Gut-Brain Connection

Overview

Do we really have one brain? Is there actually a connection between our gut and brain? Well, it turns out that our body has a “second brain” situated in our bellies. That is why many of us tend to have those “butterflies in the stomach” when we are anxious. Our emotions affect our gut functions and vice versa. This two-way communication between the brain and gut is now regarded as the keystone for a variety of neuropsychiatric ailments like anxiety, depression, attention-deficit hypersensitivity disorder (ADHD), autism etc.

What is the Second Brain technically?

To be precise, the “second brain” is referred to as the “Enteric Nervous System (ENS).” [1] The ENS is an assortment of millions of neurons lodged in the walls of our tummies. This ENS not only help us with the intricate process of food digestion but it also gives our gut the power to feel the inside mechanisms.

The Second Brain Impacts the Gut Ecology

This ENS strongly influences the composition of bacteria residing in our gut (the Microbiome). [2] A good amount of healthy gut bacteria, in turn, can produce a range of neuroactive substances, such as catecholamines, γ-aminobutyric acid, melatonin, and serotonin, all of which are critical to the regulation of emotions, mood, and behavior. [3] Thus, the second brain-Microbiome interaction may serve to promote intestinal and brain health at the same time.

The Gut Feelings

It is important to note, however, that the ENS can’t directly work like the big brain to control several bodily functions. It is there to establish a crosstalk between the gut and the brain. This communication is what accounts for those “gut feelings or intuitions” that many of us encounter from time to time. [4]

Any irritation in our gut may transmit signals to our brain that can drive changes in mood and behavior. This same theory forms the basis of functional gastrointestinal disorders like IBS, which often co-exist with anxiety and depression or the other way around. [4]

Antidepressants are being prescribed to IBS patients

Antidepressants may help relieve symptoms of IBS by their action on the nerve cells and chemicals in the gut ̶ not because the symptoms are all “in the head.” Hence, these medications are prescribed in IBS owing to the apparent gut-mind connection. [5]

Inflammatory changes in the Gut in Autism

Another fact that supports the gut-brain link is the presence of inflammation of the gut lining in individuals with autism. [6] Autism is a neurodevelopmental disorder that begins in early childhood. Autistic people are prone to developing GI symptoms like constipation and diarrhea as well as inflammatory GI diseases like inflammatory bowel disease. [6]

The intestines of autistic children are found to be highly permeable to inflammatory and damaging substances. Experts also report that the integrity and function of the barrier between the blood and brain (called blood-brain barrier) are compromised in children with autism. [7] This barrier normally wards off inflammatory and harmful agents from entering the brain. However, given the altered integrity of the intestinal and blood-blood barriers in autism, inflammation-promoting substances enter the brain and trigger widespread inflammation of neurons.

Along these lines, the use of probiotics, prebiotics, fecal microbiota transplantation (FMT), and diet may serve as potential therapies for children with autism. [5]

More to Discover About the Gut-Brain Connection

Despite the presence of the extensive evidence regarding the mind-gut link, scientists believe that this domain entails more exploration.

References

1. Avetisyan M, Schill EM, Heuckeroth RO. Building a second brain in the bowel. The Journal of Clinical Investigation. 2015;125(3):899-907. doi:10.1172/JCI76307.
2. Rolig AS, Mittge EK, Ganz J, et al. The enteric nervous system promotes intestinal health by constraining microbiota composition. Gore J, ed. PLoS Biology. 2017;15(2):e2000689. doi:10.1371/journal.pbio.2000689.
3. Petra AI, Panagiotidou S, Hatziagelaki E, Stewart JM, Conti P, Theoharides TC. Gut-microbiota-brain axis and effect on neuropsychiatric disorders with suspected immune dysregulation. Clinical therapeutics. 2015;37(5):984-995. doi:10.1016/j.clinthera.2015.04.002.
4. Mayer EA. Gut feelings: the emerging biology of gut–brain communication. Nature reviews Neuroscience. 2011;12(8):10.1038/nrn3071. doi:10.1038/nrn3071.
5. Clouse RE. Antidepressants for irritable bowel syndrome. Gut. 2003;52(4):598-599.
6. Li Q, Han Y, Dy ABC, Hagerman RJ. The Gut Microbiota and Autism Spectrum Disorders. Frontiers in Cellular Neuroscience. 2017;11:120. doi:10.3389/fncel.2017.00120.
7. More Support for Gut-Brain Link in Autism – Medscape – Jan 30, 2017. Accessed on Nov. 6, 2017.