Effect of ischemic preconditioning on the expression of putative neuroprotective genes in the rat brain

Previous studies have demonstrated that sublethal ischemic insults protect from subsequent ischemia in the intact brain. There are two windows for the induction of tolerance by ischemic preconditioning (IPC). One occurs within 1 h following IPC, and the other one develops from 1 to 3 days after IPC. The goal of this study was to determine whether IPC neuroprotection may be mediated by expression of known neuroprotective genes and to characterize the temporal and spatial expression patterns of these genes. IPC was produced by bilateral carotid artery occlusions and hypotension (50 mmHg) for 2 min. After various survival times, the expression of MAP-2, brain-derived neurotrophic factor (BDNF), c-jun, c-fos, nerve growth factor (NGF) and HSP70 was assessed by in situ hybridization of coronal brain sections with 35S labeled probes. BDNF, NGF, and c-jun were significantly upregulated in the hippocampus. c-fos was detected in the hippocampus, cortex and striatum. HSP70 mRNA was induced in the cortex, hippocampus, striatum, and thalamus. MAP-2 showed no change in expression, confirming previous studies that no cell death occurs following IPC. The increase in expression of these stress-related, neurotrophic and immediate early genes in response to a mild preconditioning insult may help mediate the protection of vulnerable neurons to subsequent lethal ischemic insults.