Gut microbes may have helped build the human brain — and may still be shaping how it works today.
Humans have the largest brain size relative to body size of all primates, but scientists still know surprisingly little about how mammals with brains large ones have evolved to satisfy the huge energy requirements necessary to develop and maintain them.
A team of researchers from Northwestern University (NU) has now provided the first direct experimental evidence that gut microbiome helps shape differences in brain function between primate species.
The results of his , published last week in Proceedings of the National Academy of Sciences show that the intestinal bacteria can directly influence the development and functioning of the brain.
During the course of the study, when scientists transferred microbes from different primates to mice, the Animal brains began to resemble to those of the original host species.
Microbes from primates with large brains stimulated brain energy and learning pathways, while others triggered very different patterns.
The results suggest that gut microbes may have played a hidden role in the formation of the human brainand may influence mental health.
“Our study shows that microbes act on features that are relevant to our understanding of evolution, and particularly the evolution of human brains,” he said. Katie Amatoassociate professor of biological anthropology and principal investigator of the study, at NU.
The new findings build on previous work from Amato’s lab, which showed that gut microbes from primates with larger brains produce more metabolic energy when transferred to mice. This extra energy is essential because brains need a large amount of fuel to develop and function.
The new study went further, by examine your own brain. Amato’s team wanted to know whether the gut microbes of primates with different relative brain sizes could effectively change the functioning from the brains of host mice.
To test this hypothesis, the team conducted a rigorously controlled experiment, during which gut microbes from two species of primates with large brains and a species of primate with a small brain in mice that had no microbes of their own.
After eight weeks, researchers observed clear differences in activity cerebral. Mice that received microbes from small-brained primates showed distinct patterns of brain function compared to mice that received microbes from primates with large brains.
In mice given microbes from large-brained primates, scientists found greater activity in genes linked to energy production and synaptic plasticity, the process that allows the brain to learn and adapt. These same pathways were much less active in mice that received microbes from primates with smaller brains.
“What was extremely interesting is that we were able to compare data we had from the host mouse brains with data from real monkey and human brains, and to our surprise, many of the patterns we saw in the mouse brain gene expression were the same patterns observed in real primates themselves,” Amato said.
“In other words, we managed to make the brains of mice resemble primate brains where the microbes came from”, notes Amato.
The researchers also discovered another unexpected result. Mice that received microbes from primates with smaller brains showed gene expression patterns associated with ADHDschizophrenia, bipolar disorder and autism.
Previous studies have found correlations between conditions like autism and differences in the composition of the gut microbiome. However, direct evidence that gut microbes contribute to these conditions has been limited.
“This study provides further evidence that microbes can contribute causally to these disorders — specifically, the gut microbiome is shaping brain function during development“says Amato.
“Based on our findings, we can speculate that if the human brain is exposed to microbes’ wrong actions‘, its development will change, and we will see symptoms of these disorders”, explains the researcher.
“I.e, if we are not exposed to the ‘right’ human microbes early in life, the our brain will work differentlyand this can lead to symptoms of these conditions”, concludes Amato.
