The cerebellar corticonuclear and nucleocortical projections in the cat as studied with anterograde and retrograde transport of horseradish peroxidase. IV. The paraflocculus.

The cerebellar parafloccular corticonuclear and nucleocortical connections were studied in the cat by means of anterograde and retrograde transport of horseradish peroxidase. Previous investigations have given evidence that the cortex of the paraflocculus can be subdivided into three zones. These zones are recognized as C2, D1 and D2. The material presented is compatible with the findings from previous reports with other methods that each of these zones sends its Purkinje axons to separate regions within the cerebellar nuclei. These terminal fields are the lateral part of nucleus interpositus posterior (the alleged nuclear zone C2) and the dentate nucleus and its transition area with nucleus interpositus anterior (the supposed nuclear D zones). The parafloccular continuous mediolateral band extending from the NL through the NL-NIA transition area into the lateral NIP. This observation is in concordance with our previous findings concerning the termination of the cerebellar corticonuclear fibres (Dietrichs and Walberg 1979, 1980; Dietrichs 1981). Within the NL and NL-NIA transition area the Purkinje axons from the ventral paraflocculus terminate ventral to those from the dorsal paraflocculus. The nucleocortical projection shows the same zonal arrangement as the corticonuclear-nucleocortical reciprocity. The findings are discussed with reference to previous studies on the parafloccular corticonuclear and nucleocortical connections, and some comments are made concerning the cerebellar zonal subdivision of this cortical area.