Michael Gershon pioneered the field of neurogastroenterology. He coined the term "second brain" in 1996 to refer to his findings that the gut contains a lot of neural chemistry. For instance, it produces 95 percent of our body's serotonin. The digestive process begins when a specialized cell called an enterochromaffin squirts serotonin into the wall of the gut, where up to 7 different types of serotonin receptors are housed. The receptors communicate with cells that release digestive enzymes or initiate peristaltic movement in the intestines. Serotonin also communicates with the brain, updating it on what's happening in the gut. 90% of this communication is one way, travelling from the gut to the head. And much of the communication is unpleasant. Serotonin often causes feelings of nausea. "The gut is not an organ from which you wish to receive frequent progress reports," says Gershon.^[https://www.nytimes.com/2005/08/23/health/the-other-brain-also-deals-with-many-woes.html] A serotonin transporter called SERT, which lines the wall of the gut, is responsible for carrying serotonin out of the gut once digestion has been initiated. People who do not have enough SERT suffer from irrititable bowel syndrome, a debilitating condition that causes abdominal pain, bloating, and alternating diarrhea and constipation. First, too much serotonin causes diarrhea. Then the receptors are overwhelmed and shut down, causing constipation. Another important type of cell in the gut is the mast cell. During stressful or traumatic situations, the barrier between the lumen (the interior of the gut) and the rest of the bowel can be broken, allowing unwanted substances across. The big brain causes mast cells to produce histamines and other inflammatory agents to expel the unwanted substances, causing diarrhea. Chronic mast cell production causes the gut wall to be tender and inflamed. --- **Other References** [[Your Dog Is Your Mirror#Gut-Brain]] [[Reference Notes/Radical Wholeness#^bd9b33]]