The models of spinal cord injury in adult rats used in this study. Schematic illustrations of (a-c) white matter of the dorsal column and (d) the dorsolateral funiculus white matter pathways of the spinal cord. (a,d) Dorsal views of the rat brain and spinal cord. (b) horizontal and (c) sagittal views of the dorsal column white matter pathways at the C1/C2 cervical vertebrae of the spinal cord. (a) Dorsal column white matter on the right side was transected (shaded area) at the C1/C2 spinal level, and the ability of either BDA-labeled endogenous axons or axons from microtransplanted GFP-expressing adult sensory neurons (DRGs) to cross injuries bridged with GDAs or GRPs was assayed. (b) Injections of GDA or GRP cells (black diamonds) suspended in medium were made directly into the centers of the injury sites as well as their rostral and caudal margins in the cervical spinal cord. (c) A discreet population of endogenous ascending axons within the cuneate and gracile white matter pathways of dorsal columns was labeled by BDA injection at the C3/C4 spinal level (5 mm caudal to the lesion site, shaded). Alternatively, microtransplants of GFP+ DRGs were injected 500 μm caudal to the injury site. (d) The right-side dorsolateral funiculus white matter containing descending axons of the rubrospinal tract was transected at the C3/C4 spinal level and GDAs or GRPs were transplanted as described for dorsal column injuries. To trace axotomized rubrospinal tract axons, BDA was injected into the left-side red nucleus (RN) 8 days before the end of each experiment. CC, central canal; Cf, cuneate fasciculus; CST, corticospinal tract; DF, dorsolateral funiculus; Gf, gracile fasciculus; GM, gray matter; RST, rubrospinal tract; T1, level of the first thoracic vertebra.