sAPPα protects organotypic hippocampal slices from excitotoxic cell death. (A) Representative brightfield image of a rat organotypic hippocampal slice. (B) Composite hippocampal slice showing high PI fluorescence, associated with total cell death in CA1 and CA3 and the dentate gyrus (DG) inner (ib) and outer blades (ob). Total cell death was induced by maintaining the slice at room temperature for 24 h in the absence of elevated CO2 levels. (C) Minimal PI fluorescence in the DG of a PBS-treated control slice. (D) Widespread PI fluorescence in the DG 48 h after NMDA challenge. (E) Reduced PI fluorescence in the DG following treatment with sAPPα and NMDA. (F) Regional analysis of PI fluorescence in organotypic hippocampal slices. Fold change: NMDA or NMDA + sAPPα PI fluorescence relative to PBS-treated control. NMDA treatment resulted in a >2 fold increase in PI fluorescence across all regions compared to PBS-control treated slices. Co-incubation with sAPPα and NMDA significantly reduced PI fluorescence in the CA1, DG/ib and DG/ob compared to NMDA alone. 1-way ANOVA with a Bonferroni post-hoc test: *p < 0.05, **p < 0.01, n = 4 animals, 19 slices/group.