Global Cerebral Ischemia Due to Cardiocirculatory Arrest in Mice Causes Neuronal Degeneration and Early Induction of Transcription Factor Genes in the Hippocampus

To analyze the role of specific genes and proteins in neuronal signaling cascades following global cerebral ischemia, it would be useful to have a reproducible model of global cerebral ischemia in mice that potentially allows the investigation of mice with specific genomic mutations. We first report on the development of a model of reversible cardiocirculatory arrest in mice and the consequences of such an insult to neuronal degeneration and expression of immediate early genes (IEG) in the hippocampus. Cardiocirculatory arrest of 5 min duration was induced via ventricular fibrillation in mechanically ventilated NMRI mice. After successful cardiopulmonary resuscitation (CPR), animals were allowed to reperfuse spontaneously for 3 h (n=7) and 7 days (n=7). TUNEL staining revealed a selective degeneration of a subset of neurons in the hippocampal CA1 sector at 7 days. About 30% of all TUNEL-positive nuclei showed condensed chromatin and apoptotic bodies. Immunohistochemical studies of IEG expression performed at 3 h exhibited a marked induction of c-Fos, c-Jun, and Krox-24 protein in all sectors of the hippocampus, peaking in vulnerable CA1 pyramidal neurons and in dentate gyrus. In contrast, sham-operated animals (n=3) did not reveal neuronal degeneration or increased IEG expression in the hippocampus when compared with untreated control animals (n=3). In conclusion, we present a new model of global cerebral ischemia and reperfusion in mice with the use of complete cardiocirculatory arrest and subsequent CPR. Following 5 min of ischemia, a subset of CA1 pyramidal neurons was TUNEL-positive at 7 days. The expression of IEG was observed in all sectors of the hippocampus, including selectively vulnerable CA1 pyramidal neurons. This appears to be a good model which should be useful in evaluating the role of various genes in transgenic and knockout mice following global ischemia.