Immunocytochemical features of the vestibular nuclei in the monkey and cat

Immunocytochemical studies of the vestibular nuclei (VN) were done in the squirrel monkey and cat using polyclonal antisera. Brain stem sections were processed using the Avidin-Biotin peroxidase complex with diaminobenzidine as the chromagen. Choline acetyltransferase immunoreactivity (ChAT-IR) was most prevalent in the caudal medial (MVN), inferior (IVN) and peripheral superior (SVN) VN. Nearly all cells of groups x and z were ChAT-positive. None of the giant cells of the lateral vestibular nucleus (LVN) was ChAT-IR. Glutamate immunoreactivity (GLU-IR) was abundant in all VN and in cells of the vestibular ganglion (VG). Gamma-aminobutyric acid immunoreactivity (GABA-IR), was found in cells of rostral MVN, cell group y and in granules about giant cells in dorsal LVN. Substance P immunoreactive (SP-IR) was present in a small cells in MVN, IVN and the VG and in granules surrounding all large cells in LVN in both monkey and cat; SP-IR granules were most intense in ventral LVN in the monkey. Some cells in the dorsal parts of the fastigial nucleus (FN) were outlined by SP-IR granules in both species. Leucine-enkephalin immunoreactivity (ENK-IR) was identified only in granules surrounding cells of group x in the monkey. GLU was the only immunoreactive substance found in the giant cells of LVN. The disposition of ChAT-IR in the VN suggested participation in commissural systems, as well as projections to spinal cord and/or cerebellum. Small GABA-IR neurons in MVN probably represented both commissural and projection neurons; GABA-IR granules about cells in dorsal LVN and some cells in MVN and SVN appeared to represent Purkinje cell (PC) terminals. SP-IR granules surrounding cells in ventral LVN appeared to represent terminals of small SP-positive VG cells. The source of SP-IR granules around cells in dorsal LVN and some cells in FN and SVN remains unknown, but these fibers may originate from portions of the reticular formation known to contain large numbers of SP-positive neurons.