Coexpression of GABABR1 and GABABR2 Receptor Subunits in the Rat Vestibular Nucleus

The expression patterns of the two subunits of the metabotropic GABA B receptor, GABA B R1 and GABA B R2, vary among various neural regions and their relative expression in the rat central vestibular system remains unknown. To identify the expression patterns of these two subunits of the metabotropic GABA B receptor in the vestibular nucleus of adult rats, double immunofluorescence experiments were performed. GABA B R1 or GABA B R2 immunoreactivity was observed in neurons and neuropilar elements of the vestibular nuclear complex and its subgroups x and y. These neurons were oval, multipolar, fusiform or triangular in shape. In contrast to other brain regions, individual neurons or neuropil within the various vestibular subnuclei and subgroups displayed comparable levels of GABA B R1 and GABA B R2 immunoreactivity. Double immunofluorescence experiments further demonstrated the coexpression of GABA B R1 and GABA B R2 receptor subunits in individual central vestibular neurons. The present findings provide histological evidence of the heterodimeric nature of GABA B receptors that mediate inhibitory neurotransmission in the rat vestibular nuclei.