New research on nicotine may help show why it’s often hard to quit smoking for good.

The finding: Nicotine may tweak the brain’s cravings. Or as the researchers put it, nicotine made the reward systems in rats’ brains more sensitive.

The effect didn’t fade quickly. It lasted more than a month after the rats stopped getting nicotine, the study shows.

That lingering effect could leave the brain craving nicotine after smoking stops, and it might also lead people to eat more and gain weight after quitting smoking, the researchers note.

The study appears in Neuropsychopharmacology’s online edition.

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Cravings Tweaked

The study was done by Paul Kenny, PhD, and Athina Markou, PhD. They work in the neuropharmacology department of The Scripps Research Institute in La Jolla, Calif. Kenny is a research associate; Markou is an associate professor.

The researchers trained rats to seek nicotine. The rats pressed a lever to get food pellets. After pressing the right lever a certain number of times, the rats got a shot of nicotine. That basically let the rats determine how much nicotine they got.

There was a catch. The rats could only get nicotine at certain times of the day. The rats that had the greatest access to nicotine took full advantage of it. They consumed a lot more nicotine than rats with more limited nicotine access.

The researchers also checked the brain sensitivity to nicotine one hour before and 15 minutes after consuming nicotine.

Nicotine “increased the sensitivity of brain reward systems,” write the researchers.

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Long-Lasting Impact

Eventually, the researchers stopped giving the rats nicotine. The increased brain reward sensitivity lasted at least 36 days after that, the study shows.

That was “surprising,” write Kenny and Markou. They note that nicotine’s lengthy brain impact may help explain why smoking can be so addictive.

Nicotine might leave a lingering memory in the brain, resetting the brain’s cravings to a new, higher level, the researchers write. They note that they haven’t seen that impact with other drugs such as cocaine.

More studies will follow, states a news release. Some upcoming studies will probe cravings for food and more nicotine, opening the door to weight gain and smoking relapse in former smokers.

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By Miranda Hitti, reviewed by Brunilda Nazario, MD

SOURCES: Kenny, P. Neurospyschopharmacology, Sept. 28, 2005, online edition. News release, Nature.