AMPA receptors serum-dependently mediate GABAA receptor α1 and α6 subunit down-regulation in cultured mouse cerebellar granule cells

Depolarization of cultured mouse cerebellar granule cells with potassium or kainate results in developmentally arrested state that includes down-regulation of GABAA receptor α1, α6 and β2 subunit expression. These subunits are normally strongly expressed in cerebellar granule cells from second postnatal week throughout the adulthood. In the present study we demonstrate that selective activation of AMPA subtype of glutamate receptors down-regulates α1 and α6 subunit mRNA expression. Removal of AMPA agonist from culture medium restores expression of these subunits indicating reversibility of the down-regulation. In serum-free culture medium AMPA receptor activation did not down-regulate α1 or α6 subunit expression. Furthermore, the down-regulation was strongly attenuated when the cells were cultured in the presence of dialysed fetal calf serum. The results indicate that down-regulation of GABAA receptor α1 and α6 subunits by AMPA receptor activation is dependent on the presence of low molecular weight compounds present in fetal calf serum. In order to study mouse cerebellar granule cell maturation and/or regulation of GABAA receptor subunit expression in culture, the experiments should be performed in the absence of fetal calf serum.