Locomotor recovery in spinal-transected lamprey: regenerated spinal coordinating neurons and mechanosensory inputs couple locomotor activity across a spinal lesion.

Larval lampreys recover locomotor function several weeks after receiving complete spinal transections. In behaviorally recovered whole-animals, the phase-coupling of locomotor activity across a lesion was similar to that observed along the body in normal, unlesioned lampreys. Two factors were found to contribute to recovery of locomotor coupling above and below a spinal transection. Firstly, under in vitro conditions regenerated spinal coordinating neurons could couple brainstem-evoked locomotor activity above and below a lesion in the absence of mechanosensory inputs. Secondly, in whole-animals mechanosensory inputs were capable of coupling locomotor activity across an acute, mid-body spinal transection in the absence of direct neural coupling through spinal coordinating neurons. Since neither regenerated coordinating neurons nor mechanosensory inputs resulted in phase-lags that were as stable as those observed in recovered whole-animals, presumably both mechanisms contribute significantly to the restoration of locomotor coupling across a healed spinal lesion.