Sequential changes in glial fibrillary acidic protein and gene expression following parasagittal fluid-percussion brain injury in rats

This study documents the regional and temporal patterns of glial fibrillary acidic protein (GFAP) RNA and protein expression after parasagittal fluid- percussion (F-P) brain injury (1.7 to 2.2 atm) in male Sprague-Dawley rats. In situ hybridization was conducted in 28 rats with a S-35-labeled antisen se riboprobe to GFAP at 0.5, 2, and 6 hours and 1, 3, and 30 days after tra umatic brain injury (TBI) or sham procedures. Immunocytochemical staining o f GFAP was conducted in 20 rats at 1, 3, 7, and 30 days after TBI or sham p rocedures. At 0.5 and 2 hours after TBI, increased GFAP mRNA was restricted to superficial cortical areas underlying the impact site. At 24 hours, inc reased GFAP mRNA was observed throughout the traumatized hemisphere except within the histopathologically vulnerable lateral parietal cortex and exter nal capsule. Contralateral expression within the hippocampus and cingulate and lateral cortices was also observed. Three days after TBI, GFAP mRNA exp ression was prominent overlying pial surfaces, in cortical regions surround ing the contusion, and within the hippocampus and lateral thalamus. Immunoc ytochemical visualization of GFAP at 1 and 3 days demonstrated reactive ast rocytes overlying the pial surface, surrounding the cortical contusion, and within ipsilateral white matter tracts, hippocampus, and lateral thalamus. At 30 days, GFAP mRNA and protein expression were present within the deepe r cortical layers of the lateral somatosensory cortex and lateral thalamus and throughout ipsilateral white matter tracts. These data demonstrate a co mplex pattern of GFAP mRNA and protein expression within gray and white mat ter tracts following F-P brain injury. Patterns of GFAP gene expression may be a sensitive molecular marker for evaluating the global response of the brain to focal injury in terms of progressive neurodegenerative as well as regenerative processes.