Expression and dendritic mRNA localization of GABAC receptor ρ1 and ρ2 subunits in developing rat brain and spinal cord

The cellular distribution of GABA(C) receptor rho1 and rho2 subunits in the rat central nervous system remains controversial. We investigated how these subunits were distributed in cerebellum, hippocampus and spinal cord at postnatal day 1, 7 or in adult life. We found that in the adult cerebellum rho1 and rho2 mRNAs were expressed in Purkinje cells and basket-like cells only. In the hippocampus both subunits were expressed throughout the CA1 pyramidal layer, dentate gyrus and scattered interneurons with maximum staining intensity at P7. In the adult hippocampus in situ staining was predominantly found on interneurons. GABA(C) antibody labelling in P7 and adult hippocampus was largely overlapping with the in situ staining. Western blot analysis showed GABA(C) receptor in retina, ovary and testis. In the spinal cord the rho2 signal was consistently stronger than rho1 with overlapping expression patterns. At P1, the most intensely labelled cells were the motoneurons while on P7 and adult sections, interneurons and motoneurons were likewise labelled. On spinal neurons both rho1 and rho2 mRNAs showed somatodendritic localization, extending out for >100 mum with punctate appearance especially in adult cells. A similar spinal distribution pattern was provided with polyclonal antibody labelling, suggesting close correspondence between mRNA and protein compartmentalization. Electrophysiological experiments indicated that P1 spinal motoneurons did possess functional GABA(C) receptors even though GABA(C) receptors played little role in evoked synaptic transmission. Our results suggest a pattern of rho1 and rho2 subunit distribution more widespread than hitherto suspected with strong developmental regulation of subunit occurrence.