Light and confocal microscopic studies of evolutionary changes in neurofilament proteins following cortical impact injury in the rat

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.