The central projections from central and peripheral parts of the lateral crista in the mongolian gerbil were investigated by using scratch method and extracellularly applied horseradish peroxidase in the ampullary portion of labyrinth. The central and peripheral surfaces of the lateral crista were scratched selectively with an electrolytically sharpened fine needle and filled up the vestibule with 30% horseradish peroxidase solution. In 48 hours of experiment, with sliding microtome, the brain stem serial sections of 50 μm were made. The tissue was processed with the diaminobenzidine procedure of cobalt-glucose oxidase method. The primary afferent fibers from the central part of the lateral crista innervated central area of superior, medial and inferior vestibular nuceli respectively. The fibers from the peripheral part of flocculus side terminated in the dorso-lateral portion of superior and medial vestibular nucleus and dorsal portion of descending vestibular nucleus. The fibers from the peripheral part of oval window side projected into the dorso-medial portion of superior vestibular nucleus, ventro-medial portion of medial vestibular nucleus and dorsal portion of descending vestibular nucleus. The neurons received the afferent fibers from the central part of crista were larger than those from the periphery. In neurons of paracochlear glial substance, the fibers only from the central part of the lateral crista were projected. Above results suggest that different informations from the central and peripheral parts of the lateral crista transfer to each specific areas in the major vestibular nuclei. However, to clarify the functional significance of these results, the quantitative analysis of the upper central pathways and neurophysiological study related to the vestibular reflex arcs will be needed.
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