by Tony Isaacs

(The Best Years in Life) We're all familiar with the term "gut feeling". As it turns out, the term may be more apt than we realize. In recent years, research has increasingly identified the role the gut can have on mood and behavior, leading many scientists to refer to the gut as the "second brain". Now, for the first time, researchers have found conclusive evidence that conditions such as anxiety can originate in the gut instead of the brain.

In a study just published in the journal Gastroenterology, researchers at McMaster University found that bacteria residing in the gut influence brain chemistry and behavior. The research is important because several common types of gastrointestinal disease are frequently associated with anxiety or depression. In addition there has been speculation that some psychiatric disorders, such as late onset autism, may be associated with an abnormal bacterial content in the gut.

"The exciting results provide stimulus for further investigating a microbial component to the causation of behavioral illnesses," said Stephen Collins, professor of medicine and associate dean of research at McMaster's Michael G. DeGroote School of Medicine. Collins and Premysl Bercik, assistant professor of medicine, conducted the research in the Farncombe Family Digestive Health Research Institute.

Working with healthy adult mice, the researchers found that disrupting the normal bacterial content of the gut with antibiotics produced changes in behavior; the mice became less cautious or anxious. This change was accompanied by an increase in brain derived neurotrophic factor (BDNF), which has been linked to depression and anxiety.

When oral antibiotics were discontinued, bacteria in the gut returned to normal and Collins reported that there was "restoration of normal behavior and brain chemistry."

To confirm that bacteria can influence behavior, the researchers colonized germ-free mice with bacteria taken from mice with a different behavioral pattern. They found that when germ-free mice with a genetic background associated with passive behavior were colonized with bacteria from mice with higher exploratory behavior, they became more active and daring. Similarly, normally active mice became more passive after receiving bacteria from mice whose genetic background is associated with passive behavior.

Collins said that his team's research indicates that while many factors determine behavior, the nature and stability of bacteria in the gut appear to influence behavior and disruptions from antibiotics or infections might produce changes in behavior. Bercik said that these results lay the foundation for investigating the therapeutic use of probiotic bacteria in the treatment of behavioral disorders, particularly those associated with gastrointestinal conditions.

The gut is home to about 1,000 trillion bacteria. The gut also contains around 100 million nerve cells (neurons), more than in either the spinal cord or the peripheral nervous system. This multitude of neurons in the enteric nervous system enables us to "feel" the inner world of our gut and its contents. Neurons in the gut also use serotonin to signal back to the brain - and 95% of all serotonin in the body is in the gut. About 90 percent of the fibers in the primary visceral nerve, the vagus, carry information from the gut to the brain.

Generally when people think of "gut feelings" they are thinking about instinctive-like reactions such as the "butterflies" or "hollow feelings" one may get due to fear, bad news or an upcoming daunting task. Now it is apparent that other serious conditions may originate at least partially in the gut. Maintaining a healthy digestive system, including a healthy intestinal flora mix, could be a key in helping prevent and control such conditions.

Note: This author does not approve of the inhumane use of animals for laboratory experiments.

Sources included:

http://www.sciencedaily.com/releases/2011/05/110517110315.htm
http://www.scientificamerican.com/article.cfm?id=gut-second-brain
http://www.psychologytoday.com/articles/199905/our-second-brain-the-stomach