Figure 26

The efferent pathway from the hippocampal formation to the hypothalamus expresses βIII-tubulin. This panel shows cytoarchitectural structures of the hippocampal formation displayed in layers through a parasagittal cut at the fimbria (f) level. The left half of the panel is a figure of GFAP (red) and DAPI (blue) staining. The right half of the panel represents areas of βIII-tubulin staining revealed by DAB with nuclear counterstaining with hematoxylin. Note the dense GFAP staining in the anuclear gap (ag) of the SVZ and in the glia limitans in the subpial zone (spz) of the subicular complex (sc) and entorhinal cortex (ec). The βIII-positive fibers in the fimbria are likely to be axons from subicular complex neurons. These neurons form bundles that run superiorly (black arrow) toward the SPZ of the hippocampal sulcus (hs) and through the white matter (wm) (shown in higher magnification in Figure 29) before reaching the fimbria. If the pathways from the septal and hypothalamic nuclei to the hippocampal formation express βIII-tubulin, one would expect to detect βIII-tubulin in fibers reaching the hippocampus proper (CAs) or the dentate gyrus (DG); however, this type of staining is practically unobserved in the Figure (DG). Finally, the scarce βIII-positive fibers at the entorhinal cortex (Figure named EC) led us to the conclusion that the only pathway with abundant βIII-positive staining in the hippocampal formation is its efferent pathway from the subicular complex. For a view of βIII-tubulin positive fibers at a coronal plane, see Figure 31. Numbers 1-9 refer to locations analyzed at higher magnifications in Figures 27, 28, and 29. (cp) choroid plexus at the choroidal fissure; (fds) fimbriodentate sulcus. White arrows: granule cell layer (gcl) of the dentate gyrus. Scale bars: Figures showing all hippocampal formation layers (GFAP and βIII-tubulin) = 5,000 μm; remaining figures = 200 μm.