THE JOURNAL OF COMPARATIVE NEUROLOGY ,7562340 (1995) Zonal Organization of the Climbing Fiber Projection to the Flocculus and Nodulus of the Rabbit: A Combined Axonal Tracing and Acetylcholinesterase Histochemical Study

The localization and termination of olivocerebellar fibers in the flocculus and nodulus of the rabbit were studied with anterograde axonal transport methods [wheatgerm agglutininhorseradish peroxidase (WGA-HRP) and tritiated leucinel and correlated with the compartments in the white matter of these lobules delineated with acetylcholinesterase histochemistry (Tan et al. J. Comp. Neurol., 1995, this issue). Olivocerebellar fibers originating from the caudal dorsal cap travel through floccular compartments FC2 and FC4 to terminate as climbing fibers in floccular zones FZII and FZIv. Fibers from the rostral dorsal cap and the ventrolateral outgrowth traverse compartments FC1 and FC3, which are interleaved with compartments FC2 and FC4! and terminate in zones FZ1 and FZiIi. Fibers from the rostral pole of the medial accessory olive traverse the Cz compartment and terminate in the Cz zone. FZ1-111 extend into the adjoining folium (folium p) of the ventral paraflocculus. The C2 zone continues across folium p into other folia of the ventral paraflocculus and into the dorsal paraflocculus. Four compartments and five zones were distinguished in the nodulus. Medial compartment XC1 contains olivocerebellar fibers from the caudal dorsal cap and subnucleus p that terminate in the XZi zone. Olivocerebellar fibers from the rostral dorsal cap and the ventrolateral outgrowth occupy XC2 and terminate in XZII. The XC, compartment contains fibers from both the caudal dorsal cap and from the rostral dorsal cap and the ventrolateral outgrowth. The latter terminate in a central portion of the XZIv zone. The dorsomedial cell column projects to the XZIll zone, which is present only in the dorsal part of the nodulus. The rostral medial accessory olive projects to the XZV zone, which occupies the lateral border of the nodulus. These results confirm and extend the conclusions of Katayama and Nisimaru (119881 Neurosci. Res. 5:424-438) on the zonal pattern in the olivo-nodular projection in the rabbit. Additional observations were made on the presence of a lateral A zone (Buisseret-Delmas [19881 Neurosci. Res. 5475-493) in the hemisphere of lobules VI and VII. Retrograde labeling of the nucleo-olivary tract of Legendre and Courville (119871 Neuroscience 21:877-891) was observed after WGA-HRP injections into the inferior olive including the rostral dorsal cap and the ventrolateral outgrowth. The anatomical and functional implications of these observations are discussed. a 1995 Wiley-Liss, lnc. Indexing terms: cerebellum, inferior olive, nucleo-olivary tract, dorsal cap, ventrolateral outgrowth The flocculus and nodulus are involved in several motor systems relayed by the vestibular nuclei. Best known is the A~.cepted Scptembcr 9, 1yy4, Of the flocculus in the adaptive Of eye movemerits (It09 197% 1982, 19g4; Robinson, 1976; Ito et al., Address reprint requests to J. Voogd, Department of Anatomy, Erasmus IJniversity Rotterdam, P.O. Box 1738, 3000 DR Rotterdam, The Nether1982a,b; Nagao, 1983, 1988). The flocculus receives a visual lands. o 1995 WILEY-LISS. INC.