Smoking in pregnancy linked to brain changes and teenage drug experimentation

Children born to mothers who smoked during pregnancy are more likely to experiment with drugs in their teens, the findings of a new study suggest.

Research carried out by the University of Nottingham and a number of Canadian Universities found that children exposed to cigarette smoke in the womb were more likely to experiment with drugs, such as alcohol, cigarettes and marijuana, during adolescence.

The study, published in the Archives of General Psychiatry, suggests that prenatal exposure to maternal smoking may interfere with the development of the brain – particularly a part of the brain associated with evaluating rewards and regulating emotion called the orbitofrontal cortex.

MRI scans of almost 400 teenagers found that in those whose mothers had smoked while pregnant, the orbitofrontal cortex (OFC) was thinner. Scientists found a correlation between thinning of the OFC and the likelihood of drug experimentation – the thinner the OFC, the more different drugs had been tried during adolescence.

The most commonly used illegal substances among the participants in the study were alcohol, cigarettes, marijuana, stimulants and psychedelic drugs.

The evidence suggests that maternal cigarette smoking may re-wire the 'reward' circuitry of the brain of the unborn child, altering the psychoactive effects of drugs and, in turn, drug-seeking behaviour.

Nottingham academics worked on the study with Canadian colleagues at the University of Montreal, McGill University and the University of Quebec in Chicoutimi.

They noted that cigarette smoking during pregnancy is not uncommon – between 16 and 60 per cent of pregnant women smoke, with prevalence varying from country to country and according to socioeconomic group. There is growing evidence of increased rates of behavioural problems among offspring exposed to maternal cigarette smoking in the womb and after birth.

Professor Tomas Paus, Director of The University of Nottingham's Brain and Body Centre and the senior author of the study, said: "These findings demonstrate significant consequences of prenatal exposure to maternal cigarette smoking on the offspring brain. But our findings need to be interpreted with caution: we could only show an association, not a causal effect of maternal smoking on brain and behaviour. Such causality can be (and has been) demonstrated only in experimental models. It is also important to note that almost half of the children of mothers smoking during pregnancy showed no differences in the brain and behaviour – suggesting that something protected them from the adverse effect of cigarette smoke".

Dr Shahrdad Lotfipour, the first author of the study and currently a post-doctoral fellow at the University of California in Los Angeles, said: "It was my training in pharmacology and neuroscience that helped me understand what might be going on in the human brain ... An integration of both fields turned out to be important at the end."

(Source: University of Nottingham: Archives of General Psychiatry: November 2009)

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