Time course of locomotor recovery and functional regeneration in spinal-transected lamprey: kinematics and electromyography

The time course of recovery of locomotor function was examined with kinematic analysis and muscle recordings in larval lampreys 2-32 weeks after rostral spinal cord transection at the level of the third gill (approximately 10% of body length, BL). Animals began to recover locomotor movements within 2-4 weeks of spinal cord transection, but the amplitude of locomotor movements in the tail region was less than in normal animals. At 2 weeks post-transection, locomotor activity was limited to 20% BL, and at 3 weeks after spinal transection activity could be recorded at least as far as 40% BL. At 4 weeks after spinal transection, well-coordinated locomotor muscle activity was often present as far as 60% BL. At 8 weeks of recovery and longer, well-coordinated locomotor activity was present consistently at least as far as 60% BL, and the amplitudes of locomotor movements were restored to normal values. At each recovery time examined the ranges of locomotor parameters (cycle time, burst proportion, and intersegmental phase lag) overlapped with those in normal animals. Thus, the gradual recovery of the amplitude of locomotor movements in the caudal body is associated with the gradual return of coordinated muscle activity at progressively more caudal levels along the body. The mechanisms responsible for this gradual recovery of locomotor function are discussed in relation to our recent anatomical and in vitro studies.