Overall, we see an effect of EcoHIV infection status alone on tight junction protein expression, particularly in the hippocampus of male mice, where claudin-5 and ZO-1 expression is significantly decreased across all treatment groups (morphine, fentanyl, and saline controls) in EcoHIV-infected mice as compared to the uninfected controls within the same treatment group. This evidence concerns the gene CLDN5 and infection.