Teenagers who smoke face a greater risk of developing depression in later life, according to a new study.
In the study conducted using mouse model, the researchers found that nicotine given to adolescent rats induced a depression-like state characterized by a lack of pleasure and heightened sensitivity to stress in their adult lives.
They believe that the discovery has important implications for humans.
"This study is unique because it is the first one to show that nicotine exposure early in life can have long-term neurobiological consequences evidenced in mood disorders," said lead researcher and Psychology Professor Carlos Bolanos from Florida State.
"In addition, the study indicates that even brief exposure to nicotine increases risk for mood disorders later in life," he added.
The researchers injected adolescent rats twice daily with either nicotine or saline for 15 days.
After the treatment period ended, they subjected the rats to several experiments designed to find out how they would react to stressful situations as well as how they would respond to the offering of rewards.
They found that rats that were exposed to nicotine engaged in behaviours symptomatic of depression and anxiety, including repetitive grooming, decreased consumption of rewards offered in the form of sugary drinks and becoming immobile in stressful situations instead of engaging in typical escape-like behaviours.
They were able to alleviate the rats'' symptoms with antidepressant drugs or, ironically, more nicotine.
Bolanos said that exposure has toxic effects in several brain regions and neurotransmitter systems at distinct periods of development.
Since the brain continue to develop throughout adolescence, the researchers theorize that nicotine may negatively influence these systems resulting in altered functionality later in life.
The study is published in the journal Neuropsychopharmacology.