CHRONIC ETHANOL INCREASES N-METHYL-D-ASPARTATE-STIMULATED NITRIC-OXIDE FORMATION BUT NOT RECEPTOR DENSITY IN CULTURED CORTICAL-NEURONS

The effects of prolonged ethanol exposure on excitatory amino acid rec eptor stimulated nitric oxide (NO) formation were examined in primary rat cortical neuronal cultures. Chronic ethanol (4 days, 100 mM) poten tiated N-methyl-D-aspartate (NMDA)-stimulated NO formation as determin ed by measuring the conversion of [H-3]arginine to [H-3]citrulline. In contrast, chronic ethanol had no effect on NO formation stimulated by kainate, lpha-amino-3-hydroxy-5-methyl-4-isoxalonepropionic acid, or the calcium ionophore ionomycin. Potassium chloride-stimulated NO form ation was also enhanced by chronic ethanol treatment, but this effect was not seen in the presence of the ionotropic glutamate receptor anta gonists MK-801 and 6-cyano-7-nitroquinoxaline-2,3-dione. Immunoblot an alysis of expression of NR1, NR2A, and NR2B receptor subunits showed n o difference between control and chronic ethanol-treated cultures. In support of this apparent lack of change in receptor density, there was no difference in the specific binding of I-125-MK-801 between control and chronic ethanol-treated groups. These results demonstrate that pr olonged ethanol exposure selectively enhanced NMDA receptor-stimulated NO formation, which may play an important role in alcohol dependence, withdrawal, and alcohol-associated brain damage. These results also s uggest that chronic ethanol-induced increases in NMDA receptor functio n may not be due to a simple increase in the number of NMDA receptors or change in NMDA receptor subunit composition but may instead reflect more complicated and subtle changes.