Scientists say the finding shows the essential role gut bacteria plays in the development of normal social behaviour and they point out that gut problems are common in people with autism, a disorder characterised by alterations in social behaviour.

Professor Ted Dinan, professor of psychiatry and a principal investigator in the Alimentary Pharmabiotic Centre (APC) at UCC, said they had been studying the influence of gut bacteria on the brain for years and they had already established that the serotonin system, which plays a role in regulating mood, “doesn’t develop properly if you don’t have enough bacteria in the gut”.

Adults have approximately one kilo of bacteria in the gut and Prof Dinan said these microbiota can influence brain development and function.

“In our studies involving mice, we found animals raised in a germ-free environment (without microbiota in their gut) spent more time interacting with objects than other animals and so have distinctly autistic patterns of behaviour,” Prof Dinan said.

He said at the core of their paper was that for the social development of animals, they needed a normal range of bacteria in the gut.

Microbiotic-deficient mice used in the study showed “reduced preference” for novel social situations, in other words, they weren’t that interested in investigating a new mouse on the scene over a familiar mouse. The scientists said this resembles social cognition deficits observed in patients with neurodevelopmental disorders. They said children with autism exhibit increased repetitive behaviours and microbiota-deficient mice also show enhanced repetitive grooming when placed in a new situation.

Interestingly, when bacteria was introduced after weaning it reversed the observed social avoidance and repetitive behaviours, but had no effect on social cognition impairments.

Professor John F Cryan, senior author on the publication and had of the Department of Anatomy & Neuroscience at UCC, said although the findings emanate from experimental models “they clearly highlight that the absence of critical bacteria during early life affects behaviours relevant to autism and thus further investigations into how the microbiota affects the wiring of the brain are required”.

* The research was published yesterday in the leading international psychiatry journal, Molecular Psychiatry.