Fig. 3. Completeness of the spinal cord crush wound. (A) Schematic diagram of the dorsal view of a goldfish brain to show the location of the crush site at the spinomedullary level (SML). Biocytin was applied to a cut wound (1-2 mm caudal to the SML; not shown) 8 days after a crush wound at the SML to determine if any fibers were spared damage (see text for details). For reference, the Mauthner cells (M-cells) and their axons (M-axons) are superimposed on the diagram. Ce, cerebellum; FL, facial lobe; VL, vagal lobe; C, caudal; R, rostral. (B,C) Photomicrographs of 60-µm transverse tissue sections. The brain midline is centered on and the ventral edge of the brain is located at the bottom edge of each photomicrograph. (B) Section 1.5 mm rostral to the crush wound. The ventral area shown here has no biocytin-filled fibers and is representative of the entire medulla oblongata at this level. In fact, this fish had no biocytin-filled fibers rostral to the wound site, indicating that all fibers were damaged. (C)Section near the site of the SML crush. A few biocytin-filled fibers can be seen at this level. Scale bar, 100 µm for B and C.