Electrical epidural stimulation (ES) of the lumbar spinal cord (L2 to S1) has previously been shown to improve locomotor function in complete transection models of rat spinal cord injury (SCI) (Ichiyama et al., 2005), and is facilitated by pharmacological treatment and daily bipedal locomotor training (TR) (Ichiyama et al., 2008b; Ichiyama et al., 2008a; Van den Brand et al., 2012). Whilst, bipedal treadmill stepping is improved, this functional recovery does not translate into un-assisted overground stepping. We have also recently demonstrated that exercise up-regulates inhibitory chondroitin sulphate proteoglycans (CSPGs) in the lumbar spinal cord in intact animals (Smith et al., 2015). This is potentially restricting synaptic plasticity and therefore further functional recover. Previous evidence has demonstrated functional improvements when combining rehabilitation of forelimb function and application of Chondroitinase-ABC (ChABC) following SCI (Garcia-Alias et al., 2009; Wang et al., 2011a). The premise for this thesis therefore, is that addition of lentiviral Chondroitinase (LV-ChABC) locally after injury would greatly enhance synaptic plasticity; thus, enabling ES and TR to drive functional recovery.
Adult Sprague-Dawley rats received a severe spinal contusion injury (T9/10), epidural implantation at segmental levels L2 and S1 and intra-spinal injections of LV-ChABC or saline (control) ~1mm above and below the level of the lesion. Rats were then randomly assigned to one of four groups: cage control, training only, ES only (40 Hz; L2) or Combination (ES+TR). Rats in trained groups stepped bipedal-to-quadrupedally on a body weight supported treadmill (5-16 cm/s) (5 days/week, 20 mins/day) for 8 weeks. By the end of the 8-week period rats in the Saline-Combination group showed improvements not only in supported treadmill stepping ability but also in open field locomotion (BBB), with combination Saline/LV-ChABC treated animals achieving the highest overall increase in mean BBB score compared to Saline/LV-ChABC controls. Furthermore, kinematics analysis also revealed differences in stepping characteristics and pattern following 8 weeks of training. We did not observe any electromyography (EMG) responses in hindlimb muscles following cortical stimulation in any animal from any group, and no increased sensitivity to mechanical pain stimulation. Therefore, our results suggest that a combination of step training and epidural stimulation in an incomplete model of SCI successfully improved locomotor function further than either therapy administered alone. Combination treatment animals not only improved in treadmill step performance but were also able to transfer this skill to an open field task without the presence of stimulation. Interestingly, addition of LV ChABC produced differences in both kinematic profiles and withdrawal responses to mechanical paw pressure. These promising results indicate that the combination of ES, locomotor training and LV-ChABC is a viable treatment for functional recovery after severe SCI.
