Multiple zonal projections of the basilar pontine nuclei to the cerebellarcortex of the rat

This study revealed a sagittal zonal pattern of projections to the cerebell ar cortex after hydraulic or iontophoretic injections of anterograde tracer s (tritiated leucine, wheat germ agglutinin-horseradish peroxidase, or biot inylated dextrane amine) in the basilar pontine nuclei of Wistar rats. The zonal pattern of projection was observed only after injections of small siz e, whereas large injections labeled diffusely wide areas of the cerebellar cortex, masking the zonal projection because the fusion of contiguous strip es. Diverging projections to discrete sets of sagittal stripes in the two s ides of the cerebellar cortex arose from single injections. The stripes of fiber terminals were sharply delimited on both sides by areas, interstripes , either virtually void of labeling or with a much lower density of labelin g. Thus, the areas of the cerebellar cortex were parceled in sets of sagitt al compartments, stripes and interstripes, by the pontine projections. Up t o five compartments (three stripes and two interstripes) were observed in t he paraflocculus, in the copula pyramidis, and in vermal lobule IX. Up to n ine compartments (five stripes and four interstripes) were found in the cru s I, the lobulus simplex, the paramedian lobule, and vermal lobules VI-VIII . Up to seven compartments (four stripes and three interstripes) were found in the crus II. Single injections into the basilar pontine nuclei usually labeled symmetric areas of the cerebellar cortex, which, in some cases, sho wed similar number of stripes. When this was not the case, the stripes were usually more numerous in the contralateral than in the ipsilateral side. A ll areas of the cerebellar cortex were projected upon, with zonation patter ns from different regions of the basilar pontine nuclei. The projections of the basilar pontine nuclei to the cerebellar cortex were arranged accordin g to a fixed pattern specific for each cortical area, independently of the number of stripes labeled within. The mean width of the stripes visualized in the single cortical areas of different rats was similar, despite the dif ferent size of the injections. The length of the stripes ranged widely in t he various areas of different rats. The data collected in this study are co nsistent with the idea that all the messy afferents to the cerebellar corte x are arranged with a zonal pattern. (C) 2001 Wiley-Liss, Inc.