HEAT-SHOCK PROTEIN AND C-FOS EXPRESSION IN FOCAL MICROVASCULAR BRAIN-DAMAGE

Cortical brain damage was produced in rats by a focal pulse from a Nd- YAG laser, and evolution of the lesion was evaluated at 30 min, and 2, 8, and 24 h with respect to microvascular perfusion, blood-brain barr ier (BBB) permeability, and expression of both the heat-shock/stress p rotein, hsp72, and the c-fos proto-oncogene transcription factor. A do uble-labeling fluorescence technique employing intravenously injected Evans blue albumin (EBA) and fluorescein-labeled dextran was used to m ap and measure BBB damage and microvascular perfusion in fresh frozen brain sections. Hsp72 and c-fos mRNAs were localized by in situ hybrid ization, and the respective proteins were identified by immunocytochem istry. Parallel sections were stained for glial fibrillary acidic prot ein and for routine histologic examination. Striking hsp72 mRNA expres sion was evident by 2 h in an similar to 300 mu m wide rim surrounding an area of expanding BBB damage. Increased hsp72 mRNA was observed on ly in regions of preserved microcirculation, where the hsp72 protein w as subsequently localized exclusively in the vasculature at 24 h after the insult. Hsp72-positive endothelial cells spanned the narrow margi n between the lesion and histologically normal, glial fibrillary acidi c protein (GFAP)-positive cortical tissue. There was no hsp72 expressi on in the area of subcortically migrating edema fluid. Inductions of c -fos mRNA and Fos protein were not strikingly evident around the focal brain lesion, but were observed transiently throughout the injured he misphere at 30 min and 2.5 h, respectively, indicating that spreading depression was triggered by the focal injury. These results are in str iking contrast to those previously obtained from studies of models of focal ischemic or traumatic brain injury, which are characterized by a complex pattern of glial and neuronal hsp72 expression in the periphe ry of an infarct, and which suggest that the tightly demarcated lesion produced by the Nd-YAG laser lacks these components of graded injury that are evident following other types of focal brain damage.