ANTIBODIES SPECIFIC FOR GABA(A) RECEPTOR ALPHA-SUBUNITS REVEAL THAT CHRONIC ALCOHOL TREATMENT DOWN-REGULATES ALPHA-SUBUNIT EXPRESSION IN RAT-BRAIN REGIONS

Chronic administration of ethanol results in the development of tolerance and dependence. The molecular mechanism underlying these behavioral actions of ethanol is poorly understood. Several lines of evidence have suggested that some of the pharmacological actions of ethanol are mediated via a potentiation of GABAergic transmission. Chronic ethanol administration results in a reduction in the GABA(A) receptor-mediated Cl-36- uptake in cortical synaptoneurosomes and primary cultured neurons. We and others have shown that it also results in a 40-50% reduction in GABA(A) receptor alpha-subunit mRNA levels in the rat cerebral cortex. In the present study, we investigated the expression of alpha1, alpha2, and alpha3 subunits of the GABA(A) receptor in the cerebral cortex and the alpha1 subunit in the cerebellum by immunoblotting using polyclonal antibodies raised against alpha1-, alpha2-, and alpha3-Subunit polypeptides following chronic ethanol treatment. These results reveal that chronic ethanol administration to rats results in a 61 +/- 4% reduction in level of the GABA(A) receptor alpha1 subunit (51 kDa), 47 +/- 8% reduction in level of the alpha2 subunit (53 kDa), and 30 +/- 7% reduction in level of the alpha3 subunit (59 kDa) in the cerebral cortex and a 56 +/- 5% reduction in content of the alpha1 subunit in the cerebellum. In summary, this ethanol-induced reduction in content of the GABA(A) receptor alpha subunits may underlie alterations in the GABA(A) receptor function and could be related to cellular adaptation to the functional disturbance caused by ethanol.