Plasticity of reflexes from the foot during locomotion after denervating ankle extensors in intact cats

Although sensory feedback is important in regulating the timing and magnitude of muscle activity during locomotion few studies have evaluated how it changes after peripheral nerve lesions. To assess this, reflexes evoked by stimulating a nerve before and after denervating other nerves can be quantified to determine changes. The aim of this study was to investigate consequences of denervating ankle extensor muscles, the lateral gastrocnemius, and soleus (LGS) on reflexes from the plantar foot surface evoked by stimulating the tibialis (Tib) nerve. Three cats (n = 3) were trained to walk on a treadmill and chronically implanted with electrodes in 14 hindlimb muscles bilaterally to record EMG activity. A stimulating cuff electrode was placed around the left Tib nerve (Tib) nerve at the ankle to evoke reflexes. Several control values of EMGs, limb kinematics, and Tib nerve reflexes were obtained during locomotion for at least 3 wk before the left LGS nerve was cut. We found that the locomotor EMG bursts of several muscles was altered, with a large increase in amplitude in the early days postneurectomy followed by a gradual decrease toward intact values later on. There were changes in the stimulated locomotor EMG bursts (Tib nerve reflexes) of ipsilateral flexors and extensors and of contralateral ankle extensors, which dissociated from changes in baseline locomotor EMG (e.g., nonstimulated bursts during reflex trials). The functional significance of these changes in muscle activity and reflex pathways on the recovery of locomotion after denervating ankle extensors is discussed.