Serotonin, a chemical known for its role in the brain production of feelings of well-being and happiness, may reduce the ability of some intestinal pathogens to cause infections, according to a team of researchers from UT Southwestern Medical Center (United States) in a study published in the journal ‘Cell Host and Microbe’.
Although the vast majority of serotonin research has focused on the brain, about 90 percent of this neurotransmitter, a chemical that nerve cells use to communicate with each other, is produced in the gastrointestinal tract.
Because gut bacteria are significantly affected by their environment, experts wondered if serotonin produced in the gut can affect the virulence of pathogenic bacteria that infect the gastrointestinal tract.
To do this, experts analyzed ‘Escherichia coli O157’, a species of bacteria that causes periodic outbreaks of food-borne and often fatal infections. The team cultured these pathogenic bacteria in ‘Petri dishes’ in the laboratory and subsequently exposed them to serotonin.
Gene expression tests showed that serotonin significantly reduced the expression of a group of genes that these bacteria use to cause infections. Also, additional experiments with human cells showed that the bacteria could no longer cause lesions associated with the infection if they were exposed to serotonin.
The researchers then examined how serotonin affected virulence in living hosts. For this, and using mice, they analyzed how serotonin could change the capacity of ‘Citrobacter rodentium’, a mouse intestinal bacterium that is often used as an analogue of ‘E. coli ‘in humans, to infect and make their hosts sick.
These mice were genetically modified to produce excess or insufficient serotonin in their gastrointestinal tracts. Thus, scientists found that those who overproduced this neurotransmitter were less likely to be colonized by ‘C. rodentium ‘after exposure to this bacterium or relatively minor illness.
Other experiments identified the serotonin receptor on the surfaces of ‘E. coli ‘and’ C. rodentium ‘, a protein known as’ CpxA’. Because many species of gut bacteria also have CpxA, experts note that serotonin may have wide-ranging effects on gut bacterial health.