The human gut microbiome plays a vital role in the body, communicating with the brain and maintaining the immune system. gut-brain axisSo it's not entirely far-fetched to suggest that microbes may play an even bigger role in our neurobiology.
fishing for microorganisms
for years, Irene Salinas A simple physical fact fascinates me: the distance between the nose and the brain is quite short. The evolutionary immunologist, who works at the University of New Mexico, studies mucosal immune systems in fish to better understand how human versions of these systems, such as the lining of our intestines and nasal cavity, work . She knows that the nose is full of bacteria, and they're “really very close” to the brain – mere millimeters from the olfactory bulb, which processes smell. Salinas has always suspected that bacteria might be seeping into the olfactory bulb from the nose. After years of curiosity, he decided to confront his doubts in one of his favorite model organisms: fish.
Salinas and his team began extracting DNA from the olfactory bulbs of trout and salmon, some caught in the wild and some reared in his laboratory. (Significant contributions to the research were made by Amir Mani, the paper's lead author.) They planned to look at DNA sequences in the database to identify any microbial species.
However, these types of samples 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 this topic effectively. If they found bacterial DNA in the olfactory 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 whole-body microbiomes of the fish. They took samples of the brain, intestines and blood of the remaining fish; They even took blood from several brain capillaries to ensure that any bacteria they discovered was present in the brain tissue itself.
“We had to go back and work again [the experiments] “Many times, to be sure,” Salinas said. The project took five years – but even in the early days it was clear that the fishes' brains were not barren.
As Salinas expected, some bacteria were present in the olfactory bulb. But she was surprised to find that there was even more in the rest of the brain. “I thought there wouldn't be bacteria in other parts of the brain,” she said. “But it turned out that my hypothesis was wrong.” There were so many organisms in the fish brains that it took only a few minutes to detect bacterial cells under a microscope. As an additional step, his team confirmed that the microbes were actively living in the brain; They were not inactive or dead.
Olam was impressed by his profound approach. Salinas and his team, he said, “answered the same question using all these different methods, using all these different methods — all of which produced solid data that there are actually living microorganisms in the salmon brain.” Are.”
But if so, how did they get there?
attack on the fort
Researchers have long suspected that the brain may have a microbiome because all vertebrates, including fish, have a microbiome. a blood-brain barrierThese blood vessels and surrounding brain cells are strengthened to serve as gatekeepers that allow only certain molecules in and out of the brain and keep out invaders, especially larger molecules such as bacteria. . So Salinas naturally wondered how the minds in his study had become colonized.
By comparing microbial DNA obtained from the brain with DNA collected from other organs, her laboratory found a subgroup of species that did not appear anywhere else in the body. Salinas hypothesized that these species may have colonized the brains of fish early in their development, before their blood-brain barriers were fully formed. “In the beginning, anything can go in; It's a free for all,” she said.