Regional Induction of c- Fos and Heat Shock Protein-72 mRNA following Fluid-Percussion Brain Injury in the Rat

To evaluate the cellular response to traumatic brain injury, the expression of mRNA for c-fos and the 72-kDa heat shock protein (hsp72) was determined using in situ hybridization following lateral fluid-percussion injury (2.2–2.4 atm) in rat brain. At 2 h after injury, induction of c-fos mRNA was observed throughout the cortex ipsilateral to the site of injury, while increased expression of hsp72 mRNA was restricted to regions of the cortex surrounding the contusion area. An increase in c-fos mRNA, but not hsp72 mRNA, was observed bilaterally in the CA₃ subfield of the hippocampus and the granule cells of the dentate gyrus and in the thalamus ipsilateral to the impact site. By 6 h, increased expression of c-fos mRNA was observed only in the corpus callosum on the impact side; hsp72 mRNA persisted in the deep cortical layers and upper layers of the subcortical white matter below the site of maximal injury. By 24 h, both c-fos and hsp72 mRNA had returned to control levels in all regions of the brain. These results demonstrate that lateral fluid– percussion brain injury triggers regionally and temporally specific expression of c-fos and hsp72 mRNA, which may be suggestive of differential neurochemical alterations in neurons and glia following experimental brain injury.