Abnormal development of the auditory brainstem 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 edition of The Journal of Physiology.
Nicotine exposure during pregnancy has previously been shown to harm the brain development of a fetus. Mothers who smoke, use e-cigarettes, or nicotine replacement therapy have an increased risk of premature delivery, decreased child birth weight, and an increased rate of sudden infant death. It has also been linked in several studies to hearing problems.
The new research suggests for the first time that the auditory brainstem—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. Children with impaired auditory brainstem function are likely to have learning difficulties and problems with language development.
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—an age that is approximately equivalent to primary school children. 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 brainstem 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 and the molecular mechanisms of how nicotine influences the development of neurons in the auditory brainstem.”
“If mothers smoke during pregnancy and their children show learning difficulties at school, they should be tested for auditory processing deficits,” she added.
Source: The Physiological Society
Image credit: The Journal of Physiology
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