Differential effects of chronic ethanol treatment on N-methyl-D-aspartate R1 splice variants in fetal cortical neurons

Functional N-methyl-D-aspartate receptors consisting of NR1 and NR2 subunit s are an important site of action of ethanol. Chronic ethanol treatment inc reases the NR1 polypeptide levels in vivo and in vitro. Chronic ethanol tre atment in vitro does not significantly alter the NR1 mRNA levels, even thou gh under similar culture conditions ethanol (50 mM, 5 days) enhances the ha lf-life of NR1 mRNA in fetal cortical neurons. To address this phenomenon, we determined by reverse transcription-polymerase chain reaction and Wester n blotting whether ethanol (50 mM, 5 days) has a splice variant-specific ef fect on the expression of the NR1 subunit in mouse fetal cortical neurons. This report analyzes for the first time the distribution of all NR1 splice variants in these neurons. Our data indicate the presence of NR1-3a,b and N R1-4a,b splice variants in cortical neurons. Chronic, ethanol treatment sig nificantly decreased the mRNA levels of exon 5-containing NR1 splice varian ts (NR1-3b and NR1-4b) (-E5/+E5 = 4.6 in untreated neurons and 6.1 in ethan ol-treated neurons) and had no effect on the mRNA levels of NR1-3 (+E21/-E2 2) and NR1-4 (-E21/-E22) splice variants. At the polypeptide level,. chroni c ethanol treatment significantly reduced exon 5-containing splice variants (NR1-3b and NR1-4b). However, ethanol (50 mm, 5 days) induced a significan t increase in polypeptide levels of NR1-4 (-E21/-E22), without any effect o n NR1-3 (+E21/-E22) polypeptide levels. These results demonstrate that chro nic ethanol treatment, has a selective effect on the expression of NR1 spli ce variants at both the mRNA and polypeptide levels in mouse fetal cortical neurons.