Cold injury in mice: a model to study mechanisms of brain edema and neuronal apoptosis

Small rodents, mice in particular, have been widely used for genetic manipulation because of the extensive knowledge in development, embryology and other molecular aspects of this species. However, the use of mice for neurobiology research in the area of brain edema and neuronal injury has not been common. Here we summarize the studies of cold injury-induced brain edema and neuronal apoptosis using mice. Blood-brain barrier (BBB) permeability, demonstrated by extravasation of a serum albumin tracer, Evans Blue, was increased immediately after the injury and returned to the control level by 24 hr. Water content was maximized at 24 hr, whereas a secondary lesion gradually progressed up to 72 hr after cold injury. The mechanism of the development of the cold injury-induced edema and the secondary lesion, involving of oxygen radicals in particular, was determined using superoxide dismutase (SOD)-1 transgenic (Tg) mice with overexpressed copper, zinc-SOD. All of the parameters, BBB permeability, water content and secondary lesion, were attenuated in the Tg mice as compared to littermate non-Tg mice. This clearly demonstrates that oxygen radicals, superoxide anion in particular, mediate cold injury. We also studied whether apoptosis contributes to brain injury following cold injury. Staining with terminal deoxynucleotidyl transferase-mediated uridine 5'-triphosphate-biotin nick end labeling showed the apoptotic cells widespread throughout the entire lesion while still remaining in the margin. DNA laddering was exhibited by gel electrophoresis. These studies indicate that oxidative mediates the development of cold injury-induced edema and the secondary injury, and induces apoptotic cell death. We believe that cold injury in mice provides a simple animal model to study the pathogenesis of brain edema and apoptosis in genetically altered animals.