Morphological evidence for a monosynaptic connection between cerebellar Purkinje cells and vestibulospinal tract neurons in the larval clawed toad, Xenopus laevis.

A double-labeling technique was used to trace synaptic connections between the efferent neurons of the cerebellum (Purkinje cells) and vestibulospinal tract neurons in larvae of the clawed toad, Xenopus laevis. The efferent cerebellar projection was labeled with horseradish peroxidase (HRP) while in the same preparations the brainstem neurons projecting to the spinal cord were labeled with cobaltous lysine. It was found that the distribution of the Purkinje cell terminal boutons overlaps significantly with the location of vestibulospinal neurons in the brainstem. Moreover, several close appositions were seen between Purkinje cell boutons and the dendrites and somata of these latter neurons. The close appositions seen in light microscopy were confirmed by subsequent electron microscopy. This study shows that early in development (at least well before metamorphosis) a cerebello-vestibulospinal connection exists in Xenopus laevis. This connection is likely to persist throughout metamorphosis to the adult state.