Cerebral blood flow threshold and regional heterogeneity of heat shock protein 72 induction following transient forebrain ischemia in rats

Heat shock proteins (HSPs) induced by brain ischemia may play an important role in neuroprotection from neuronal degeneration. In this study, we exami ned the cerebral blood flow (CBF) threshold to produce regional differences in HSP72 induction after transient forebrain ischemia in spontaneously hyp ertensive rats (SHRs). Female SHRs were subjected to 20 min of cerebral isc hemia induced by bilateral carotid artery occlusion. The CBF was measured b y laser Doppler flowmetry. At forty-eight hours after cerebral ischemia and reperfusion, the rats were decapitated and the brains were removed. Specif ic areas (hippocampal CA1, CA2-3, dentate gyrus, dorsolateral and ventromed ial striatum, and parietal cortex) were thereafter dissected from the brain . The amounts of HSP72 in these samples were determined using Western blot analysis. In the hippocampus, HSP72 was induced when the CBF decreased to l ess than 18-25% of the resting level. The mean values of HSP72 produced in the CA1 area, CA2-3 area, and the dentate gyrus following ischemia and repe rfusion treatment were 4.44 +/- 1.43 (+/-SD) ng/mu g prtein, 3.51 +/- 0.72 ng/mu g protein and 3.77 +/- 1.05 ng/mu g protein, respectively. In the par ietal cortex, the amount of HSP72 induction was less pronounced (2.55 +/- 0 .40 ng/mu g protein), while HSP72 was hardly detected at all in the striatu m, even under conditions of very severe CBF reduction and reperfusion, We d emonstrated the existence of both a CBF threshold (i.e., approximately 20% of the resting level) for HSP72 induction and regional heterogeneity for th e induction of HSP72 protein.