Germs versus Depression

24. May 2007
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The fight against depression has a new sensation - bacteria win in brightening the mood. And too much hygiene in the childhood might cause depressed adults. Does psychiatry face a similar revolution like gastroenterology once did with the Helicobacter pylorii?

For decades, fighting depression is one of the tasks in the repertoire of neurologists and psychiatrists – but now an oncologist might have opened the floodgates to a novel therapy. By coincidence, the physician Mary O'Brien, working at the British Royal Marsden Hospital, found out: Mycobacterium vaccae initiates a yet unknown defence mechanism in the organism of the infected. This mechanism could result in patients in a good mood without any trace of depression.

By accident

Many clues point in that direction. Originally, O'Brien wanted to test the efficacy of a vaccine with M. vaccae as a therapeutic on patients with lung cancer. Because the efficiency of those microbes killed by heat is downright spectacular, even treating autoimmune diseases with this vaccine seems very promising for several years now.

The bacilli will suppress the tumor growth in cancer patients – this was one of the hopes of O'Brien. But the results – although positive – were quite different from the original expectations: Cognitive functions as well as frame of mind of the treated patients improved in such a way that it caught the attention of the scientist Chris Lowry of the British Bristol University. He started an especially designed study of animal experiments. His presumption: The bacteria entering the organism via vaccination could boost the serotonin production in the brain by means of the “immune response system”. Just how could that one work though?

Obviously by the quantity of released cytokines, as Lowry now reports in the professional magazine Neuroscience. According to him, the messengers stimulate certain serotonergic neurones in the Nucleus raphe dorsalis. This sensorial nerve stimulation results in a release of serotonin which – as we all know – calls a hold to depression.

Only happy mice

Just how strong the used bacteria worked, Lowry was able to observe in his laboratory mice. In a short time, the vaccinated mice were absolutely stress-free and in an excellent mood. Compared to unvaccinated animals, the vaccinated ones swam in a bucket – an ability given by mother nature only to happy mice so to speak. The apparent brightened mood of the lung cancer patients in O'Brien's study obviously might be based on similar correlations in the serotonin factory of the body.

The actual relevance of those cognitions does only show, once you take a look at the greater context of the relationship between immune system and the making of serotonin. It could be that not only the wondrous M. vaccae activate the serotonin production via the immune response and the Nucleus raphe dorsalis. Other bacteria might lead to similar results – such are the hopes of the physicians around O'Brien and Lowry.

No dirt isn't good either

For a long time it has a known fact that missing contact with bacteria due to too much hygiene might cause an increased number of children with asthma and allergies. Physicians now fear, after Lowry's publication, that this might be the same regarding depressions – another indication hitting the goal in hygiene hypothesis.

But not each and everyone who spent his childhood in a spotless clean environment has to end as a depressed grown-up. Genetic factors and yet unknown biochemical correlations in the brain will keep neurologists busy. But somewhere along the way of their search for better options in depression therapy, the day will come, when they will have to rely on new allies: Midgets from the Microbe Empire.

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