The organisation of the cerebellorubral projection: an experiment study in the rat.

Abstract

AbstractThe organization, distribution and extent of the cerebellorubral projection in the rat was investigated employing silver impregnation techniques. Cerebellar lesions of varying size were introduced stereotaxically into the deep cerebellar nuclei in a series of 32 rats and the midbrains were stained with the method of Fink and Heimer. Following large lesions which involved all of the cerebellar nuclei and their emerging fibres, numerous degenerating fibres of passage were observed to course within the brachium conjunctivam, to decaussate at the level of the inferior colliculus, and to enter the ventromedical aspect of the contralateral red nucleus. The red nucleus of the rat consists of a caudal magnocellular portion in which giant and large cells predominate and a rstral parvocellular part consisting mainly of small and medium sized cells. Within the red nucleus, coarse preterminal and terminal degeneration was distributed throughout the magnocellular portion, particularly in relation to the cell bodies and proximal dendrites. Degeneration within the parvocellular part of the nucleus was less abundant, finer in calibre and was parvocellular part of the nucleus was less abundant, finer in calibre and was scattered throughout the neuropil. Following discrete lesions of the nucleus interpositus, preterminal and terminal degeneration was restricted to the magnocellular red nucleus and it was similar in calibre and distribution to that observed in the same area following total lesions. No terminal degeneration was encountered in the parvocellular region at any time following lesions of the nucleus interpositus and only degenerating fibres of passage were seen coursing through the parvocellular region en route to thalamic levels. After lesions restricted to the nucleus lateralis, degenerating fibres were again observed coursing within the brachium conjuctivum and entering the red nucleus. In cases with nucleus lateralis lesions a pattern opposite to that observed following nucleus interpositus lesions was evident. Only passing fibres occurred within the magnocellular region and terminal degeneration was limited to the parvocellular part where it was randomly distributed, moderate in amount and fine in calibre.This investigation has shown that the nucleus in the rat receives a major projection from the contralateral cerebellar nuclei and that a differential distribution of fibres from the nucleus interpositus and the nucleus lateralis terminates within the rubrospinal and rubroolivary portions of the red nucleus respectively.