Nicotine's effects in rats differ depending on whether the animal is male or female and lives alone or in groups, a new study conducted by the Uniformed Services University of the Health Sciences reports. These findings may have implications for human nicotine effects.
For male rats, nicotine altered activity levels and exploratory behaviors. In contrast, nicotine did not affect activity and exploratory behaviors of female rats but did alter behaviors that may reflect anxiety. Whether nicotine increased or decreased these behaviors depended on the animal's living conditions. For males that lived in groups, nicotine increased activity and exploration; for males that lived individually nicotine had the opposite effects, decreasing activity and exploration. In females, nicotine affected the amount of time female animals spent in the center of an open arena -- a situation rats are believed to find anxiety-provoking. Specifically, among females who lived in groups, nicotine increased time spent in the center, suggesting that these animals experienced reduced anxiety as a result of nicotine administration.
"Our studies with rats may reflect human sex differences in reasons for smoking. For example, women often report that they smoke to cope with emotional and social situations and to alleviate negative affect. It is striking that in our study female rats living in groups and, treated with nicotine, manifested behaviors that may indicate decreased anxiety," says Martha M. Faraday, head of the study.
The researchers reported their findings in the current issue of Nicotine & Tobacco Research.
"Men are likely to report smoking for reasons of arousal, to alleviate boredom, or to relax. Interestingly, in this experiment nicotine's effects in male rats occurred on behaviors that primarily index activity, arousal, and exploration," Faraday explains.
The scientists worked with 96 female and 96 male laboratory rats implanted with minipumps that delivered continuous doses of nicotine to some of the rats and a saline solution to others serving as a comparison group. Some rats lived in individual housing, others in groups. The animals' overall activity, exploration, and time spent in the center of an open field were measured by infrared photocell systems connected to computers.
"Animal models are useful because they allow the researcher to peel away some of the complexity of the human condition -- the influence of culture, a lifetime of learning, social environments, family interactions and many other factors," says Faraday. "If you can demonstrate that a drug or environment produces an effect in a rat that humans also report, then it is likely that the human experience is at least in part biologically based and 'hard-wired' rather than a completely psychological process.
"Much of our knowledge about why people smoke and why it is so hard to quit has come from nearly 50 years of animal work on smoking and nicotine. But despite the extensive animal literature on nicotine's actions, little work has been done on social environment or social context as a factor in nicotine's actions. These are powerful determinants of human behavior, and examination of these factors in rats might illuminate some of the individual human differences in human smoking behavior. If we better understood how social influences affect smoking, we also might be able to develop more effective smoking cessation and smoking prevention programs," Faraday said.
The research was supported by funding from the Uniformed Services University of the Health Sciences, Department of Defense.
Nicotine & Tobacco Research is the official peer-reviewed quarterly journal of the Society for Research on Nicotine and Tobacco. For information about the Journal, contact its editor, Gary E. Swan, 650-859-5322.
Posted by the Center for the Advancement of Health http://www.cfah.org. For information about the Center, call Petrina Chong, pchong@cfah.org 202-387-2829.
Journal
Nicotine & Tobacco Research