Autoradiographic tracing of the cerebellar projections from the lateral reticular nucleus in the cat.

The autoradiographic technique was used for tracing the efferent fibers from the lateral reticular nucleus (LRN) in cats. The terminal fields lie within the granular layer of both the ipsi- and the contralateral cerebellar cortex. The projections are symmetrical, but more pronounced on the ipsilateral side. The main portion of LRN projects to lobuli I--V, to the rostral part of lobulus VI, the most caudal part of lobulus VII, to lobulus VIII, as well as to lobulus simplex, the medial parts of the lobulus ansiformis and to the lobulus paramedianus. Medio-laterally arranged bands of dense mossy fiber terminations, directed rostro-caudally, lend support to an organized projection of the lateral reticulocerebellar fibers and further evidence for a division of the cerebellar cortex into longitudinal zones (Voogd et al., 1967, 1969). Evidence for a cerebellar re-representation of the LRN spinal segmental arrangement is not obvious, although it can not be excluded. The fibers to the contralateral side seem to mainly follow the course of the olivo-cerebellar fibers, crossing at brain stem levels. Following the general criteria for the identification of a terminal field, few, if any, fibers can be traced to the cerebellar nuclei and to regions outside the cerebellum.