Effects of maternal smoking continue long after birth

Washington: Moms-to-be, take note! The effects of maternal smoking continue long after birth, according to a new study which found that early exposure to nicotine can trigger widespread genetic changes that affect formation of connections between brain cells.

The finding helps explain why maternal smoking has been linked to behavioural changes such as attention deficit and hyperactivity disorder (ADHD), addiction and conduct disorder, researchers said. 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, they said.

"When this regulator is induced in mice, they pay attention to a stimulus they should ignore," said Marina Picciotto from Yale University in the US. An inability to focus is the hallmark of ADHD and other behavioural disorders, which have been linked to maternal smoking and exposure to second-hand smoke. However, till now scientists did not understand how early environmental exposure to smoking could create behavioural problems years later.

In the new study, researchers found that mice exposed to nicotine during early development did indeed develop behavioural problems that mimic symptoms of ADHD 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.

Researchers found that genes essential to the creation of brain synapses were heavily effected. They 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 ADHD.

"It is exciting to find a signal that could explain the long-lasting effects of nicotine on brain cell structure and behaviour," said Marina Picciotto from Yale University.
"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," said Picciotto. The findings were published in the journal Nature
Neuroscience.