Spasticity in rats with sacral spinal cord injury

We have investigated sacral spinal cord lesions in rats with the goal of de veloping a rat model of muscular spasticity that is minimally disruptive, n ot interfering with bladder, bowel, or hindlimb locomotor function. Spinal transections were made at the S2 sacral level and, thus, only affected the tail musculature, After spinal transection, the muscles of the tail were in active for 2 weeks, Following this initial period, hypertonia, hyperreflexi a, and clonus developed in the tail, and grew more pronounced with time. Th ese changes were assessed in the awake rat, since the tail is readily acces sible and easy to manipulate, Muscle stretch or cutaneous stimulation of th e tail produced muscle spasms and marked increases in muscle tone, as measu red with force and electromyographic recordings, When the tail was unconstr ained, spontaneous or reflex induced flexor and extensor spasms coiled the tail, Movement during the spasms often triggered clonus in the end of the t ail, The tail hair and skin were extremely hyperreflexive to light touch, w ithdrawing quickly at contact, and at times clonus could be entrained by re peated contact of the tail on a surface, Segmental tail muscle reflexes, e. g., Hoffman reflexes (H-reflexes), were measured before and after spinaliza tion, and increased significantly 2 weeks after transection. These results suggest that sacral spinal rats develop symptoms of spasticity in tail musc les with similar characteristics to those seen in limb muscles of humans wi th spinal cord injury, and thus provide a convenient preparation for studyi ng this condition.