In a controlled lab experiment, researchers implanted gut microbes from two large-brain primate species (human and squirrel monkey) and one small-brain primate species (macaque) into microbe-free mice:
Within eight weeks of making changes to the hosts’ microbiomes, they observed that the brains of mice with microbes from small-brain primates were indeed working differently than the brains of mice with microbes from large-brain primates.
In the mice with large-brain primate microbes, the researchers found increased expression of genes associated with energy production and synaptic plasticity, the physical process of learning in the brain. In the mice with smaller-brain primate microbes, there was less expression of these processes.
“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,” Amato said. “In other words, we were able to make the brains of mice look like the brains of the actual primates the microbes came from.”
Another surprising discovery the researchers made was a pattern of gene expression associated with ADHD, schizophrenia, bipolar and autism in the genes of the mice with the microbes from smaller-brain primates.