Mycobacterium vaccae activates a specific group of serotonin brain cells and causes functional improvement.

University of Bristol – Treatment of mice with a ‘friendly’ bacteria, normally found in the soil, altered their behavior in a way similar to that produced by antidepressant drugs, reports research published in the latest issue of Neuroscience.

These findings, identified by researchers at the University of Bristol and colleagues at University College London, seems to substantiate the idea an imbalance in the immune system leaves some individuals vulnerable to mood disorders like depression.

Dr Chris Lowry, lead author on the paper, said: “These studies help us understand how the body communicates with the brain and why a healthy immune system is important for maintaining mental health. They also leave us wondering if we shouldn’t all be spending more time playing in the dirt.”

Interest in the project arose after human cancer patients being treated with the bacteria Mycobacterium vaccae unexpectedly reported increases in their quality of life. Lowry and his colleagues reasoned that this effect could be caused by activation of neurons in the brain that contained serotonin.

When the team looked closely at the brains of mice, they found that treatment with M. vaccae activated a specific group of nerve cells that produce the brain chemical serotonin, and increased serotonin metabolism in the ventromedial prefrontal cortex. This part of the brain is involved in social and emotional processing and decision-making. A relative deficit of serotonin activity in certain parts of the brain is thought to cause depression in people. Mycobacterium vaccae’s beneficial effects on the behavior of mice may be due to increasing the release of serotonin in parts of the brain that regulate mood.

Future studies will be designed to determine if M. vaccae, other bacteria, or pharmaceutical compounds have antidepressant properties through activation of this group of serotonin neurons. One wonders whether this same group of serotonergic brain cells is activated by other factors such as exercise, hormone levels, omega-3 fatty acids intake, and even herbal adaptogens, and deactivated by chronic bad stress that predisposes to depression. The abstract of this study can be found here:

Immune response, serotonin and antidepressant effect of friendly soil bacteria