SELECTIVE NEURITE OUTGROWTH OF CULTURED CORTICAL-NEURONS ON SPECIFIC REGIONS OF BRAIN CRYOSTAT SECTIONS

During development, axons of the mammalian cerebral cortex show a high degree of selectivity in their growth into specific regions of the ce ntral nervous system (CNS). A number of studies have shown that growin g axons are guided by permissive or inhibitory membrane-bound molecule s. Cryostat sections of the developing brain provide a useful assay to investigate possible membrane-bound guidance cues because such cues a re retained in their normal in situ locations in specific regions of t he CNS. Moreover, cryostat sections can also be subjected to various t reatments that affect membrane-bound molecules. Therefore, to determin e the ability of such cues to regulate the growth and guidance of cort ical neurites into specific brain regions at different stages of devel opment, we used an in vitro assay system in which explants from newbor n hamster cortex were plated onto various regions of cryostat sections from developing and adult hamster brain. Neurite outgrowth from corti cal explants onto the cryostat sections was visualized with a fluoresc ent vital dye. Results showed first that cortical neurites grew robust ly on neonatal cryostat sections but only sparsely on sections from ad ult hamster. Second, cortical neurites grew preferentially on regions of the neonatal sections such as the cortex, basal ganglia, brainstem, thalamus, and colliculus, which are either pathways or targets for co rtical axons in vivo. In contrast, cortical neurites avoided growing o n the cerebellum and olfactory bulb, which are neither targets nor pat hways for cortical neurites invivo. Results also showed that cortical neurites extending onto cortical regions of neonatal sections preferre d to grow along the radial axis of the cortex. Finally, heat treatment of the neonatal sections drastically reduced cortical neurite outgrow th. Taken together, these results suggest that the growth and guidance of cortical neurites is influenced by substrate-bound, developmentall y related, heat-sensitive guidance cues preserved in the cryostat sect ions. (C) 1996 Wiley-Liss, Inc.