Changes in intra- and interlimb reflexes from hindlimb cutaneous afferents after staggered thoracic lateral hemisections during locomotion in cats.

When the foot dorsum contacts an obstacle during locomotion, cutaneous afferents signal central circuits to coordinate muscle activity in the four limbs. Spinal cord injury disrupts these interactions, impairing balance and interlimb coordination. We evoked cutaneous reflexes by electrically stimulating left and right superficial peroneal nerves before and after two thoracic lateral hemisections placed on opposite sides of the cord at 9-13 weeks interval in seven adult cats (4 males and 3 females). We recorded reflex responses in ten hindlimb and five forelimb muscles bilaterally. After the first (right T5-T6) and second (left T10-T11) hemisections, coordination of the fore- and hindlimbs was altered and/or became less consistent. After the second hemisection, cats required balance assistance to perform quadrupedal locomotion. Short-latency reflex responses in homonymous and crossed hindlimb muscles largely remained unaffected after staggered hemisections. However, mid- and long-latency homonymous and crossed responses in both hindlimbs occurred less frequently after staggered hemisections. In forelimb muscles, homolateral and diagonal mid- and long-latency response occurrence significantly decreased after the first and second hemisections. In all four limbs, however, when present, short-, mid- and long-latency responses maintained their phase-dependent modulation. We also observed reduced durations of short-latency inhibitory homonymous responses in left hindlimb extensors early after the first hemisection and delayed short-latency responses in the right ipsilesional hindlimb after the first hemisection. Therefore, changes in cutaneous reflex responses correlated with impaired balance/stability and interlimb coordination during locomotion after spinal cord injury. Restoring reflex transmission could be used as a biomarker to facilitate locomotor recovery.