PARENTS who smoke are well known to have a higher risk of losing a baby to sudden infant death syndrome, or cot death. Now a team of scientists thinks they know why: nicotine could mess up some babies鈥� breathing.
Some babies who die from SIDS may succumb to sleep apnoea鈥� where they stop breathing during the night. In most adults and babies, the fall in blood oxygen levels caused by apnoea wakes them up and they begin to breathe again. But with SIDS, this reflex can fail, and Jean-Pierre Changeux and colleagues at the Pasteur Institutein Paris and the Karolinska Institute in Stockholm decided to investigate why.
To mimic apnoea, they put mice in a chamber which could be fed with air containing different levels of oxygen. Some of the mice lacked a gene that codes for a receptor found in nerves that binds to the neurotransmitter acetylcholine. Crucially, nicotine also binds to the receptor, and chronic exposure to nicotine can desensitise it, so it needs more acetylcholine to function properly.
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They found that sleeping mice that lacked this gene did not wake up if the oxygen level was reduced to a low level, though they did start breathing more deeply. Normal mice started gasping for breath, and this jolted them out of their sleep.
The receptor is also vital for another response to sleep apnoea: it controls the deep breathing you need to do to recover from it. While mice lacking the receptor started breathing deeply when exposed to low oxygen levels, the deep breathing continued even after the oxygen was restored to normal.
The researchers concluded that the receptor must suppress deep breathing when it鈥檚 no longer needed. They also reason that exposing a baby to nicotine could trigger the receptor to suppress the urge to breathe deeper 鈥� with disastrous consequences if the baby suffered a bout of apnoea.
鈥淭his shows for the first time that the natural control of breathing involves acetylcholine, and this receptor, and that nicotine can affect it,鈥� Changeux told New 杏吧原创. Prolonged exposure to nicotine before birth could make the receptor less sensitive, damaging the mechanism for rousing a baby from sleep apnoea. At the same time, exposing the baby to nicotine from cigarettes might inhibit the deep breathing response to low blood oxygen, making the baby less able to recover.
Knowing the specific receptor involved might allow the development of treatments to try and prevent the disorder, Changeux says.