping that work such as ours, which identifies a specific receptor type, can lead to drugs that target those specific receptors."
The effect of the nicotine-cell combination is to increase the release of dopamine, which is involved in all addictive behavior, McGehee says.
"The one fascinating thing is that all abused substances have this common feature," he says. "They all cause elevation of dopamine levels."
Nicotine appears to cause addiction by strengthening the ability of nerve cells in a certain area of the brain pleasure center, the ventral tegmental area, to release dopamine, McGehee and Mansvelder have found. The nicotine molecule achieves that by interacting with a receptor on the part of the nerve cell that sends signals to the brain pleasure center.
"The effects we are seeing are due to activation of a very specific center," McGehee says. "This is not a central mechanism for other drugs, but there may be some interesting overlap where more than one drug is used."
McGehee and Mansvelder worked with slices of tissue from the brains of rats that were exposed to nicotine for limited periods of time. Exposure for just two minutes, comparable to the time needed to smoke a cigarette, caused lasting changes in the connections between nerve cells, sending the message that nicotine intake is pleasurable.
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