Localization of rat glycine receptor α1 and α2 subunit transcripts in the developing auditory brainstem

Abstract

Glycine receptors (GlyRs), aside from GABAA receptors, mediate fast postsynaptic inhibition in the mammalian nervous system. Spatial and temporal expression of the genes encoding ligand-binding α subunits (α1-α4) and the structural β subunit leads to the formation of various GlyR isoforms. Currently, the idea of the GlyRs containing the "adult" α1 subunit replacing those with the "neonatal" α2 subunit during early postnatal development predominates. Here, we describe the patterns of expression of the GlyR α1 and α2 subunit genes in the rat auditory brainstem between postnatal day (P) 0 and P20, by using both nonradioactive and radioactive in situ hybridization. We show that the α1 subunit mRNA appears throughout the auditory brainstem during the first 8 postnatal days, which resembles the time of onset described within the spinal cord. In the rostral auditory nuclei (nuclei of the lateral lemniscus and inferior colliculus), the α1 subunit transcript appears later (P8) than in the caudal nuclei (cochlear nuclear complex and superior olivary complex; P0). Surprisingly, we found that low levels of the α2 subunit transcript are present in the auditory brainstem at birth and persist throughout the period analyzed. However, α2 subunit mRNA is present at high levels in other neonatal brainstem structures, such as cranial motor nuclei. Therefore, we conclude that the changes in GlyR composition in the auditory brainstem deviate from the classic α2 to α1 subunit switch observed in spinal cord. Our data suggest that genes for other GlyR subunits (e.g., α3 and α4) may be expressed during early development in the auditory brainstem. © 2001 Wiley-Liss, Inc.