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Gut-brain axis

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This weeks papers Reber et al. 2016 and Buffington et al. 2016 present a super interesting look into the gut-brain axis. Regarding both of these papers, it was amazing to see how potent favorable or unfavorable gut microbiome compositions are in affecting neuronal signaling and overall behavior.
Reber et al. shows how immunoregulatory immunization with specifically heat killed M.vaccae can serve as a protective factor against chronic subordinate stress induce colotis as well as behavioral symptoms due to chronic stress as such. Interestringly, this paper depleted regulatory T cell activity via the anti CD25 antibody in order to show that the antiinflammatory mechanism induced by m vaccae immunization is depented on the secondary regulatory mechanisms offered by Treg proliferation and signaling. But, when T reg signaling was removed, this did not seem to cause a significant change in behavior . Therefore, this begs the consideration of what othe rmechanisms may be at play in order for the microbes to affect brain function. It is certainly possible that another cell type or pathway is invold especially with 5-HT systematic alterations involved. But considering the microbiome can shape immune function so directly in which seems to directly cause colitis, as well as stress which can induce colitus, it is certainly a convoluted path. I would have liked to see an experiment in which T regs were blocked but antiinflammatory cytokine milieu was intorduced to see if it had the same effect . Overall, it woul dbe even mor einsightful to hone in on the true mechanism behind this gut-brain link. 
Buffington et al. looks at similar communictation between the gut and the brain but instead how maternal high fat diet can induce microbial changed of L. reuteri and further predispose ASD symptoms. L reuteri live colonization as well as oxytocin administration is used as a possible way rescue social deficits. But, one shortcoming here again is the mechanism involved. It would have been good here to also look at colitis or the immune profiel of the mice. It is also known the L reuteri tends to shift T cell proliferation tiwards Th17 in which is pro-inflammatory. Therefore, maybe in this case a proinflammatory profile somehow affects social behavior. 
In sum, these papers were extremely fun to read with very well thought out experiment but certianly extending into the rest of the GBA field, a lot more work must be done to really understand the mechanistic underpinnings at play. 

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