Cracking the black box – and putting it back together again: Animal models of spinal cord injury

Animal models of spinal injury for studying back pain and SCI

INTRODUCTION

Back pain is a common ailment affecting individuals around the globe. Animal models to understand the back pain mechanism, treatment modalities, and spinal cord injury are widely researched topics worldwide. Despite the presence of several animal models on disc degeneration and Spinal Cord Injury, there is a lack of a comprehensive review.

MATERIAL AND METHOD

A methodological narrative literature review was carried out for the study. A total of 1273 publications were found, out of which 763 were related to spine surgery in animals. The literature with full-text availability was selected for the review. Scale for the Assessment of Narrative Review Articles (SANRA) guidelines was used to assess the studies. Only English language publications were included which were listed on PubMed. A total of 113 studies were shortlisted (1976-2019) after internal validation scoring.

RESULT

The animal models for spine surgery ranged from rodents to primates. These are used to study the mechanisms of back pain as well as spinal cord injuries. The models could either be created surgically or through various means like use of electric cautery, chemicals or trauma. Genetic spine models have also been documented in which the injuries are created by genetic alterations and knock outs. Though the dorsal approach is the most common, the literature also mentions the anterior and lateral approach for spine surgery animal experiments.

CONCLUSION

There are no single perfect animal models to represent and study human models. The selection is based on the application and the methodology. Careful selection is needed to give optimum and appropriate results.

The Dorsal Column Lesion Model of Spinal Cord Injury and Its Use in Deciphering the Neuron-Intrinsic Injury Response

The neuron‐intrinsic response to axonal injury differs markedly between neurons of the peripheral and central nervous system. Following a peripheral lesion, a robust axonal growth program is initiated, whereas neurons of the central nervous system do not mount an effective regenerative response. Increasing the neuron‐intrinsic regenerative response would therefore be one way to promote axonal regeneration in the injured central nervous system. The large‐diameter sensory neurons located in the dorsal root ganglia are pseudo‐unipolar neurons that project one axon branch into the spinal cord, and, via the dorsal column to the brain stem, and a peripheral process to the muscles and skin. Dorsal root ganglion neurons are ideally suited to study the neuron‐intrinsic injury response because they exhibit a successful growth response following peripheral axotomy, while they fail to do so after a lesion of the central branch in the dorsal column. The dorsal column injury model allows the neuron‐intrinsic regeneration response to be studied in the context of a spinal cord injury. Here we will discuss the advantages and disadvantages of this model. We describe the surgical methods used to implement a lesion of the ascending fibers, the anatomy of the sensory afferent pathways and anatomical, electrophysiological, and behavioral techniques to quantify regeneration and functional recovery. Subsequently we review the results of experimental interventions in the dorsal column lesion model, with an emphasis on the molecular mechanisms that govern the neuron‐intrinsic injury response and manipulations of these after central axotomy. Finally, we highlight a number of recent advances that will have an impact on the design of future studies in this spinal cord injury model, including the continued development of adeno‐associated viral vectors likely to improve the genetic manipulation of dorsal root ganglion neurons and the use of tissue clearing techniques enabling 3D reconstruction of regenerating axon tracts. © 2018 The Authors. Developmental Neurobiology Published by Wiley Periodicals, Inc. Develop Neurobiol 00: 000–000, 2018

Animal models of spinal cord injury: a systematic review

STUDY DESIGN

PRISMA-guided systematic review.

OBJECTIVES

To provide a comprehensive framework of the current animal models for investigating spinal cord injury (SCI) and categorize them based on the aims, patterns and levels of injury, and outcome measurements as well as animal species.

SETTING

Sina Trauma and Surgery Research Center, Tehran University of Medical Sciences, Tehran, Iran.

METHODS

An electronic search of the Medline database for literature describing animal models of SCI was performed on 1 January 2016 using the following keywords: 'spinal cord injuries' and 'animal models'. The search retrieved 2870 articles. Reviews and non-original articles were excluded. Data extraction was independently performed by two reviewers.

RESULTS

Among the 2209 included studies, testing the effects of drug's or growth factor's interventions was the most common aim (36.6%) followed by surveying pathophysiologic changes (30.2%). The most common spinal region involved was thoracic (81%). Contusion was the most common pattern of injury (41%) followed by transection (32.5%) and compression (19.4%). The most common species involved in animal models of SCI was the rat (72.4%). Two or more types of outcome assessments were used in the majority of the studies, and the most common assessment method was biological plus behavioral (50.8%).

CONCLUSIONS

Prior to choosing an animal model, the objectives of the proposed study must precisely be defined. Contusion and compression models better simulate the biomechanics and neuropathology of human injury, whereas transection models are valuable to study anatomic regeneration. Rodents are the most common and probably best-suited species for preliminary SCI studies.

Slope analysis of somatosensory evoked potentials in spinal cord injury for detecting contusion injury and focal demyelination

In spinal cord injury (SCI) research there is a need for reliable measures to determine the extent of injury and assess progress due to natural recovery, drug therapy, surgical intervention or rehabilitation. Somatosensory evoked potentials (SEP) can be used to quantitatively examine the functionality of the ascending sensory pathways in the spinal cord. A reduction of more than 50% in peak amplitude or an increase of more than 10% in latency are threshold indicators of injury. However, in the context of injury, SEP peaks are often obscured by noise. We have developed a new technique to investigate the morphology of the SEP waveform, rather than focusing on a small number of peaks. In this study, we compare SEP signals before and after SCI using two rat models: a contusion injury model and a focal experimental autoimmune encephalomyelitis model. Based on mean slope changes over the signal, we were able to effectively differentiate pre-injury and post-injury SEP values with high levels of sensitivity (83.3%) and specificity (79.2%).