UCLA

Transplantation of olfactory bulb-derived olfactory ensheathing cells (OECs) is a promising therapy to facilitate the regrowth of axons and promote functional recovery following injury. This study combines OEC transplantation and epidural stimulation during a climbing task following a severe transection of the thoracic spinal cord of inbred Fischer 344 rats. To examine propriospinal connectivity of axons across the injury site, we injected two strains of a transsynaptic retrograde tracer, pseudorabies virus (PRV); GFP-PRV was injected into the tibialis anterior of one rat hindlimb and RFP-PRV was injected into the soleus of the other. We analyzed the PRV-labeled neurons in the lumbar spinal cord to evaluate the extent of each PRV injection and to detect populations of cholinergic and Pax2-expressing PRV-labeled interneurons. Several dually infected PRV interneurons from antagonistic muscles were detected in the lumbar cord. We also found that there were more Pax2-expressing PRV-labeled interneurons in media- compared to OEC- or fibroblast-treated rats. Next, we looked at the injury site block and found that many rats displayed incomplete lesions and that a proportion of PRV-labeled neurons above the lesion site are V2a or cholinergic interneurons. In addition, we located PRV-labeled neurons several segments above the injury site in a location and distribution characteristic of sympathetic preganglionic neurons. PRV-labeled V2a interneurons were detected near sympathetic preganglionic neurons, as well as in the intermediate thoracic spinal cord. Overall, our results demonstrate that tissue sparing may facilitate regeneration or reorganization of propriospinal circuits following injury after cellular transplantation and epidural stimulation.