To examine the direct effects of neurosteroids on gamma-aminobutyric acid type A (GABA(A)) receptor expression, we exposed developing neuronal cells (P19) in vitro to 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha,5alpha-THP, allopregnanolone). Quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) analysis revealed a concentration-dependent decrease in GABA(A) receptor alpha4 subunit mRNA expression that reversed 24 h after steroid withdrawal. These data suggest that variations in neurosteroid levels regulate the pattern of GABA(A) receptor subunit expression and may alter the trophic effects of GABA.