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Brain-gut microbiome interactions

Buffington (2016)
In the figures for experiments that measure interaction time, the authors included a graph for contact duration in addition to interaction time but they don’t mention contact duration in the text. What’s the relevance of contact duration here/what does it add? The results appear relatively consistent with the results of interaction time. I don’t think that the authors would waste previous figure space on graphs that don’t add any value.
I thought the sociability vs. social novelty tests were interesting. I don’t know much about mice so I was a bit surprised that they prefer a new mouse over a familiar mouse. I would have expected them to prefer spending time with a familiar mouse but I guess it makes sense if they want to explore and investigate this novel mouse that has just entered their space. In the experiment examining the effect of social interaction on long-term potentiation in VTA DA neurons, the results show that interaction with an unfamiliar mouse triggered LTP in the VTA (in MRD offspring) but not interaction with a familiar mouse. Along the same lines, this isn’t what I would have expected. I would have expected the opposite results. I would expect interacting with a familiar mouse to be rewarding since the mice would already have a shared bond. Why is social novelty rewarding? I could see exploring a new mouse to reduce anxiety and fear about it but I was surprised that it was actually rewarding to mice.
What is the relationship between sociability and social avoidance? In the sociability test, the MHFD spend similar amounts of time in the empty chamber and the Mouse 1 chamber so while they don’t prefer the Mouse 1 chamber like the MRD mice, they also don’t prefer the empty chamber and from the one activity diagram included, they don’t appear to prefer the middle chamber either. If the mice were to avoid Mouse 1, I would expect to see them spending more time in the empty chamber than in the Mouse 1 chamber. I would expect sociability and social avoidance to have an inverse relationship but here we see decreased sociability without seeing increased social avoidance.
A doubt I still have is that in the co-housing experiment, how can we know how much of the rescue is from shared microbiota and how much is from social learning? The results show that co-housing is effective in rescuing social behaviors and that microbiota individually also rescues social behaviors (from germ-free mice experiment) but I’m interested in knowing how just social learning compares to shared microbiota in rescuing social deficits.
I was confused by the weighted and unweighted UniFrac measures and don’t understand what either of them means so I’m not sure if one of them being significant while the other one isn’t is a bad thing.
I thought it was so fascinating that this one bacteria being present in the gut made such a big impact on social behaviors. I didn’t realize that the brain and social behaviors were so closely linked and that bacteria in the gut could influence neuropeptide levels in the brain. Overall I really enjoyed reading this paper and thought that it flowed really well. The questions and ideas I had about what they should also investigate after each section were answered in the next one and each experiment clearly builds on the results from the last to really strengthen their points and conclusions.

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