Gut Reactions: How Microbes May Affect Pain Tolerance


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Walk into any grocery store cleaning aisle and you will be inundated with alcohol-based sanitizers and antimicrobial products. Due to the horror stories of infections and world-wide pandemics, our anti-germ culture puts people at constant odds against bacteria. However, the right bacteria at the right place and time can actually be beneficial.

Containing about 100 trillion microorganisms, the gut is part the gut-brain axis, which is the biochemical signalling network between the nervous and gastrointestinal system (Luczynski et al.). The gut microbiome is the most diverse in our bodies, and it plays a role in maintaining homeostasis, signalling cells, and regulating our metabolisms (NPR). Recently, researchers from the Microbiome Institute at the University College Cork in Ireland have verified a new ability of the gut microbiome: regulating pain tolerance.

Lead by Professors John Cryan and Ted Dinan, along with post-doctoral fellows Dr. Pauline Luczynski and Monica Tramullas, researchers found that the number of stomach and intestinal bacteria in mice had a large influence on the brain and spinal cord, ultimately affecting the degree to which those mice felt pain in their internal organs.

In pursuit of a novel mechanism for visceral pain, the Cork researchers tested mice with and without gut microbes. By observing mice that were bred in germ-free (GF) environments, researchers found that those without microbes exhibited increased stimuli to pressure and increased sensitivity to pain compared to germ-exposed, conventionally colonized (CC) mice (Science Daily).

Because GF mice lacked the proper biochemical pathways from gut bacteria, their spinal cord had increased expression of toll-like receptor genes, which are responsible for innate immunity, and cytokine genes, which are related to the immune system. In the brain, GF mice had enlarged periaqueductal grey regions, which correspond to descending pain modulation, and smaller anterior cingulate cortexes, which correspond to emotion, decision-making, and impulse control (Luczynski et al.). Interestingly, GF mice experienced a decrease in their pain symptoms when their gastrointestinal systems were exposed to high concentrations of microbes from fecal matter.

While this research still is new, these findings can offer insights into potential treatment option for those who suffer from gastrointestinal disorders, like Irritable Bowel Syndrome (IBS) and functional dyspepsia. About 60-70 million Americans suffer from gastrointestinal disorders, and studies like the one done by the Cork researchers take an important step to understanding possible gut-brain axis mechanisms and finding potential treatments (NIH).