Sudden Infant Death Syndrome: Abrupt stop in breathing linked to low serotonin levels

Babies who present a serotonin deficiency may be more at risk of Sudden Death Infant Syndrome (SIDS), researchers claim. The neurotransmitter could play an important role in the infants' breathing, and a lack of it could lead to asphyxia.

The study, published in the journal Experimental Physiology, looks at ways to tackle one of the most mysterious causes of death in newborns around the world. In the UK, just under 300 babies die from SIDS every year. The problem is that scientists have not yet been able to pinpoint what causes SIDS and whether there are effective ways to treat and prevent it.

Here, the researchers follows up on previous findings, which suggested that the brains of infants who died from SIDS displayed lower levels of serotonin and serotonin receptors. While serotonin is best known for its role in regulating mood, there is evidence that it also helps avoid lengthy reflex apnoea - a short pause in breathing which can lead to infant deaths.

Serotonin and apnoea duration

The researchers decided to test whether having little serotonin meant experiencing longer phases of apnoea which has long been suspected for triggering SIDS.

The study involved inducing reflex apnoea in baby rats, by pouring small amounts of water in their upper respiratory tract. They were then injected with serotonin-altering drugs, to test the effects of serotonin on apnoea's duration. The scientists discovered that when the levels of serotonin increased as a result of the injection, and when a particular serotonin receptor called 5HT<sub>3 was activated, apnoea lasted on average for two seconds instead of 10.

The fact that babies who died from the syndrome seemed to present less serotonin in their brains, combined with these latest results in rats, point to the crucial role of the neurotransmitter in reducing the risks of SIDS. Though more research is needed to investigate how clinical results for rodents can apply to human babies, the study authors say this is a first step towards closing the knowledge gap on SIDS.

They subsequently hope to examine if newborns who died had low levels of the specific 5HT3 receptor. Understanding this could pave the way for new preventive methods and treatments targeting said receptor.