Cytochrome c associated apoptosis during ATP recovery after hypoxia in neonatal rat cerebrocortical slices

Cellular injury was evaluated in superfused cerebrocortical slices (350 µm) from 7‐day‐old Sprague–Dawley rats exposed to 30 min hypoxia followed by 4 h of reoxygenation. At the end of hypoxia homogenous cytosolic immunoreactivity of cytochrome  c increased approximately fourfold, cytochrome  c intensity in western blot analyses increased more than fivefold, and whole cell and cytosolic cleaved caspase‐9 underwent 50% and 100% increases, respectively. Immunostaining of sections taken 1.5 h after hypoxia showed: (i) more than a threefold increase in cleaved caspase‐9; (ii) localization of cleaved caspase‐9 to the interior and peripheral exterior of nuclei; and (iii) homogeneously distributed cytochrome  c in the cytosol. Western blot analysis for 1.5 h after hypoxia showed that cytosolic caspase‐9 returned to control values, while whole cell caspase‐9 stayed approximately the same, suggesting translocation of caspase‐9 to nuclei. By 4 h after hypoxia there was significant nuclear fragmentation and an increase in TUNEL positive staining. 31 P/ 1 H nuclear magnetic resonance (NMR) confirmed substantial decreases of ATP and phosphocreatine during hypoxia, with rapid but incomplete recovery being close to steady state 1 h after reoxygenation. At all time points after hypoxia the primary injury was cytochrome  c associated apoptosis.