NMDAR subtype 2B/2B- and 2A/2B-selective antagonists protect hippocampal neurons from HIV/MDM neurotoxicity. Hippocampal cultures were preincubated for 1 h with subtype-specific NMDA receptor antagonists and then exposed to MDM supernatants for 24 h. The number of surviving neurons was assayed by counting of MAP-2-reactive cells (^#p < 0.05 vs same day HIV-Jago; *p < 0.01 vs same day HIV-Jago.) Hippocampal cultures were exposed to the NR2B noncompetitive antagonists ifenprodil (10 μm; A) Ro25–6981 (10 μm; B). C, Conantokin-G, a competitive NR2B antagonist that inhibits 2B/2B- and 2A/2B-containing NMDA receptors, was used at 6 μm. D, Zinc, a noncompetitive antagonist of NR2A at nanomolar concentrations, was used at 500 nm. E, NVP-AAM077, a competitive NR2A antagonist that inhibits NMDARs containing 2A/2A or 2A/2B subunits, was used at 500 nm.