The social microbiome: Eubacterium links gut microbiota to prosocial behavior in stressed and naïve rats, a gut-brain axis study

Background: Prosocial behavior is associated with positive health outcomes, but the underlying biological mechanisms remain unclear, especially regarding the role of the gut microbiome. Results: We used the Helping Behavior Test to assess prosocial tendencies in rats and compared gut microbiome profiles between prosocial and non-social individuals across two experiments. In the first, we linked nucleus accumbens mRNA expression to microbiome composition in naïve rats. Prosocial behavior was associated with enriched Eubacterium species and genes tied to immune and neurotransmitter functions. An in vitro follow-up tested effects of additives on Eubacterium ventriosum. In the second experiment, we studied how early life stress (maternal separation) influenced prosocial behavior and the microbiome. Microbiome differences aligned with social behavior. Different stressors led to distinct microbiome profiles, especially among non-social rats, with variations in Bacillota and Bacteroidota abundance. Conclusions: Overall, these detailed analyses provide insights into the behavioral, molecular, and microbial bases of prosocial behavior, highlighting the complex relationships between prosocial behavior, the gut-brain-microbiota axis, and early life experiences.