Figure 1.

Model to test sensory axon protection after spinal cord contusion. A, Top, The T9 contusive spinal cord injury (SCI) results in secondary degeneration of primary sensory axons that project to the gracile nucleus (GN). Hindlimb sensory axons are anterogradely traced by injecting CTB into both sciatic nerves. Reagents are infused though a catheter placed in the CSF through an L5/6 lumbar puncture. SEPs are recorded from an epidural electrode. Experimental designs, Infusions (black horizontal bar) lasted 7 or 28 d, and CTB was injected 3 d before histological processing. In one experiment, sensorimotor function was tested by grid walking (grid). In another, sensory function was tested by SEP induced from the hindlimb and confirmed by a dorsal column transection (TXN). B, Normal primary sensory projections to the gracile nucleus can be visualized by CTB tracing. Scale bar, 200 μm. C, The projections are reduced 7 d after contusion. D, With increasing spinal cord displacement by the impactor, more innervation is lost. The 0.3 mm displacement enables us to detect beneficial, detrimental, or neutral effects of test reagents.