New York: Mothers-to-be, please take note! Maternal smoking can trigger widespread genetic changes that affect formation of connections between brain cells long after birth, warns a study. Maternal smoking has been linked to behavioural changes such as attention deficit and hyperactivity disorder, addiction and conduct disorder. An inability to focus is the hallmark of attention deficit hyperactivity disorder (ADHD) and other behavioural disorders which have been linked to maternal smoking and exposure to second-hand smoke. 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. "When this regulator is induced in mice, they pay attention to a stimulus they should ignore,'' said senior study author Marina Picciotto from Yale University in the US. "It is exciting to find a signal that could explain the long-lasting effects of nicotine on brain cell structure and behaviour," Picciotto added in a paper published online in the journal Nature Neuroscience. The results suggest that mice exposed to nicotine during early development did indeed develop behavioural problems that mimic symptoms of attention deficit disorder in humans. Furthermore, the scientists found that genetic changes were maintained even in adult mice. "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," Picciotto stated.