CHRONIC ETHANOL TREATMENT PRODUCES A SELECTIVE UP-REGULATION OF THE NMDA RECEPTOR SUBUNIT GENE-EXPRESSION IN MAMMALIAN CULTURED CORTICAL-NEURONS

Our previous work has shown that chronic ethanol treatment upregulated NMDA receptor function and binding in mammalian cortical neurons. How ever, the potential molecular mechanisms involved in these phenomenon have yet to be elucidated. In the present study, using RNase protectio n assay, we investigated the effect of chronic ethanol treatment on th e NMDA receptor subunits R1, R2A, and R2B mRNA levels in cultured cort ical neurons. We found that chronic ethanol (50 mM, 5 days) exposure d id not change the NMDA receptor R1 and R2A subunits mRNA levels. In co ntrast, the NMDA receptor R2B subunit mRNA level was increased by simi lar to 40% with respect to the control values. The levels of the R2B s ubunit mRNA returned to the control values following the removal of et hanol for 72 h. In order to determine the involvement of the NMDA rece ptors in the action of chronic ethanol exposure, we further investigat ed the effect of the NMDA receptor antagonists on the upregulation ind uced by chronic ethanol exposure. The results indicate that the increa sed R2B subunit level was reversed by concomitant chronic exposure of the cortical neurons to the NMDA receptor competitive (10 mu M; CPP), and non-competitive (1 mu M; MK-801) antagonists, but not by the non-N MDA receptor antagonist, CNQX (10 mu M), or the L-type calcium channel blocker, nitrendipine (10 mu M). Taken together, these results sugges ted that chronic ethanol exposure selectively upregulated the NMDA rec eptor subunit R2B mRNA level in cortical neurons, and this increased N MDA receptor gene expression appears to be a NMDA receptor mediated pr ocess. The altered NMDA receptor gene expression may be responsible fo r the observed upregulation of the NMDA receptor binding and function in the cortical neurons following chronic ethanol exposure.