Intestinal microbes may affect the brain development of the next generation?

Autism spectrum disorder (ASD) is a type of neurodevelopmental disorder, and scientists have found that the effects of microbes appear to be "passed on from generation to generation."

Some epidemiological studies have shown that children born to mothers who were hospitalized due to infection during pregnancy have a higher risk of autism.

Results from animal experiments support this link: if pregnant mice are injected with double-stranded RNA to simulate viral invasion, their offspring are more likely to exhibit repetitive behaviors, social abnormalities, etc., similar to the symptoms of human autism.

Dr. Gloria Choi from the Massachusetts Institute of Technology and Dr. Jun Huh from Harvard Medical School have collaborated on several papers to try to find out why.

They found that in order to defend against invading microorganisms, the mother mice's immune cells produce a cytokine called IL-17.

This cytokine may cross the placenta and enter the developing brain of the fetus, bind to receptors in specific brain areas, and affect the neural activity of the offspring.

However, not every mother who is infected during pregnancy will give birth to a child with autism, so the research team further looked for what triggers the immune system to become overactive in some mothers.

In a study published in Nature, they found segmented filamentous bacteria in the intestine.

The picture below shows segmented filamentous bacteria (green) in the intestine, which can overstimulate the immune system of infected pregnant mice and affect the brain development of the fetus (Image source: Reference; Credit: Dan Littman, Alice Liang, Doug Wei and Eric Roth)

Another research team has discovered another intestinal bacteria that is associated with autism and has the potential to be used to treat autism.

In 2019, Dr. Mauro Costa-Mattioli, a neurobiologist at Baylor College of Medicine, accidentally discovered that mice with autism model lacked a specific bacteria in their intestines: Lactobacillus reuteri.

Supplementing with this bacteria significantly alleviated the mice's symptoms.

Based on this discovery, a research team is conducting clinical trials to try to have autistic children take Lactobacillus reuteri, compared with a placebo, to see if their symptoms improve.

A strain of Lactobacillus reuteri we developed has completed human clinical trials and has shown good results in intervening in the symptoms of ASD. It has the potential to be developed into a live bacterial drug💊.

Sgritta, Martina, et al. (2019) Mechanisms underlying microbial-mediated changes in social behavior in mouse models of autism spectrum disorder. Neuron 101.2 : 246-259.