title: Intrinsic neuronal properties control selective targeting of regenerating motoneurons.
abstract: Despite advances in microsurgical techniques, recovery of motor function after peripheral nerve injury is often poor because many regenerating axons reinnervate inappropriate targets. Consequently, surgical repair must include treatment strategies that improve motor axon targeting. Development of such treatments will require a better understanding of the molecular mechanisms governing selective motor axon targeting. This study used a well-established model of nerve transection and repair to examine (1) whether intrinsic differences exist between different pools of motoneurons after peripheral nerve injury, (2) if such differences regulate selective axon targeting, (3) if regenerating motor axons must express polysialic acid (PSA) in order to preferentially reinnervate muscle and (4) whether brief electrical stimulation improves regeneration accuracy because it increases PSA expression on regenerating axons. We found that different motor pools differentially express PSA after injury and that the capacity to re-express PSA appears to be an intrinsic neuronal property established during development. Second, motoneuron pools not up-regulating PSA did not preferentially reinnervate muscle after injury. Third, brief electrical stimulation of the proximal nerve stump immediately after injury only improved selective motor axon targeting if the motoneurons were capable of up-regulating PSA. Finally, the benefits of stimulation were completely abolished if PSA was removed from the regenerating axons. These results indicate that (1) intrinsic neuronal differences between motor pools must be considered in the development of treatments designed to improve axon targeting and (2) therapeutics aimed at increasing PSA levels on regenerating motor axons may lead to superior functional outcomes.
authors.affiliation: Department of Anatomy and Neurobiology, Sir Charles Tupper Medical Building, Dalhousie University, Halifax, Nova Scotia, Canada B3H 1X5.
authors.forename: Colin K
authors.initials: CK
authors.lastname: Franz
authors.forename: Urs
authors.initials: U
authors.lastname: Rutishauser
authors.forename: Victor F
authors.initials: VF
authors.lastname: Rafuse
mesh_terms: D000818:Animals; D001369:Axons / Q000502:physiology*; D019771:Axotomy; D004558:Electric Stimulation; D005267:Femoral Nerve / Q000293:injuries* / Q000473:pathology / Q000601:surgery; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D023421:Models, Animal; D009046:Motor Neurons / Q000378:metabolism / Q000502:physiology*; D009416:Nerve Regeneration / Q000502:physiology*; D019006:Neural Cell Adhesion Molecules / Q000378:metabolism; D012794:Sialic Acids / Q000235:genetics / Q000378:metabolism; D015854:Up-Regulation
chemical_list: D019006:Neural Cell Adhesion Molecules; D012794:Sialic Acids; C021319:polysialic acid