Co-exposure to HIV-1 Tat and morphine for 12 h alters the proliferation index and population of Sox2+ cells in vitro. Neither nestin+ (A, D) nor Olig2+ (C, F) populations were affected by any combination of Tat, morphine, or naloxone treatment at 12 h. However, both the percentage of the population that was Sox2+ and the proliferation of cells at this stage of differentiation were decreased by Tat and morphine co-exposure (B, E). (* p<0.05, ** p<0.01; with Duncan post-hoc test, n = 4–6, Morph = Morphine (500 nM), Tat (100 nM), Nal = naloxone (1.5 μM).