Human tau protein as well as PHF1 tau could be detected in the EC and hippocampus of rTgTauEC (Figures S3A and S3B), confirming the histological data showing human tau protein present in the hippocampal formation. This observation of human tau protein and pathology in areas that largely do not express the human tau transgene indicates that tau pathology spreads from cells expressing the transgene to downstream neurons. Indeed, combined fluorescence in situ hybridization AZD8055 purchase (FISH) and immunofluorescent staining for both human tau protein and Alz50 revealed neurons with human tau and/or misfolded tau that do not have detectable

levels of human tau transgene in the EC (Figures 3D and 3E), hippocampal fields (Figures S3C and S3D), and anterior cingulate cortex (Figure S3E) showing a dissociation between htau expression and human tau protein accumulation. In the EC, quantification of human tau mRNA and Alz50-positive cells revealed that only 33.3% of the Alz50-positive neurons in EC expressed human tau mRNA at 12 months, indicating a spread of misfolded tau to neighboring neurons within the EC without detectable transgene expression (Figure 3F). By 24 months of age, an astonishing 97% of Alz50-positive neurons (96.4% ± 6.45% SD; p < 0.001)

did not have any detectable human transgene expression, showing that the propagation to neighboring cells increased with age (Figure 3F) and indicating that transgene expressing neurons may be lost Afatinib molecular weight (as will be discussed later). Alz50-positive aggregates were also found in large numbers of neurons

without detectable transgene expression in the DG, anterior cingulate cortex, CA1, and CA3, all major targets of the EC (Witter et al., 1988). Importantly, unlike the anterior cingulate cortex, cortical areas that showed limited transgene expression outside of the EC, but do not receive direct input from the EC, did not show any tau aggregation. Moreover, the cerebellum, which expresses human P301L tau mRNA, did not develop any fibrillar accumulation of htau in the soma. These experiments with FISH showing human tau protein and Alz50-positive aggregates in cells without PD184352 (CI-1040) detectable levels of human tau mRNA confirm the transmission of human tau from neuron to neuron and rule out the possibility that the transgene promoter was nonspecifically expressing human tau in these hippocampal neurons (i.e., becoming “leaky” in older animals). To confirm that the absence of human tau mRNA in the FISH experiments was not due to limited sensitivity of the technique, we used FISH to label human tau mRNA and immunofluorescence with HT7 to label human tau protein in sections from 17-month-old animals.