Cytoskeletal derangements of cortical neuronal processes three hours after traumatic brain injury in rats: An immunofluorescence study

Semiquantitative Western blot analyses have shown that traumatic brain injury (TBI) can produce significant loss of cytoskeletal proteins (neurofilament 68 [NF68], neurofilament 200 [NF200] and microtubule associated protein 2 [MAP2]) possibly by calpain-mediated proteolysis. Thus, we employed immunofluorescence (light and confocal microscopy) to study the histopathological correlates of acute neurofilament and MAP2 protein decreases observed 3 hours following unilateral cortical injury in rats. TBI induced dramatic alterations in NF68, NF200, and MAP2 immunolabeling in dendrites within and beyond contusion sites ipsilateral and contralateral to the injury site. Marked changes in immunolabeling were associated with but not exclusively restricted to regions of dark shrunken neurons labeled by hematoxylin and eosin staining, a morphopathological response to injury suggesting impending cell death. Light microscopic studies of NF200 immunofluorescence revealed a prominent fragmented appearance of apical dendrites of pyramidal neurons within layers 3 and 5, as well as a loss of fine dendritic arborization within layer 1. Confocal microscopy detected varying degrees of NF200 disassembly associated with these areas of neurofilament fragmentation. Light microscopic studies of NF68 immunofluorescence detected subtle and less severe structural changes including smaller breaks and focal vacuolization of apical dendrites. Light microscopic immunofluorescence of MAP2 revealed changes similar to those seen for NF200. Acute axonal alterations detected with NF68 were minimal compared to immunofluorescence changes seen in dendritic regions. Therefore, preferential dendritic cytoskeletal derangements may be an early morphological feature of experimental traumatic brain injury in vivo. In addition, these cytoskeletal derangements may not be exclusively restricted to sites of contusion and cell death.