Do hypothalamo-cerebellar fibres terminate in all layers of the cerebellar cortex?

The terminal distribution of hypothalamo-cerebellar fibres has been studied with anterograde transport of the wheat germ agglutinin-horseradish peroxidase complex in the cat and rat. The hypothalamo-cerebellar fibres appear to enter all three layers of the cerebellar cortex. Anterogradely labelled branching axons were found in the granular layer and near the Purkinje cell perikarya. In addition, anterogradely filled hypothalamo-cerebellar axons could be traced into the molecular layer, where they ramified. The branches ran parallel to the long axis of the folia, resembling parallel fibres. Our findings give evidence that the hypothalamo-cerebellar fibres are neither mossy fibres nor climbing fibres, but represent a third type of cerebellar cortical afferents. Fibres of this third category are tentatively called multi-layered fibres. It appears from the literature that some other cerebellar afferent projections show the same general pattern of cortical terminal distribution.