Differentially expressed GABAA-receptor subunits result in structurally and functionally receptor assemblies following excitatory afferent synaptic transmission.

Cerebellar granule cells isolated from postnatal day 7 rat pups are ideal for studying epigenetic events associated with the regulation of neuronal gene expression. These cultures contain from 90 to 95% glutamatergic granule cells and express mRNAs encoding a variety of ionotropic and metabotropic glutamate receptors as well as virtually all of the GABAA-receptor subunit mRNAs to different extents. A unique feature of this culture system is that the neurons undergo time-dependent maturation changes in vitro that mimic many of the characteristics of these receptors occurring in vivo. Granule cell cultures in vitro require depolarizing concentrations of KCl for long-term growth and survival. Both N-methyl-D-aspartate (NMDA) and GABA have been reported to exert trophic actions on these cells replacing the requirement for maintaining the cultures in high KCl. Cerebellar granule cells maintained under different conditions in vitro can be induced to alter their patterns of maturation, as indicated by the different temporal changes in gene expression of receptor subunit mRNAs and proteins. The focus of the current studies is the effect of NMDA afferent synaptic signaling on the changes in mRNA content and functional properties of GABAA receptors and how this may relate to comparable changes shown to occur in vivo.