Figure 3

Sensory axons may not regenerate. (A) Cartoon showing tracer application sites in relationship to the SCI. Tracer was applied to the sciatic nerve in the hindlimb to label sensory axons (green) and, in 6-week regenerates, rostral to the injury to label descending axons (magenta). Tracer applied to the sciatic nerve labels primarily neurons in spinal ganglia S1 and T-1 (solid lines) and occasionally neurons in T-2 (dotted lines). (B) Cross-section through spinal cord and spinal ganglia at T-1, 1 day after SCI and tracer application to the sciatic nerve. The tracer labels sensory neurons in the spinal ganglia (sg), motor neurons (mn), dorsal column axons (dc), and motor neuron axons (mna) exiting to form the ventral root. (C-E) Sections through a 3-week regenerate. Sensory axons were labeled with biotinylated dextran amine (BDA; green), and all axons were labeled with 3A10 (magenta in (D, E)). (C) Cross-section at T-1. Inset, spinal ganglia on labeled side. (D, E) Longitudinal sections through the SCI at the level of the dorsal columns (D), and a more ventral level where there are wisping axons (E). Schematic cross-sections of the spinal cord in the upper right corner show where the section is along the D-V axis. (F-H) Cross-sections through a 6-week regenerate that had recovered swimming function at T-1 (F), at T-4, about 500 μm caudal to the SCI (G), and through the center of the SCI at T-4/T-5 (H). Sensory axons were labeled with rhodamine dextran amine (RDA; green), and descending axons were labeled with BDA (magenta). Inset in (F), spinal ganglia on labeled side. Inset in (H), phase image of injury site. Nuclei are shown in blue. D, dorsal; V, ventral; R, rostral; C, caudal. All scale bars: 200 μm ((C-H) are the same scale; insets in (C, F) are the same scale).