Locomotor recovery after deafferentation of one side of the cat's trunk

Abstract

To distinguish the effects of a “purely postural” abnormality of the trunk upon phasic limb movements in cats, dorsal roots T5 through T13 were cut extradurally on one side. A profound deficit was seen in posture (trunk curvature, loss of pelvic fixation, fixed limb postures), phasic limb responses (loss of placing, hopping) and in locomotion, (both free and conditioned) which was abolished initially. The basic deficit appeared to be a loss of body-contact-righting, resulting from the imbalanced projection of impulses from the trunk. Locomotor recovery occurred in two stages: (i) recovery of generalized, poorly controlled locomotion and (ii) recovery of accurate locomotion. Postural deficits ameliorated but persisted. During recovery, cats compensated for impaired postural control by improved phasic limb movements, e.g., recovery of accurate locomotion was always preceded by return of tactile placing. The role of limb movements in recovery from trunk deafferentation was tested, after recovery had taken place, by deafferenting the ipsilateral hind limb. The initial deficit in posture reappeared plus a hind limb deficit due to deafferentation. Recompensation followed again in two stages, with increasing activity of descending supra- and propriospinal reflexes, suggesting that a different pathway was responsible for this second recovery. After trunk deafferentation the first stage (generalized movements) of recovery might be mediated by unmasking of latent synapses or denervation supersensitivity. The second stage (accurate movements) may depend on sprouting of hind limb afferents which would act to increase hind limb reflex input and substitute for impaired postural control.