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 r esults in a downregulation of the GABA-benzodiazepine receptor complex . In the present study, the mRNA levels, as well as polypeptide expres sion, for the GABA(A) receptor alpha(2) and alpha(3) subunits in cultu red embryonic mouse cerebral cortical neurons (7 day old) were examine d using northern analysis and immunoblotting techniques following chro nic 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 conditio ns. This agonist-induced reduction in the GABA(A) receptor alpha(2) an d alpha(3) subunit mRNA was blocked by the concomitant exposure of neu rons to R 5135, an antagonist of GABA(A) receptor. The polypeptide exp ression for the GABA(A) receptor alpha(2) and alpha(3) subunits in chr onically GABA-treated neurons also showed a decline and this change wa s also blocked by the concomitant exposure of cells to GABA and R 5135 . These results indicate that the chronic exposure of the GABA(A) rece ptor complex to agonist downregulates the expression of the alpha subu nits of the receptor complex, which may be related to an observed decr eases in the number of binding sites and GABA-induced Cl-36-influx in the cortical neurons.