Effects of calcium and calcium antagonists against deprivation of glucose and oxygen in guinea pig hippocampal slices.

To provide evidence to support the calcium hypothesis of cerebral ischemia, we examined the effects of extracellular calcium and calcium antagonists (verapamil, flunarizine, nicardipine) on in vitro 'ischemia' using guinea pig hippocampal slices. As a model of in vivo ischemia we used a state of both glucose and oxygen deprivation. Recovery of dentate antidromic field response and histological changes were used as indices of cell damage. After 10 min of deprivation in standard Krebs-Ringer solution, the field potentials exhibited minimum recovery and dentate neurons were severely damaged. Damaged neurons had pyknotic nuclei and swollen cytoplasms. Drugs were added and the calcium concentration was changed during 30 min of pre-deprivation and during deprivation. In the first experiment we demonstrated that pre-treated calcium antagonists protect the dentate granule cells against glucose and oxygen deprivation. The order of the protective potency was flunarizine greater than verapamil much greater than nicardipine. In the second experiment we also showed that neuronal damage caused by deprivation is dependent on the extracellular concentration of calcium. Our data show that extracellular calcium is partially responsible for 'ischemic' neuronal injury in the hippocampal slice. Both low calcium and voltage-gated calcium channel blockers can preserve an antidromic population spike. Conversely, high calcium in the bath can worsen the damage caused by in vitro 'ischemia' to hippocampal slices.