CHRONIC GABA TREATMENT DOWN-REGULATES THE GABA(A) RECEPTOR ALPHA(2) AND ALPHA(3) SUBUNIT MESSENGER-RNAS AS WELL AS POLYPEPTIDE EXPRESSION IN PRIMARY CULTURED CEREBRAL CORTICAL-NEURONS

Chronic GABA exposure of mammalian primary cultured cortical neurons results in a downregulation of the GABA-benzodiazepine receptor complex. In the present study, the mRNA levels, as well as polypeptide expression, for the GABA(A) receptor alpha(2) and alpha(3) subunits in cultured embryonic mouse cerebral cortical neurons (7 day old) were examined using northern analysis and immunoblotting techniques following chronic GABA treatment. The alpha(1) subunit mRNA or polypeptide could not be detected in these neurons. The steady state levels of mRNA for the GABA(A) receptor alpha(2) and alpha(3) subunits showed a decrease in comparison with untreated neurons. There was no change in the level of the beta actin or poly(A)(+) RNA under the same experimental conditions. This agonist-induced reduction in the GABA(A) receptor alpha(2) and alpha(3) subunit mRNA was blocked by the concomitant exposure of neurons to R 5135, an antagonist of GABA(A) receptor. The polypeptide expression for the GABA(A) receptor alpha(2) and alpha(3) subunits in chronically GABA-treated neurons also showed a decline and this change was also blocked by the concomitant exposure of cells to GABA and R 5135. These results indicate that the chronic exposure of the GABA(A) receptor complex to agonist downregulates the expression of the alpha subunits of the receptor complex, which may be related to an observed decreases in the number of binding sites and GABA-induced Cl-36-influx in the cortical neurons.