RESUMO
One of the striking features of the vestibular hair cells is the polarized arrangement of their stereocilia and their consequent characteristic of best activation/deactivation directions. Furthermore each of the vestibular end organs is characterized by a distinct organization of these polarized cells. Specifically, all the hair cells in the crista of an individual canal have the same polarity, and the macula are each divided in halves along the striola where the polarities of the hair cells show mirror image symmetry. We utilized the technique of post-fixation transganglionic neuronal tracing with immunofluorescent lipid soluble dyes in new born and 8 day old mice to investigate whether these polarity characteristics influence the pattern of connections between the end organs and their central targets: the vestibular nuclei and cerebellum. We found the cerebellar projection originates preferentially from the medial and superomedial half of the utricular and saccular macula, respectively, while the vestibular projection originates primarily from their lateral and superolateral half respectively. This indicates that striola defines almost mutually exclusive central projections, as well as opposing hair cell polarities. It is suggested that, this macular organization provides an inhibitory side loop through the cerebellum to produce synergetic tuning effects in the vestibular nuclei. In the canals, the entire crista projects to the vestibular nuclei, but the projection to the vestibulocerebellum originates preferentially from the medial half of each of the cristae. The reason for this pattern is not clear, but it may compensate for unequal activation of crista hair cells