Adaptive locomotor plasticity in chronic spinal cats after ankle extensorsneurectomy

After lateral gastrocnemius- soleus (LGS) nerve section in intact cats, a r apid locomotor compensation involving synergistic muscles occurs and is acc ompanied by spinal reflex changes. Only some of these changes are maintaine d after acute spinalization, indicating the involvement of descending pathw ays in functional recovery. Here, we address whether the development of the se adaptive changes is dependent on descending pathways. The left LGS nerve was cut in three chronic spinal cats. Combined kinematics and electromyogr aphic (EMG) recordings were obtained before and for 8 d after the neurectom y. An increased yield at the ankle was present early after neurectomy and, as in nonspinal cats, was gradually reduced within 8 d. Compensation involv ed transient changes in step cycle structure and a longer term increase in postcontact medial gastrocnemius (MG) EMG activity. Precontact MG EMG only increased in one of three cats. In a terminal experiment, the influence of group I afferents from MG and LGS on stance duration was measured in two ca ts. LGS effectiveness at increasing stance duration was largely decreased i n both cats. MG effectiveness was only slightly changed: increased in one c at and decreased in another. In cat 3, the plantaris nerve was cut after LG S recovery. The recovery time courses from both neurectomies were similar ( p > 0.8), suggesting that this spinal compensation is likely a generalizab le adaptive strategy. From a functional perspective, the spinal cord theref ore must be considered capable of adaptive locomotor plasticity after motor nerve lesions. This finding is of prime importance to the understanding of functional plasticity after spinal injury.