Electrical responses in hippocampal slices after prolonged global ischemia: effects of neuroprotectors

A simple and reproducible animal model of global ischemia, induced by decapitation in 30-day-old Wistar rats, has been developed. It allows to perform electrophysiological analysis of the postischemic reperfusion period in the brain slices. Periods of ischemia up to 40 min increase population spikes measured in the CA1 area of the hippocampus during 2-5 h of reperfusion. Thus after 30-min decapitation-induced ischemia (at t(ischem)=25 degrees C), the mean amplitude of the recorded maximum orthodromic population spikes was 159% of the control obtained in the non-ischemic animals. Longer ischemic episodes result in the depression of the population spikes. After 2 h of ischemia, the amplitude of population spikes was about 89% of control. After 3 h of decapitation ischemia, the neurons could not be reactivated. The duration of ischemic episode needed for the irreversible depression of the electrical activity of the brain neurons drastically depends on the temperature at which the ischemic brain is maintained. Thus, only 2 h were needed at 30 degrees C as compared to nearly 3 h at 25 degrees C. We have found that intraperitoneal injection of neuroprotectors which precedes decapitation enables reactivation of the post-ischemic neurons even after very long periods of global ischemia. Thus, MK-801, a non-competitive NMDA receptors antagonist, or NBQX, a blocker of AMPA receptors, administrated 15 min before the long-term (90 min) decapitation ischemia (30 degrees C), induced dose-dependent recovery of population spike with ED(50) values 0.2 mg/kg and 3 mg/kg respectively. Our results demonstrate that, in spite of the high vulnerability of hippocampal neurons to hypoxia and ischemia, their electrical activity can be restored after prolonged (more then 1 h) decapitation ischemia. Administration of NMDA or AMPA antagonists enhances recovery.