New research suggests that there is a kind of “brain in the belly” – called the enteric nervous system – that responds to psychological distress.
For a long time, psychological problems were believed to cause many stomach problems. But the relationship may be just the reverse -- physical problems of the stomach can cause psychological distress. New research suggests that there is a kind of brain in the belly. This “brain” is called the enteric nervous system (ENS). What’s more, treatments for psychological disorders may also help ease stomach problems.
The Enteric Nervous System and Stomach Problems
The ENS is composed of a vast network of neurons located throughout the gastrointestinal (GI) tract. This neuron network communicates with the brain and spinal cord. There are as many neurons in the small intestine as in the spinal cord, and the same hormones and chemicals that transmit signals in the brain have been found in the gut, including serotonin, norepinephrine, nitric oxide, and acetylcholine. The brain and the ENS communicate constantly, and their functions sometimes overlap. For example, both “brains” control emptying of the stomach. Still, it appears that more messages are sent from the ENS. The ENS warns the brain about any toxins in the stomach so that both brains can coordinate an appropriate response. It also sends the brain signals of hunger and satiety.
Stomach Problems
Until the bacterium Helicobacter pylori was identified as the culprit in most cases of peptic ulcer -- a discovery that recently won the Nobel Prize -- doctors usually blamed stress and anxiety for ulcers. Now many researchers believe that the pain produced by ulcers produces the stress. The ENS may also be behind irritable bowel syndrome (IBS), which can cause diarrhea and constipation without detectable physical abnormalities. A recent study published found that people with IBS have significantly lower levels of serotonin in cells lining the stomach. Although serotonin is best known for its role as a mood-boosting brain chemical, it is also involved in many digestive functions and in the perception of pain. In fact, more serotonin is found in the stomach than in the brain, and the GI tract is very sensitive to changes in its serotonin level. The researchers concluded that IBS may arise from abnormalities in serotonin levels responsible for digestive functions.
Targeting The ENS
The fact that the ENS and the brain use the same chemicals and hormones may be why drugs designed to affect the brain can improve certain digestive diseases. Low doses of antidepressants -- for example, Paxil (paroxetine), Prozac (fluoxetine), and Zoloft (sertraline) -- can improve the symptoms of Crohn’s disease and IBS for many people. Some of the newest drugs for IBS -- Zelnorm (tegaserod) and Lotronex (alosetron) -- are geared toward balancing serotonin levels in the digestive system. Although these drugs have some serious side effects, they are a great leap forward in the treatment of digestive disorders, because they specifically target the ENS. Research into the workings of the “brain in the belly” is still preliminary. But as we learn more about the ENS, more effective treatments for digestive diseases will undoubtedly be discovered, though the wait may be a decade or more.
