Distribution of a GABAB-like receptor protein in the rat central nervous system.

Using a homology-based bioinformatics approach we have identified the human and rodent orthologues of a novel putative seven transmembrane G protein coupled receptor, termed GABA(BL). The amino acid sequence homology of these cDNAs compared to GABA(B1) and GABA(B2) led us to postulate that GABA(BL) may be a putative novel GABA(B) receptor subunit. We have developed a rabbit polyclonal antisera specific to the GABA(BL) protein and assessed the distribution of GABA(BL) in the rat CNS by immunohistochemistry. Protein expression was particularly dense in regions previously shown to contain known GABA(B) receptor subunits. Dense immunoreactivity was observed in the cortex, major subfields of the hippocampus and the dentate gyrus. GABA(BL) labelling was very conspicuous in the cerebellum, both in the granule cell layer and in Purkinje cells, and was also observed in the substantia gelatinosa and ventral horn motor neurons of the spinal cord. GABA(BL) immunoreactivity was also noted in a subset of parvalbumin positive hippocampal interneurons. Our data suggest a widespread distribution of GABA(BL) throughout the rat CNS.