CHICAGO, March 8 - A root cause of sudden infant death syndrome (SIDS) may be disturbances of serotonin levels in key pacemaker cells in the brain. In babies, the normal response to hypoxia is to gasp, which wakes the baby and resets the breathing mechanism, according to Jan-Marino Ramirez, Ph.D., a professor of biology and anatomy at the University of Chicago. That reflex, which kicks in when a baby isn't getting enough oxygen for any reason, is governed by a set of pacemaker neurons in the respiratory neural network, Dr. Ramirez and colleagues had previously shown. In the March 8 issue of the Journal of Neuroscience, they build on the former work by showing that if those pacemaker cells don't have enough serotonin or can't use what's there, the gasping reflex is stifled. In a series of experiments using brain tissue from mice, the researchers blocked serotonin receptors in so-called cadmium-insensitive pacemaker cells. When those cells were placed in a hypoxic condition, the blockade prevented them from emitting the electrical signals characteristic of gasping. The blockade reduced so-called "fictive gasping" - gasping in vitro - from about 20 gasps to two or three. The researchers performed the experiment with two different serotonin receptor blockers, piperidine and ketanserin. That "indicates that if there's a problem with serotonin, the gasping is gone," Dr. Ramirez said. "And when these children don't gasp, they don't wake up." The researchers noted that "caution must be used when extrapolating in vitro findings to the situation in vivo," but added that the findings "may have important implications for understanding the failure of auto-resuscitation in SIDS victims." Several studies have shown that gasping is disrupted in SIDS victims, as is the serotonergic system in the areas of the brainstem responsible for breathing, the investigators said, adding that the current work may be the link between the two observations. The data suggest, they said, "that disturbances in the serotonergic system may underlie the failure to gasp appropriately and auto-resuscitate" even though hypoxia stimulates increased release of serotonin. Dr Ramirez said normal breathing is a complicated system, involving not only cadmium-insensitive pacemakers, but also another set of neurons, dubbed the cadmium-sensitive pacemakers, both of which can sustain breathing without the other. Other pacemaker neurons may also play role, the researchers noted. "The network becomes more vulnerable to situations like hypoxia, because under these conditions, respiration relies on only one group of pacemakers that become the critical drivers of [breathing] rhythm," he said. In the U.S., SIDS is the primary cause of death before the age of one; about 3,000 infants die each year from SIDS, according to the CDC. ...Serotonin is a monoamine neurotransmitter synthesised in serotonergic neurons in the CNS. Also, in the central nervous system, serotonin is believed to play an important role in the regulation of mood, sleep, vomiting, sexuality, and appetite. Serotonin has been thought to play a part in many other disorders also, such as biochemistry of depression, migraine, biploar disorder, and anxiety.