Short-chain fatty acids (SCFA) including acetate, propionate and butyrate are major byproducts of bacterial fermentation, and have been shown to play roles in the gut microbiome regulation of microglia, blood brain barrier, immune function and other endpoints24303132. To determine if these metabolites are involved in the behavioral effect of microbiome depletion on cocaine responses, we carried out a series of experiments repleting SCFA in antibiotic-treated animals. We again measured the effect of this manipulation in the 5 mg/kg CPP paradigm, as this was our most robust antibiotic-induced phenotype. As above, animals treated with antibiotics showed a robust preference for 5 mg/kg cocaine, while control animals showed minimal cocaine preference (Fig. 5 grey and blue bars). While SCFA supplementation on its own had no effect on cocaine preference, SCFA supplementation in antibiotic-treated animals resulted in a CPP response equivalent to control mice (Fig. 5 hatched bars; one-way ANOVA F(3,39) = 9.41; p < 0.0001 - with Holm-Sidak post-hoc tests). These results are strongly suggestive that these bacterial fermentation products are crucial for the behavioral changes seen in animals with depleted gut microbiota.
