Cerebellar efferents in the lizard Varanus exanthematicus. I. Corticonuclear projections.

The organization of the cerebellar corticonuclear projections, i.e., the projections from the Purkinje cell layer to the cerebellar nuclei and the vestibular nuclear complex, was investigated with the horseradish peroxidase (HRP) technique in the lizard Varanus exanthematicus. After HRP slow-release gels were implanted in the cerebellar nuclei or various parts of the vestibular nuclear complex, the following longitudinally oriented zones of labeled Purkinje cells could be distinguished: a medial zone projecting to the medial cerebellar nucleus; an intermediate zone projecting to the vestibular nuclear complex, especially the ventrolateral vestibular nucleus, but probably also the dorsolateral vestibular nucleus; a caudolaterally located area of the cerebellar cortex projecting to the lateral cerebellar nucleus; and the flocculus and the adjacent lateral part of the Purkinje cell layer with projections to the middle and caudal parts of the vestibular nuclear complex, i.e., the descending and ventromedial vestibular nuclei. All projections of the Purkinje cells appeared to be strictly ipsilateral. It can be concluded that in reptiles a longitudinal organization of cerebellar corticonuclear projections exists, which may be basic for terrestrial vertebrates.