Projections from the lateral reticular nucleus to the cerebellar cortex and nuclei in the cat

The fiber projection from the lateral reticular nucleus (LRN) to the cerebellum was examined in the cat. Electrolytic lesions were placed in a confined area of the LRN using a parapharyngeal approach, and the ensuing degeneration was studied in sections stained by the Nauta and the Fink-Heimer methods. Fibers from the LRN ascend the ipsilateral restiform body, terminating bilaterally but chiefly in the ipsilateral cerebellum. In the ipsilateral cortex projections were found to lobules I to V, with denser terminations in sublobules IVb to Ve. The projections are stronger in the intermediate-lateral zones than in the vermis proper. There is also a dense projection to sublobules VId and VIf and to the medialmost part of the simple lobule (HVI). Scanty termination was seen in the medialmost part of crus I. There is a moderate projection to the caudalmost folium of sublobule VIIb and to the rostral folia of sublobule VIIIa and the paramedian lobule. The contralateral projection by fibers crossed within the cerebellum is far less dense but clearcut in the anterior lobe, the rostral folia of lobule VI and the medial part of the simple lobule. In the ipsilateral nuclei strong projections were found to rostral portions of the medial nucleus (M) and the caudal two thirds of the anterior interpositus nucleus (IA) with predominance in the lateral part of the latter. A focal projection was found to rostrodorsal portions of the posterior interpositus nucleus (IP). No projection was found to the lateral nucleus (L). Contralaterally there is a weak projection to the rostral part of M and the medial parts of IA and IP.