Fig. 3
Dark vs typical microglia’s interactions with parenchymal elements. Representative 5 nm resolution scanning electron microscopy images taken in the ventral hippocampus CA1 stratum lacunosum-moleculare of 20-month-old APP-PS1 and C57BL/6J male mice. A Typical microglia (TM) in C57BL/6J mice contacting a blood vessel (labeled BV) and myelinated axons (labeled ma) as well as axon terminals (labeled A), B TM far from a plaque interacting with axon terminals and dendritic spines (labeled S), C TM near a plaque interacting with a few axon terminals, D dark microglia (DM) near a plaque is contacting axon terminals. Graphs representing the number of axon terminals (E), all synaptic interactions (F), percentage of cells associating with the vasculature (G), myelinated axons (F), as well as the percentage of cells touching a myelinated axon (J). Data shown are expressed as means ± S.E.M. * p < 0.05, ** p < 0.01, using a Kruskal–Wallis test with a Dunn’s multiple comparisons post hoc test. Statistical tests were performed on n = 9–12 microglia per animal with N = 3 mice/group, for a total of 111 microglial cell bodies analyzed. Red outline = plasma membrane, yellow outline = nuclear membrane, blue outline = basement membrane, ma = myelinated axons, A = axon terminals, S = dendritic spines, orange asterisk = mitochondria, green asterisk = altered mitochondria, blue asterisk = endoplasmic reticulum, red arrow = Golgi apparatus, lb = lipid body, 3rd = tertiary lysosome, 2nd = secondary lysosome, Lg = lipofuscin granules, pink pseudo-coloring = dystrophic neurites