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 prog ressive degradation of cytoskeletal proteins including neurofilaments (e,g, , neurofilament 68 [NF68] and neurofilament 200 [NF2001]) within the first 24 h after injury. Thus, we employed immunofluorescence (light and confocal microscopy) to study the histopathological correlates of progressive neuro filament protein loss observed at 15 min, 3 h, and 24 h following unilatera l cortical injury in rats, TBI produced significant alterations in NF68 and NF200 immunolabeling in dendrites and cell bodies at contusion sites ipsil ateral to injury, as well as in the noncontused contralateral cortex, Chang es in immunolabeling were associated with, but not exclusively restricted t o, regions previously shown to contain dark shrunken neurons labeled by hem atoxylin and eosin staining, a morphopathological response to injury sugges ting impending cell death. Immunofluorescence microscopic studies of neurof ilament proteins in the ipsilateral cerebral cortex detected prominent frag mentation of apical dendrites of pyramidal neurons in layers 3-5 and loss o f fine dendritic arborization within layer 1, While modest changes were obs erved 15 min follow-injury, more pronounced loss of dendritic neurofilament immunofluorescence was detected 3 and 24 h following injury. Confocal micr oscopy also revealed progressive alterations in NF68 immunoreactivity in de ndrites following TBI, While some evidence of structural alterations was ob served 15 min following TBI, dendritic breaks were readily detected in conf ocal micrographs from 3 to 24 h following injury. However, disturbances in axonal NF68 by immunofluorescence microscopy in the corpus callosum were no t detected until 24 h after injury. These studies confirmed that derangemen ts in dendritic neurofilament cytoskeletal proteins are not exclusively res tricted to sites of impact contusion. Moreover, changes in dendritic cytosk eletal proteins are progressive and not fully expressed within the first 15 min following impact injury, These progressive dendritic disruptions are c haracterized by disturbances in the morphology of neurofilament proteins, r esulting 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, (C) 2000 Academic Press.