Somatotopically organized transient projections from the primary somatosensory cortex to the cerebellar cortex

The organization of transient projections from the primary somatosensory cortex (S-I) to the cerebellar cortex in neonatal kittens was examined using orthograde intraaxonal labeling techniques. Tritiated amino acid injections into face, forelimb and hindlimb areas of representation in S-I labeled mossy fiber-like terminals of cerebrocerebellar axons in different areas of the cerebellar cortex bilaterally. The hindlimb area of S-I projected to lobules I-IV in the anterior lobe and to ventral folia of the paramedian lobule (PML). Injections into forelimb areas of S-I labeled terminals in lobules IV and V and in intermediate and dorsal folia of the PML. The face area of S-I projected to the lobules V and VI, to medial folia in the ansiform and simplex lobules and to dorsal PML folia. Labeled terminals were more numerous in the cerebellar cortex contralateral to the S-I injections, except in lobules I and II and the ventral PML where the density of hindlimb input was approximately the same on both sides. These observations were supplemented by findings that small wheat germ agglutinin-horseradish peroxidase (WGA-HRP) injections into the dorsal or ventral PML resulted in retrogradely labeled layer V pyramidal neurons in lateral (face and forelimb) and medial (hindlimb) areas of S-I respectively. The somatotopic organization of transient S-I cerebrocerebellar projections is very similar to the topography of cerebellar somatosensory afferent pathways in adult cats.