Differences between rats and rabbits in NMDA receptor-mediated calcium signalling in hippocampal neurones

In vivo microdialysis combined with the measurement of Ca-45(2+) efflux fro m prelabelled hippocampus demonstrated a pronounced N-methyl-D-aspartate (N MDA)-evoked Ca-45(2+) release to the dialysate in the rat dentate gyrus (DG ) and CA1, whereas in rabbit a slight release of Ca-45(2+) was observed onl y in the DG. In vitro, we noticed that the NMDA-evoked increase in Fura-2 d etected intracellular Ca2+ concentration in synaptoneurosomes from the rat, but not from the rabbit hippocampus, was strongly inhibited by the ryanodi ne receptor (RyR) antagonists dantrolene and ryanodine. To establish the me chanism of these differences, we characterised their possible dependence on the expression of RyR and their co-localisation with the calcium binding p rotein calbindin D-28k. A pronounced expression of [H-3]ryanodine binding s ites in the rat DG, which is only slight in the CA1, was demonstrated where as in rabbit they were only found in the DG, The pattern of expression of c albindin D-28k immunoreactivity and RyR in the rat and rabbit hippocampus w as similar. These results suggest that the functional role of RyR in the ge neration of the NMDA receptor-mediated intracellular Ca2+ signalling in the rabbit hippocampal neurones is marginal when compared to the rat, These di fferences reflect a diverse expression of RyR in both species. The correspo nding differences in calbindin D-28k immunoreactivity are most probably sec ondary in nature, (C) 2001 Elsevier Science Inc.