Differential expression of GABA A receptor subunit mRNAs in ethanol-naive withdrawal seizure resistant (WSR) vs. withdrawal seizure prone (WSP) mouse brain

Abstract

Several lines of evidence suggest an important role for ethanol interactions with GABA A receptors in the development of the ethanol withdrawal syndrome. The present study was undertaken to determine whether there is a genetic relationship between ethanol withdrawal seizure severity and the expression of particular GABA A receptor subunits in mouse lines selectively bred for differential sensitivity to ethanol withdrawal seizures. Since GABA A receptor subunit levels are subject to modulation by ethanol, the levels of GABA A receptor α1, α6 and β2 subunit mRNAs were measured in cerebellum while α1 and β2 subunit levels were determined in cerebral cortex of ethanol-naive WSR and WSP mice. Poly(A) + RNA was isolated from groups of 6–10 animals and the GABA A receptor subunit mRNA levels were quantified by Northern blot analysis using subunit selective cRNA probes. In the cerebellum, greater levels of each of these subunit mRNAs were detected in WSR1 mice compared to WSP1 mice. The levels of GABA A receptor α1 subunit mRNAs were approximately 26 ± 16 percent greater for the 4.4 kb transcript and 84 ± 23 percent greater for the 4.8 kb transcript in WSR mice vs WSP mice. GABA A receptor α6 subunit (2.7 kb) mRNA levels in cerebellum were 159 ± 58 percent greater in WSR mice than WSP mice, while β2 subunit mRNA levels were 110 ± 30 percent greater in WSR than WSP mice. These results were replicated for the α1 and α6 subunits in WSR2 vs WSP2 mouse cerebella. No differences in β-actin mRNA levels were detected on the same RNA blots. Data normalized to β-actin mRNA levels showed similar differences between WSR and WSP mice. In contrast, no differences in GABA A receptor α1 or β2 subunit mRNA expression were detected in cerebral cortex between the WSR and WSP mouse lines. These data suggest that withdrawal seizure severity and the increased sensitivity to GABA A receptor antagonists in WSP vs. WSR mice may be related to differences in GABA A receptor gene expression in specific brain regions.