Axonal branching in the projections from precerebellar nuclei to the lobulus simplex of the rat's cerebellum investigated by retrograde fluorescent double labeling.

The projections to lobulus simplex and Crus I of the cerebellum from various brainstem nuclei have been examined in adult rats by using the retrograde fluorescent double labeling technique. True blue was injected into the lobulus simplex on one side and nuclear yellow on the other and the brainstem was examined for labeled neurons. The lateral reticular nucleus, pontine tegmental reticular nucleus, and nucleus praepositus hypoglossi were similar to the equivalent nuclei in other species but all contained double- as well as single-labeled neurons and it was concluded that these nuclei have neurons whose axons branch to both sides of the cerebellum. More neurons in the rostral part of the lateral reticular nucleus were bilaterally projecting than in the caudal and the significance of this in relation to its afferents is considered. The individual neurons in the pontine nuclei, inferior olivary nucleus, and cuneate nuclei only appear to project to one side and the recent evidence for axonal branching of pontine neurons in the cat is discussed.