Intermediate filament change in astrocytes following mild cortical contusion

Astrocytes are known to become reactive as a result of various types of lesions. They upregulate astrocytic-specific intermediate filament glial fibrillary acidic protein (GFAP) and show a positive signal for the intermediate filament vimentin, a protein primarily found in developing astrocytes. An animal model for cortical contusions has been developed that manifests many of the neuropathologies seen in human closed head injury. The model involves an electronic controlled pneumatic impact device (ECPI), which can deliver precise and controlled cortical contusions to an animal. This model can be used to study astrocyte response to injury, leading to a better understanding of glial reaction to head trauma in humans. Young adult male Fisher 344 rats were subjected to a mild dorsal lateral cortical impact. The astrocytic intermediate filaments GFAP and vimentin were upregulated in a time-dependent manner 2 days after injury. By 30 days following contusion these intermediate filaments returned to near preinjury levels. Using the same injury model bromodeoxynridine (BrdU) was injected in additional animals on the day of sacrifice, 1, 2, 4, and 10 days after injury, to label cells synthesizing new DNA. Double labeling utilizing fluorescence immunocytochemistry indicated that on postinjury day 2 very few GFAP-positive cells were double labeled with BrdU. No double-labeled cells were seen at the other time points. These data suggest that astrocyte proliferation may not be a major response to mild cortical contusion and that vimentin expression may not necessarily be associated with astrocytic proliferation in response to injury.