Previous studies have shown that
traumatic brain injury (TBI) produces progressive degradation of
cytoskeletal proteins including neurofilaments (e.g., neurofilament 68 [
NF68] and
neurofilament 200 [NF200]) within the first 24 h after injury. Thus, we employed immunofluorescence (light and confocal microscopy) to study the histopathological correlates of progressive
neurofilament protein loss observed at 15 min, 3 h, and 24 h following unilateral cortical injury in rats. TBI produced significant alterations in
NF68 and NF200 immunolabeling in dendrites and cell bodies at
contusion sites ipsilateral to injury, as well as in the noncontused contralateral cortex. Changes in immunolabeling were associated with, but not exclusively restricted to, regions previously shown to contain dark shrunken neurons labeled by
hematoxylin and
eosin staining, a morphopathological response to injury suggesting impending cell death. Immunofluorescence microscopic studies of
neurofilament proteins in the ipsilateral cerebral cortex detected prominent fragmentation of apical dendrites of pyramidal neurons in layers 3-5 and loss of fine dendritic arborization within layer 1. While modest changes were observed 15 min following injury, more pronounced loss of dendritic neurofilament immunofluorescence was detected 3 and 24 h following injury. Confocal microscopy also revealed progressive alterations in
NF68 immunoreactivity in dendrites following TBI. While some evidence of structural alterations was observed 15 min following TBI, dendritic breaks were readily detected in confocal micrographs from 3 to 24 h following injury. However, disturbances in axonal
NF68 by immunofluorescence microscopy in the corpus callosum were not detected until 24 h after injury. These studies confirmed that derangements in dendritic neurofilament
cytoskeletal proteins are not exclusively restricted to sites of impact
contusion. Moreover, changes in dendritic
cytoskeletal proteins are progressive and not fully expressed within the first 15 min following impact injury. These progressive dendritic disruptions are characterized by disturbances in the morphology of
neurofilament proteins, resulting in fragmentation and focal loss of
NF68 immunofluorescence within apical dendrites. In contrast, alterations in axonal
cytoskeletal proteins are more restricted and delayed with no pronounced changes until 24 h after injury.