Chronic ethanol upregulates NMDA and AMPA, but not kainate receptor subunit proteins in rat primary cortical cultures

The present study examined the effects of chronic ethanol exposure on the e xpression of N-methyl-D-aspartate (NMDA), alpha-amino-3-hydroxy-5-methyl-4- isoxalone (AMPA) and kainate receptor subunit proteins in rat cortical neur onal cultures grown in media containing 2 mM thigh) or 0.1 mM (low) glutami ne. Immunoblot analysis of NMDA (NR1, NR2A, NR2B, end NR2D), AMPA(GluR1 and GluR2/3), and kainate (GluR6/7) subunit polypeptides in 3-, 5-, 8-, 10-, a nd 12 day-old-cultures showed that NMDA receptor subunits NR1, NR2A, and NR 2B and AMPA receptor subunits GluR2/3 progressively increased as a function of time, whereas levels of NMDA subunit NR2D were high at day 3 and progre ssively declined to barely detectable levels by day 12, Levels of AMPA subu nit GluR1 and the kainate subunit GluR6/7 remained stable throughout the ti me course, Replacing the culture media with low glutamine media at culture day 5 did not alter the levels of subunit proteins measured at culture days 9 and 13, However, exposure of low glutamine cultures to 100 mM ethanol fo r 4 days (starting at culture day 9) significantly increased the levels of NMDA receptor subunits (NR1, NR2A, and NR2B) end AMPA receptor subunits (Gl uR1 end GluR2/3), but had no effect upon kainate receptor subunits (GluR6/7 ) or the synapse-associated proteins synapsin I and PSD-95, In contrast, ch ronic ethanol did not alter the levels of any of these subunit proteins in cells grown in high glutamine, These data demonstrate that under certain ex perimental conditions, prolonged exposure to ethanol upregulates NMDA and A MPA receptor subunit proteins, but has no effect upon kainate receptor subu nit proteins, Because we have previously shown that acute ethanol can inhib it NMDA and AMPA, but not kainate, receptor function in these cultures, the increase in subunit expression likely reflects an adaptive response to the inhibitory effects of ethanol and suggests that both NMDA end AMPA recepto rs may play an important role in adaptation of the CNS to chronic ethanol.