Long-term changes in neuronal degeneration and microglial activation in the hippocampal CA1 region after experimental transient cerebral ischemic damage

Delayed neuronal death following transient cerebral ischemia is mixed with apoptosis and necrosis, and the activation of microglia are activated after the ischemic insult. In the present study, we examined the long-term changes in neuronal degeneration and microglial activation in the gerbil hippocampal CA1 region after 5 min of transient cerebral ischemia using specific markers for neuronal damage and microliosis. Transient ischemia-induced neuronal death was shown in CA1 pyramidal cells 4 days after ischemia/reperfusion (I/R). However, neuronal degeneration of the pyramidal cells were observed up to 45 days in the CA1 region after I/R. Microglial activation was also observed in the CA1 region after I/R. Isolectin B4- (IB4) immunoreactive (+) microglia appeared in the CA1 region 4 days after I/R. On the other hand, ionized calcium-binding adapter molecule 1 (Iba-1)+ microglia was markedly increased after I/R, and peaked at 15 days after I/R. Thereafter, Iba-1 immunoreactivity was decreased with time-dependant manner in the ischemic CA1 region. These results indicate that neuronal degeneration of CA1 pyramidal cells may last about 45 days in the CA1 region after ischemic damage, and microglial activation may be diverse according to their function, such as phagocytosis, after I/R.