Cerebellovestibular projection from the posterior lobe cortex in the rabbit: an experimental study with the retrograde HRP method. I. Topographical relationships.

The sources of corticovestibular projections from the cerebellar posterior lobe vermis and hemisphere in the rabbit were investigated by the retrograde horseradish peroxidase (HRP) tracing method. Following iontophoretic injections into various subdivisions of the vestibular nuclear complex (VNC), labelled Purkinje neurones were identified ipsilaterally in all vermal lobules (VI through IX) and some regions of the hemisphere. The results indicate that projection is profuse and directed to all four nuclei of VNC. The labelling suggests some topographical relationships between lobules and especially sublobules of the posterior lobe and individual nuclei of VNC. The major projection originates from lobules VI and IX. A moderate projection derives from lobule VIII whereas that from lobule VII is small. Projections from the hemisphere arise mainly from crus I and crus II of the ansiform lobule. Those from the copula pyramidis, lobule HV and the ventral paraflocculus are sparse. In the present study a topographical relationships were more precisely established than before because the technique revealed VNC afferents from individual sublobules of the cerebellar posterior lobe cortex.