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

Summary The cerebellar corticonuclear and nucleocortical connections of the anterior lobe were studied in the cat by means of anterograde and retrograde transport of HRP.Previous experimental studies have given evidence that the cortex of the anterior lobe can be subdivided in a mediolateral direction into seven longitudinal zones: A, B, C₁, C₂, C₃, D₁ and D₂. An analysis of the present material shows that the Purkinje axons from each cortical zone have their own terminal region within the cerebellar nuclei, and that these areas correspond to those receiving terminal corticonuclear fibres from the same zones in other parts of the cerebellum (Dietrichs and Walberg 1979, 1980). The terminal fields are the rostral part of the fastigial nucleus (the nuclear A zone), the medial nucleus interpositus anterior (the nuclear B zone), the ventromedial nucleus interpositus posterior (the nuclear C₁ zone), the dorsolateral nucleus interpositus posterior (the nuclear C₂ zone), the lateral nucleus interpositus anterior and the medial part of the transition area between the dentate nucleus and nucleus interpositus anterior (the nuclear C₃ zone), the lateral part of this transition area and the medial dentate nucleus (the nuclear D₁ zone) and the lateral part of the dentate nucleus (the nuclear D₂ zone). The nuclear zones have no sharp borders. The seven main terminal fields are connected by areas where scanty terminal fibres occur, indicatin that the Purkinje axons from each folium of the anterior lobe from medial to lateral terminate along a continuous band which loops through the cerebellar nuclei.With few exceptions the nucleocortical projection shows the same zonal arrangement as the corticonuclear, but there is in addition a weak nucleocortical connection to the anterior lobe from the middle and caudal parts of the fastigial nucleus.These and other findings are discussed with reference to previous studies on the corticonuclear and nucleocortical projections, and some comments are made concerning the zonal subdivision of the anterior lobe.