The human gut microbiome plays an important role in the body, communicating with the brain and maintaining the immune system. The gut-brain axis. So it’s not entirely far-fetched to suggest that microbes may play an even bigger role in our neurobiology.
Fishing for microbes
over the years, Irene Salinas Fascinated by a simple physical fact: The distance between the nose and the brain is very small. The evolutionary immunologist, who works at the University of New Mexico, studies the mucosal immune system in fish to understand how human versions of these systems, such as the lining of our intestines and nasal cavity, work. are The nose, she knows, is full of bacteria, and they’re “really, really close” to the brain—just millimeters from the olfactory bulb, which processes smell. Salinas has always thought that bacteria could leak from the nose into the eardrum. After years of curiosity, he decided to face his doubts in his favorite model creatures: the fish
Salinas and his team began by extracting DNA from the olfactory bulbs of trout and salmon, some caught in the wild and some raised in his lab. (Significant contributions to the research were made by the paper’s lead author, Amir Mani.) They planned to look up DNA sequences in a database to identify any microbial species.
These types of samples, however, are easily contaminated – either by bacteria in the laboratory or from other parts of the fish’s body – which is why scientists have struggled to study the subject effectively. If they found bacterial DNA in the bulb, they would have to convince themselves and other researchers that it actually originated in the brain.
To cover their bases, Salinas’ team also studied the fish’s whole-body microbiomes. They sampled the brains, intestines and blood of the remaining fish; They also took blood from several brain capillaries to make sure that any bacteria they discovered remained in the brain tissue.
“We had to go back and do it again [the experiments] Many, many times to be sure,” Salinas said. The project took five years – but even in the early days it was clear that fish brains were not barren.
As Salinas expected, the olfactory bulb hosted some bacteria. But she was surprised to find that the rest had more in mind. “I thought other parts of the brain wouldn’t have bacteria,” he said. “But it turns out my hypothesis was wrong.” The fish’s brain hosted so much that it took minutes to find the bacterial cells under the microscope. As an additional step, his team confirmed that microbes were actively living in the brain; They were not dormant or dead.
Olam was impressed by their comprehensive approach. Salinas and his team circled the same question, “using all these different methods — all of which produced convincing data that actually the microbes living in the salmon’s brain are,” he said.
But if there are, how did they get there?
Assault on the fort
Researchers have long suspected that the brain may have a microbiome because all vertebrates, including fish Blood-brain barrier. These blood vessels and surrounding brain cells are strengthened to act as gatekeepers that allow only certain molecules in and out of the brain and keep out larger molecules such as invaders, especially bacteria. keep So Salinas naturally wondered how the mind in his study was colonized.
By comparing microbial DNA from the brain with DNA collected from other organs, his lab found a subset of species that didn’t appear anywhere else in the body. Salinas hypothesized that these species may have colonized the fish’s brain early in their development, before their blood-brain barriers were fully formed. “Soon, anything can go in; it’s a free-for-all,” he said.
