CEREBELLOVESTIBULAR PROJECTION FROM THE POSTERIOR LOBE CORTEX IN THE RABBIT - AN EXPERIMENTAL-STUDY WITH THE RETROGRADE HRP METHOD .2. ZONAL ORGANIZATION

The mediolateral distribution of neurones of origin of the corticovest ibular projection from the cerebellar posterior lobe in the rabbit was studied with the retrograde horseradish peroxidase (HRP) tracing meth od. 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 ver mal lobules from VI to IX, as well as in crus I and crus II of the ans iform lobule, the copula pyramidis, lobule HV and the ventral parafloc culus. However, when projections from individual sublobules were exami ned, a clearly visible zonal pattern was found. Thus, Purkinje neurone s projecting to VNC were arranged in longitudinal bands with medial an d lateral boundaries quite well demarcated. These bands had a differen t width and were found to be located at different distances from the m idline. The present findings constitute the first indication of a zona l organization of corticovestibular projections from individual sublob ules of the cerebellar posterior lobe in the rabbit. This zonal arrang ement of VNC afferents is discussed with the special emphasis on the c erebellar longitudunal zones and related to previous studies on other species.