EVIDENCE OF EARLY TOPOGRAPHIC ORGANIZATION IN THE EMBRYONIC OLIVOCEREBELLAR PROJECTION - A MODEL SYSTEM FOR THE STUDY OF PATTERN-FORMATION PROCESSES IN THE CENTRAL-NERVOUS-SYSTEM

Many projection systems within the peripheral and central nervous syst em are topographically organized, and it has become increasinging clea r that interactions which occur during development determine the proje ction patterns these systems exhibit in the adult. The olivocerebellar system was chosen as a model system for this study of afferent patter n formation because it has several characteristics which lend themselv es to a study of this type. Applications of horseradish peroxidase wer e made to both the cerebellar primordium and to the inferior olive of embryonic and neonatal mice using an in vitro perfusion system to supp ort the tissue during the transport period. Fibers labeled after restr icted olivary applications are limited to particular mediolateral regi ons of the cerebellum. Similarly, olivary cells retrogradely labeled a fter discrete cerebellar applications are restricted to particular oli vary subdivisions. The results indicate that the olivocerebellar proje ction displays elements of topographic organization as early as E15 an d that the pattern displayed is roughly comparable to that of the adul t mammal. The observed trajectories of olivocerebellar fibers and thei r concomitant association with both Purkinje and cerebellar nuclear ce lls during embryonic development suggests a role for either or both ce ll types in the pattern formation process. (C) 1993 Wiley-Liss, Inc.