Recent research has raised questions about the existence of a microbiome in the human brain, similar to other organs in the body. A study published in Science Advances found bacterial communities in the brains of healthy vertebrates, specifically fish, challenging the long-held belief that the human brain is protected from bacterial penetration by the blood-brain barrier.
Scientists from the University of New Mexico discovered bacteria in the brains of salmon and trout, with some microorganisms showing adaptations that allow them to breach the blood-brain barrier and survive in brain tissues. While the physiology of fish differs from humans, the study’s findings have led to speculation about the potential existence of a brain microbiome in mammals.
The research revealed that bacteria were not only present in the olfactory bulbs of the fish, but also in other parts of the brain, suggesting that some bacteria may have entered the brain early in development or through the bloodstream and intestines. Certain types of bacteria were found to release molecules that could temporarily open the blood-brain barrier, allowing them to enter the brain and evade the immune response.
Prior studies have indicated the presence of bacterial genes in the brains of individuals with neurological diseases, further supporting the idea of a brain microbiome. By studying the microbiome in fish brains, researchers hope to gain insights into the potential role of bacteria in brain physiology, including their impact on metabolism and immunity.
Ongoing experiments on mice are underway to investigate the presence of a microbiome in mammalian brains. If confirmed, this discovery could shed light on the functions of bacteria in the brain, and whether they play a significant role in regulating bodily processes similar to the gut microbiome through the gut-brain axis. The question of whether bacteria in the brain are incidental or serve a crucial function remains unanswered.