Olfactory ensheathing glia enhances reentry of axons into the brain from peripheral nerve grafts bridging the substantia nigra with the striatum

Abstract

Reconstruction of lost axonal pathways in the central nervous system (CNS) is possible with the use of peripheral nerve grafts (PNG). However, these permit the entry of axons, while their reentry back into the CNS is compromised. Olfactory ensheathing glia (OEG) may permit this reentry of axons if cografted with PNG. We compared the number of tyrosine-hydroxylase positive (TH+) fibers reinnervating PNGs and crossing the graft-striatum interface in PNG placed between the substantia nigra and the striatum in rats receiving both PNG and OEGs and animals receiving PNG only. More TH fibers were seen inside the grafts when OEG was cografted. Although the number of fibers decreases along the graft's length, this effect is less severe when OEG is present. TH+ fibers are seen crossing the PNG-striatum interface in the OEG group. This is correlated with a higher synaptic density at the striatum near the graft when OEG is co-grafted. While these results must be replicated in animal models of Parkinsonism, their implications may apply both to the treatment of Parkinson's disease and to other pathologies, such as spinal cord lesions, where regeneration of long axonal pathways is necessary.