A bacterial strain, when present in the gut, causes mothers to neglect their offspring, new research in mice has found.
The findings, published in Science Advances, showed that a specific bacterial strain in the gut affects maternal behaviour.
"The study found that when a specific strain of E. coli was grown in the guts of female mice, it caused them to neglect their offspring," explains Prof Martina Wallace, UCD School of Agriculture and Food Science, who participated in the research.
“It gives more evidence that there is a gut-brain connection and this is important during all stages of life,” says Wallace who conducted the research while at the University of California, San Diego.
“We developed a method to determine how much milk the pups were consuming from the dams. We found that pups from mothers with this E. coli strain were consuming less milk,’ Wallace adds.
Prof Janelle Ayres, head of the Salk Molecular and Systems Physiology Laboratory in San Diego, led the research effort.
“To our knowledge, this is the first demonstration that the intestinal microbiota is important for promoting healthy maternal behaviour and bonding between mom and offspring in an animal model,” Ayres adds.
“It adds to the ever-growing evidence that there’s a gut-brain connection, and that microbes are important for regulating the behaviour of the host that they’re inhabiting,” she believes.
The bacteria that inhabit the gut – which are collectively known as microbiota – has been linked with depression, anxiety and autism.
However, it has proven difficult for scientists to make a direct link between strains of bacteria and specific types of behaviour.
Ayres and her team investigated groups of mice that each had a particular strain of E.coli bacteria present in their gut.
It was found that mice with a strain called O16:H48 MG1655 mothered offspring that showed stunted growth.
The O16:H48 MG1655 strain is present in human guts where scientists believed it had no positive or negative effects.
Ayres’ team found mice offspring were smaller because they were malnourished, but they didn’t know why this was happening.
“We found that the pups’ behaviour was normal, and the milk made by the mothers was of normal, healthy composition and was being produced in normal amounts,” she says.
“We eventually figured out that being colonised with this particular bacteria led to poor maternal behaviour. The mice were neglecting their pups,” Ayres notes.
In follow-up experiments, the scientists found neglected young mice could be rescued from stunted growth by either giving them a growth factor called IGF-1 or handing them off to foster mouse mothers that could take care of them properly.
This demonstrated that the mice pups were stunted in growth because of something in the mother’s behaviour rather than anything the pups were doing, or not doing, themselves.
Yujung Michelle Lee, a former graduate student in Ayres' lab and now based at Genentech, also took part in the research.
“It is very interesting to me that establishment of a healthy mother-infant relationship is driven by factors beyond hormones, and that the microorganisms residing in our bodies play a significant role in it,” Lee points out.
Ayres would like to discover how, exactly, bacteria in the gut are provoking changes in mouse behaviour.
The findings so far suggest the bacteria might be affecting the levels of serotonin; a hormone linked with happiness and well-being. They would also like to determine whether bacteria in the gut can provoke changes in human behaviour in a similar way.
“It’s very hard to study these relationships in humans, because the human microbiota contains hundreds of different species of microorganisms,” says Ayres. “But once we understand more about the mechanisms in animal models, we may be able translate our findings to humans to determine whether the microbes and their effects might be the same.”