Recovery of bipedal locomotion in bonnet macaques after spinal cord injury: footprint analysis

Analysis of the recovery of gait after spinal cord injury has been widely demonstrated in rat and cat models using different behavioral tests and scoring systems. The present investigation was aimed to quantitatively analyze the degree of functional recovery in bipedal locomotion of bonnet macaques after inflicting spinal cord hemisection lesion. To measure the degree of locomotor recovery, we recorded four gait variables, viz., tip of opposite foot (TOF), print length (PL), toe spread (TS), and intermediary toes (IT) using a footprint analyzing technique. Monkeys were trained preoperatively to perform the monopedal hop or bipedal locomotion on runways. Footprints of trained monkeys were recorded using the nontoxic ink and white paper before and after surgery. Surgical hemisection was induced unilaterally in the right side of spinal cord at T12-L1 level of trained monkeys. In hemiplegic monkeys, initially there was a substantial decrease in TOF and PL variables of the paretic limb, which then gradually increased for longer duration and reached the near presurgical values by the 7th and 5th postoperative month, respectively. In contrast to TOF and PL, the recovery of TS and IT variables was quicker, which dramatically increased at first and then slowly recovered to levels not significantly different from the corresponding preoperative values by the 4th postoperative month. The nonparetic limb has also showed mild alterations in all footprint variables but reached the normal values much faster compared to the paretic limb. The alterations in footprint variables of hemiplegic monkeys were examined for a postoperative period of up to 1 year. The findings of this study suggest that the mechanisms underlying locomotor recovery of lesioned macaques may be correlated to the mature function of spinal pattern generator for locomotion under the impact of residual descending and afferent connections. Further, this study also indicates the functional contribution of progressive strengthening of undamaged nerve fibers through a collateral sprouts/synaptic plasticity formed in partially lesioned cord of macaques.