TNF-induced neurotoxicity in DA cells and neurons is attenuated by SMase inhibitors. A, TNF-induced cytotoxic cell death is dependent on SMase hydrolysis of sphingomyelin. Diff-MN9D cells were pre-treated for 30 minutes with 5 μM desipramine (Des) or 10 μM GW4869 or 1 μM ARC39 followed by 5 ng/mL TNF for 48 hrs prior to MTS viability assay. Cell viability was measured by the MTS assay described under Methods. All values represent group means +/− SEM, n =3 - 4. One-way ANOVA with Tukey’s post-hoc; # denotes difference between TNF and vehicle at p < 0.001, * and *** denote difference from TNF alone at p < 0.05 or p < 0.001, respectively. B, TNF induced dose-dependent death of primary ventral mesencephalon DA neurons with SMase inhibitors affording robust rescue; 5 μM Desipramine (Des); 10 μM GW4869. All values represent group means +/− SEM, n =3 - 4. One-way ANOVA, Tukey’s post-hoc test to compare the extent of dose-dependent cell death in response to increasing concentrations of TNF and two-way ANOVA with Tukey’s post-hoc test to compare inhibitor conditions to 10 ng/mL TNF without inhibitors. * denotes p < 0.05, ** denotes p < 0.01, *** denotes p < 0.001.