Sup35NM seeds tau aggregation in P301S tau transgenic mice. A‐D, Increase in AT8 immunohistochemistry (AT8) and Gallyas staining (GALL) positive neurons in the unilateral CA3 field after intrahippocampal Sup35NM fibril inoculation in P301S tau transgenic mice. AT8 and Gallyas positive neurons comparing P301S tau mice inoculated with C57BL/6 mouse brain homogenates (B6‐bh), ‐5TyrSup35NM solution, and Sup35NM fibrils (A, C; one‐way analysis of variance, followed by Tukey's test), and corresponding histology (Bregma level –2.6 mm). Comparison between non‐injected (contralateral) and injected (ipsilateral) side (B, D; paired t‐tests), and representative histological findings (Bregma level –2.4 mm). *P < .05, **P < .01, n.s. = non‐significant; indicated is the mean number of positive CA3 neurons per section ± standard deviation. For detailed quantitative data see Table S2 in supporting information