The Brain and Microbiota in the Gut

There are hundreds of billions of bacteria living in our guts. Fortunately, our relationship with most of them is symbiotic. Specifically, bacteria in our gut can affect our nervous and immune systems, and our brains can affect the balance of microbiomes. This relationship is referred to as the brain-gut axis. Reber et al. (2016) and Buffington et al. (2016) are two studies investigating “good” bacteria in the brain-gut axis and its role in stress, and social and synaptic deficits, respectively.
Featured in the paper by Reber et al., M. vaccae, bacteria found naturally in the environment was heat-killed and administered in a vaccine to mice. Researchers found that in response to stress, this vaccine promoted proactive coping behaviors, more resilience to stress, and reduced colon inflammation, compared to unvaccinated mice. The authors also point to the “old friends” hypothesis, which claims that modern day hygiene has prevented humans from being exposed to environmental organisms that would benefit our immune system. In the past, research (1) has shown that babies who lived with dogs were healthier than babies who did not. This is thought to be mediated by the fact that dogs introduce environmental bacteria that babies would not otherwise be exposed to. Reber et al. is onto something really important. Given that Buffington et al. found a critical period where mice microbiome alteration could make a difference, I think introducing M. vaccae at different stages of development would also be interesting to see.

Respiratory Tract Illnesses During the First Year of Life: Effect of Dog and Cat Contacts
Eija Bergroth, Sami Remes, Juha Pekkanen, Timo Kauppila, Gisela Büchele, Leea Keski-Nisula
Pediatrics Aug 2012, 130 (2) 211-220; DOI: 10.1542/peds.2011-2825

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