Immediate-early gene expression in ovine brain after cardiopulmonary bypass and hypothermic circulatory arrest

Background. Cardiopulmonary bypass (CPB) and hypothermic circulatory arrest (HCA) are associated with neurological injury. Altered immediate- early gene expression occurs rapidly in the brain in response to ischemia, hypoxia, and severe metabolic stress, which results in long-term changes in the molecular phenotype of neurons. This study determined the effects of CPB and HCA on the expression of the immediate early gene c-fos. Methods: Neonatal lambs were subjected to 2 h of CPB at 38°C (n = 4) or 60 min (n = 6), 90 min (n = 7), and 120 min (n = 6) of HCA at 15°C. One hour after terminating CPB at 38°C, the brains were analyzed for FOS-encoding mRNA and FOS-like immunoreactivity in the hippocampal formation. Other animals (n = 15), subjected to the same CPB and HCA protocol, were allowed to survive 3-5 days before their brains were examined for dead neurons. Results: Minimal c- fos mRNA and FOS proteins were observed in neurons of animals subjected to normothermic bypass and of those that served as controls. Non-neuronal FOS proteins were observed in the choroid plexus, ependyma, and blood vessels at all times, including normothermic CPB, but not in the control animals without CPB. The magnitude of c-fos mRNA expression in hippocampal neurons increased directly with the duration of HCA. In contrast, expression of FOS proteins peaked after 90 min of HCA and declined significantly thereafter. Dead neurons were seen in surviving animals after 2 h of HCA only. Conclusions: Cardiopulmonary bypass and HCA alter immediate-early gene expression in the brain. Translational processes are impaired after 120 min of HCA and correlate with neuron death in the hippocampus.