Expression of GABAB receptor in vestibular nuclear neurons of rats

Abstract

GABAergic transmission is involved in both cerebellar and commissural inhibition of vestibular nuclear neurons. To locate the metabotropic GABAB receptor subunits in the vestibular nucleus, we immunostained for GABABR1 and GABABR2 in the medulla of adult Sprague–Dawley rats. In some experiments, off-vertical axis rotation, a scanning stimulus which sequentially stimulates all receptor hair cells on the utricle, was used to functionally activate Fos expression in vestibular nuclear neurons. Nearly all utriclerelated Fos immunopositive neurons expressed GABABR1 or GABABR2-immunoreactivity. Furthermore, double immunoreactivities of GABABR1 and GABABR2 were found in neuropilar elements as well as perikarya of neurons in the vestibular nuclei. These neurons were frequently associated with glutamic acid decarboxylase (GAD) immunopostive terminal-like puncta. Such puncta were so numerous in the dorsal lateral vestibular nucleus that they often outlined the soma. Within the vestibular nuclear complex, neurons that co-expressed GABABR1/GAD or GABABR2/GADimmunoreactivity were only found in the spinal vestibular nucleus. This constituted about 50% of the GABABR1 or GABABR2 immunopositive neurons in the spinal vestibular nucleus. Our findings therefore provide immunocytochemical evidence for the occurrence of heterodimeric GABAB receptor on GAD-containing neurons and utricle-related neurons in the rat vestibular nuclear complex. Acknowledgement: Supported by HK RGC.