Comparative immunohistochemical localisation of Gaba(B1a), Gaba(B1B) and Gaba(B2) subunits in rat brain, spinal cord and dorsal root ganglion

GABA(B) receptors are G-protein-coupled receptors mediating the slow onset and prolonged synaptic actions of GABA in the CNS. The recent cloning of tw o genes, GABA(B1) and GABA(B2), has revealed a novel requirement for GABA(B ) receptor signalling. Studies have demonstrated that the two receptor subu nits associate as a GABA(B1)/GABA(B2) heterodimer to form a functional GABA B receptor. In this study we have developed polyclonal antisera specific to two splice variants of the GABA(B1) subunit, GABA(B1a) and GABA(B1b) as we ll as an antiserum to the GABA(B2) subunit. Using affinity-purified antibod ies derived from these antisera we have mapped out the distribution profile of each subunit in rat brain, spinal cord and dorsal root ganglion. In bra in the highest areas of GABA(B1a), GABA(B1b) and GABA(B2) subunit expressio n were found in neocortex, hippocampus, thalamus, cerebellum and habenula. In spinal cord, GABA(B1) and GABA(B2) subunits were expressed in the superf icial layers of the dorsal horn, as well as in motor neurotics in the deepe r layers of the ventral horn. GABA(B) receptor subunit immunoreactivity in dorsal root ganglion suggested that expression of GABA(B1b) was restricted to the large diameter neurones, in contrast to GABA(B1) and GABA(B2) subuni ts which were expressed in both large and small diameter neurones. Although expression levels of GABA(B1) and GABA(B2) subunits varied we found no are as in which GABA(B1) was expressed in the absence of GABA(B2), This suggest s that most, if not all, GABA(B1) immunoreactivity may represent functional GABA(B) receptors. Although our data are in general agreement with functio nal studies, some discrepancies in GABA(B1) subunit expression occurred wit h respect to other immunohistochemical studies. Overall out data suggest th at GABA(B) receptors are widely expressed throughout the brain and spinal c ord, and that GABA(B1a) and GABA(B1b) subunits can associate with GABA(B1) to form both pre- and post-synaptic receptors. (C) 2001 IBRO, Published by Elsevier Science Ltd. All rights reserved.