New scientific evidences suggest that the trillions of bacteria living in our gut have a huge effect on our brain – much larger than we thought.
Our digestive system houses trillions of bacteria that play a major role in numerous biological processes, such as supplying nutrients in the body, breaking down indigestible compounds, and defending the body against other pathogenic microbes. It has been taught that the gut serves as the second nervous system of the human body and is capable of functioning even without input from the brain. Still, these two vital systems remain connected to each other through the "the gut-brain axis", and changes in either system can cause a dramatic impact on the other.
Two research teams, headed by Rochellys Diaz Heijtz of New York University and Thomas Neufeld from the University of Minnesota found that completely eliminating the gut in animal models had surprising effects on the subjects’ anxiety levels. For instance, when tested under conditions that would normally induce stress, mice that lack resident bacteria were found to have significantly less anxiety and anxiety-related behaviours than the mice with normal intestinal microbes.
Gut microbes affect mental health
To investigate further, both teams explored the possibility of the gut bacteria influencing the activation of genes vital to brain function. They found that the genes involved in regulating neuron survival and signalling, along with genes that encode for receptors that bind neurotransmitters, were changed. For example, in bacteria-free mice, several neurotransmitters, including the serotonin, were altered within regions of the brain associated with motor control and anxiety-like behaviour.
Their findings suggest that the gut bacteria have some level of influence on the DNA transcription, particularly on genes essential to brain function.
The research teams also examined whether the gut flora influence brain changes during the earliest stages of life. In the experiments, young microbe-free mice were administered with normal levels of intestinal flora to study how these bacteria affected neurogenesis or the process where neurons are generated from stem cells and progenitor cells during pre-natal development. Researchers found that the gut flora increased the activation of the genes responsible for the maturation of neurons in the young mice. This led them to conclude that the gut bacteria are critical to neuronal growth and proper brain development during the foetal stage. Furthermore, the poor establishment of the gut bacteria may potentially lend to the occurrence of anxiety-based disorders.
Targeting microbes as treatment options
Put together, these new findings may lead to the development of new treatments for various mental illnesses such as autism, anxiety, and depression. These may include administration of probiotics or faecal transplant procedures that would modify gut flora community structures.
The new findings were published in the journal The Conversation.