Further evidence of olfactory ensheathing glia facilitating axonal regeneration after a complete spinal cord transection
Research Highlights
► OEG can facilitate regeneration of axons after a complete spinal cord transection. ► Bipedeal hindlimb stepping in rats injected with OEG after transection. ► Climbing ability improved in rats injected with OEG after transection. ► Recovery of Motor Evoked Potentials in occurred in only OEG rats. ► Motor Evoked Potentials were modified by 5-HT, NA and Glycinergic antagonists.
Introduction
While the results of studies on the effects of olfactory ensheathing glia (OEG) in repairing an injured spinal cord have been highly variable, so have the experimental paradigms used to determine the reparative potential of these cells, differing in the type and severity of injury, mixture of cell types, duration of transplant, transplantation procedures, and parameters used to define regeneration (Frannsen et al., 2007). One of the more important questions yet to be answered conclusively is whether OEG can facilitate regeneration of axons after a complete spinal cord transection. We therefore hypothesized that OEG implanted immediately after a complete spinal cord transection can restore functional connections between the rostral and caudal spinal cord stumps. Previous studies showed improvement in hindlimb function in OEG spinal rats, but it is unclear whether this improvement was attributable to regeneration of axons and/or to reorganization of the neurons in the caudal stump (Ramón-Cueto et al., 2000, Lu et al., 2002, Keyvan-Fouladi et al., 2003; Verdú et al., 2003, García-Alías et al., 2004, Polentes et al., 2004, López-Vales et al., 2007, Kubasak et al., 2008). Some anatomical data are consistent with the presence of regeneration, but these data are not conclusive (Ramón-Cueto et al., 2000, Takeoka et al., 2009, Takeoka et al., 2010). In the present study we focused on a battery of functional (behavioral, electrophysiological, and pharmacological) assessments during 6 months post-transection and OEG injections, some of which were performed before and after re-transection of the spinal cord.
We observed motor-evoked potentials (MEP) only in OEG rats. These MEP were modified by step training and their amplitudes could be modulated by yohimbine, a NA receptor antagonist, cyproheptadine, a 5-HT2 receptor antagonist, and/or strychnine, a glycinergic receptor antagonist. In addition, the MEP were eliminated when the spinal cord was re-transected rostral to the original transection site.
Section snippets
Spinal cord transection
All procedures were approved by the Chancellor's Animal Research Committee at the University of California, Los Angeles and followed the American Physiological Society Animal Care Guidelines. All surgical procedures were performed under aseptic conditions with the rats deeply anesthetized using isoflurane gas via facemask as needed. The spinal cords of 42 Wistar Hannover rats, 10–12 week old, were transected completely at spinal cord level T8–T9 as previously described (Kubasak et al., 2008).
Step training and pharmacologically induced improvements in stepping ability in Media rats
Stick diagrams and trajectories for a single step of a rat representing the untrained and trained Media groups with and without injections of 5-HT receptor agonists are shown in Figs. 2A and B, respectively. The EMG activity of the soleus and TA muscles corresponding to these rats for single and a mean of 10 steps are shown in Figs. 2C and D, respectively. These data show that the reciprocal activity between the TA and soleus was clearer in the trained than untrained groups and clearest in the
Discussion
In the present study we show that in addition to improved hindlimb function, injection of OEG facilitated regeneration of axons across a complete mid-thoracic spinal cord transection. More specifically as in previous studies, we observed that OEG spinal rats had a better climbing performance than Media rats 6 months after injection of OEG (Ramón-Cueto et al., 2000, Muñoz-Quiles et al., 2009). TA and soleus EMG activity in OEG rats was higher than in Media rats, particularly in the soleus when
Acknowledgments
This work was supported by the National Institute of Neurological Disorders and Stroke Grant NS054159. We thank Maynor Herrera for providing excellent animal care and surgical support, Sharon Zdunowski for her technical support, Dr. Lance Cai and Andy Fong for their help in developing the robotic system, and Dr. Niranjala Tillakaratne for her constructive guidance and valuable discussions. Also a special thanks to Dr. Cintia Muñoz-Quiles for her guidance and support with OEG preparations and
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