In vitro ischemia-induced intracellular Ca²⁺ elevation in cerebellar slices: a comparative study with the values found in hippocampal slices

Abstract

Changes in levels of intracellular calcium ion ([Ca²⁺]_i) induced by in vitro ischemic conditions in gerbil cerebellar and hippocampal slices were investigated using a calcium imaging system and electron microscopy. When the cerebellar slice was perfused with a glucose-free physiological medium equilibrated with a 95% N₂/5% CO₂ gas mixture (in vitro ischemic medium), a large [Ca²⁺]_i elevation was region-specifically induced in the molecular laver of the cerebellar cortex (a dendritic field of Purkinje cells). When the hippocampal slice was perfused with in vitro ischemic medium, a large [Ca²⁺]_i elevation was region-specifically induced in CA1 field of the hippocampal slices. Electron microscopic examinations showed that the large [Ca²⁺]_i elevations occurred in Purkinje cells and CA1 pyramidal neurons. To isolate Ca²⁺ release from intracellular Ca²⁺ store sites, the slices were perfused with Ca²⁺-free in vitro ischemic medium. the increases in [Ca²⁺]_i in both cerebellar and hippocampal slices were significantly lower than those observed in the slices perfused with the Ca²⁺-containing in vitro ischemic medium. However, the suppression of the [Ca²⁺]_i-elevation in the molecular layer of the cerebellar slices was smaller than that in the CA1 field of the hippocampal slices. These results reinforce the hypothesis that calcium plays a pivotal role in the development of ischemia-induced neuronal death, and suggest that Ca²⁺ release from intracellular Ca²⁺ store sites may play an important role in the ischemia-induced [Ca²⁺]_i elevation in Purkinje cells.