The Social Microbiome: Prosocial Behavior Associated with the Gut-Brain Microbiota Axis in Nave Rats and following Early-Life Stress

Prosocial behavior is associated with positive health outcomes, but the underlying biological mechanisms remain unclear, especially regarding the role of the gut microbiome. Using the 'Helping Behavior Test', we evaluated prosocial tendencies in rats. We also investigated differences in gut microbiome profiles between prosocial and non-prosocial rats in two experimental settings. In the first experiment, we examined the relationship between nucleus accumbens mRNA expression and microbiome composition in the context of helping in naïve rats. Based on these results, an in vitro study tested the effects of various additives on the taxon Eubacterium ventriosum. In the second experiment, we investigated the effects of early life stress (maternal separation) on prosocial behavior and microbiome profiles. We found compositional differences in the microbiome according to prosocial behavior. These taxa were also associated with several genes and pathways, including immune markers. Additionally, we observed distinct microbiome profiles between the control and three stress groups. Interestingly, the prosocial rats from the stress groups differed from each other, mainly in the relative abundance of the Firmicutes and Bacteroidetes phyla, indicating distinct microbiome changes following different stress exposures. Overall, these detailed analyses provide insights into the relationships among prosocial behavior, the gut-brain-microbiota axis, and early life experiences.