Proceedings of The Physiological Society

University of Leeds (2002) J Physiol 544P, S018

Communications

GABAA receptor subunit expression in the rat nucleus tractus solitarii

E.J. Spary, S. Saha and T.F.C. Batten

Institute for Cardiovascular Research, School of Medicine, Leeds University, Leeds LS2 9JT, UK


The synaptic action of the inhibitory transmitter λ-aminobutyric acid (GABA) in the nucleus tractus solitarii (NTS) of the medulla is mediated by both GABAA and GABAB receptors (Kubo & Kihara, 1987; Suzuki et al. 1993). GABAA receptors can be composed of five structurally and pharmacologically different classes of subunit proteins, which exist in at least 16 major isoforms: α1-6, β1-3, λ1-3, δ, π, u and ψ (see Barnard et al. 1998). Recently, we have detected the expression of mRNAs encoding six GABAA receptor subunits (α1, α2, α3, β2, β3, λ2) in the rat NTS by polymerase chain reaction (PCR), and confirmed the cellular localisation of the receptor proteins using specific antibodies (Saha et al. 2001). Both PCR and immunohistochemistry showed that the GABAA α5 subunit is absent in the NTS. Here we have investigated the presence of further subunits of the GABAA receptor in rat NTS.

Adult Wistar rats were humanely killed by decapitation or perfusion under deep anaesthesia (halothane, 5 % in O2). Total RNA was isolated from punches of freshly dissected, unfixed NTS tissue and reverse transcribed to first strand cDNA. The cDNA was amplified by PCR using primers specific for the GABAA subunits α4, α6, β1, λ1, λ3, δ, π, u and ψ. The presence of some of these subunits (β1, λ3, δ) was indicated by PCR, and this was confirmed by immunohistochemistry on sections from perfused tissue using antibodies specific for the individual subunits. These gave a labelling pattern in the NTS consisting of moderate to strongly labelled cell bodies interspersed with immunolabelled punctata in the neuropil. The differential patterns of immunoreactivity in neuronal somata and dendrites of NTS neurones were generally in agreement with the PCR results, confirming that mRNA expression is correlated with receptor protein synthesis. The α6, λ1, π, u and ψ subunits were detected at low expression levels by PCR, but immunolocalization in the NTS could not be confirmed. The results suggest that neurones in the NTS can express GABAA receptors comprising various combination of α, β, λ and δ subunits, with regional differences in expression within the nucleus that might be related to specific autonomic functions.

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