NMDAR1 MESSENGER-RNA EXPRESSION AND GLUTAMATE-RECEPTOR STIMULATED INCREASE IN CYTOSOLIC CALCIUM-CONCENTRATION IN RAT AND MOUSE CEREBELLAR GRANULE CELLS

We have previously reported that, unlike their rat counterparts, the s urvival of mouse cerebellar granule cells is independent of chronic st imulation whether owing to elevated K+-induced depolarization or NMDA (N-methyl-D-aspartate) receptor activation. One explanation could be t hat during the critical period mouse granule cells are very sensitive to NMDA receptor stimulation by endogenous glutamate released in the c ultures. If so, this might be reflected by an increased expression of NMDA receptors or an increased response to their activation. We tested this hypothesis by measuring (a) the concentration of mRNA for the ob ligatory NMDA receptor subunit, NMDAR1, and (b) the glutamate/NMDA sti mulated increase in cytosolic Ca2+-ion concentration in cultures al ph ysiological or elevated K+-ion concentration. The expression of NMDAR 1 mRNA was measured by competitive PCR of reversely transcribed mRNA a nd was normalized to that of the constitutively expressed H3.3 histone mRNA. The glutamate and NMDA stimulated increase in cytosolic Ca2+-io n concentration was measured using the fluorescent Ca2+-chelator Fluo3 . In contrast to the hypothesis, we found NMDAR1 mRNA expression to be lower in mouse than in rat granule cells cultured for 4 days at physi ological K+-ion concentration. However, the NMDA stimulated increase i n cytosolic Ca2+-ion concentration did not differ in 4-day rat and mou se cultures. Although the glutamate-stimulated increase in cytosolic C a2+-ion concentration in 2-day cultures was higher in mouse granule ce lls than in rat granule cells, the developmental profile of the glutam ate-stimulated increase in cytosolic Ca2+-ion concentration was the sa me in both cases. In conclusion, we found no obvious evidence for incr eased NMDA receptor activity in mouse cerebellar granule cells culture d at physiological K+-ion concentration. Copyright (C) 1996 Elsevier S cience Ltd