Mixed rat neuronal cultures were exposed to TatΔ31–61, nitrosylated Tat, anti-Tat antibody, and/or NMDA. Mitochondrial membrane potential was measured 15–18 hours later. (A) NMDA caused toxicity versus untreated controls (p<0.01), which the mutant Tat-antiTat immune complex could not attenuate. (B) Nitrosylated Tat-antiTat immune complex could not attenuate toxicity caused by NMDA. Concentrations: Tat 200nM, antibody 5ng/μl, NMDA 125 μM. Data represents mean ± SEM of at least five independent experiments, analyzed by ANOVA with Neumann-Keuls post-test.