A recent study by researchers at Northwestern University has found that the gut microbiome plays a direct role in shaping how the brain functions across different primate species. The research aimed to understand how mammals with larger brains have evolved to meet the high energy demands needed for brain growth and maintenance.
The team built on previous work showing that microbes from larger-brained primates, when introduced into mice, produced more metabolic energy—a key factor for supporting bigger brains. In this new experiment, scientists implanted gut microbes from two large-brain primate species (human and squirrel monkey) and one small-brain primate species (macaque) into microbe-free mice.
After eight weeks, they observed differences in brain activity between the groups. Mice with microbes from large-brain primates showed higher expression of genes related to energy production and synaptic plasticity, which is involved in learning. In contrast, mice with microbes from smaller-brained primates had lower expression of these genes.
"What was super interesting is we were able to compare data we had from the brains of the host mice with data from actual macaque and human brains, and to our surprise, many of the patterns we saw in brain gene expression of the mice were the same patterns seen in the actual primates themselves," said Amato. "In other words, we were able to make the brains of mice look like the brains of the actual primates the microbes came from."
The researchers also found a pattern of gene expression linked to conditions such as ADHD, schizophrenia, bipolar disorder, and autism in mice given microbes from smaller-brained primates. While past studies have shown correlations between gut microbiome composition and conditions like autism, this study provides more evidence for a causal relationship.
"This study provides more evidence that microbes may causally contribute to these disorders -specifically, the gut microbiome is shaping brain function during development," Amato said. "Based on our findings, we can speculate that if the human brain is exposed to the actions of the 'wrong' microbes, its development will change, and we will see symptoms of these disorders, i.e., if you don't get exposed to the 'right' human microbes in early life, your brain will work differently, and this may lead to symptoms of these conditions."
Amato noted potential clinical implications for understanding psychological disorders and suggested further research could reveal rules about how gut microbes interact with brain physiology across different species.
"It's interesting to think about brain development in species and individuals and investigating whether we can look at cross-sectional, cross-species differences in patterns and discover rules for the way microbes are interacting with the brain, and whether the rules can be translated into development as well."
The study titled "Primate gut microbiota induce evolutionarily salient changes in mouse neurodevelopment" will be published by Proceedings of the National Academy of Sciences of the United States of America.
