Down-regulation of the GABA receptor subunits mRNA levels in mammalian cultured cortical neurons following chronic neurosteroid treatment

Abstract

We have recently shown that chronic neurosteroid, 5α3α, treatment produced down-regulation of the GABA receptor binding and function, and heterologous uncoupling on the GABA A receptor complex in cultured mammalian cortical neurons. In order to explore the underlying mechanism of these observed down-regulation and heterologous uncoupling phenomenon, we investigated the effect of chronic 5α3α (1 μM; 5 days) treatment on the GABA A receptor subunits mRNA levels, using RNase protection assay. We found that chronic neurosteroid, 5α3α, treatment decreased the β- and α-subunits mRNA levels while not altering the γ 2S-subunit mRNA levels in the cortical neurons. The decrease in the β-subunits mRNA levels suggests a decrease in the presence of the β-subunits in the composition of GABA A receptors. This phenomenon may explain the down-regulation of the GABA A receptor binding and function. A decrease in the α 3-subunit mRNA level suggests a corresponding decrease in the α 3-subunit in the composition of GABA A receptor isoforms, relative to other isoforms. This observation may be responsible for the chronic neurosteroid-induced uncoupling and decreased efficacy. In summary, chronic 5α3α treatment produced down-regulation of the GABA A receptor β- and α-subunit mRNA levels, and these changes may be associated with the down-regulation, heterologous uncoupling, and decreased efficacy of GABA A receptor complex in the cultured mammalian cortical neurons.