Abstract: Objective In order to understand how Cajal-Retzius cells are involved in the regulation to the apical dendrite growth of pyramidal cell and hippocampal lamination. Methods With DiI tracing, the alvear path and perforant path were visualized in 120 mice at various ages. The apical dendrite growth of pyramidal cells, the histogenesis of mossy fibers and the distribution of Reelin positive cells were studied with tubulin, neuronal nuclei and reelin immunofluorescent labeling. Results Alvear path and perforant path were started from entorhinal cortex, and they distributed in alveus and molecular layer of hippocampus. There were numerous Reelin positive cells in the alvear area and hippocampal molecular layer, suggesting those reelin positive cells were involved in the path-finding. With age increasing, the apical dendrites of pyramidal cell grew and extended into molecular layer to form the inner molecular layer. Later, the inner molecular layer widened gradually, and it occupied stratum lucidum and stratum radiatum. The perforant fibers in stratum lucunosum-moleculare were so coincident with the location of CR cells in CA1, suggesting regulation of CR cells in the apical dendrite growth in inner molecular layer. Conclusion Reelin positive cells can function as a guidance to the pathfinding of alvear path and perforant path. Meanwhile, the developmental characteristics of CR cells suggest that CR cells play important roles in the dendritic growth of pyramidal cells, hippocampal lamination and hippocampal l

Key words: Hippocampus, Cajal-Retzius cell, Pyramidal cell, Apical dendrite, Nerve fiber, Immunofluorescence, Mouse