The Brain Gut Connection in IBS

Dysfunction in the connection between the brain and the gut may be a contributing factor in irritable bowel syndrome (IBS).

IBS is far from simple, and researchers are looking beyond the gut and toward the complex communication systems that link the gut to the brain to try and understand IBS.

Biology Basics

Communication among all of the parts of our bodies occurs through the passing of information from nerve to nerve.

This communication takes place along the following pathways:

• Central nervous system (CNS): the brain and the spinal cord
• Peripheral nervous system (PNS): nerve pathways that extend beyond the brain and spinal cord.

The peripheral nervous system is further divided into two parts:

• Somatic nervous system: responsible for the voluntary control of muscles and reaction to external sensations.
• Autonomic nervous system: responsible for the motor and sensation responses of our internal organs (viscera).

Enteric Nervous System

The enteric nervous system (ENS) is a part of the autonomic nervous system that is responsible for regulating the process of digestion. The ENS manages motility (movement of muscles), secretion of fluid and blood flow. The dysfunction of the enteric system is a major factor in IBS.

Up the Down Staircase

Communication is a two-way street when it comes to the brain and the digestive system. Several pathways link the brain and the intestines with information flowing back and forth on a continual basis. This close connection is most clearly seen in our response to stress (perceived threat), which suggests that this communication network is very important for our survival.

Researchers are finding evidence that dysfunction along these up and down pathways may be contributing to the abdominal pain, constipation, and/or diarrhea that are the symptoms of IBS. Nerves in the gut that are experiencing excessive sensitivity can trigger changes in the brain.

Thoughts, feelings, and activation of parts of the brain that have to do with anxiety or arousal can stimulate exaggerated gut responses. A malfunction may also be found along the many different pathways that connect the brain and gut. Dysfunction in the brain-gut communication system interferes with the body’s ability to maintain homeostasis, a state in which all systems are working smoothly.

The Role of Serotonin

The means by which one nerve cell communicates with the next is through chemicals called neurotransmitters. An extremely important neurotransmitter for digestive functioning is serotonin (5-HT). It is estimated that up to 95 percent of the serotonin in the human body is found in the digestive tract. Serotonin is considered to be a vital part of the communication system between the brain and the gut. Serotonin seems to play a part in motility, sensitivity, and secretion of fluids. Movement, pain sensitivity and the amount of fluid in the stool—you can see why serotonin has been a focus for IBS researchers.

Differences have been found in serotonin levels between patients who suffer from diarrhea vs. those who have constipation. in one research study, patients with diarrhea had higher than normal levels of serotonin in their blood following a meal, while patients who suffered from constipation had lower than normal levels of serotonin. This difference underlies the efforts to develop a medication that either increases or decreases serotonin levels by targeting specific receptor sites (5-HT3 and 5-HT4) to treat IBS. There are several new medications in this category to treat IBS-D and IBS-C.

A newer IBS research direction is a focus on a class of proteins called serotonin reuptake transporters (SERTs). SERTs are responsible for removing serotonin after it has been released. There is some indication that there are differences in SERT activity when IBS or inflammation is present. One school of thought is that the excess of serotonin interferes with the process of homeostasis, thus preventing the digestive system from functioning in a normal way.

Knowledge Is Power

How can you translate your new knowledge into helping to better manage your IBS? Obviously, you don’t have the power to directly affect your serotonin levels. However, there are two areas where your actions have a direct impact on the communication system between the brain and the gut.

Through the use of relaxation exercises, you can actively work to turn off the stress response, in which gut changes come about in response to thoughts and feelings. You could also consider the gastrocolic reflex in which colon contractions are stimulated by eating a large meal or fatty foods when deciding what foods to eat. For diarrhea, it would be better to eat smaller meals, while for constipation, a large meal would be preferable to trigger a bowel movement.

The understanding that the problems in IBS extend way beyond having a “sensitive stomach” can help you to develop a variety of strategies for addressing these very problems.