Differential and transient expression of GABA(A) receptor α-subunit mRNAs in the developing rat CNS

Abstract

The expression of mRNAs coding for α1, α2, α3, α5, and α6 subunits of the GABA(A) neurotransmitter receptor was followed during the development of the rat CNS by in situ hybridization histochemistry. Expression of these subunit mRNAs in tissue sections of embryonic day 15 and 17 (E15, E17) whole rat and in brain at ages > E17 to adult were varied, transient, and region specific. Subunit mRNAs first detected at E15 were those coding for the α2 and α3 subunits. At E17, α2, α3, and α5 mRNAs were present in abundance in numerous areas in the CNS, with lower but significant amounts of α6 being present in the cortical neuroepithelial layers. However, α6 subunit mRNA expression in the cortex declined until little or no α6 mRNA was detected at E19. α1 subunit mRNA first appeared at E19 in the cortex, followed by expression in the hippocampus by postnatal 5 (PN5). Particularly high expression of α2 and α5 subunit mRNAs was detected throughout the developing CNS, but they were most abundant in the olfactory bulb neurons. The high levels of α2 and α5 subunit mRNAs began to decline around PN5 to the amounts observed in adult. These results demonstrate that numerous GABA(A) receptor α-subunits are expressed before birth in a region- and age-specific manner. This complex and varied expression supports the hypothesis that GABA may play a role in cellular and synaptic differentiation.