Gut bacteria relieve autistic symptoms in mice

A group of researchers from the California Institute of Technology in Pasadena has shown that mice showing autistic-like symptoms can benefit from being given bacteria that are naturally found in the gut.

Gut bacteria have been previously linked to autism in several ways.  In 2011, a study was published indicating that children with autism had significantly fewer Bacteroides (fundamental digestive system bacteria) than other children.  Many children with autism have gastrointestinal troubles and are picky eaters.  But this link between autism and gut bacteria is poorly understood.

The researchers involved in this current study (Sarkis Mazmanian and Paul Patterson) are interested in the link between the immune system and autism.  They found last year that offspring of mice who had been infected with a flu-like virus when pregnant were more likely to develop autistic-like behaviours: they were less social, squeaked less and showed repetitive behaviour.  They also had a ‘leaky’ gastrointestinal tract meaning bacteria moved in and out of the gut; futhermore, their gut bacteria were significantly different from other mice.

In work presented at last month’s TEDx conferenece in Pasadena, Mazmanian and Patterson’s group fed the autistic-like mice Bacteroides fragilis, a common bacteroide.  This led to changes in the mice’s gut, immune system and behaviour.  Their gut cells seemed become more strongly connected and stopped producing a signalling molecule that normally increases the immune response.  Strikingly, these gut bacteria also affected behaviour: the mice squeaked more with the opposite sex and reduced their repetitive behaviours. In this way adding gut bacteria reduced their autistic-like responses.

This suggests that probiotics could help relieve some of the negative symptoms of autism and further implicate a role for the immune system in this disorder.  It also shows how the bacteria we carry around inside us could be affecting our brain and behaviour more than we think.

Watch the video about how microbes affect the brain here: tedxcaltech.caltech.edu/content/elaine-hsiao