It is well known that there are relationships between gastrointestinal (GI) disorders such as irritable bowel syndrome and psychiatric disorders including anxiety disorders. Another aspect of these relationships was highlighted recently in an article in the Proceedings of the National Academy of Sciences (PNAS) that demonstrated that bacteria in the gut are likely to affect the brain and may influence psychiatric symptoms including anxiety and depression.
This study investigated the effects of a strain of Lactobacillus on mouse models of behaviors that correlate with human conditions such as anxiety and depression. Lactobacillus is a "good" type of bacteria that lives normally in our GI system. These bacteria, or similar bacteria, are found in certain foods, including yogurt. Mice who received chronic feedings of these good bacteria exhibited behaviors in various testing procedures that correlate with fewer symptoms of anxiety and depression in humans.
How is this possible?
The GI system interacts with the brain via several mechanisms. One mechanism involves the vagus nerve. The vagus nerve plays a number of critical roles including conveying information from various body regions to the brain and vice versa. This nerve and its brain connections have become increasingly important in psychiatry and are targets for a novel form of treatment called "vagus nerve stimulation" (VNS), which may be helpful for patients with depression who have not responded to other treatment approaches. In VNS, a form of electrical pacemaker is used to activate the nerve. VNS is also used to treat patients with treatment-resistant epilepsy.
GABA (gamma amino butyric acid) is the major fast inhibitory neurotransmitter in the brain and is involved in many aspects of brain function. The GABA system in specific brain regions can be involved in the regulation of anxiety and stress and is the primary target for benzodiazepine-type anti-anxiety medications such as Valium (diazepam), Xanax (alprazolam), and Ativan (lorazepam).
The PNAS study found changes in the GABA system of several brain regions in the mice fed the good bacteria. In addition, when the vagus nerve was cut in these animals, the anti-anxiety and antidepressant effects of the GI bacteria were eliminated. The influence of the gut bacteria on the brain's GABA system was also eliminated. These results indicate that something related to good bacteria in the GI system influences the vagus nerve and that the vagus nerve then interacts with the GABA system and changes behavior.
In our opinion, it is likely that other neurotransmitter systems, possibly including the serotonin system, are influenced by various GI bacteria.
The take home message from this study is that our GI system can influence our brain and our behaviors. In turn, our brain influences our gut. The strong possibility that the foods we eat influence how we feel and how we act via effects on the GI system opens up new avenues of research that may lead to creative ways to treat people who suffer from various psychiatric disorders.
This type of research gives new meaning to the phrase "gut feeling."
This column was written by Eugene Rubin MD, PhD and Charles Zorumski MD.