Microglia alignment in Iba1 stained tissue from the primary sensory cortex after diffuse brain injury. (A) Iba1 immunoreactivity is apparent in the primary somatosensory barrel field (S1BF) region of the cortex of midline fluid percussion injured animals (mFPI). The arrows mark principal regions of microglial hyper-intensity in the 7 day post-injury animals; sham animals show no appreciable microglia activation. (B) At higher power cellular pathological processes result in microglial hyper-intensity and morphological activation at 7 days post-injury, but not in uninjured sham animals. (C) The time course of microglial activation at the site of hyperactivity shows peculiar morphological alignment of microglia in the S1BF region at 1, 2, 7 and 28 days post-injury. At 1 day post-injury, microglia morphology shows reduced ramification with swollen or stretched cell bodies. These morphological changes are more evident at 2 days post-injury. By 7 days post-injury, microglia are elongated perpendicular to the dural surface across cortical layers, with morphology reminiscent of rod microglia. At 28 days post-injury, microglia alignment is reduced and morphology begins to regain its ramification. Maximal morphological alignment appears to be at 7 days post-injury. (D) Montage of photomicrographs showing a train of at least 10 aligned microglia 2 days post-injury.