Behavioural assessment of functional recovery after spinal cord hemisection in the bonnet monkey (Macaca radiata)

Abstract

In spinal cord research, current approaches to behavioural assessment often fail in defining the exact nature of motor deficits or in evaluating the return of motor behaviour from lost functions following spinal cord injury. In addition to the assessment of gross motor behaviour, it is often appropriate to use complex tests for locomotion to evaluate the masked deficits in the evaluation of functional recovery after spinal cord injury. We designed a series of sensitive quantitative tests for reflex responses and complex locomotor behaviour in the form of a combined behavioural score (CBS) to assess the recovery of function in the Bonnet monkey (Macaca radiata). Monkeys were tested for various motor/reflex components, trained to cross different complex runways, and to walk on a treadmill bipedally. The overall performance of animal’s motor behaviour and the functional status of individual limb movement during bipedal locomotion was graded and scored by the CBS. Surgical hemisection was then performed on the right side of the spinal cord at the T12-L1 level. Spinal cord hemisected animals showed a significant alteration in certain reflex responses such as grasping, extension withdrawal, and placing reflexes, which persisted through 1 year of follow-up. The spinal cord hemisected animals traversed the complex locomotor runways (Narrow beam and Grid runway) with more steps and few errors, at similar levels to control animals. These observations indicate that the various motor/reflex components and bipedal locomotor behaviour of spinal cord hemisected monkeys return to control levels gradually. These results are similar to those obtained in rat models by other investigators. These results demonstrate that the basic motor strategy and the spinal pattern generator for locomotion (SPGL) in adult monkeys for the accomplishment of complex motor tasks is similar, but not identical, to that in adult rats. This suggests that the mechanisms underlying recovery are probably similar in rats and monkeys, but that primates may take a longer duration to achieve the same functional end point.