Asymmetry of hindlimb muscle activity and cutaneous reflexes after tendon transfers in kittens

The mechanical actions of various ankle muscles were changed by surgically crossing or transferring the tendons in kittens. After the kittens grew to adults, both hindlimbs were implanted with multiple electromyogram (EMG) re cording and cutaneous nerve stimulation electrodes to compare the activity of altered and normal muscles. The tendon transfers showed a remarkable ten dency to regrow toward normal or only slightly altered mechanical action. I n these animals and in the sham-operation controls, the patterns of muscle activity and reflexes were symmetrical in corresponding muscles of the two legs, although they could differ substantially between animals, particularl y for the cutaneous reflexes. Eleven animals had at least some persistent a lterations in muscle action. Their cutaneous reflex patterns tended to be a symmetric, in some cases quite markedly. EMG activity during unperturbed lo comotion and paw-shaking was more symmetrical, but there were some changes in altered muscles and their synergists. The central pattern generators for locomotion and paw-shaking and particularly for cutaneous reflexes during locomotion appear to be at least partially malleable rather than entirely h ardwired. This may provide a tool for studying their development and spinal plasticity in general.