Effect of hypotension severity on hippocampal CA1 neurons in a rat global ischemia model

Neuronal death in the hippocampal CA1 subregion has been shown to occur in a delayed manner after transient global ischemia. The 2-vessel occlusion model is one of the most frequently used global ischemia paradigms in rodents. Although researchers often fail to induce bilateral delayed CA1 neuronal death, the importance of hypotension severity has not been fully discussed. We induced 10 min of global ischemia with 2-vessel occlusion and various severities of hypotension in rats, and the subsequent neuronal damage and neurogenesis in the hippocampal CA1 pyramidal cell layer were immunohistochemically studied. Neuronal apoptosis after global ischemia was also characterized by terminal deoxynucleotidyl transferase-mediated uridine 5'-triphosphate-biotin nick end labeling (TUNEL). The mean arterial blood pressure of 31-35 mmHg was the most appropriate range of hypotension in this model because of low mortality and consistent bilateral CA1 injury. Most of the neurons in the CA1 pyramidal cell layer lost neuron specific nuclear protein and became TUNEL-positive 3 days after ischemia. There was no evidence of apoptosis or neurogenesis at 7-28 days. There were ischemia-tolerant neurons in the CA1 pyramidal cell layer that survived delayed neurodegeneration, however, further studies are necessary to characterize the property of these neurons.