Hippocampal Neuronal Death following Deep Hypothermic Circulatory Arrest in Dogs: Involvement of Apoptosis

Abstract

This study was undertaken to evaluate the histological nature of brain damage caused by deep hypothermic circulatory arrest during cardiopulmonary bypass. Total body cooling to 15°C and rewarming were performed with a conventional cardiopulmonary bypass technique using the femoral artery and vein. Dogs were assigned to one of three groups. In group 1 (n = 4), cardiopulmonary bypass was maintained in a state of deep hypothermia (15°C) for 90 min, group 2 animals (n = 5) underwent 60 min of deep hypothermic circulatory arrest at 15°C, and group 3 (n = 6) underwent 90 min of deep hypothermic circulatory arrest at 15°C. All dogs were killed by perfusion fixation 72 h after cardiopulmonary bypass. The CA1 regions of the hippocampi were examined by light and electron microscopy. Biotinylated dUTP was used for nick-end labeling of apoptotic cells mediated by terminal deoxytransferase. No morphological change was observed in group 1 dogs, and very little in group 2 dogs. More severe neuronal damage was observed in group 3. The nuclei of many cells were shrunken and showed nick-end labeling. Dense chromatin masses were detected electron microscopically in the nuclei of CA1 pyramidal cells. Neuronal cell death observed in CA1 pyramidal cells 72 h after 90 min of deep hypothermic circulatory arrest at 15°C involves apoptosis. Therefore, according to this model, the maximum duration of deep hypothermic circulatory arrest should not be allowed to exceed 60 min.