The expression patterns of the two subunits of the metabotropic GABAB receptor, GABABR1 and GABABR2, 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 GABAB receptor in the vestibular nucleus of adult rats, double immunofluorescence experiments were performed. GABABR1 or GABABR2 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 GABABR1 and GABABR2 immunoreactivity. Double immunofluorescence experiments further demonstrated the coexpression of GABABR1 and GABABR2 receptor subunits in individual central vestibular neurons. The present findings provide histological evidence of the heterodimeric nature of GABAB receptors that mediate inhibitory neurotransmission in the rat vestibular nuclei.