Happiness could be found in the mud ...

A mixed research team from the University of Bristol and University College London has discovered that bacteria found in the soil turned on a group of neurons that synthesize the brain chemical serotonin, named also "the happiness hormone".

When the researchers treated lab mice with a 'friendly' bacteria, normally encountered in the soil, they altered their behavior in a way that resembled the effect of antidepressant drugs, as they noted in their study published in the latest issue of Neuroscience.

The new discovery could help in understanding why an imbalance in the immune system makes some patients prone to mood disorders like depression. "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", said lead researcher Dr Chris Lowry, from Bristol University.

The researchers had observed that human cancer patients, after being treated with the bacteria Mycobacterium vaccae, unexpectedly signaled increases in their quality of life.

This bacterium is related to the bacterium that induces tuberculosis and lives naturally in soil, and was first isolated from cow dung in Austria. Lowry's team believes that the effects induced by M. vaccae could be triggered by activation of neurons in the brain that produce serotonin and when the researchers took a closer look at the brains of mice, they found that indeed their theory was true.

The lack of serotonin in the brain is linked to depression in people, thus M. vaccae's effects on the behavior of mice may be due to increasing the release of serotonin in parts of the brain connected to the mood.

Future researches are still needed to determine if M. vaccae, other bacteria, or pharmaceutical compounds have antidepressant properties through the activation of this group of serotonin producing neurons.