Expression of GABA A receptor subunits in rat brainstem auditory pathways: cochlear nuclei, superior olivary complex and nucleus of the lateral lemniscus

Abstract

Inhibition by GABA is important for auditory processing, but any adaptations of the ionotropic type A receptors are unknown. Here we describe, using in situ hybridization, the subunit expression patterns of GABA A receptors in the rat cochlear nucleus, superior olivary complex, and dorsal and ventral nuclei of the lateral lemniscus. All neurons express the β3 and γ2L subunit messenger RNAs, but use different α subunits. In the dorsal cochlear nucleus, fusiform (pyramidal) and giant cells express α1, α3, β3 and γ2L. Dorsal cochlear nucleus interneurons, particularly vertical or tuberculoventral cells and cartwheel cells, express α3, β3 and γ2L. In the ventral cochlear nucleus, octopus cells express α1, β3, γ2L and δ. Spherical cells express α1, α3, α5, β3 and γ2L. In the superior olivary complex, the expression profile is α3, α5, β3 and γ2L. Both dorsal and ventral cochlear nucleus granule cells express α1, α6, β3 and γ2L; unlike their cerebellar granule cell counterparts, they do not express β2, γ2S or the δ subunit genes. The δ subunit's absence from cochlear nucleus granule cells may mean that tonic inhibition mediated by extrasynaptic GABA A receptors is less important for this cell type. In both the dorsal and ventral nuclei of the lateral lemniscus, α1, β3 and γ2L are the main subunit messenger RNAs; the ventral nucleus also expresses the δ subunit. We have mapped, using in situ hybridization, the subunit expression patterns of the GABA A receptor in the auditory brainstem nuclei. In contrast to many brain regions, the β2 subunit gene and γ2S splice forms are not highly expressed in auditory brainstem nuclei. GABA A receptors containing β3 and γ2L may be particularly well suited to auditory processing, possibly because of the unique phosphorylation profile of this subunit combination.