To determine if alterations in intestinal microbiota influence the behavioral and molecular responses to cocaine, adult male mice were given a cocktail of antibiotics in their drinking water for 7–10 days before the start of any cocaine treatments (Fig. 1a), a procedure known to markedly reduce gut bacteria423. Daily fluid intake did not differ between groups over the course of the experiment (Fig. 1b - two-tailed t-test: p = 0.22; t = 1.23), and neither group demonstrated an appreciable change in their body weight during this time (Fig. 1c - two-way ANOVA: p ≥ 0.39 for time, treatment and interaction effects). Reduction of the gut microbiota with prolonged treatment with antibiotics resulted in markedly enlarged ceca (Fig. 1d,e – two-tailed t-test: p < 0.0001; t = 17.7) as has been previously reported in antibiotic-treated and germ-free mice2324. qPCR analysis of 16S rRNA from cecal contents was demonstrated a 72% reduction in bacterial content in mice treated with broad-spectrum antibiotics (Fig. 1f – two-tailed t-test: p < 0.0001; t = 7.03).
