The human gut microbiome plays an important role in the body, communicating with the brain and maintaining the immune system. gut-brain axis. Therefore, it is not at all far-fetched to suggest that microbes may play an even larger role in neurobiology.
catch microorganisms
For many years Irene Salinas He has been fascinated by the simple physiological fact that the distance between the nose and the brain is very close. Evolutionary immunologists working at the University of New Mexico are studying the mucosal immune systems of fish to better understand how human versions of the system, such as the intestinal lining and nasal passages, function. As she knows, the nose is full of bacteria, which are “really, really close” to the brain, just a few millimeters from the olfactory bulb, which processes smell. Salinas always had a hunch that bacteria was leaking from her nose to her olfactory bulb. After years of curiosity, she decided to confront her doubts about her favorite model creature, the fish.
Salinas and her team started by extracting DNA from the olfactory bulbs of trout and salmon, both wild-caught and lab-raised. (An important contribution to the study was made by Amir Mani, the paper’s first author.) They planned to search for DNA sequences in databases to identify microbial species.
However, this type of sample is easily contaminated by bacteria from the lab and 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 really came from the brain.
To cover their bases, Salinas’ team also studied the whole body microbiome of the fish. They sampled the remaining brain, internal organs and blood of the fish. They drew blood from many capillaries in the brain to confirm that the bacteria they discovered was present in the brain tissue itself.
“I had to go back and start over. [the experiments] Again and again, just to be sure,” Salinas said. The project took five years, but even in its early stages it was clear that fish brains are not sterile.
As Salinas expected, some bacteria were present in the olfactory bulb. But she was shocked to learn that the rest of the brain has even more functions. “I thought there would be no bacteria in other parts of the brain,” she says. “But my hypothesis turned out to be wrong.” There are so many bacteria in the fish brain that it took only a few minutes to find the bacterial cells under the microscope. As an additional step, her team confirmed that the microbes were actively living in the brain. They were not dormant or dead.
Orm was impressed by their thorough approach. Salinas and her team “used all different methods to circle the same question, all of which yielded compelling data that there were indeed live microorganisms in the salmon brain.” ,” he said.
But if it exists, how did it get there?
Breaking into the fortress
Researchers have long been skeptical that the brain also has a microbiome, since all vertebrates, including fish, have a microbiome. blood brain barrier. These blood vessels and surrounding brain cells are hardened to act as gatekeepers, allowing only some molecules to enter and exit the brain and preventing the entry of invaders, especially larger molecules such as bacteria. So Salinas naturally wondered how the brains in his lab had become colonized.
By comparing microbial DNA taken from the brain with DNA collected from other organs, her lab discovered a subset of species that are not present elsewhere in the body. Salinas hypothesized that these species may have colonized the fish brain early in development, before the blood-brain barrier was fully formed. “Early on, anything can go in. It’s free,” she said.
