Cigarette smoking is considered a leading cause of preventable death worldwide and implicated in as many as 440,000 deaths in the United States each year by the U.S. Centers for Disease Control and Prevention.

In the United States, about 20 percent of people still smoke cigarettes and half claim they try to quit each year, though only 10 percent do so and most change their minds within 48 hours. Learning about withdrawal and difficulty of quitting can lead to more effective treatments to help smokers quit and so a new study on nicotine addiction measured a behavior that can be similarly quantified across species like humans and rats; the responses to rewards during nicotine withdrawal. 

Response to reward is the brain's ability to derive and recognize pleasure from natural things such as food, money and sex. The reduced ability to respond to rewards is a behavioral process associated with depression in humans. In prior studies of nicotine withdrawal, investigators used very different behavioral measurements across humans and rats, limiting our understanding of this important brain reward system.

Using a translational behavioral approach, the researchers found that nicotine withdrawal similarly reduced reward responsiveness in human smokers - particularly those with a history of depression - as well as in nicotine-treated rats. 

Co-author Michele Pergadia, Ph.D., associate professor of clinical biomedical science at Florida Atlantic University, notes that replication of experimental results across species is a major step forward, because it allows for greater generalizability and a more reliable means for identifying behavioral and neurobiological mechanisms that explain the complicated behavior of nicotine withdrawal in humans addicted to tobacco. 

"The fact that the effect was similar across species using this translational task not only provides us with a ready framework to proceed with additional research to better understand the mechanisms underlying withdrawal of nicotine, and potentially new treatment development, but it also makes us feel more confident that we are actually studying the same behavior in humans and rats as the studies move forward," said Pergadia.

They plan to pursue future studies that will include a systematic study of depression vulnerability as it relates to reward sensitivity, the course of withdrawal-related reward deficits, including effects on relapse to smoking, and identification of processes in the brain that lead to these behaviors. 

Pergadia emphasizes that the ultimate goal of this line of research is to improve treatments that manage nicotine withdrawal-related symptoms and thereby increase success during efforts to quit. "Many smokers are struggling to quit, and there is a real need to develop new strategies to aid them in this process. Therapies targeting this reward dysfunction during withdrawal may prove to be useful."