Time course analysis of changes in neuronal loss, oxidative stress, and excitotoxicity in gerbil hippocampus following ischemia and reperfusion under hyperthermic conditions

Oxidative stress and excitotoxicity are the major causes of neuronal death/loss in the brain following ischemia and reperfusion (IR). Hyperthermia is known to exacerbate ischemic neuronal damage; however, the underlying mechanisms remain unclear. This study investigated the mechanisms underlying neuronal damage caused by IR injury (IRI) under hyperthermic conditions in the gerbil hippocampal CA1 region. Gerbils were controlled at normothermia (37.5±0.2°C) or hyperthermia (39.5±0.2°C). After temperature control for 30 min, the animals received IRI (following 5 min of transient forebrain ischemia) or sham ischemia, and were subsequently sacrificed at 0, 3, 6, 12, 24, 48, and 120h after IRI. Neuronal death was examined using neuronal nuclear antigen immunohistochemistry and Fluoro-Jade B histofluorescence. Oxidative stress was analyzed by immunohistochemistry for 8-Hydroxy-2'-deoxyguanosine (8OHdG) and superoxide dismutase 2 (SOD2). Excitotoxicity was investigated by immunohistochemistry and western blotting for glutamate transporter 1 (GLT1). Immunohistochemical staining for glial fibrillary acidic proteins (GFAP) was performed to detect reactive astrogliosis. Loss of pyramidal neurons was detected earlier (48h post-IRI) in the hyperthermia-IRI group than in the normothermia-IRI group (120h post-IRI). Further, 8OHdG and SOD2 immunoreactivity in the hyperthermia-IRI group was significantly higher than that in the normothermia-IRI group. Changes in GLT1 immunoreactivity in both groups were biphasic, indicating that the immunoreactivity and protein levels were significantly lower in the hyperthermia-IRI group. GFAP immunoreactivity was enhanced following neuronal loss, indicating that the immunoreactivity was significantly higher in the hyperthermia-IRI group. Taken together, these results suggest that brain IR under hyperthermic conditions can aggravate neuronal damage in the hippocampal CA1 region through severe oxidative stress and excitotoxicity.