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Microbiota and Gut-Brain-Axis

Author: Christine Chen

Editors: Viola Chen and Kevy Chen

Artist: Carys Chan

The gut-brain axis (GBA) is a communication highway that connects the brain and the gut. Signals can travel between the central nervous system, which is in the brain, and the nervous system, which is in the gut. This connection links the emotional and cognitive centers in the brain with the function of the intestines. Recent research has shown that the role of gut microbiota influences this interaction, which is a two-way street where the brain affects the gut microbiota and the microbiota affects the brain. In real-life scenarios, the disruption of balance in the gut microbiota can be associated with autism, anxiety, depression, and irritable bowel syndrome. 

In the past few decades, scientists have studied the crucial role of the microbiota in the regulation of the gut and the brain. This has given rise to the concept of the microbiota-gut-brain axis, which is increasingly studied in mental health, neurodegenerative disorders, neurodevelopmental disorders, etc. The composition of the microbiota is determined by infections, antibiotic use, environmental stress, genetics, and much more. However, as someone ages, the microbial diversity increases. Several conditions have been linked to the microbiota, and future research will concentrate on uncovering mechanisms to explore interventions and therapies for neuropsychiatric disorders. The balance and diversity of the bacteria will contribute to the overall well-being of the body. Although everyone’s microbiota is unique, it generally consists of bacteria from phyla like Firmicutes and Bacteroides, which are essential to maintaining the body’s balance. 

The communication system between the gut and the brain, known as the “gut-brain axis” (GBA), is an axis that maintains the balance of the digestive system and has effects on emotional motivation and cognitive functions. The GBA involves the brain, spinal cord, autonomic nervous system, gut nervous system, and hypothalamic pituitary adrenal axis. Essentially, the autonomic nervous system will carry the signals from the gut to the brain and back, while the hypothalamic pituitary adrenal axis responds to stress and releases stress hormones. These hormones impact various organs, such as the brain and the functional cells in the gut. 

Some researchers have conducted studies on the GBA that include the observation of patients with hepatic encephalopathy, a brain dysfunction, who showed improvements after taking oral antibiotics. This indicated the connection between gut bacteria and brain function. Additionally, there are new findings that suggest its influence on anxiety, depression, and autism. Another example is the effect of an imbalance in the gut microbiota and its influence on Irritable Bowel Syndrome (IBS). IBS is considered a disorder that involves the microbiome of the GBA. Animals have also been used in some studies. The animals that did not display microbial colonization were shown to have delayed gut function as well as abnormal neuromuscular activity, changes in stress reactivity, and memory dysfunction. These studies have shown that animals without microbial colonization displayed abnormal gut function, abnormal neuromuscular activity, changes in stress reactivity, and memory dysfunction. These abnormalities were restored when the animals were recolonized with bacteria. Microbial colonization normalizes the responses of the brain, especially in early life. The use of probiotics, such as Lactobacillus rhamnosus JB-1, demonstrates its influence on gene expression in the brain, relieving anxiety and stress.

Even small amounts of stress can alter the type of bacteria in the gut. The brain directly influences it by changing its signaling in the gut; the gut is thus more prone to inflammation and infection. Since the brain regulates the various functions of the gut, like movement and mucus production, stress can affect the gut's permeability, allowing substances to pass through and trigger an immune response. Hence, the next time you are stressed, remember that there is something important happening not only in your brain but also in your gut.



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