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 floc culus and nodulus of the rabbit were studied with anterograde axonal t ransport methods [wheatgerm agglutinin-horseradish peroxidase (WGA-HRP ) and tritiated leucine] and correlated with the compartments in the w hite matter of these lobules delineated with acetylcholinesterase hist ochemistry (Tan et al. J. Comp. Neurol., 1995, this issue). Olivocereb ellar fibers originating from the caudal dorsal cap travel through flo ccular compartments FC2 and FC4 to terminate as climbing fibers in flo ccular zones FZ(II) and FZ(IV). 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 FZ(I) and FZ(III). Fibers from the rostral pole of the medial accessor y olive traverse the C-2 compartment and terminate in the C-2 zone. FZ (I-III) extend into the adjoining folium (folium p) of the ventral par aflocculus. The C-2 zone continues across folium p into other folia of the ventral paraflocculus and into the dorsal paraflocculus. Four com partments and five zones were distinguished in the nodulus. Medial com partment XC(1) contains olivocerebellar fibers from the caudal dorsal cap and subnucleus beta that terminate in the XZ(I) zone. Olivocerebel lar fibers from the rostral dorsal cap and the ventrolateral outgrowth occupy XC(2) and terminate in XZ(II). The XC(4) 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 po rtion of the XZ(IV) zone. The dorsomedial cell column projects to the XZ(III) zone, which is present only in the dorsal part of the nodulus. The rostral medial accessory olive projects to the XZ(V) zone, which occupies the lateral border of the nodulus. These results confirm and extend the conclusions of Katayama and Nisimaru ([1988] Neurosci. Res. 5:424-438) on the zonal pattern in the olivo-nodular projection in th e rabbit. Additional observations were made on the presence of a later al A zone (Buisseret-Delmas [1988] Neurosci. Res. 5:475-493) in the he misphere of lobules VI and VII. Retrograde labeling of the nucleo-oliv ary tract of Legendre and Courville ([1987] Neuroscience 21:877-891) w as observed after WGA-HRP injections into the inferior olive including the rostral dorsal cap and the ventrolateral outgrowth. The anatomica l and functional implications of these observations are discussed. (C) 1995 Wiley-Liss, Inc.