Women who smoke while pregnant run the risk of babies with behavioural problems
Smokers are damaging the health of their child long after they have been born, the study warned. Babies born to smoking mums are more at risk of behavioural problems such as attention deficit and hyperactivity disorder.
Nicotine causes lasting changes in the brain cell structure and behaviour of offspring.
Exposure in the womb to the stimulant drug can trigger widespread genetic changes that affect formation of connections between brain cells long after birth.
This may explain why children born to smokers suffer from ADHD, addiction and conduct disorder.
Nicotine does this by affecting a master regulator of DNA packaging, which in turn influences activity of genes crucial to the formation and stabilisation of synapses between brain cells.
Professor Marina Picciotto of Yale University’s Child Study Centre and the Departments of Neuroscience and Pharmacology, said: “When this regulator is induced in mice, they pay attention to a stimulus they should ignore.
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An inability to focus is the hallmark of attention deficit hyperactivity disorder and other behavioural disorders, which have been linked to maternal smoking and second-hand smoke.
Until now scientists did not understand how early environmental exposure could create behavioural problems years later.
The study found mice exposed to nicotine during early development did indeed develop behavioural problems that mimic symptoms of attention deficit disorder in humans.
They then did extensive genomic screening of mice exposed to nicotine and found higher levels of activity in a key regulator of histone methylation – a process that controls gene expression by changing the DNA wrapping around chromosomes.
Genes essential to the creation of brain synapses were heavily effected.
Scientists also found that these genetic changes were maintained even in adult mice.
However, when researchers inhibited the master regulator of histone methylation, these adult mice were calmer and no longer reacted to a stimulus they should ignore.
In a final test, they triggered expression of this regulator in mice never exposed to nicotine, and the mice exhibited behaviour that mimicked attention deficit disorder.
Prof Picciotto added: “It is exciting to find a signal that could explain the long-lasting effects of nicotine on brain cell structure and behaviour.
“It was even more intriguing to find a regulator of gene expression that responds to a stimulus like nicotine and may change synapse and brain activity during development.”
The study was published in the journal Nature Neuroscience.