Bilateral dorsal funicular lesions alter sensorimotor behaviour in rats

Abstract

Spinal cord injury models often involve damage to the corticospinal tract (CST) because of the functional importance of this pathway in humans. In rats, the main component of the CST travels in the dorsal funiculus and cannot be damaged without concurrent damage to overlying sensory fibers. To distinguish deficits due to the loss of CST from those due to sensory fiber damage, we bilaterally axotomized ascending sensory fibers in dorsal columns without CST damage in one group of rats (ascending sensory pathways, ASP) and compared the results to a group with damage to ascending sensory fibers with CST damage (ASP + CST). We assessed the ability of rats to perform a skilled reaching task and to walk over a horizontal ladder. We also measured the forces exerted on the ground (ground reaction forces, GRF) and limb contact patterns produced during overground locomotion. After ASP lesions alone, endpoint measurements of reaching success and footslip errors on the ladder showed transitory impairments, although detailed analysis revealed persistent deficits in skilled forelimb movements. ASP + CST lesions caused persistent deficits in reaching success and ladder footslips throughout the 8-week post-surgical period. Measurement of GRFs and limb timing during overground locomotion revealed differences in both groups at 8 weeks post-surgery compared to pre-surgical values, but no differences between ASP and ASP + CST groups. These results emphasize the normal contribution of both ascending sensory axons and CST axons during skilled limb movements and support a role for ascending sensory information, but not descending CST input, during overground locomotion. These results also illustrate the value of using sensitive methods to reveal detailed behavioural changes after spinal injury.