Fig. 4.

Transverse sections of the optic nerve showing ganglion cell axons that have been anterogradely labeled with DiI. Axon bundles within the optic nerve project topographically to specific regions of the retina (A–C; successive sections from the same optic nerve). The origin of the transverse sections in panels A–C is shown in the schematic (red bars). Panel D shows that at the level of the glial lamina (left image), axons are segregated into bundles, whilst further posteriorly along the optic nerve within the myelinated region (right image), the axons have dispersed and no longer maintain their spatial relationship. This is also discernible upon longitudinal section (E; dashed square represents the optic nerve head region). Further posteriorly, the bundles appear to coalesce. Using a transgenic mouse that expresses GFP in sparse populations of ganglion cell axons (GFP-M), a traced axon is seen to deviate from it’s original location at the periphery of the optic nerve (F; arrowheads). The asterisk depicts a remnant of the sclera/retinal pigment epithelium. Ax, axons; V, blood vessel. Scale bar = 100 µm in panel A; 20 µm in panel C (applies to panels B and C); 20 µm in panel D; 200 µm in panel F (applies to panels E and F).