Figure 1 – Schematic for experimental design.

Mice for these experiments were conventionally colonized and maintained on untreated water (H₂O), conventionally raised and treated with broad spectrum antibiotics for two weeks prior to injections (Abx), and those that were born and maintained fully germ-free throughout their lifespan (GF). Mice from each group received seven daily injections of saline or morphine (20mg/kg) and were euthanized 24 hours after the final injection, and the nucleus accumbens (NAc) dissected out for RNA isolation and transcriptional profiling.