Caspase-9 activation in hemisphere injected with tau oligomers. Immunofluorescence using an antibody for pro-caspase-9 was performed. (A and B) Caspase-9 activation (green fluorescence) was observed in hemispheres injected with tau oligomers (A) or fibrils (B). However, the levels of activation were significantly higher in the hemispheres injected with oligomers compared with fibrils, which is not significant. (C and D). No activation of caspase-9 was observed in the hemispheres injected with tau monomers (C) or PBS (D). Nucleus was stained with DAPI (blue). (Scale bars = 10 μm.).