Gut-Brain Axis

The papers for this week aimed to investigate the role of the gut-brain axis in stress and neurodevelopmental disorders. While we know that our microbiome influences brain function and certainly has some down-stream effects on behavior, the exact mechanisms by which this happens are complex and still not fully understood. 

Reber et al. demonstrated that immunization with an immunoregulatory environmental microorganism (M. vaccae) can rescue a stress phenotype induced with subordinate colony housing. I found the data in this paper very compelling, and the data clearly shows that immunized mice exhibit many more “proactive” behaviors than non-immunized mice, but I did wonder if there was a way to get a more complete picture of dominance status. Here, they compared the number of proactive behaviors (attacks, chasing) to reactive behaviors (flight, avoiding), to determine the dominance score of every animal. However, they only did this with male mice with other male aggressors, and I felt that their definition of proactive behaviors was incomplete. For instance, could they have monitored the vocalizations of the mice, or perhaps motion tracking? Also, what would the data look like if the aggressor was a lactating female? 

The second paper, by Buffington et al., examined the correlation between maternal obesity and neurodevelopmental disorders in offspring, particularly with respect to autism. Most interestingly, pairing MHFD (maternal high-fat diet) mice with MRD (maternal regular diet) mice restores the microbiome of the MHFD mice, and ultimately improves their social behavior. They also repeated a similar experiment by re-introducing L. reuteri into the microbial landscape of MHFD mice, which promotes oxytocin levels and therefore plays an important role in social behaviors. What I found interesting is that re-introducing L. reuteri had no effect on repetitive behaviors or anxiety of the mice (as exemplified in the marble burying paradigm), and only altered the social behavior of the mice. Does this in fact suggest that repetitive behaviors are not dependent on the microbiome? I certainly would have expected anxious behaviors to be influenced by the microbiome, so I would have liked to see a more detailed analysis of this