Differential expression of NMDA-evoked 45Ca release in rat hippocampal regions in vivo.

Recently we detected NMDA-induced 45Ca release in the rat dentate gyrus in vivo, attributable to the Ca2+ induced Ca2+ release (CICR) from the endoplasmic reticulum via ryanodine channels. In these experiments we compare expression of NMDA-evoked 45Ca release in the rat dentate gyrus (DG), CA1 and subiculum (SUB). The rationale behind introducing this study is that these hippocampal regions are known to differ in their levels of ryanodine receptors. The release of 45Ca was studied using in vivo microdialysis combined with measurements of 45Ca efflux from prelabelled hippocampal regions. It was shown that NMDA-induced 45Ca release, highly pronounced in the rat DG/CA4, is significantly less expressed in the CA1, whereas in the SUB an NMDA-evoked decrease in 45Ca efflux was noted. This corresponds to distribution of ryanodine receptors in the rat hippocampus, known from the literature. Expression of NMDA-evoked 45Ca release in these rat hippocampal regions which are enriched in ryanodine receptors supports our working hypothesis that CICR via ryanodine channels may be mainly responsible for 45Ca release.