N-methyl-D-aspartate receptor-mediated, calcium-induced calcium release in rat dentate gyrus/CA4 in vivo.

Previously, by using in vivo microdialysis, we demonstrated a huge release of 45Ca2+ from prelabeled tissues to dialysate that was evoked by application of N-methyl-D-aspartate (NMDA) to the rat dentate gyrus (DG) and sector 4 of the cornu ammonis. To establish the mechanism of this phenomenon, in the present study, we characterized its NMDA receptor dependence, investigated the mechanism of 45Ca2+ removal from the cells, and evaluated the possible involvement of calcium-binding protein calbindin D28k and of ryanodine receptors. Microdialysis experiments demonstrated a dose-response relation between NMDA and 45Ca2+ release and sensitivity of this phenomenon to inhibition by 10 microM MK-801 and 5 mM 5-(N,N-dimethyl)-amiloride, thus indicating the NMDA receptor dependence and a role of Na+/Ca2+ exchanger in mediating 45Ca2+ release from cells.

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.

N-methyl-D-aspartate-induced 45Ca2+ release from pre-labelled adult rat hippocampus in vivo.

We report the results of microdialysis experiments investigating the NMDA-induced release of intracellular Ca2+ in different brain regions. Microdialysis probes were implanted stereotaxically into the striatum, thalamus and hippocampus dentate gyrus (DG) of adult rats. Dialysates were analysed for alterations in the concentration of ionized Ca2+ in an initially calcium-free medium and for changes in 45Ca efflux from the pre-labelled endogenous Ca2+ pools.