DEVELOPMENT OF THE OLIVOCEREBELLAR PROJECTION

The establishment of orderly axonal projections is one of the essentia l steps in the formation of central networks. In this review, we discu ss several of the current hypotheses on the mechanisms and molecules w hich govern this developmental process, using the olivocerebellar syst em as a model. During the formation of the olivocerebellar projection, there is a simultaneous and independent process of parcellation of th e inferior olive and of the cerebellum. During embryogenesis, Purkinje cells in the cerebellar cortex and inferior olivary neurons are subdi vided into small subsets of biochemically distinct compartments. We pr opose that this parcellation is involved in matching groups of olivary neurons to their corresponding subsets of target Purkinje cells. In v itro, the rotation of the anteroposterior axis of the cerebellum is fo llowed by an equivalent inversion of the olivocerebellar projection. O livary axons still project to the same Purkinje cells, suggesting that the formation of the olivocerebellar projection is regulated by posit ional information shared between pre-and postsynaptic neurons. We sugg est that, in the chick embryo, the cell adhesion molecule BEN/SC1/DM-G RASP could be one of the target recognition molecules controlling the development of the olivocerebellar projection. These results also emph asize that coarse grained projection maps can form through chemoaffini ty mechanisms, independent of the activity of the interacting neurons.