Cerebellovestibular projection from the posterior lobe cortex in the rabbit: an experimental study with the retrograde HRP method. II. Zonal organization.

The mediolateral distribution of neurones of origin of the corticovestibular projection from the cerebellar posterior lobe in the rabbit was studied with the retrograde horseradish peroxidase (HRP) tracing method. After iontophoretic injections confined to various subdivisions of the vestibular nuclear complex (VNC) labelled Purkinje neurones were found ipsilaterally in widespread mediolateral cortical regions of vermal lobules from VI to IX, as well as in crus I and crus II of the ansiform lobule, the copula pyramidis, lobule HV and the ventral paraflocculus. However, when projections from individual sublobules were examined, a clearly visible zonal pattern was found. Thus, Purkinje neurones projecting to VNC were arranged in longitudinal bands with medial and lateral boundaries quite well demarcated. These bands had a different width and were found to be located at different distances from the midline. The present findings constitute the first indication of a zonal organization of corticovestibular projections from individual sublobules of the cerebellar posterior lobe in the rabbit. This zonal arrangement of VNC afferents is discussed with the special emphasis on the cerebellar longitudinal zones and related to previous studies on other species.