Modulation of locomotion by a nerve graft across a spinal transection in rat

Adult rats received a complete mid-lower thoracic spinal cord transection and a peripheral nerve autograft was inserted across the transection site. Testing 3-4 months later showed that, after decerebration, stimulation of the mesencephalic locomotor region (MLR) induced forelimb but not hindlimb locomotion. However, in 5/7 animals, tail pinch interrupted MLR stimulation-induced forelimb stepping, while pinna pinch induced hindlimb muscle twitch. These effects were not present following complete section of the nerve graft or in 6 control animals which did not receive a graft. Exposure of the cut mid-portion of the grafts to DiI revealed the presence of labeled axons entering the spinal cord through both ends of the graft in those animals which showed the above effects. There was no transport in the 2 cases in which tail pinch interruption of MLR-induced stepping or pinna pinch-induced hindlimb muscle twitch did not occur. We conclude that non-specific information which can modulate locomotion may be flowing through the graft.