Mild hypothermia reduces zinc translocation, neuronal cell death, and mortality after transient global ischemia in mice

The authors sought to determine whether Zn2+ translocation associated with neuronal cell death occurs after transient global ischemia (TGI) in mice, as has been previously shown in rats, and to determine the effect of mild hypothermia on this reaction. To validate the TGI model, carbon-black injection and laser-Doppler flowmetry were compared in three strains of mice (C57BL/6, SV129, and HSP70 transgenic mice) to assess posterior communicating artery (PcomA) development and cortical perfusion. In C57BL/6 mice, optimal results were obtained when subjected to 20-minute TGI. Brain and rectal temperature measurements were compared to monitor hypothermia. Results of TGI were compared in normothermia (NT; 37degreesC) and mild hypothermia groups (HT; 33degreesC) by staining with Zn2+-specific fluorescent dye, N-(6-methoxy-8-quinotyl)-para-toluenesulfonamide (TSQ) and hematoxylineosin 72 hours after reperfusion. The Zn2+ translocation observed in hippocampus CA1, CA2, and Hilus 72 hours after 20 minutes of TGI was significantly reduced by mild hypothermia. The number of degenerating neurons in the HT group was significantly less than in the NT group. Mild hypothermia reduced mortality significantly (7.1% in HT, 42.9% in NT). Results suggest that mild hypothermia may reduce presynaptic Zn2+ release in mice, which protects vulnerable hippocampal neurons from ischemic necrosis. Future studies may further elucidate mechanisms of Zn2+-induced ischemic injury.