THE EFFERENT FIBRES OF THE CEREBELLAR NUCLEI AND THEIR DISTRIBUTION ON THE CEREBELLAR PEDUNCLES IN THE CAT

Abstract

The determination and mapping of the origin within the cerebellar nuclei of the various cerebellofugal components of the cerebellar peduncles by means of the method of retrograde reaction was studied. The site and extent of the retrograde changes in the nerve cells of the cerebellar nuclei following a variety of lesions inflicted upon the cerebellar peduncles and the brain stem in kittens warrant these conclusions: the great majority possibly all the cells of the cerebellar nuclei send their axons to the brain stem; the fibers from the lateral and interpositus nuclei join in the ipsilateral superior cerebellar peduncle to form the major part of the brachium conjunctivum; about one quarter of the nerve cells of the lateral and interpositus nuclei most of them located in the caudal half of the nuclei remain intact after transection of the decussation of the brachium conjunctivum indicating that a considerable number of the axons from these nuclei do not decussate; the fibers from the medial nucleus leave the cerebellum by way of the superior and inferior cerebellar peduncles. The great majority of the fibers join the inferior peduncles in the cat distributed approximately equally on the 2 sides. The direct fibers (tract fastigiobulbaris rectus) have their cells of origin in the rostral half of the medial nucleus while the crossed fibers (fasciculus uncinatus) are derived from cells in the caudal 2/3 of the nucleus. Some of the fibers from the medial nucleus (presumably 10-15%) join the contralateral brachium conjunctirum. These fibers decussate within the cerebellum and do not decussate in the midbrain. Transection of the middle cerebellar peduncle was not followed by detectable retrograde changes In the cerebellar nuclei. The method of retrograde reaction failed to give informations concerning the origin of the fibers of the brachium con-junctivum that pass rostralward beyond the red nucleus.