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Our gut is home to a vast and diverse community of microorganisms known as the gut microbiome; this interesting community plays a vital role in our health. Lately, the connection between the gut microbiome and the nervous system, known as the “gut-brain axis”, has drawn great attention due to the impressive discoveries scientists have made.
The Gut-Brain Connection
Our gut contains a massive number of microorganisms; estimates suggest being around one trillion, outnumbering our body’s cell number, including approximately one thousand species. This microorganism ecosystem harboring the gut is changeable and influenced by factors such as diet, environmental factors, overall health, and age.
The Enteric Nervous System (ENS) is a network of neurons within the wall of the entire gut, starting from the esophagus, down to the rectum; it controls the function of the gastrointestinal tract. Our gut is connected to our brain through the vagus nerve, which enables bidirectional communication. This communication is achieved through the fascinating interplay of neurotransmitters and neuropeptides, hormones, and the immune system. This communication is explained as follows:
- The Neuroanatomical Pathway: The Vagus Nerve
The vagus nerve and the gut microbiota may interact directly or indirectly. Some bacterial products might interact directly with the vagus nerve; in other cases, the vagus nerve needs a bridge, in this case Entroendocrine Cells (EECs), to sense the bacterial products. Directly or indirectly, the vagus nerve transfers those signals to the brain, which in return influence our overall health.
- Neuroendocrine Pathway
The Entroendocrine Cells (EECs) in our gastrointestinal tract produce hormones and peptides that have a function linked to our nervous system including Glucagon-like peptide-1, Cholecystokinin, and Serotonin (controls your mood, sleep, thermoregulation, memory, and learning). The gut microbiota can also affect the hypothalamic-pituitary-adrenal axis (our stress response system). The gut microbiota imbalance (dysbiosis) leads to increased inflammatory molecules that can cross the blood-brain barrier (BBB) and activate the hypothalamic-pituitary-adrenal axis.
- The Immunological Pathway
The gut-associated lymphoid tissues (GALT) represent 70% of our body’s immune system; it fights against harmful invasion in the gut. When gut microbiota is compromised, an increased level of inflammatory molecules is produced which cross the blood-brain barrier leading to an increased inflammatory state in the brain.
- Neuroactive Molecules
The bacteria in our gut can produce neurotransmitters involving Serotonin (Around 90% of our body’s Serotonin is made in the gut), Dopamine (nearly half of our body’s Dopamine is produced in the gut), γ-Aminobutyric acid (GABA), Norepinephrine, Noradrenaline, and Acetylcholine. They can also produce short-chain fatty acids (SCFAs) some of which have important neurological functions.
Link to Diseases
Research supports that imbalance in the gut microbiome is associated with anxiety and depression-like behavior. Another study confirmed the role of gut microbiota in autism and mood disorders. Experiments also revealed the contribution of gut microbiome in Schizophrenia. Researchers confirmed the link between inflammation induced by gut microbiota and neuroinflammation-related diseases, such as Alzheimer’s.
Undoubtedly, maintaining a healthy gut microbiome is crucial for our health:
- Probiotics are beneficial bacteria; they can be taken as supplements to compensate for the imbalance in gut bacteria to treat or prevent diseases.
- Prebiotics are high-fiber foods for your intestinal bacteria helping them function properly and effectively and maintain a healthy gut; examples include vegetables, fruits, and whole grains.
- Antibiotics are used to kill bad bacteria; misusing antibiotics reduces the number of beneficial bacteria in our gut, allowing pathogens to take hold. They also influence the balance of gut microbiota, leading to diverse health problems.
- Diet influences our gut microbiota; if we do not have a health problem, we can improve our gut health only by watching what we eat. Beneficial foods include fiber-rich foods, fermented food, polyphenols-rich foods, omega-3 fatty acids, and Tryptophan-rich food.
To conclude, the gut microbiome plays a significant role in our health. This crucial microorganism community is changeable depending on factors including diet, stress, environmental factors, etc.; understanding the gut-brain axis opens the doors for potential therapeutic interventions.
References
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www.caltech.edu
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