New animal research from Florida State University suggests that smoking during adolescence may increase the risk of depression during adulthood, Medical News Today reported Jan. 29.

Researcher Carlos Bolaños-Guzmán and colleagues injected adolescent rats with either nicotine or saline solution for 15 days, then tested the rats' responses to stressful and rewarding situations both during and after exposure.

The study showed that even a single day's worth of nicotine exposure during adolescence led to rats experiencing lower sensitivity to natural rewards and enhanced sensitivity to stressful situations.

Administering either nicotine or antidepressants during adulthood caused the depression symptoms to disappear, the researchers found.

"These data suggest that adolescent exposure to nicotine results in a negative emotional state rendering the organism significantly more vulnerable to the adverse effects of stress," Bolaños said.

The results were published online Dec. 17, 2008 in the journal Neuropsychopharmacology.