Lesions of cat sacrocaudal spinal cord: a minimally disruptive model of injury.

As part of our studies of the organization of the cat sacrocaudal spinal cord (S3-Ca7), the portion of the neuraxis that innervates the tail, we have begun to evaluate the behavioral effects of hemisection or complete transection at the level of Ca1. Clinical observations that the tail strongly deviated to the side of a hemisection indicated the presence of an ipsilateral hypertonia. After complete transection of the spinal cord, the tail became ventroflexed in a midline position and exhibited spasticity, i.e., hypertonia, hyperreflexia, and clonus. Bowel and bladder functions and hindlimb gait and reflexes remained intact following either lesion. Quantitative behavioral measures corroborated our clinical observations. With the tail tethered to a force transducer, tail muscle tone was measured after the tail was passively positioned. Following a transection, resistance to dorsiflexion of the tail was greater than resistance to ventroflexion. In addition, tonic deviation of the tail was documented with videotape analysis while cats walked on a plank. Normal cats walked with the tail sharply dorsiflexed and centered. In contrast, the tail deviated ipsilaterally in cats with a hemisection, and the tail was ventroflexed in cats with a transection. These observations indicate that the sacrocaudal spinal cord provides a model with special advantages for investigation of changes in segmental motor functions following spinal cord injury. The effects of lesions on the tail are quantifiable and can resemble that spasticity observed after spinal cord injury in humans. Importantly, minimal effects on locomotive and autonomic functions were observed following hemisection or transection of the sacrocaudal spinal cord.