It is well known that neurons in the dentate gyrus (DG) of the hippocampus are resistant to short period of
ischemia.
Hyperthermia is a proven risk factor for
cerebral ischemia and can produce more extensive brain damage related with mortality rates. The aim of this study was to examine the effect of hyperthermic conditioning (H) on neuronal death,
gliosis and expressions of SODs as anti-oxidative
enzymes in the gerbil DG following 5 min-
transient cerebral ischemia. The animals were randomly assigned to 4 groups: 1) (N+sham)-group was given
sham-operation with normothermia (N); 2) (N+ischemia)-group was given 5 min-transient
ischemia with N; 3) (H+sham)-group was given
sham-operation with H; and 4) (H+ischemia)-group was given 5 min-
transient cerebral ischemia with H. H (39±0.5°C) was induced by subjecting the animals to a heating pad for 30 min before and during the operation. In the (N+ischemia)-groups, a significant neuronal death was observed in the polymorphic layer (PL) from 1 day after
ischemia-reperfusion. In the (H+ischemia)-groups, neuronal death was also observed in the PL from 1day post-
ischemia; the degree of the neuronal death was severer than that in the (N+ischemia)-groups. In addition, we examined the
gliosis of astrocytes and microglia using anti-
glial fibrillary acidic protein (GFAP) and anti- ionized
calcium-binding adapter molecule 1 (Iba-1). GFAP(+) and Iba-1(+) glial cells were much more activated in the (H+ischemia)-groups than those in the (N+ischemia)-groups. On the other hand, immunoreactivities and levels of SOD1 rather than SOD2 were significantly lower in the (H+ischemia)-groups than those in the (N+ischemia)-groups. In brief, on the basis of our findings, we suggest that cerebral ischemic insult with hyperthermic conditioning brings up severer neuronal damage and
gliosis in the polymorphic layer through reducing SOD1 expression rather than SOD2 expression in the DG.