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.