Caspase-8 and caspase-3 are expressed by different populations of corticalneurons undergoing delayed cell death after focal stroke in the rat

A number of studies have provided evidence that neuronal cell loss after st roke involves programmed cell death or apoptosis. In particular, recent bio chemical and immunohistochemical studies have demonstrated the expression a nd activation of intracellular proteases, notably caspase-3, which act as b oth initiators and executors of the apoptotic process. To further elucidate the involvement of caspases in neuronal cell death induced by focal stroke we developed a panel of antibodies and investigated the spatial and tempor al pattern of both caspase-8 and caspase-3 expression. Our efforts focused on caspase-8 because its "apical" position within the enzymatic cascade of caspases makes it a potentially important therapeutic target. Constitutive expression of procaspase-8 was detectable in most cortical neurons, and pro teolytic processing yielding the active form of caspase-8 was found as earl y as 6 hr after Focal stroke induced in rats by permanent middle cerebral a rtery occlusion. This active form of caspase-8 was predominantly seen in th e large pyramidal neurons of lamina V. Active caspase-3 was evident only in neurons located within lamina II/III starting at 24 hr after injury and in microglia throughout the core infarct at all times examined. Terminal deox ynucleotidyl transferase-mediated biotinylated UTP nick end labeling, gel e lectrophoresis of DNA, and neuronal cell quantitation indicated that there was an early nonapoptotic loss of cortical neurons followed by a progressiv e elimination of neurons with features of apoptosis. These data indicate th at the pattern of caspase expression occurring during delayed neuronal cell death after focal stroke will vary depending on the neuronal phenotype.