T he scientific community has known for centuries Essays

T he scientific community has known for centuries that humans are teeming with bacteria. However, the emergence of the "microbiome" as a scientific concept represented a turning point in our appreciation of the bacterial world . The community of microbes that live in ou r guts has received particular attention because these microorganisms can dramatically affect our health, both positively and neg atively . However, it is becoming clearer that the influence of the gut microbiome reaches fur ther than anyone first expected . Now , further evidence that microbes in the gut can influence the brain and behavi or in mice . Scientist worked with a mouse strain called NOD (short for non-obese diabetic). Every day for two weeks, one quarter of the mice were fed water through a tube, a quarter were tube-fed a mix of antibiotics, a quarter were injected with saline and a quarter were injected with the cocktail of antibioti cs . The antibiotics were sel ected to kill off most of the gut bacteria when given orally but not when injected. They were then tested in behavior for all four groups of the NOD mice. Three of the groups did not change their behavior, but strikingly the group that had been fed water through a tube did behave differently. These mice tended to avoid other mice and showed increased signs of despair-like behaviors. Importantly, these behavioral changes did not happen in mice that had been tube-fed antibiotics or in the mice that had been injected instead. Once again the scientists repeated their tests with a second strain of lab mouse called "B6 " , but none of the treatments affected their behavior. Since only the tube-fed NOD mice showed differences in behavior . Upon studying them further t hey found that the gut micr obiome of the control mice ( the mice that had been fed with water) changed slightly, whereas the gut microbiome of the mice that had been fed antibiotics changed mo re. They also showed that the NOD mice and B6 mice had distinct microbiomes before any treatment. They then inspected a brain region called the medial prefrontal cortex, which had been linked previously to depression in mouse models of the disorder. They analyzed how genes were expressed in this region and again found striking differences in the control mice. Genes involved in producing the my elin sheath were less active in these mice. The control mice also had fewer myelin sheaths in the MPC than their antibiotic-fed mice . Notably, mice that are kept isolated for prolonged periods also produce less myelin in this brain region, and avoid social contact too. Other studies of germ-free mice have reported that the microbiome ca n influence myelination as well.