Ethanol inhibits the function of the N-methyl-D-aspartate (NMDA) subtype of glutamate receptor in various neuronal systems, but the mechanism of the inhibition has not been elucidated. Previous work, using primary cultures of rat cerebellar granule cells, showed that both exposure to alcohol and activation of protein kinase C (PKC) by the phorbol ester PMA reduced the potency of the co-agonist, glycine, to enhance NMDA receptor function (measured as an increase in intracellular Ca2+), resulting in inhibition of the NMDA response at low glycine concentrations. Inhibition of NMDA receptor function by PMA and ethanol could also be overcome by PKC antagonists, implicating PKC in the inhibitory effect of ethanol. We have now compared the effects of ethanol and PKC activation of NMDA receptor function in primary cultures of rat cerebral cortical cells. The receptor in these cells was much less sensitive to ethanol inhibition, and the inhibition was not overcome by high concentrations of glycine. Furthermore, PMA treatment resulted in an increased response to NMDA at low glycine concentrations. The results indicate that PKC does not mediate ethanol inhibition of NMDA receptor function in cerebral cortical cells, and that the mechanism of ethanol inhibition can vary among brain regions and/or cell types. Possible determinants of the differing mechanisms of ethanol's actions include the subunit composition of the NMDA receptor and/or the isoforms of PKC present in the different cells.