Bipedal Locomotion of Bonnet Macaques after Spinal Cord Injury

in Motor Control
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Experimental studies concerning the analysis of locomotor behavior in spinal cord injury research are widely performed in rodent models. The purpose of this study was to quantitatively evaluate the degree of functional recovery in reflex components and bipedal locomotor behavior of bonnet macaques (Macaca radiata) after spinal contusive injury. Six monkeys were tested for various reflex components (grasping, righting, hopping, extension withdrawal) and were trained preoperatively to walk in bipedal fashion on the simple and complex locomotor runways (narrow beam, grid, inclined plane, treadmill) of this investigation. The overall performance of the animals’ motor behavior and the functional status of limb movements during bipedal locomotion were graded by the Combined Behavioral Score (CBS) system. Using the simple Allen weight-drop technique, a contusive injury was produced by dropping a 13-g weight from a height of 30 cm to the exposed spinal cord at the T12-L1 vertebral level of the trained monkeys. All the monkeys showed significant impairments in every reflex activity and in walking behavior during the early part of the postoperative period. In subsequent periods, the animals displayed mild alterations in certain reflex responses, such as grasping, extension withdrawal, and placing reflexes, which persisted through a 1-year follow-up. The contused animals traversed locomotor runways—narrow beam, incline plane, and grid runways—with more steps and few errors, as evaluated with the CBS system. Eventually, the behavioral performance of all spinal-contused monkeys recovered to near-preoperative level by the fifth postoperative month. The findings of this study reveal the recovery time course of various reflex components and bipedal locomotor behavior of spinal-contused macaques on runways for a postoperative period of up to 1 year. Our spinal cord research in primates is advantageous in understanding the characteristics of hind limb functions only, which possibly mimic the human motor behavior. This study may be also useful in detecting the beneficial effect of various donor tissue–neuroprotective drugs on the repair of impaired functions in a bipedal primate model of spinal injury.

Suresh Babu is with the Department of Neurological Sciences, Rush University Medical Center, Chicago, Illinois 60612; Anand and Jeraud are with the Department of Physiology, Rajah Muthiah Medical College, Annamalai University, Chidambaram, India; Periasamy is with the Department of Physiology, Vellore Medical College, Vellore, India; and Namasivayam is with the Department of Physiology, Dr. ALM PG Institute of Basic Medical Sciences, University of Madras, Chennai, India.