PERIPHERAL NEURONS DEPEND ON CNS-DERIVED GUIDANCE CUES FOR PROPER NAVIGATION DURING LEECH DEVELOPMENT

In leech, major nerve pathways are pioneered by CNS neurons and eviden ce from dye-injection and antibody experiments suggest that they may s erve as guides for later differentiating neurons. In this study we hav e directly tested this hypothesis by examining the consequences of CNS ablation on the navigation in the periphery of a well-defined populat ion of afferent sensory neurons. We show that in the absence of CNS-de rived axons the axonal growth cones of this population of peripheral n eurons extend with little directionality and instead of forming orderl y projections, default into forming circular fasciculated pathways wit h each other. This suggests that CNS-derived guidance cues are absolut ely required for the correct navigation of these peripheral sensory ne urons. (C) 1995 Academic Press, Inc.