The cerebellar nucleo-olivary and olivo-cerebellar nuclear projections in the cat as studied with anterograde and retrograde transport in the same animal after implantation of crystalline WGA-HRP. II. The fastigial nucleus.

The bidirectional connections between the inferior olive and the fastigial nucleus were studied by means of anterograde and retrograde transport after implantation of crystalline wheat germ agglutinin-horseradish peroxidase (WGA-HRP) complex into the fastigial nucleus. The fastigio-olivary fibres terminate in the caudal half of the medial accessory olive, nucleus beta and the dorsal cap, and the olivo-fastigial projection has its origin within the same olivary regions. A topical arrangement is indicated for both pathways. The lateral part of the medial accessory olive appears to be connected with the lateral part of the fastigial nucleus, while the medial part of the medial accessory olive appears to be connected with more medial fastigial regions. Retrogradely labelled olivo-fastigial neurons were often located within the terminal field of anterogradely labelled fastigio-olivary fibres, indicating that the olivo-fastigial and fastigio-olivary projections are at least in part reciprocally organized. The findings are discussed and related to previous studies on the olivo-cerebellar nuclear and cerebellar nucleo-olivary pathways. Some methodological considerations are made, and comments are made concerning the active area for uptake and transport from the stained area at the WGA-HRP injection site.