A University study to be published in the journal Psychopharmacology provides insight into why people may gain weight after they quit smoking.

The experiment, led by psychiatry researcher Darlene Brunzell, investigated the effort mice would expend for food by monitoring the number of times they poked their nose into a hole that would eventually trigger the release of food. Those with prior nicotine exposure worked harder for the food, Brunzell said.

“They would nose poke much longer and harder before quitting,” she said.

The same study also uncovered a cause for nicotine’s highly addictive properties. The drug was found to elicit a large responses to cues — little things the mind associates with the drug and which can prompt craving.

Both discoveries could aid people attempting to stop smoking, said Stephanie O’Malley, psychiatry professor and director of the Division of Substance Abuse Research in the Yale School of Medicine’s Psychiatry Department. Nicotine’s long term effect on mice’s efforts to obtain food could parallel human weight gain after ceasing smoking. The study of cues could produce treatments that help people refrain from smoking.

These findings particularly affect students, as approximately 28 percent of college students are current smokers, O’Malley said.

Nicotine use seems harder for humans to discontinue than researchers expected, said Marina Picciotto, senior author on the study and professor of psychiatry, pharmacology and neurobiology. People generally have a harder time than other animals quitting a nicotine addiction, she said.

“If you give rats, mice [or] monkeys nicotine they will take it, but they will be less compulsive about their use than for some other drugs of abuse,” Picciotto said.

One reason behind nicotine’s unusually addictive nature is the presence of cues, she said. Cues can range from the smell of smoke and the look of the cigarette pack, to the feel of the cigarette in hand or even the atmosphere of the bar where one usually smokes. These cues can elicit cravings and determine behavior, Picciotto said.

“Nicotine is very good about making the cue which you experience when you are smoking control your behavior,” Picciotto said.

Brunzell’s research suggests nicotine’s ability to enhance the cue-behavior association is dependent on the presence of a certain subunit in nicotinic receptors in mice brains. The receptor subunits had been previously implicated in the primary reinforcement of nicotine, but the results show that they may be important for nicotine’s enhancement of the cues associated with smoking, Brunzell said. Without the subunit, the nicotine’s usual enhancing of the cue-behavior association is not observed, she said.

Brunzell’s finding might also help develop drugs to help smokers kick the habit. Currently, drug researchers are testing a partial agonist of a specific nicotinic receptor, which both partially promotes and impedes the subunit’s normal function, Picciotto said.

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