Olivary branching projections to the flocculus, nodulus and uvula in the rabbit. II. Retrograde double labeling study with fluorescent dyes.

The previous electrophysiological study reported that some of the Purkinje cells in the vestibulocerebellum were innervated by branching climbing fibers. To identify the cells of origin of these branching climbing fibers, a pair of retrograde fluorescent tracers, propidium iodide in combination with 4', 6-diamidino-2-phenylindole or diamidino yellow, were injected into two sites in the flocculus, nodulus and uvula. Proportions of double labeled neurons out of all labeled neurons in each subdivision of the contralateral inferior olive were studied. In cases of injections into the flocculus and nodulus, 13% (maximum 27%) of all the labeled neurons in the dorsal cap and 6% (maximum 12%) in the ventrolateral outgrowth were double labeled. In cases of injections into the nodulus and uvula, 20% neurons (maximum 34%) of the labeled neurons in the dorsal cap and 8% of those in the nucleus beta were double labeled. The present retrograde labeling study revealed that some dorsal cap neurons project to the uvula, which has not been reported previously in the rabbit. Injections into the flocculus and uvula caused only slight double labeling (0.4%) in the inferior olive.