Fig. 4

Microglial number and morphology is dramatically altered in T5x mice. Microglia were immunohistochemically labeled with IBA1 and then quantified by IMARIS bitplane analysis of confocal Z-stacks to determine the effects of Aβ, and tau pathology on microglial number and morphology. Analysis was performed within the CA1 (a) and dentate gyrus (b) of the hippocampus and the parietal association cortex (c), revealing a significant 2–3 fold increase in microglial number in T5x versus WT mice in each of these regions (p < 0.0001). T5x mice exhibited a similar 2-fold increase in microglial number relative to Thy-Tau22 mice in all 3 regions (d). Within CA1, T5x microglial number was also substantial higher than 5xfAD littermates (p < 0.0001). However, T5x mice exhibited a more subtle increase in comparison to 5xfAD mice within the dentate gyrus (p = 0.02) and cortex (p = 0.07). e Automated quantification of microglial process length (e) and branching (f) also revealed several significant differences withT5x microglia exhibit significantly shorter process length and decreased microglial branching compared to all other genotypes in CA1 (p < 0.01) and to Thy-Tau22 and WT groups within the dentate gyrus and cortex, (p < 0.05). h-k Examination of microglia in hippocampus CA1 revealed a unique population of rod-like microglia in T5x mice. β3-tubulin immunoreactivity (green, g) were associated with a microglial response, IBA-1 labeled microglia (red, h) were imaged within the stratum radiatum. Interestingly, this examination revealed a very specific pattern of microglial morphology within T5x mice that was not present in any of the other three genotypes. The appearance of elongated, linearly organized microglia is reminiscent of highly activated ‘rod-like’ microglia that are found in association with neurodegenerative changes [11, 87]. Thus, the microglia appear to mount a very specific response to hippocampal dendritic degeneration within T5x mice. Data are represented as mean ± SEM, n ≥ 8 mice/group. * Indicates p < 0.05 for both ANOVA and Fisher’s protected least-significant difference (PLSD) post hoc tests with significance versus all other groups, whereas *over a bar indicates significance between 2 or 3 particular groups. Scale Bar = 100 μm in (a-c), 30 μm in (g-i), and 10 μm in (j)