Tau reduction prevents abnormalities in synaptic transmission and plasticity in hAPPJ20 mice. Field (A, B, D) and whole-cell (C) recordings were made from acute hippocampal slices. A, Paired-pulse ratio in the medial perforant pathway was reduced in hAPPJ20/Tau+/+ mice but normal in hAPPJ20/Tau−/− mice (hAPP × tau interaction, p < 0.01 by two-way ANOVA; **p < 0.01 vs all other groups by post hoc tests; n = 8 slices from 3–4 mice per genotype.) B, Theta burst stimulation-induced LTP at the medial perforant path synapse was impaired in hAPPJ20/Tau+/+ mice, and this deficit was blocked by tau reduction (repeated-measures ANOVA on data from minutes 51–60, p < 0.01; n = 10–12 slices from 3–4 mice per genotype). C, Evoked NMDA and AMPA currents were recorded by whole-cell patch clamp on dentate granule cells. NMDA/AMPA ratios were depressed in hAPPJ20/Tau+/+ mice, and this deficit was blocked by tau reduction (hAPP × tau interaction, p < 0.001 by two-way ANOVA; ***p < 0.001 vs all other groups by post hoc tests; n = 15–18 cells from 4 mice per genotype). D, Synaptic strength in area CA1 was significantly decreased in hAPPJ20/Tau+/+ mice (repeated-measures ANOVA, p < 0.01) but normal in hAPPJ20/Tau−/− mice (n = 10–12 slices from 3–4 mice per genotype).