The gut has been called “the second brain”. Research reveals that the enteric nervous system (ENS), a branch of the autonomic nervous system that is found in the GI tract, can communicate with, and function independently of the brain. The enteric nervous system of the gut is comprised of about 500 million neurons. The enteric nervous system can “think”, “remember” and “learn” on its own accord.

The enteric nervous system lines the mucosa of various organs: esophagus, stomach, small intestine, large intestine, pancreas, gall bladder, and biliary tree.

The ENS is involved in the regulation of several essential digestive functions. Most notably:

Peristalsis, intestinal motility: bowel muscular contractions

Digestive enzyme secretion: to break down food particles

Participates in the regulation of esophageal muscles: moving food to your stomach

Motility of the gall bladder, releasing bile into the duodenum

Assists the hormone secretin in releasing pancreatic enzymes

Exchange of fluids and electrolytes in the gut

Blood flow through the gastric mucosa

Also involved in the regulation of the gastic and esophageal sphincters: preventing acid food from entering the throat, and allowing food to pass into the duodenum from the stomach

Uses more than 30 neurotransmitters, including serotonin, GABA, dopamine, acetylcholine

Many researchers postulate that the enteric neurons have an important role to play in regulating behavior. This is likely due to the fact that the enteric nervous system communicates with the brain via the vagus nerve. It is known that strains of intestinal bacteria have a powerful regulatory effect on the enteric neurons. It is also known that these same bacterial colonies can induce behavior-modifying effects.

In 2011, researchers from the Journal of Neurogastroenterology stated: “As Bifidobacterium longum decreases excitability of enteric neurons, it may signal to the central nervous system by activating vagal pathways at the level of the enteric nervous system.”

What this means is that behavior is directly linked to intestinal bacteria and gut function.



Behavior & Leaky Gut

It is now well established that gut permeability, known as “leaky gut” has a direct effect on behavior. Studies such as this have demonstrated the link between intestinal permeability, gut infections and depression.

A key mechanism with how intestinal permeability plays a crucial role in behavioral disorders is most due to the effect that pathogens and bacterial species have on brain and neurotransmitter function. For example, streptococcal infections have shown to cause symptoms of OCD (obsessive compulsive disorder), tics, and Tourette’s. Additionally, the immune response that is invoked from strep and other infections, causes tremendous systemic inflammation, including to that of the brain.

The outer casing of gram-negative bacteria, known as lipo-polysaccharides (LPS), have shown in studies to induce massive systemic inflammation, including the release of pro-inflammatory cytokines such as TNF-a in the brain, as well as brain microglial activation.

Because of the essential role of “tight junctions” in the gut lining for protecting the organism from invading antigens, a diminishment of the tight junctions leads to an increased level of permeability, allowing various pathogenic microbes easy access into circulation. This permeability of the gut wall induces high levels of inflammatory activity in the brain, nervous system and in many other locations in the body.

Additionally, leaky gut will also feature imbalanced gut flora, and especially in the presence of pathogens and with an overgrowth of opportunistic organisms. This may involve imbalances in the same gut bacteria that communicate with the brain via the vagus nerve. So behavior and brain function are affected by the gut in more than one way.