Abstract:

Objective To understand Reelin’s roles in the pathfinding of perforant fibers and commissural fibers between wild-type (WT) and Reeler mice. Methods A total of 123 WT mice and Reeler mice from embryonic day 16 (E16) to postnatal day 7 (P7) were used for this study. The perforant fibers and commissural fibers were labeled with DiI and DiO tracing (anterograde and retrograde). Results 1. Perforant fibers were mainly projected from the neurons in the layers Ⅱ to Ⅳ of entorhinal cortex. They entered the stratum lacunosum-molecular layer in hippocampus proper as early as E16, while the perforant fibers reached the dentate gyrus (DG) at P1. The perforant fibers terminated in the outer two thirds of the molecular layer of the dentate gyrus at P7. Compared with WT mice, the perforant fibers in Reeler mice developed retardantly and distributed in disorder. 2. Fornix commissural fibers rose from the pyramidal cells of the CA3, hilus neurons and the Ⅱ-Ⅳ layers neurons of the entorhinal cortex at E16. Compared with WT mice, Reeler mice almost had no significant difference in the development of fornix fiber. 3. Corpus callosum was mainly projected from the neurons of layersⅡ-Ⅳ of neocortex and corpus striatum, which started to project toward contralateral cortex at E18 and reached the contralateral striatum at P3. However, the corpus callosum fibers of Reeler mice entered to the contralateral neocortex later than in WT mice. Conclusion Reelin may serve as a guiding cue for the development of perforant pathway and commissural fibers. Without Reelin, the commissural and perforant pathways develop retardantly, and their original neurons in cortical plate are in disorder.

Key words: Reelin, Perforant pathway, Commissural fibers, Development, Nissl staining, Mouse