A lack of 鈥済ood bacteria鈥� in childhood could be permanently changing the way the brain is wired up 鈥� at least if they affect people the same way they do mice.
Changes in our gut bacteria have been implicated in several mental health disorders, such as schizophrenia and depression, but it鈥檚 unclear whether these differences actually cause the problems or are knock-on effects. Now a lack of certain bacteria has been found to cause faulty patterns of connections between brain cells in rodents.
The microbes are a group called Bifidobacteria, which are among the most common bacteria in the guts of babies and children. Human breast milk contains compounds called oligosaccharides that encourage these microbes to grow, crowding out harmful bugs.
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Previous research has suggested Bifidobacteria are becoming , perhaps because of antibiotic use and less breastfeeding.
To find out what the effects might be, of Baylor College of Medicine in Texas bred 鈥済erm-free鈥� mice, which were born and raised in sterile cages so they had no gut bacteria. He then put four species of Bifidobacteria into the stomachs of one group of young mice.
Once they reached adulthood, these mice, along with normal animals for comparison, were put through a range of behavioural tests, before samples were taken from a part of the brain called the cerebellum, involved in movements and learning.
Too well connected
The mice lacking any bacteria were worse at learning new information and had . They also had an unusually large number of connections, or synapses, between their brain cells compared with normal mice. The findings were reported at the conference in Atlanta, Georgia, earlier this month.
We know that the number of synapses normally falls during childhood and adolescence through a process called pruning, which is important in fine-tuning neural circuits. 鈥淭oo many synapses can create chaos in the neural networks,鈥� says Versalovic.
The germ-free mice had fewer brain cells called microglia in an active state, which are responsible for pruning.
The brains of mice that had Bifidobacteria re-introduced looked more similar to normal mice 鈥� but only if the bacteria had been returned when the animals were very young. There鈥檚 a window of opportunity while the brain is developing, says Versalovic. 鈥淚f you colonise too late in life it doesn鈥檛 work.鈥�
We may have come to depend on metabolites made by our gut bacteria during evolution, says of the South Australian Health and Medical Research Institute. Bifidobacteria 鈥渁re present in such high numbers, suggesting they have a fundamental contribution,鈥� he says.
Some groups are investigating giving Bifidobacteria in the form of probiotic drinks. And oligosaccharides are added to some types of infant formula milk.
