MAPT and Alzheimer disease: PHF1 did not co-localize with excitatory neuronal markers at any age in either the entorhinal cortex or the hippocampus (Additional file 1: Fig. S3), suggesting that the excitatory neuronal loss in TgF344-AD rats is driven by Aβ pathology; alternatively, we cannot rule out the possibility that tau pathology caused excitatory neuronal death prior to detection of the PHF1 epitope.