Sarkis K. Mazmanian, a professor of biology, said to study this gut--microbiota--brain interaction, the researchers used a mouse model of autism previously developed at Caltech in the laboratory of Paul H. Patterson, the Anne P. and Benjamin F. Biaggini Professor of Biological Sciences.
"Traditional research has studied autism as a genetic disorder and a disorder of the brain, but our work shows that gut bacteria may contribute to ASD-like symptoms in ways that were previously unappreciated," Mazmanian said in a statement. "Gut physiology appears to have effects on what are currently presumed to be brain functions."
In humans, having a severe viral infection raises the risk that a pregnant woman will give birth to a child with autism. Patterson and his lab reproduced the effect in mice using a viral mimic that triggers an infection-like immune response in the mother and produces the core behavioral symptoms associated with autism in the offspring.
The study, published in the journal Cell study, found that the "autistic" offspring of immune-activated pregnant mice also exhibited gastrointestinal abnormalities. In particular, the gastrointestinal tracts of autistic-like mice were "leaky," which means that they allow material to pass through the intestinal wall and into the bloodstream. This characteristic, known as intestinal permeability, has been reported in some autistic individuals.
"To our knowledge, this is the first report of an animal model for autism with comorbid gastrointestinal dysfunction," said first author Elaine Hsiao, a senior research fellow at Caltech.
However, when the researchers the researchers treated the mice with Bacteroides fragilis, a bacterium that has been used as an experimental probiotic therapy in animal models of gastrointestinal disorders, the leaky gut was corrected. Probiotics -- in supplements and in food such as yogurt -- simultaneously encourage beneficial bacteria to flourish in the body while hindering the growth of harmful microorganisms.
In addition, observations of the treated mice showed their behavior changed -- they were more likely to communicate with other mice, had reduced anxiety and were less likely to engage in a repetitive digging behavior.
"The B. fragilis treatment alleviates gastrointestinal problems in the mouse model and also improves some of the main behavioral symptoms," Hsiao said. "This suggests that gastrointestinal problems could contribute to particular symptoms in neurodevelopmental disorders."
The researchers said they are planning a trial to test the probiotic treatment on the behavioral symptoms of human autism.