Gut-Brain-Immune Axis

Abnormal neurological functioning of children with neurodevelopmental disorders such as autism, ADHD, learning disabilities and Sensory Processing Disorder now takes on a whole new meaning in light of recent research on the gut-brain-immune axis, which includes understanding the multitude of:

Over the last number of years, new research studies have become increasingly more compelling that gut microbes, the brain and the immune system are all communicating with each other in an intricately well-connected system.

We now know that the microbiome, the “bacterial ecosystem” that is home to trillions of microorganisms and bacteria, is connected to the brain and the immune system and plays a crucial role in modern day conditions such as anxiety, depression, obsessive compulsive behaviors, mood disorders and so on. Understanding this crucial connection will help parents know that the secret to healing their children and the best place to begin their healing journey is with the gut.

How Does All of This Work?

There are hundreds of millions of neurons that connect the brain to the enteric nervous system which is the part of the nervous system that controls the gastrointestinal system (gut). The entire digestive tract from the esophagus to the anus is connected by a vast network of neurons linking to the enteric nervous system from the gut to the brain via the vagus nerve.

The vagus nerve is the main line of communication between the gut and the brain, and research has shown that some gut microbes can activate the vagus nerve. The vagus nerve is known as the ‘wandering nerve’ which comes from its Latin derivative, and its job is to be in constant communication with the brain by sending updated sensory information.

The brain has been shown to directly impact the gut environment by regulating the gut mucosal immunity of the gastrointestinal tract. In fact, 80% of immune cells are located in the gut. The microbiota, the community of healthy microorganisms in the microbiome, communicate what is going on in the gut mucosal lining to the brain and vice versa. The brain communicates directly with the immune system, which in turn has a direct impact on mood and behavior. This complex communication among the microbiome (gut bacteria), the brain and the immune system is what is called the gut-brain-immune axis.

If the microbiome has good healthy beneficial bacteria and microorganisms, then the brain will neurologically function appropriately, the immune system will be strong, and healthy and mood and behavior will be positive. If the pathogenic gut microbes take over the microbiome and destroy the good healthy microorganisms, then these pathogens cross the blood brain barrier into the brain causing an inflammatory condition that eventually becomes chronic.

Chronic inflammation breaks down the immune system and alters behaviors and moods, leading to high anxiety, depression, mood disorders, and obsessive and aggressive behaviors.

Mood Neurotransmitters

Scientists have also found that gut microbes from the gut bacteria can create neuro-active compounds called neurotransmitters, which communicate with the brain. 95% of the neurotransmitter serotonin, 50% of the neurotransmitter dopamine, and the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) all affect mood and behaviors.

Serotonin is a very important neurotransmitter that regulates mood, sleep, appetite, social behavior, memory, and digestion. Dopamine regulates mood, sleep, behavior, decision-making, cognition, and is linked to reward and motivation. GABA is calming, reduces anxiety and aggressive behaviors, is vital in speech and language, and improves eye contact, social behavior and focus and concentration.

These mood neurotransmitters are another one of the ways that gut microbes communicate with the brain and alter the functioning of the immune system.

Gut Microbes

There are other ways gut microbes communicate with the brain and alter immune system functioning. One way is through food – gut bacteria is involved in the digestion process and depending on what substances are created from the breakdown of foods, the brain can be affected in many different ways. For example, under certain conditions such as Leaky Gut Syndrome, stress, infection, viruses and heavy metal toxicity, bad bugs such as super bugs — disease-causing bacteria — can all leak through the permeated gut wall and into the blood stream.

These toxic pathogens all communicate with the brain through cells in the blood vessels. This is a perfect example of what we see with children with autism who have Leaky Gut Syndrome.

Viruses, bacteria, and heavy metal toxicity leak through the permeated gut lining and get into the blood stream, triggering neurological reactions in the brain. The gut bacteria have a direct effect on areas of the brain that control behaviors, mood, stress, personality, food choices and food cravings, anxiety, fears, obsessive behaviors,  social interactions, and many other neurological functions we see in children with autism.

Autism Spectrum Disorder Research

Derrick MacFabe MD, PhD, a Canadian researcher, was actually the first researcher to scientifically prove this gut-brain-immune connection through mouse studies. He discovered how gut bacteria can alter behaviors in children with autism. Dr. MacFabe found that children with autism had a history of antibiotic exposure or hospitalization, gastrointestinal symptoms, abnormal food cravings and unique intestinal bacterial populations that were related to the severity of their symptoms.

His research on the role of enteric short-chain fatty acid fermentation products — in particular one strain called proprionic acid (PPA), a toxic metabolite of Clostridia difficile was found in the gastrointestinal tract of children with autism.

PPA is a compound of many gastrointestinal bacteria and a common food preservative, but causes neurochemical changes such as neuroinflammation, oxidative stress, mitochondrial dysfunction, glutathione depletion, and altered phospholipid/acetylcarnitine levels all consistent with findings in children with autism. The results from laboratory studies showed that rats treated with PPA developed behaviors similar to autism such as seizures and repetitive, perseverative and antisocial behaviors.

What is clear about PPA is that many systems within the body are affected such as: neurotransmitters, intracellular acidification and calcium release, fatty acid metabolism, immune function, and the alteration of gene expression. Environmental triggers may be the etiology behind PPA, but it is quite clear that the role of the microbiome has an effect on metabolism, immune, mitochondrial function and gene expression in children with autism.

Sources & References

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