APOPTOSIS IN A NEONATAL RAT MODEL OF CEREBRAL HYPOXIA-ISCHEMIA

Background and Purpose-The mechanisms of excitotoxic cell death in cer ebral ischemia are poorly understood. In addition to necrosis, apoptot ic cell death may occur. The purpose of this study was to determine wh ether an established model of cerebral hypoxia-ischemia in the neonata l rat demonstrates any features of apoptosis. Methods-Seven-day-old ne onatal rats underwent bilateral, permanent carotid ligation followed b y 1 hour of hypoxia, and their brains were examined 1, 3, and 4 days a fter hypoxia-ischemia. The severity of ischemic damage was assessed in the dentate gyrus and frontotemporal cortex by light microscopy. Immu nocytochemistry was performed to detect the cleavage of actin by caspa ses, a family of enzymes activated in apoptosis. Terminal deoxynucleot idyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) reacti vity was examined in the cortical infarction bed and dentate gyrus. Ne onatal rat brain DNA was run on agarose gel electrophoresis to detect DNA fragmentation. Ethidium bromide-staining and electron microscopy w ere used to determine whether apoptotic bodies, I of the hallmarks of apoptosis, were present. Results-The frontotemporal cortex displayed e vidence of infarction, and in most rats the dentate gyrus showed selec tive, delayed neuronal death. Immunocytochemistry demonstrated caspase -related cleavage of actin. TUNEL and DNA electrophoresis provided evi dence of DNA fragmentation. Ethidium bromide-staining and electron mic roscopy confirmed the presence of chromatin condensation and apoptotic bodies. Conclusions-Features of apoptosis are present in the describe d model of cerebral hypoxia-ischemia. Apoptosis may represent a mode o f ischemic cell death that could be the target of novel treatments tha t could potentially expand the therapeutic window for stroke.