Fig. 5

Microglia apposition on synaptic structures. a Representative images of microglia interactions with dendritic spines/shaft at different z-levels of stack. Neuronal dendrites and spines were filled with biocytin and stained with streptavidin-Alexa 488 (green) and microglia were visualized with Iba1 and P2RY12 + (red) immuno-labeling. White pixels indicate an overlap between two channels. Scale bars: 20 µm and 5 µm. b Schematic diagram of criteria for determining microglia appositions on dendritic shafts or spines, classified as either contact (touching) or neighboring (within 1 microns). c Box-and-whisker plots with vertical scatter plots of individual neurons showing the density of microglia appositions (contacting and neighboring) on dendritic shaft and spine. The vehicle group had higher densities of microglial–apical shaft (one-way ANOVA, main effect, p = 0.07; Fisher’s LSD post hoc, veh vs. EV, p = 0.009) and microglial–apical spine (p = 0.038) appositions compared to EV group, and a trend for greater total appositions in the vehicle than in the control group was found (ctr. vs. veh., p = 0.058). d Total microglial appositions (contacts and neighboring on spines and shafts) on different segments of apical/basal dendrites in ventral PMC. Mid-apical dendrites had higher densities of microglial contacts only in veh compared to control (ctr. vs veh, p = 0.03; ctr. vs EV, p = 0.84). For c-d Ctr: n = 10 cells from 3 monkeys; Veh group: n = 10 cells from 3 monkeys; EV group: n = 7 cells from 2 monkeys. e Box-and-whisker plots with vertical scatter plots of individual cases showing the fraction of VGLUT2 colocalized with microglia, which was higher in both groups with lesions in M1 compared to control group (ctr. vs. veh, p = 0.009; ctr. vs. EV, p < 0.001). Ctr: n = 3; Veh group: n = 4; EV group: n = 5 monkeys. f Representative images of dual channel labeling of microglia (red) and VGLUT2 (green), with right panel showing the inset (yellow box) at higher resolution, with colocalized VGLUT2–microglia label masked in white. Box-and-whisker plots: bars show interquartile range and median (horizontal line) with error bars = 95% confidence interval; *p < 0.05, **p < 0.01