Involvement of caspase-3 in cell death after hypoxia-ischemia declines during brain maturation

The involvement of caspase-3 in cell death after hypoxia-ischemia (HI) was studied during brain maturation. Unilateral HI was produced in rats at post natal day 7 (P7), 15 (P15), 26 (P26), and 60 (P60) by a combination of left carotid artery ligation and systemic hypoxia (8% O-2). Activation of caspa se-3 and cell death was examined in situ by high-resolution confocal micros copy with anti-active caspase-3 antibody and propidium iodide and by bioche mical analysis. The active caspase-3 positive neurons were composed of more than 90% HI damaged striatal and neocortical neurons in P7 pups, but that number was reduced to approximately 65% in striatum and 34% in the neocorte x of P15 pups, and approximately 26% in striatum and 2% in neocortex of P26 rats. In P60 rats, less than 4% of the damaged neurons in striatum and les s than 18 in neocortex were positive for active caspase-3. Western blot ana lysis demonstrated that the level of inactive caspase-3 in normal forebrain tissue gradually declined from a high level in young pups to very low leve ls in adult rats. Concomitantly, HI-induced active caspase-3 was reduced fr om a relatively high level in P7, to moderate levels in P15 and P26, to a b arely detectable level in P60 rats. The authors conclude that the involveme nt of caspase-3 in the pathogenesis of cell death after HI declines during neuronal maturation. The authors hypothesize that caspase-3 may play a majo r role in cell death in immature neurons but a minor role in cell death in mature neurons after brain injury.