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

Inhibition by GABA is important For auditory processing, but any adaptation s of the ionotropic type A receptors are unknown. Here we describe, using i n 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 2 L subunit messenger RNAs, but use different ct subunits. In the dorsal coch lear nucleus, fusiform (pyramidal) and giant cells express alpha1, alpha3, beta3 and gamma 2L. Dorsal cochlear nucleus interneurons, particularly vert ical or turboculoventral cells and cartwheel cells, express alpha3, beta3 a nd 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 profil e is alpha3, alpha5, beta3 and gamma 2L. Both dorsal and ventral cochlear n ucleus granule cells express alpha1, alpha6, beta3 and y2L; unlike their ce rebellar 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 GABA A receptors is less important for this cell type. In both the dorsal and ve ntral nuclei of the lateral lemniscus, alpha1, beta3 and y2L are the main s ubunit messenger RNAs; the ventral nucleus also expresses the delta subunit . We have mapped, using in situ hybridization, the subunit expression pattern s 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 no t highly expressed in auditory brainstem nuclei. GABA(A) receptors containi ng beta3 and y2L may be particularly well suited to auditory processing, po ssibly because of the unique phosphorylation profile of this subunit combin ation. (C) 2001 IBRO. Published by Elsevier Science Ltd. All rights reserve d.