Hyperthermia Aggravates Neuronal Apoptosis following Global Ischemia in Gerbils

Hyperthermia exacerbates neuronal injury during ischemic stroke in animal models and humans. In this study, we examined whether hyperthermia affects the neuronal apoptosis in the brain with ischemia/reperfusion injury. Gerbils were challenged for 5 min transient cerebral ischemia under the condition of brain temperature at either 37℃ (normothermia, NT) or 39℃ (hyperthermia, HT), followed by reperfusion for 48h. Apoptotic cell death was evaluated by terminal deoxyribonucleotidyl transferase-mediated dUTP-biotin nick end-labeling (TUNEL) and immunostaining of Sax, pro-apoptosis member. We also surveyed the state of astrocyte and microglial cells including subtypes of nitric oxide synthase (NOS) in the same brain areas. The numbers of TUNEL-positive neurons were increased within neocortex and hippocampus in HT group, but not in NT and sham group at 48h after reperfusion. The numbers of Sax-positive neurons were increased within the hippocampus, thalamus, neocortex and piriform cortex in HT group, but not within neocortex and piriform cortex in NT group. The glial fibrillary acidic protein (GFAP) immunoreactivity of HT group was increased in the hippocampal region compared with that of NT group. In contrast with NT group, the intensive activation of microglial cells by isolectin B4 staining was observed in the hippocampus, thalamus and neocortex region in HT group. The iNOS- and eNOS-positive cells were highly increased within the hippocampal CA1 region in HT group. Therefore, our results suggest that hyperthermia may be one of the crucial factors in acceleration of the neuronal apoptosis by the elevation of iNOS expression through the activation of microglia and astrocyte after ischemic injury.