Further studies on the fiber connections of the central cervical nucleus in the cat.

The course and cerebellar termination of the axons of the cells in the central cervical nucleus (CCN) was studied in five cats after injections of wheat germ agglutinin-horseradish peroxidase conjugate (WGA-HRP) into the C1-4 segments involving the CCN. In two cats a hemisection was performed ipsilateral to and above the injections in order to prevent transport of WGA-HRP from cerebellar-projecting neurons in lamina VI, just dorsal to the CCN. Labeled axons were found in the brain stem contralateral to the injections just lateral to the spinal trigeminal tract and the vestibular nuclei, and in the reticular formation. Some fibers terminated in the vestibular nuclei (especially group X), the reticular formation, and the inferior olive. The axons entered the cerebellum via the superior cerebellar peduncle. In the cerebellum mossy fiber terminals were found bilaterally in the deep vermal parts of lobules I-VIII. Only in cases without lesions were terminals found in the paramedian lobule ipsilateral to the injection, suggesting that neurons in lamina VI, but not in the CCN, project to the paramedian lobule. In the brain stem retrogradely labeled neurons (possible afferents to the CCN) were found in the vestibular (lateral, inferior and medial) nuclei, the reticular formation, and the trigeminal (spinal and mesencephalic) nuclei. The cerebellar distribution of mossy fiber terminals suggests that spinocerebellar fibers from lower parts of the spinal cord passing through the injection area do not transport WGA-HRP to their terminals.