Our stomachs contain millions of beneficial microorganisms that help us with digestion. Their importance in our health and well-being is highlighted by reports that show the role an abnormal gut microbiome plays in the development of obesity. Other studies also suggest a close interaction between our immune system and the microorganisms. This interaction is large enough that it may even have an impact on certain types of cancer therapy. Indeed, research into the role that the gut microbiome plays on our physiology is becoming one of the most exciting scientific fields.
Intriguingly, mounting evidence suggests that these microorganisms could even influence our brain function, from mood to cognitive functions. For example, the gut microbiome influences signaling pathways involved in stress, leading to a potential impact on anxiety and depressive behavior.
How can we explain this relationship between the gut and the brain? A recent paper published in Biological Psychiatry unveils a potential mechanism for the gut-brain axis. By affecting the growth of new neurons in the adult brain, microorganisms are shown to play unexpected roles in regulating the brain’s plasticity.
Adult neurogenesis is a complex and elaborate process by which new neurons are born in the brain during adulthood. One of the main areas where active neurogenesis occurs is the hippocampus, a region that controls memory formation and potentially mood regulation as well. Understanding factors that influence adult neurogenesis may allow scientists to manipulate them for therapeutic purposes, such as for treatments of traumatic brain injuries and neurodegenerative conditions.
Recently, adult neural stem cells have also been shown to participate in the development of depressive illnesses and memory disorders, such as Alzheimer’s. Given that the gut microbiome has also been implicated in mood and learning, the authors of the study investigated whether gut microorganisms can influence rates of adult neurogenesis. In order to raise germ-free mice, the researchers raised mice in special conditions that do not expose them to microorganisms. These germ-free mice allow the scientists to study the influence of gut microorganisms on the brain’s biology.
Through the use of molecular markers that identify neural stem cells, the report found that germ-free mice had significantly increased newborn neurons in the hippocampus. What’s even more intriguing is that putting the germs back during early life did not prevent increased neurogenesis in adulthood. This permanent effect on neurogenesis suggests that the lack of germs fundamentally rewired a developmental program that controls the function of neural stem cells. Although a variety of conditions are known to affect neurogenesis, such as exercise and stress, this is the first study that shows the unexpected role of the gut microbiome in modulating the biology of adult newborn neurons.
Is this effect on neurogenesis a direct consequence of gut microbiome changes? Given that the gut microorganisms play a role in a variety of other biological processes, it may be possible that the gut is doing something else that then results in the neurogenesis phenotype.
However, this study is still exciting in that it has uncovered a hugely unexpected relationship between brain plasticity and the gut. As the saying goes, “You are what you eat.” Our diet has changed drastically in modern times with the rise of fast food and products filled with ambiguous chemicals. It may be possible that recent modifications may have partially contributed to the rise in psychological disorders, given that changes in diet can alter the gut microbiome.
Please note All comments are eligible for publication in The News-Letter.