Translation of the rat thoracic contusion model; part 2-forward versus backward locomotion testing

Study design: Experimental animal study. Objectives: Locomotion analyses in rat spinal cord contusion injury (SCI) models are widely used for the evaluation of recovery of supraspinal locomotor control. However, many commonly used locomotion tests are inadequate to test for spinal cord integrity as they assess motor function that can be highly mediated through below-level propriospinal pattern-generating circuitry, independently of below-level perception. Here we report a behavioral motor test that is more sensitive for spinal cord integrity, even 6 weeks after injury: the backward locomotion rotating rod. Setting: University of California - San Diego. Methods: A modified rotating rod test was run in reverse. The rod diameter was increased and thin rubber lining was added. As a reference, we included commonly used motor tests: BBB score, catwalk gait analysis, motor-evoked potentials, single frame analyses, a forward rotating rod test and the 551 inclined ladder test. Results: Unlike commonly used motor tests, the backward locomotion rotating rod test significantly discriminates between both sham-operated (falling latency: 20.4 s s.d +/- 4.5) vs mild SCI animals, and mild vs moderate SCI animals (differences between each group at acute, subacute and chronic phases: >= 6s, P