In the Buffington et al paper, it is definitely clear that there is a microbiome-brain connection. The data supports the hypothesis that the microbiome is regulating social behaviors via oxytocin levels and VTA plasticity, which is super cool. It is less clear to me that their experiments implicate neurodevelopmental changes, which they hint at in their discussion, as the effects--social deficits, oxytocin levels and VTA LTP in response to social interaction-- are reversible through L. reuteri treatment and co-housing/socialization (or some combination), indicating that there are not permanent developmental changes occurring in MHFD offspring. There looks to be a near complete recovery of the VTA-LTP phenotype and I would be surprised to see a developmental change that was not permanent or at least difficult to reverse so completely (I would expect some intermediate phenotype), but perhaps there are existing examples in which that is the case.
This paper, in combination with the Reber et al paper, are pretty remarkable in that they suggest a potential therapeutic application of microbiome manipulation to treat behavioral and mental deficit like socialization, on what appears to be a neuronal level in the Buffington et al paper, and stress/immune dysfunction in the Reber et al paper. This new avenue of therapeutics might open new doors that were previously untapped using older methods. A seemingly impossible issue to tackle, however, would be achieving target specificity because it is likely to be incredibly difficult to find microbiome alterations that have very specific effects though it might be possible to find treatments that have inconsequential off target effects