Cot death: chemical imbalance link

A chemical imbalance in the brain may be linked to some cases of cot death, new evidence suggests.

Scientists made the discovery after simulating Sudden Infant Death Syndrome (Sids) in mice. They found that low levels of the signalling molecule serotonin in the brain triggered changes in heart rate and body temperature that could lead to sudden death.

Serotonin is a neurotransmitter chemical that passes messages between brain cells. It has a number of functions and is most often associated with mood. Reduced serotonin activity can cause depression in humans, an effect reversed by anti-depressant drugs such as Prozac.

The cot-death mice were affected by serotonin in the brain stem, the lower part of the brain that is linked to the spinal cord.

The brain stem co-ordinates many fundamental body functions, including control over the heart and lungs.

Mice susceptible to Sids had a faulty biochemical regulator that was over-sensitive to serotonin. This sent a false message to the brain indicating the presence of too much of the chemical. As a result, serotonin production was reduced to dangerously low levels.

Study leader Dr Cornelius Gross, from the European Molecular Biology Laboratory in Monterotondo, Italy, said: "At first sight the mice were normal. But then they suffered sporadic and unpredictable drops in heart rate and body temperature.

"More than half of the mice eventually died of these crises during a restricted period of early life. It was at that point that we thought it might have something to do with Sids."

Neurons in the brainstem communicate with nerve cells in the spinal cord involved in temperature regulation. The scientists found that when cot-death mice were placed in a cold chamber they could not keep themselves warm.

To what extent the findings, reported in the journal Science, can be applied to humans is unclear. But the researchers say the Sids mice will help shed light on how faulty serotonin signalling can be life-threatening.