Topography of the mossy fibers in the CA3 region.A, Camera lucida drawing of mossy fibers of three adjacent (multiple-labeled) granule cells. Note numerous filopodial extensions of the large mossy terminals in A(arrowheads) and thin stalks of large mossy terminals (arrows). Boxed area ininset in A shows the position of the fibers at the CA3c–CA3b border. B, NeuroLucida reconstruction of the same three axons shown in A(diamonds, triangles, and squares label mossy terminals) and an additional mossy fiber of a fourth granule cell (circles) located posterior to the triple-labeled neurons. The original coronal images are rotated to emphasize the spatial characteristics of the fibers. In the transversal view (left), fibers are visible only in CA3cand CA3b, because in CA3a they run perpendicular to this plane. In the dorsal view (right), the entire semicircular route of the mossy fibers can be followed. Note the parallel organization of the fibers. Insets show the angles of view (arrows) on a coronal block.D, Dorsal; A, anterior; L, lateral. C, Wire diagram of the three mossy fibers shown in A (two of them are considered as complete) depicting the distribution of mossy terminals. Note that shorter interbouton distances prevail in the CA3c subregion. Scale bars: A, 50 μm; B, 400 μm; C, 200 μm.str.luc., Stratum lucidum; str.pyr., stratum pyramidale.