Abnormal development of the auditory brain stem in children and subsequent hearing problems can be the result of nicotine exposure, both before and after birth, according to a mouse model study published in the February 12 edition of The Journal of Physiology. The new research suggests for the first time that the auditory brain stem—an area of the brain which plays a role in analyzing sound patterns—may develop abnormally in children when pregnant mothers are exposed to nicotine before and after giving birth.

In the study, the researchers added nicotine to the drinking water of pregnant mice to reach blood nicotine levels similar to heavy human smokers. The offspring of the mice were exposed to nicotine before birth and via the mother’s milk until they were 3 weeks old. The scientists then analyzed the brains of the offspring mice by measuring the firing properties and signaling abilities of their neurons. The results were then compared to a control group of offspring from pregnant mice with no nicotine exposure. Neurons that get input from the cochlea (sensory organ in the ear) were less effective at transmitting signals to other auditory brain stem neurons in mice exposed to nicotine. Moreover, these signals were transmitted with less precision, deteriorating the coding of sound patterns. The researchers postulate that this could be part of the underlying causes for auditory processing difficulties in children of heavy smoking mothers.

“We do not know how many other parts of the auditory system are affected by nicotine exposure,” said Ursula Koch, professor at the Freie Universität Berlin and lead investigator of the study. “More research is needed about the cumulative effect of nicotine exposure”.

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