Our two recent studies on the potential of olfactory ensheathing glial cell (OEC) transplantation provide conclusive evidence of functional re-connectivity and sensorimotor recovery in adult rats after a complete spinal cord transection. Based on these findings, the axon regeneration induced by OEC treatment facilitated some desired sensorimotor functions, but suppressed others. This proposal asks if the OEC effect on hindlimb motor function can be enhanced in both magnitude and specificity with different activity- based interventions. The central hypothesis is that the regenerative effects of OEC can be enhanced by activity-dependent mechanisms, such as epidural spinal cord stimulation (ES) combined with a serotonergic agonist, and training for a motor task (climbing or step training). Much work from our laboratory has focused on the effects of chronic, low intensity ES in completely paralyzed mammals, and although the mechanism is still unclear, ES plus the serotonergic agonist quipazine activates the lumbosacral neural circuitry and greatly enhances locomotion in spinal rats. Our recent work in a human model shows that ES, when combined with motor training, can trigger functional regenerative events and recovery of independent standing and volitional control of lower limb movements. To further develop strategies to amplify the magnitude of the OEC-mediated effects observed previously, two Specific Aims are proposed using fibroblast- and OEC-treated complete spinal cord transected rats and extensive electrophysiological, anatomical, and functional assessments.
Specific Aim 1 will determine whether the regenerative effects of OEC transplantation are greater than those of the fibroblast controls, and if ES and quipazine (to modulate spinal excitability) or a "voluntarily" initiated training of a climbing task (to engage supraspinal pathways) will promote OEC-facilitated axonal regeneration and sensorimotor recovery.
Specific Aim 2 asks if the regenerative effects of OEC transplantation are more robust when enhanced by the combined treatments of ES and voluntary climb training or the treatments of ES and treadmill step training. We anticipate that both the magnitude and specificity of the regeneration initiated by OEC transplantation will be most enhanced by ES and climb training, and that these interventions will stimulate the supraspinal and propriospinal networks to improve performance of selected sensorimotor tasks. Innovative features of these studies include the sophisticated measurements of evoked potentials in awake behaving spinal rats, a comprehensive battery of functional evaluation tools, and tracing experiments to detect regeneration of supraspinal and propriospinal neurons. The significance of these studies is to determine the extent to which both the amount of axon regeneration across the transection site and the specificity of the established re-connections can be enhanced by activity-dependent mechanisms. Ultimately, such mechanisms may be among the best candidates to enhance the functional benefits derived from OEC transplantation in completely paralyzed SCI patients.
Paralysis after a severe spinal cord injury (SCI) remains a major public health challenge due to the limited treatment options. Olfactory ensheathing cell (OEC) transplantation is a promising repair strategy that facilitates functional re-connectivity an improved sensorimotor function, but the magnitude and specificity of the effects must be enhanced. If one or more of the complementary activity-dependent treatments we propose to study, i.e., epidural spinal cord stimulation combined with a pharmacological stimulant, volitional motor training (climbing for a conditioned reward), and treadmill step training, significantly enhance the OEC effect, then these interventions could become viable, effective treatments for humans with severe SCI.