Effects of therapeutic hypothermia on white matter injury from murine neonatal hypoxic-ischemia

BACKGROUND: Therapeutic hypothermia (TH) is the standard of care for neonates with hypoxic-ischemic encephalopathy but is not fully protective in the clinical setting. Hypoxia-ischemia (HI) may cause white matter injury (WMI), leading to neurological and cognitive dysfunction. METHODS: P9 mice were subjected to HI as previously described. Pups underwent 3.5 hours of systemic hypothermia or normothermia. Cresyl violet and Perl’s iron stain for histopathological scoring of brain sections was completed blindly on all brains. Immunocytochemical (ICC) staining for myelin basic protein (MBP), microglia (Iba1), and astrocytes (GFAP) was performed on adjacent sections. Volumetric measurements of MBP coverage were used for quantitative analysis of white matter. RESULTS: TH provided neuroprotection by injury scoring for the entire group (n=44) (p<0.0002). ICC analysis of a subset of brains showed that the lateral caudate was protected from WMI (p<0.05). Analysis revealed decreased GFAP and Iba1 staining in hippocampal regions, mostly CA2/CA3. GFAP and Iba1directly correlated with injury scores of normothermic brains. CONCLUSIONS: TH reduced injury and qualitative data suggest that hippocampus and lateral caudate are protected from HI. Mildly injured brains may better show the benefits of TH. Overall these data indicate regional differences in WMI susceptibility and inflammation in a P9 murine HI model.