Cortical and striatal cultures were prepared from the same embryonic rat brains and maintained in identical culture conditions. In this way, the intrinsic, genetically imprinted differences determine the responses of cortical and striatal neurons in comparative studies. Cortical and striatal neurons differed in their sensitivity to glutamate receptor-mediated neurotoxicity as measured by the MTT cell viability assay. On the 8th day in vitro, striatal cultures were less sensitive to N-methyl-d-aspartate (NMDA)-induced toxicity than cortical, although both cultures were equally vulnerable to alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA)- or kainate-induced toxicity. The AMPA receptor-mediated cell death in cortical cultures, however, was much more dependent on preventing AMPA receptor desensitization than in striatal cultures. Furthermore, glutamate-induced neurotoxicity was primarily mediated by NMDA receptors in cortical cultures, while blockade of either NMDA or AMPA receptors gave almost complete protection against glutamate in striatal cultures. To elucidate the molecular mechanisms responsible for the observed differences, we analyzed the expression of NMDA receptor subunits (NR1, NR2A-C) at the mRNA and the protein level in cortical and striatal cultures as well as in standard cerebellar granule cell cultures. The lowest expression level of NMDA receptor subunits was found in striatal cultures, thereby providing a possible explanation for their lower sensitivity to NMDA. Remarkable differences were found between the relative rates of mRNA and protein expression for NR1 and NR2B in the three cultures, indicative of intrinsic differences in the posttranscriptional regulation of NMDA receptor subunit expression in cultures from various brain regions.
Copyright 2001 Academic Press.