Time course of brain neuronal degeneration and heat shock protein (72) expression following neck tourniquet-induced cerebral ischemia in the rat

The present study was designed to examine the regional expression of HSP72/ 73 protein after a 7.5-min period of cerebral ischemia and to compare the d istribution of HSP neurons with the localization of irreversible neuronal d egeneration as analyzed by silver impregnation technique. During 6-24 hr after cerebral ischemia clear-cut neuronal argyrophilia deve loped in several brain regions including the hippocampal hilus, nucleus ret icularis thalami, and colliculi inferiores. With the exception of the hippo campal hilus, the structures which showed silver impregnability were HSP72 negative at 6-24 hr. Despite the clear HSP72 expression seen in hippocampal CA1 neurons, a signi ficant loss of these neurons was seen at 7 days after ischemia. These data show that in some structures the presence of HSP72 is indicative of higher resistance of these neurons to ischemia-induced degeneration, ho wever, the process of delayed neuronal degeneration appears to be independe nt of the accelerated synthesis of HSP72 seen during the early period of re flow.