Is the AMPA receptor subunit GluR2 mRNA an early indicator of cell fate after ischemia? A quantitative single cell RT-PCR study

After a moderate global cerebral ischemia, two hypothetical populations of pyramidal neurons are present among the hippocampal CA1 pyramidal neurons: one that will die and another one that will survive. Prior analysis of dissected hippocampal CA1 regions has shown a reduction of the GluR1-3 mRNA following ischemia. In order to identify these changes in single neurons, quantitative single cell RT-PCR was used to analyze the expression of GluR1-4 mRNA in rats 24 h after ischemia and also in rats after tolerance inducing ischemia. Control CA1 cells had a median copy-number of 290, 247, 207 and 16 GluR1-4, respectively. The tolerant cells showed small significant up-regulations of GluR1, 3 and 4 mRNA, while the GluR2 mRNA showed a more than 4-fold up-regulation compared to control cells. All the cells from ischemic animals displayed down-regulations of GluR1-3 mRNA. The GluR4 mRNA was not detectable in the ischemic animals. Our results thus show that the CAI neurons react uniformly 24 h after a moderate ischemia independent of the fate of the neuron: thus two neuron populations with different GluR2 profiles cannot be identified in post-ischemic animals at 24 h. It seems however that an increased level of GluR2 can be used as an indicator of tolerance to ischemia. (C) 2001 Elsevier Science B.V. All rights reserved.