Differential Expression of GABA Receptor Subunit Messenger Ribonucleic Acids and Immunoreactivity in the Rat Neostriatum during Postnatal Development

Abstract

γ-Aminobutyric acid (GABA) is a major inhibitory neurotransmitter in the neostriatum. Functions of GABA are mediated by GABA_A and GABA_B receptors in the neostriatum. In order to investigate the developmental expression of GABA receptor subunits (GABA_Aα₁, GABA_Aα₃ and GABA_Aα₆; GABA_Aβ₂ and GABA_Aβ₃, and GABA_BR₁ and GABA_BR₂) in the rat neostriatum, reverse transcriptase-polymerase chain reaction (RT-PCR) and immunofluorescence were performed. Tissues were obtained from rats on postnatal day (PND) 1, PND 7 and PND 14, and from adult rats. RT-PCR indicated that GABA_Aα₁ and GABA_Aα₆ mRNA levels were low, but that GABA_Aβ₂ and GABA_Aβ₃ mRNAs levels were high during the early postnatal period. Immunofluorescence revealed that GABA_Aα₁ immunoreactivity was only observed in striatal interneurons in PND 14 and in adult rats. Immunoreactivity for GABA_Aα₆ was only observed in PND 14 and adult animals. GABA_BR₁ immunoreactivity was found to be expressed by perikarya of striatal neurons at all ages examined. In contrast, GABA_BR₂ immunoreactivity was mainly observed in choline acetyltransferase-positive striatal interneurons in PND 14 and adult rats. The present results indicate that there are differential patterns of developmental expression of GABA receptor subunits in the neostriatum, with important implications for the development of GABA systems in rat basal ganglia.