If you start smoking cigarettes, chances are you'll become addicted. But that's only part of the story, according to new research published in Psychopharmacology.  After exposing rats to passive smoke and studying how their brains responded, the authors of the studies are suggesting that just being exposed to cigarette smoke may result in nicotine dependence.  

In a set of four experiments on male Wistar rats, researchers investigated whether rats exposed passively to tobacco smoke would become dependent on nicotine.  They specifically looked at how the rats' brains responded to being exposed to tobacco smoke and whether the rats displayed withdrawal symptoms.

 For all the experiments, freely moving rats were chronically exposed to tobacco smoke for a few hours per day.  In the first experiment, the rats were fitted with an intracranial probe to measure the emotional aspects of tobacco withdrawal. 

The second experiment looked at whether being exposed to tobacco smoke decreased the rats' self-administration of nicotine.  The third experiment investigated whether rats exposed to
tobacco smoke were less motivated to eat.  Finally, in the fourth experiment, the researchers looked specifically at the effects of tobacco smoke exposure on the brain's hippocampus, or grey matter – the area of the brain most sensitive to smoke and nicotine-induced changes.

The rats exposed to tobacco smoke showed both affective and physical withdrawal signs, as well as nicotine-induced changes in the hippocampus, which demonstrates that passive exposure to tobacco smoke exposure leads to nicotine dependence.

 The authors conclude: "These studies suggest that the rat tobacco smoke exposure model can be used to investigate the effects of tobacco smoke on the human brain and to evaluate the efficacy of novel treatments for tobacco addiction."

: Elysia Small, Hina P. Shah, Jake J. Davenport, Jacqueline E. Geier, Kate R. Yavarovich, Hidetaka Yamada, Sreedharan N. Sabarinath, Hartmut Derendorf, James R. Pauly, Mark S. Gold, Adrie W. Bruijnzeel, 'Tobacco smoke exposure induces nicotine dependence in rats ', Psychopharmacology 2009, doi:10.1007/s00213-009-1716-z