Expression of GABA_A receptor subunits in brain stem auditory pathways: cochlear nuclei, superior olivary complex, and nucleus of the lateral lemniscus.

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 GABAA receptors in the rat cochlear nucleus, superior olivary complex, and dorsal and ventral nuclei of the lateral lemniscus. All neurons express the beta3 and gamma 2L subunit messenger RNAs, but use different ct subunits. In the dorsal cochlear nucleus, fusiform (pyramidal) and giant cells express alpha1, alpha3, beta3 and gamma 2L. Dorsal cochlear nucleus interneurons, particularly vertical or turboculoventral cells and cartwheel cells, express alpha3, beta3 and gamma 2L. In the ventral cochlear nucleus, octopus cells express alpha1, beta3, gamma 2L and delta. Spherical cells express alpha1, alpha3, alpha5, beta3 and gamma 2L. In the superior olivary complex, the expression profile is alpha3, alpha5, beta3 and gamma 2L. Both dorsal and ventral cochlear nucleus granule cells express alpha1, alpha6, beta3 and y2L; unlike their cerebellar granule cell counterparts, they do not express beta2, gamma 2S or the delta subunit genes. The delta subunit's absence from cochlear nucleus granule cells may mean that tunic inhibition mediated by extrasynaptic GABAA receptors is less important for this cell type. In both the dorsal and ventral nuclei of the lateral lemniscus, alpha1, beta3 and y2L are the main subunit messenger RNAs; the ventral nucleus also expresses the delta 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 beta2 subunit gene and gamma 2S splice forms are not highly expressed in auditory brainstem nuclei. GABA(A) receptors containing beta3 and y2L may be particularly well suited to auditory processing, possibly because of the unique phosphorylation profile of this subunit combination. (C) 2001 IBRO. Published by Elsevier Science Ltd. All rights reserved.