Devaud L L, Smith F D, Grayson D R, Morrow A L
Bowles Center for Alcohol Studies, University of North Carolina School of Medicine, Chapel Hill 27599-7178, USA.
Mol Pharmacol. 1995 Nov;48(5):861-8.
The molecular mechanisms that underlie ethanol dependence appear to involve alterations in GABAA receptor function and gene expression. In rat cerebral cortex, chronic exposure to ethanol alters many functional properties of GABAA receptors, including reduction of GABAA receptor-mediated chloride uptake. These functional alterations occur without a concomitant alteration in total receptor density or affinity. Previous investigations have shown that chronic ethanol exposure elicits alterations in mRNA and polypeptide levels for several abundant GABAA receptor subunits. For example, alpha 1 and alpha 2 subunit mRNA and polypeptide levels have been shown to decrease with chronic ethanol exposure. The present study was undertaken to further investigate the effects of chronic ethanol consumption on GABAA receptor subunit mRNA levels in rat cerebral cortex by using a competitive, quantitative reverse transcriptase-polymerase chain reaction assay that incorporates subunit-specific internal standards and allows for the absolute quantification of mRNA levels. We find that chronic ethanol consumption elicits a significant increase in alpha 4 subunit mRNA levels that is equal, in absolute amount, to a decrease in alpha 1 subunit mRNA levels. There is a small (30%) increase in gamma 2S but not gamma 2L subunit mRNA levels after chronic ethanol consumption. In addition, gamma 1 subunit mRNA levels are increased by 70%, whereas alpha 5, beta 1, beta 2, beta 3, gamma 3, and delta subunit mRNA levels do not change. We also reproduced results obtained previously by Northern blot analysis showing a 40% reduction in alpha 1 mRNA levels with no change in beta 2 subunit mRNA levels after chronic ethanol consumption. These results are consistent with the hypothesis that chronic ethanol consumption alters the function of GABAA receptors by eliciting changes in receptor subunit assembly. These changes may underlie the development of ethanol dependence.
乙醇依赖背后的分子机制似乎涉及γ-氨基丁酸A（GABAA）受体功能和基因表达的改变。在大鼠大脑皮层中，长期接触乙醇会改变GABAA受体的许多功能特性，包括减少GABAA受体介导的氯离子摄取。这些功能改变在总受体密度或亲和力没有相应改变的情况下发生。先前的研究表明，长期乙醇暴露会引发几种丰富的GABAA受体亚基的mRNA和多肽水平的改变。例如，已显示α1和α2亚基的mRNA和多肽水平会随着长期乙醇暴露而降低。本研究旨在通过使用竞争性定量逆转录聚合酶链反应测定法进一步研究长期乙醇摄入对大鼠大脑皮层中GABAA受体亚基mRNA水平的影响，该测定法结合了亚基特异性内标并允许对mRNA水平进行绝对定量。我们发现，长期乙醇摄入会导致α4亚基mRNA水平显著增加，其绝对量与α1亚基mRNA水平的降低相当。长期乙醇摄入后，γ2S亚基mRNA水平有小幅（30%）增加，但γ2L亚基mRNA水平没有增加。此外，γ1亚基mRNA水平增加了70%，而α5、β1、β2、β3、γ3和δ亚基mRNA水平没有变化。我们还重现了先前通过Northern印迹分析获得的结果，即长期乙醇摄入后α1 mRNA水平降低40%，而β2亚基mRNA水平没有变化。这些结果与以下假设一致，即长期乙醇摄入通过引发受体亚基组装的变化来改变GABAA受体的功能。这些变化可能是乙醇依赖发展的基础。
