The study involved injecting adolescent rats with nicotine twice a day for 15 days, a control group was injected with saline (salt) solution for comparison. When the rats had developed into adults they were tested for their responses to stressful events.

Compared with the control rats, the nicotine injected group displayed more behaviours associated with depression and anxiety; for example, repetitive grooming, decreased consumption of rewards offered in the form of sugary drinks and becoming immobile in stressful situations instead of trying to escape.

"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," Bolanos claims. "In addition, the study indicates that even brief exposure to nicotine increases risk for mood disorders later in life."

"Some of the animals in our study were exposed to nicotine once and never saw the drug again," Bolanos said. "It was surprising to us to discover that a single day of nicotine exposure could potentially have such long-term negative consequences."

One difficulty with this study is that it was conducted on rats and this makes it difficult to ascertain whether their behavioural symptoms are akin to depression in people; however, the rats' symptoms were relieved by antidepressant medication, which provides limited support for the notion that the rats were depressed. Interestingly, more injections of nicotine also relieved the depression and anxiety.

"The message to young people of course is don't smoke and don't even try it," Bolanos said. "If they do smoke, they need to be aware of the potentially long-term effects that recreational or even occasional cigarette smoking can have on their systems."