Abstract
Hypothermia (HT) by whole body (WBC) or selective head cooling (SHC) reduces hypoxic-ischemic (HI) brain injury; however, whether prolonged hypothermia and/or anesthesia disrupts immature brain development, eg, increases apoptosis, is unknown. Anesthesia increases apoptosis in immature animals. We investigated whether neuroprotective hypothermia and anesthesia disrupts normal brain development. Thirty-eight pigs <24 h old were randomized between five groups and were killed after 72 h: eighteen received a global hypoxic-ischemic insult under anesthesia, eight subsequently cooled by SHC with WBC to T(rectal) 34.5 degrees C for 24 h, followed by 48 h normothermia (NT) at T(rectal) 39.0 degrees C, while 10 remained normothermic. Sixteen underwent anesthetized sham hypoxic-ischemic, six then following normothermia and 10 following hypothermia protocols. There were four normothermic controls. The hypothermia groups demonstrated significant brain hypothermia. In the hypoxic-ischemic groups this conferred approximately 60% neuroprotection reducing histological injury scores in all brain areas. Immunohistochemical/histochemical analyses of neuronal, glial, endothelial, axonal, transcriptional apoptotic markers in areas devoid of histological lesions revealed no hypothermia/normothermia group and differences whether exposed to hypoxic-ischemic or not. Neither 36-h anesthesia nor 24-h hypothermia produced adverse effects at 4-day survival on a panel of brain maturation/neural death markers in newborn pigs. Longer survival studies are necessary to verify the safety of hypothermia in the developing brain.