Fig. 8. Rescue of granule cell orientation and layer-specific commissural input. (A,B) Scattered distribution of biocytin-labeled granule cells in the dentate gyrus of a reeler hippocampal slice culture. Granule cell dendrites and axons (red in B) extend in all directions. In A, neuronal somata were counterstained for Cresyl Violet to show the loose distribution of granule cells. (C,D) Many biocytin-labeled granule cells in the rescued granular layer of a reeler slice culture show normal dendritic and axonal orientation. Neuronal somata are counterstained for Cresyl Violet (C) to illustrate the formation of a granular layer in the reeler culture. Dashed line represents border between cultures; the boxed area is depicted in D. (E,F) The laminated projection of commissural fibers to the reeler dentate gyrus is only rescued when a compact granule cell layer has formed. (E) Co-culture of rat dentate gyrus and P4 reeler dentate gyrus. `Commissural' fibers from the rat dentate gyrus are scattered all over the reeler dentate gyrus, like their target granule cells, counterstained for Cresyl Violet. (F) By contrast, when a rat dentate gyrus is co-cultured with P0 reeler dentate gyrus, a granular layer and a compact `commissural' projection (arrowheads) have formed. Dashed lines represent borders between cultures. Scale bars: 45 µm in A,B; 50 µm in C; 30 µm in D; 70 µm in E; 50 µm in F.