Serum MicroRNAs Reflect Injury Severity in a Large Animal Model of Thoracic Spinal Cord Injury

Object Axonal regeneration may be hindered following spinal cord injury (SCI) by a limited immune response and insufficient macrophage recruitment. This limitation has been partially surmounted in small-mammal models of SCI by implanting activated autologous macrophages (AAMs). The authors sought to replicate these results in a canine model of partial SCI. Methods Six dogs underwent left T-13 spinal cord hemisection. The AAMs were implanted at both ends of the lesion in 4 dogs, and 2 other dogs received sham implantations of cell media. Cortical motor evoked potentials (MEPs) were used to assess electrophysiological recovery. Functional motor recovery was assessed with a modified Tarlov Scale. After 9 months, animals were injected with wheat germ agglutinin–horseradish peroxidase at L-2 and killed for histological assessment. Results Three of the 4 dogs that received AAM implants and 1 of the 2 negative control dogs showed clear recovery of MEP response. Behavioral assessment showed no difference in motor function between the AAM-treated and control groups. Histological investigation with an axonal retrograde tracer showed neither local fiber crossing nor significant uptake in the contralateral red nucleus in both implanted and negative control groups. Conclusions In a large-animal model of partial SCI treated with implanted AAMs, the authors saw no morphological or histological evidence of axonal regeneration. Although they observed partial electrophysiological and functional motor recovery in all dogs, this recovery was not enhanced in animals treated with implanted AAMs. Furthermore, there was no morphological or histological evidence of axonal regeneration in animals with implants that accounted for the observed recovery. The explanation for this finding is probably multifactorial, but the authors believe that the AAM implantation does not produce axonal regeneration, and therefore is a technology that requires further investigation before it can be clinically relied on to ameliorate SCI.

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Silencing long ascending propriospinal neurons after spinal cord injury improves hindlimb stepping in the adult rat

10.1101/2021.05.18.444653 ◽

2021 ◽

Author(s):

David SK Magnuson ◽

Courtney T Shepard ◽

Amanda M Pocratsky ◽

Brandon L Brown ◽

Morgan A Van Rijswijck ◽

...

Keyword(s):

Spinal Cord ◽

Spinal Cord Injury ◽

Injury Severity ◽

Dependent Manner ◽

Thoracic Spinal Cord ◽

Locomotor Function ◽

Adult Rat ◽

Thoracic Spinal ◽

Cord Injury ◽

Propriospinal Neurons

Long ascending propriospinal neurons (LAPNs) are a subpopulation of spinal cord interneurons that directly connect the lumbar and cervical enlargements. In uninjured animals, conditionally silencing LAPNs resulted in disrupted left-right coordination of the hindlimbs and forelimbs in a context-dependent manner, demonstrating that LAPNs secure alternation of the fore- and hindlimb pairs during overground stepping in the adult rat. Given their ventrolateral location in the spinal cord white matter, many LAPN axons likely remain intact following thoracic spinal cord injury (SCI), suggesting a potential role in the recovery of stepping. Thus, we hypothesized that silencing LAPNs after SCI would result in diminished hindlimb locomotor function. We found instead that silencing of spared LAPNs post-SCI restored the left-right hindlimb coordination associated with alternating gaits that was lost as a result of SCI. Several other fundamental characteristics of hindlimb stepping were also improved and the number of abnormal steps were reduced. However, hindlimb-forelimb coordination was not restored. These data suggest that the temporal information carried between the enlargements by the LAPNs after SCI may be detrimental to hindlimb locomotor function. These observations have implications for our understanding of the relationship between injury severity and functional outcome, for the efforts to develop neuro- and axo-protective therapeutic strategies, and also for the clinical study/implementation of spinal stimulation and neuromodulation.

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