Axonal degeneration and demyelination following traumatic spinal cord injury: A systematic review and meta-analysis.

The pathophysiology of spinal cord injury (SCI) related processes of axonal degeneration and demyelination are poorly understood. The present systematic review and meta-analysis were performed such to establish quantitative results of animal studies regarding the role of injury severity, SCI models and level of injury on the pathophysiology of axon and myelin sheath degeneration. 39 related articles were included in the analysis. The compiled data showed that the total number of axons, number of myelinated axons, myelin sheath thickness, axonal conduction velocity, and internode length steadily decreased as time elapsed from the injury (Pfor trend<0.0001). The rate of axonal retrograde degeneration was affected by SCI model and severity of the injury. Axonal degeneration was higher in injuries of the thoracic region. The SCI model and the site of the injury also affected axonal retrograde degeneration. The number of myelinated axons in the caudal region of the injury was significantly higher than the lesion site and the rostral region. The findings of the present meta-analysis show that the pathophysiology of axons and myelin sheath differ in various phases of SCI and are affected by multiple factors related to the injury.

Oligodendrogliogenesis and Axon Remyelination after Traumatic Spinal Cord Injuries in Animal Studies: A Systematic Review.

Extensive oligodendrocyte death after acute traumatic spinal cord injuries (TSCI) leads to axon demyelination and subsequently may leave axons vulnerable to degeneration. Despite the present evidence showing spontaneous remyelination after TSCI the cellular origin of new myelin and the time course of the axon ensheathment/remyelination remained controversial issue. In this systematic review the trend of oligodendrocyte death after injury as well as the extent and the cellular origin of oligodendrogliogenesis were comprehensively evaluated. The study design was based on Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA)-guided systematic review. PubMed and EMBASE were searched with no temporal or linguistic restrictions. Also, hand-search was performed in the bibliographies of relevant articles. Non-interventional animal studies discussing different types of myelinating cells including oligodendrocytes, Schwann cells and oligodendrocyte progenitor cells (OPCs) were evaluated. The extent of oligodendrocyte death, oligodendrocyte differentiation and remyelination were the pathophysiological outcome measures. We found 12,359 studies, 34 of which met the inclusion criteria. The cumulative evidence shows extensive oligodendrocytes cell death during the first week post-injury (pi). OPCs and peripheral invading Schwann cells are the dominant cells contributing in myelin formation. The maximum OPC proliferation was observed at around 2 weeks pi and oligodendrogliogenesis continues at later stages until the number of oligodendrocytes return to normal tissue by one month pi. Taken together, the evidence in animals reveals the potential role for endogenous myelinating cells in the axon ensheathment/remyelination after TSCI and this can be the target of pharmacotherapy to induce oligodendrocyte differentiation and myelin formation post-injury.

The fate of neurons after traumatic spinal cord injury in rats: A systematic review.

OBJECTIVES: To reach an evidence-based knowledge in the context of the temporal-spatial pattern of neuronal death and find appropriate time of intervention in order to preserve spared neurons and promote regeneration after traumatic spinal cord injury (TSCI). MATERIALS AND METHODS: The study design was based on Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA)-guided systematic review. PubMed and EMBASE were searched (24 October, 2015) with no temporal or linguistic restrictions. Hand-search was performed in the bibliographies of relevant articles. Non-interventional animal studies evaluating time-dependent neuronal death following acute mechanical trauma to the spinal cord were included. We separately evaluated the fate of various populations of neurons including propriospinal neurons, ventral motor neurons, Clarke's column neurons, and supraspinal neurons. RESULTS: We found 11,557 non-duplicated studies. Screening through the titles and abstracts led to 549 articles, 49 of which met the inclusion criteria. Both necrotic and apoptotic neuronal deaths occur after TSCI, though necrosis is the prominent mechanism. There are differences in the responses of intrinsic neurons of the spinal cord to the TSCI. Also, the extent of neuronal death in the supraspinal neurons depends on the anatomical location of their axons. CONCLUSION: In order to develop new therapies, selection of the injury model and time of intervention has a crucial role in the efficacy of therapy. In addition, examining the safety and efficacy of an intervention by reliable methods not confounded by the injury-related changes would promote translation of therapies to the clinical application.