Calpain activity in the rat brain after transient forebrain ischemia

Activity of the Ca2+-dependent protease calpain is increased in neurons aft er global and focal brain ischemia, and may contribute to postischemic inju ry cascades. Understanding the time course and location of calpain activity in the post-ischemic brain is essential to establishing causality and opti mizing therapeutic interventions. This study examined the temporal and spat ial characteristics of brain calpain activity after transient forebrain isc hemia (TFI) in rats. Male Long Evans rats underwent 10 min of normothermic TFI induced by bilateral carotid occlusion with hypovolemic hypotension (MA BP 30 mm Hg). Brain calpain activity was examined between 1 and 72 h after reperfusion. Western blot analysis of regional brain homogenates demonstrat ed a bimodal pattern of calpain-mediated alpha -spectrin degradation in the hippocampus, cortex, and striatum with an initial increase at 1 h followed by a more prominent secondary increase at 36 h after reperfusion. Immunohi stochemical analysis revealed that calpain activity was primarily localized to dendritic fields of selectively vulnerable neurons at one hour after re perfusion. Between 24 and 48 h after reperfusion neuronal calpain activity progressed from the dorsal to ventral striatum, medial to lateral CA1 hippo campus, and centripetally expanded from watershed foci in the cerebral cort ex. This progression was associated with fragmentation of dendritic process es, calpain activation in the neuronal soma and subsequent neuronal degener ation. These observations demonstrate a clear association between calpain a ctivation and subsequent delayed neuronal death and suggest broad therapeut ic window for interventions aimed at preventing delayed intracellular Ca2overload and pathologic calpain activation. (C) 2001 Academic Press.