Maternal smoking and early exposure to nicotine can lead to widespread genetic changes which can alter neuron morphology in the brain, scientists have warned. This could explain why smoking during foetal development has previously been associated to behavioural changes such as attention deficit and hyperactivity disorder (ADHD), addiction and behaviour disorders in children, years later.

The study, published in Nature Neuroscience, focused on explaining behaviour in young mice who had been exposed to nicotine during their early development.

They showed that nicotine affects a an important regulator of gene expression, which in turn leads to an impaired activity of the genes crucial to the formation and stabilisation of synapses between brain cells.

Mice with behaviour problems

The team of scientists from Yale University observed how mice exposed to nicotine during pregnancy and development reacted to different stimulus. The animals displayed an inability to focus and found it impossible to ignore a stimulus they were told to forget about.

Such a lack of concentration is often a sign of ADHD and other behavioural disorders which have in the past been linked to maternal smoking. The scientists then conducted an extensive DNA micro-array screening of the mice they had exposed to nicotine, to see if this could be explained by looking at their genome.

Regulator of gene expression

The researchers found higher levels of activity in a major regulator of histone methylation - a process responsible for controlling gene expression by changing the DNA wrapping around chromosomes.This resulted in some genes linked to the creation of brain synapses being heavily affected, and to an alteration of neuron morphology.

These alterations remained in the long term; they were also identified in adult mice, long after they had been exposed and were associated to an increased risk of behavioural disorders.

The findings thus represent the first step in explaining how early environmental exposure to smoking could create behavioural problems years later and what happens in the DNA and in the brain structures of children affected by nicotine.

"It is exciting to find a signal that could explain the long-lasting effects of nicotine on brain cell structure and behaviour," senior author Marina Picciotto said. "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."