Locomotor recovery after unilateral hindlimb deafferentation in cats

Abstract

After hindlimb deafferentation, recovery of locomotor patterns may be distinguished from recovery of accurate movements. Cats were timed while crossing wide runways requiring that locomotion be present, and narrow runways which require that it also be accurate. Locomotion recovers soon after deafferentation and becomes almost normal in speed, although accuracy is still absent. This accuracy returns 10 days postoperatively. Ventral root afferents with cell bodies in dorsal root ganglia are unnecessary for recovery. Postural reflexes (and other non-topographic feedback) are used as cues for limb guidance after removal of that limb's topographic feedback. Anatomical experiments show that a thoratic root sprouts during the recovery period. This sprouting may increase the potency of postural reflexes. Although lower thoracic roots contribute to recovery, they are not essential. Ipsilateral descending systems are essential, and represent the final common path for all recovery after deafferenting a hindlimb. Contralateral descending and afferent systems alone cannot mediate overground locomotion. Thus there is a difference between the systems which mediate overground locomotion and those used by animals in treadmill locomotion or with l-DOPA or clonidine or brain stem stimulation. The proposed mechanism underlying recovery of accurate locomotion is behavioral substitution which may be facilitated by collateral sprouting of relevant systems.