Importance of early childhood gut microbes to brain health
The public has become more aware of the importance of the microbiome – the trillions of bacteria and other microbes in the gut – to immune systems and health. Studies have shown gut flora is also important for brain health. “Our lab has shown, using different models particularly in animals, that without appropriate microbes in the gut during early infancy, the brain does not develop appropriately and this can lead to a variety of behavioural issues in the adult animal,” says GutMIND project coordinator John Cryan, professor of Anatomy and Neuroscience at University College Cork(opens in new window), Ireland. The project, with support from the EU’s Marie Skłodowska-Curie Actions(opens in new window) programme, dug deeper into mechanisms that link gut health to mental health. “We looked at the microglia – the brain immune cells – in mice and we could see there were some discrete changes in adult animals that had been given antibiotics in childhood,” Cryan notes, adding that stress can also affect microbes in the gut. This builds on the team’s previous work which looked at the neuronal pathway called the vagus nerve – a long wandering nerve that sends signals from other organs to the brain and vice versa.
Early childhood and gut microbes
There is a strong link between the microbes in the gut and the immune system, including the brain’s immune system and brain function. Gut microbes “prime the immune system,” he explains. “Babies get their gut microbes almost like a birthday present from their mothers as they emerge through the birth canal. These early bacteria then start to colonise the gut and form the developing immune system. So anything that could influence the shift, the composition of these microbes in this period, could potentially have negative consequences,” Cryan says. “We know it takes about 2 years for the microbiome to stabilise, that’s why we wanted to target this early period. We wanted to see if this is happening from the first few weeks of life or if it is later.” Laboratory mice are given antibiotics in early life, grow up to be adults and are then tested in adulthood to see how they respond. Past experiments on mice with no gut microbes at all were shown to have stress-like, depressive-like problems as well as other behavioural issues. “Microbes are like little factories that produce chemicals the body wouldn’t be able to make otherwise,” Cryan adds. “Antibiotics are basically bombing out the factories so they’re no longer available to produce these chemicals that might be health-beneficial, including for the brain.”
No big effects on adult behaviour
The team found there doesn’t seem to be as great an effect in adulthood if the microbiome is manipulated for only short periods of time in early childhood. “There are effects on behaviour but they are subtle,” according to Cryan. “This tells us that although antibiotics change the microbiome, there is some level of plasticity or compensation occurring that is preventing it from having too overt effects overall,” he explains. He believes only big changes in the microbiome for very long periods would induce negative effects in adulthood. This is somewhat good news for parents if they give children antibiotics, Cryan notes. “It shows there isn’t a huge problem with short-term exposure to antibiotics – at least if you’re a mouse.” Translational human studies are ongoing.
