Do the brain and the gut talk to each other? Let’s ask the gut microbes

Dr. Deeya Saha, Assistant Professor, Department of Bioinformatics, Kalinga University, Naya Raipur

What is a Gut-brain axis (GBA)?
GBA is defined as a bidirectional communication bridge between the central and enteric nerves, connecting cognitive and other emotional traits of brain to intestinal functions. As it is a bidirectional system both the gut and the brain can thus influence each other’s function. Recent studies show that microbes residing within the gut play a pivotal role in dictating and influencing the GBA.
Role of intestinal microbes in neurological disorder
Growing evidences indicate that alteration in the composition of gut microflora, reduction in microbial diversity in the intestine, also known as dysbiosis is associated with a number of neurological diseases. Neurodegenerative disorders like Parkinson’s, Alzheimer’s diseases to neurodevelopmental like autism spectrum disorders could be triggered by dysbiosis of the gut. In addition, depression and anxiety has also been linked to changes in the gut microbiome composition. Very little is known on the mechanisms by which gut microbiota might influence the GBA. In the following section I would briefly describe the key pathways that link gut microbiome to disruption of GBA.
Mechanisms deployed by gut microbiota to disrupt GBA
Microbe-derived metabolites: Short Chain Fatty Acids (SCFAs) are one of the best examples of gut microbe derived metabolite that can trigger production of neurotransmitters like serotonin, dopamine etc. Absence of SCFAs often correlate with lower concentrations of neurotransmitters effecting central nervous system functions.
Gut hormone secretion: Microbial residents of the gut influence gut hormone secretion and gut hormones in turn is important for gut-brain signaling.
Synthesis of neuroactive molecules: Gut microbiota synthesizes directly many neuroactive compounds like dopamine, acetylcholine, melatonin etc. which are required for normal functioning of the central nervous system.
Microbial invasion of the blood brain barrier: Sometimes bacteria can directly bypass the blood brain barrier and adhere to brain endothelium. Such instances are rather rare and the exact mechanisms of invasion remain poorly understood.
Targeting the gut microbiome for treatment of Neurological disorders
Some of the key gut microbiota-based therapeutic interventions used to treat neurological disorders are as follows:
Probiotics: They are defined as beneficial microbes that not only secrete pivotal metabolites needed for proper functioning of different organs (including brain and nervous system) but also promote growth of other beneficial microorganisms. Recently, Lactobacillus plantarum culture has been widely used to treat autism spectrum disorder.
Prebiotics: They are dietary supplement that favors the growth of beneficial microbes within the gut. E.g., Galacto oligosaccharides are used to treat anxiety disorder.
Fecal Microbiota Transplant: This is a process in which a healthy individual act as a donor and the stool or feces from them are transferred to diseased individual (recipient) via rectal tubes or other apparatus. This ensures the transfer of entire healthy gut microbe community to the patient and is a successful mode of treatment in many neurological maladies. For instance, FMT is safe and efficient in the treatment of diseases like Parkinson’s and bipolar disorders.
References
⦁ Liu et al., eBiomedicine 2022
⦁ Carabotti et al., Annals of Gastroenterology 2015