CORRESPONDENCE BETWEEN L7-LACZ-EXPRESSING PURKINJE-CELLS AND LABELED OLIVOCEREBELLAR FIBERS DURING LATE EMBRYOGENESIS IN THE MOUSE

It has been suggested that Purkinje cells (PC) play a role in organizi ng topographic relationships of several cerebellar afferent systems, i ncluding olivocerebellar fibers. This hypothesis is based on the obser vation that PC in the rat express biochemical heterogeneities during t he presumptive period of olivocerebellar fiber ingrowth to the cerebel lum. Previous studies designed to investigate the organization of muri ne olivocerebellar fibers during embryogenesis have suggested that int eractions with PC may play a role in segregating olivocerebellar fiber s after they enter the cerebellum. To determine whether PC heterogenei ties are related to olivocerebellar fiber organization, transgenic mic e carrying a beta-galactosidase (beta-gal) reporter gene linked to the promoter from the PC-specific gene L7/pcp-2 were used in neuroanatomi cal tracing experiments. Expression of the transgene mirrors endogenou s L7/pcp-2 expression, which is upregulated earliest in parasagittal s trips of the vermal cortex. Studies were conducted in vitro by using b rainstem-cerebellar explants from embryonic day 17/18 (E17/18) and 18/ 19 mice. Applications of neuroanatomical tracer (horseradish peroxidas e or neurobiotin) were made in either the caudal medial accessory oliv e (cMAO) or the rostral olive. These studies indicate that groups of o livocerebellar fibers and clusters of L7/lacZ(+) and L7/lacZ(-) Purkin je cells respect common distribution boundaries during late embryogene sis. The strong correspondence between the distribution patterns gener ated by these two markers suggests that expression of L7/pcp-2 and the topographic organization of olivocerebellar (OC) fibers are not inter dependent, but may be regulated by a common event or interaction, of a presently unknown nature, which occurs earlier during cerebellar deve lopment. (C) 1996 Wiley-Liss, Inc.