ZONAL ORGANIZATION OF THE FLOCCULOVESTIBULAR NUCLEUS PROJECTION IN THE RABBIT - A COMBINED AXONAL TRACING AND ACETYLCHOLINESTERASE HISTOCHEMICAL-STUDY

With the use of retrograde transport of horseradish peroxidase we conf irmed the observation of Yamamoto and Shimoyama ([1977] Neurosci Lett. 5:279-283) that Purkinje cells of the rabbit flocculus projecting to the medial vestibular nucleus are located in two discrete zones, FZ(II ) and FZ(IV), that alternate with two other Purkinje cell zones, FZ(I) and FZ(III), projecting to the superior vestibular nucleus. The retro gradely labeled axons of these Purkinje cells collect in four bundles that occupy the corresponding floccular white matter compartments, FC1 -4, that can be delineated with acetylcholinesterase histochemistry (T an et al. [1995a] J. Comp. Neurol., this issue). Anterograde tracing f rom small injections of wheat germ agglutin-hoseradish peroxidase in s ingle Purkinje cell zones of the flocculus showed that Purkinje cell a xons of FZ(II) travel in FC2 to terminate in the medial vestibular nuc leus. Purkinje cell axons from FZ(I) and FZ(III) OCCUPY the FC1 and FC 3 compartments, respectively, and terminate in the superior vestibular nucleus. Purkinje cell axons from all three compartments pass through the floccular peduncle and dorsal group y. In addition, some fibers f rom FZ(I) and FZ(II), but not from FZ(III), arch through the cerebella r nuclei to join the floccular peduncle more medially. No anterograde tracing experiments were available to determine the projections of the FZ(IV) and C-2 zones. The functional implications of these results ar e discussed. (C) 1995 Wiley-Liss, Inc.