Fig. 8

Ultrastructural evidence of non-phagocytic microglial processes directly contacting proximal axonal swellings undergoing acute DAI. Representative electron micrographs of Iba-1 immuno-electron-microscope-labeled microglia in the thalamus of sham (a and b) and injured (c–f) animals. Iba-1-labeled structures in a and c–f are pseudo-colored blue for clarity. Note that, microglia processes containing Iba-1 (arrows) within the thalamus of sham-injured animals (a and b) are widely dispersed with no apparent association with axonal segments. Following cFPI, however, Iba-1+ microglial processes are much more prevalent. Some phagocytic microglia (c), containing material consistent with Wallerian degeneration (asterisks), are present following injury. These phagocytic microglia are primarily localized to areas of axonal damage/Wallerian degeneration. d–f Microglial processes (pseudo-colored blue) associating with axonal swellings (pseudo-colored yellow), as identified using the common ultrastructural features observed previously for diffuse axonal injury, appeared most frequently as d Iba-1 immunolabeled (arrows) puncta adjacent to the axonal swelling (white X), however, some cases e and f allowed for the tracing of microglia processes over short distances. Importantly, the Iba-1+ microglia processes found associated with axonal swellings did not reveal ultrastructural changes consistent with phagocytosis. Scale bar: 5 μm