Hu X J, Follesa P, Ticku M K
Department of Pharmacology, University of Texas Health Science Center, San Antonio 78284-7764, USA.
Brain Res Mol Brain Res. 1996 Mar;36(2):211-8. doi: 10.1016/0169-328x(95)00223-f.
Our previous work has shown that chronic ethanol treatment upregulated NMDA receptor function and binding in mammalian cortical neurons. However, the potential molecular mechanisms involved in these phenomenon have yet to be elucidated. In the present study, using RNase protection assay, we investigated the effect of chronic ethanol treatment on the NMDA receptor subunits R1, R2A, and R2B mRNA levels in cultured cortical neurons. We found that chronic ethanol (50 mM, 5 days) exposure did not change the NMDA receptor R1 and R2A subunits mRNA levels. In contrast, the NMDA receptor R2B subunit mRNA level was increased by approximately 40% with respect to the control values. The levels of the R2B subunit mRNA returned to the control values following the removal of ethanol for 72 h. In order to determine the involvement of the NMDA receptors in the action of chronic ethanol exposure, we further investigated the effect of the NMDA receptor antagonists on the upregulation induced by chronic ethanol exposure. The results indicate that the increased R2B subunit level was reversed by concomitant chronic exposure of the cortical neurons to the NMDA receptor competitive (10 microM; CPP), and non-competitive (1 microM; MK-801) antagonists, but not by the non-NMDA receptor antagonist, CNQX (10 microM), or the L-type calcium channel blocker, nitrendipine (10 microM). Taken together, these results suggested that chronic ethanol exposure selectively upregulated the NMDA receptor subunit R2B mRNA level in cortical neurons, and this increased NMDA receptor gene expression appears to be a NMDA receptor mediated process. The altered NMDA receptor gene expression may be responsible for the observed upregulation of the NMDA receptor binding and function in the cortical neurons following chronic ethanol exposure.
我们之前的研究表明，慢性乙醇处理可上调哺乳动物皮质神经元中NMDA受体的功能及结合能力。然而，这些现象背后潜在的分子机制尚未阐明。在本研究中，我们运用核糖核酸酶保护分析技术，探究了慢性乙醇处理对培养的皮质神经元中NMDA受体亚基R1、R2A和R2B mRNA水平的影响。我们发现，慢性乙醇（50 mM，处理5天）暴露并未改变NMDA受体R1和R2A亚基的mRNA水平。相反，与对照值相比，NMDA受体R2B亚基的mRNA水平增加了约40%。去除乙醇72小时后，R2B亚基mRNA水平恢复至对照值。为了确定NMDA受体是否参与慢性乙醇暴露的作用，我们进一步研究了NMDA受体拮抗剂对慢性乙醇暴露诱导的上调作用的影响。结果表明，同时将皮质神经元暴露于NMDA受体竞争性拮抗剂（10 microM；CPP）和非竞争性拮抗剂（1 microM；MK-801）可逆转R2B亚基水平的升高，但非NMDA受体拮抗剂CNQX（10 microM）或L型钙通道阻滞剂尼群地平（10 microM）则无此作用。综上所述，这些结果表明，慢性乙醇暴露可选择性地上调皮质神经元中NMDA受体亚基R2B的mRNA水平，而这种NMDA受体基因表达的增加似乎是一个由NMDA受体介导的过程。NMDA受体基因表达的改变可能是慢性乙醇暴露后皮质神经元中观察到的NMDA受体结合及功能上调的原因。
