A Contusive Model of Unilateral Cervical Spinal Cord Injury Using the Infinite Horizon Impactor

Summary

A reliable and repeatable way to produce a cervical unilateral spinal cord injury using the Infinite Horizon impactor is described. The method takes advantage of a custom designed frame and clamp to stabilize the spine. The standardized procedure and biomechanical injury parameters result in sufficient and sustained injuries.

Abstract

While the majority of human spinal cord injuries occur in the cervical spinal cord, the vast majority of laboratory research employs animal models of spinal cord injury (SCI) in which the thoracic spinal cord is injured. Additionally, because most human cord injuries occur as the result of blunt, non-penetrating trauma (e.g. motor vehicle accident, sporting injury) where the spinal cord is violently struck by displaced bone or soft tissues, the majority of SCI researchers are of the opinion that the most clinically relevant injury models are those in which the spinal cord is rapidly contused.¹ Therefore, an important step in the preclinical evaluation of novel treatments on their way to human translation is an assessment of their efficacy in a model of contusion SCI within the cervical spinal cord. Here, we describe the technical aspects and resultant anatomical and behavioral outcomes of an unilateral contusive model of cervical SCI that employs the Infinite Horizon spinal cord injury impactor.

Sprague Dawley rats underwent a left-sided unilateral laminectomy at C5. To optimize the reproducibility of the biomechanical, functional, and histological outcomes of the injury model, we contused the spinal cords using an impact force of 150 kdyn, an impact trajectory of 22.5° (animals rotated at 22.5°), and an impact location off of midline of 1.4 mm. Functional recovery was assessed using the cylinder rearing test, horizontal ladder test, grooming test and modified Montoya's staircase test for up to 6 weeks, after which the spinal cords were evaluated histologically for white and grey matter sparing.

The injury model presented here imparts consistent and reproducible biomechanical forces to the spinal cord, an important feature of any experimental SCI model. This results in discrete histological damage to the lateral half of the spinal cord which is largely contained to the ipsilateral side of injury. The injury is well tolerated by the animals, but does result in functional deficits of the forelimb that are significant and sustained in the weeks following injury. The cervical unilateral injury model presented here may be a resource to researchers who wish to evaluate potentially promising therapies prior to human translation.

Protocol

1. Set up: Frame and Clamp Design for Holding the Animal

1. The frame and clamp to hold the animal was custom-designed to accommodate the Infinite Horizon (IH) Spinal Cord Injury Impactor.
2. The base of the frame is an aluminum platform cut into the following dimensions (30.2 cm x 20.3 cm x 1.3 cm) in order to fit into the table guide bracket that comes standard with the IH device (Figure 1A).
3. Four Flexaframe support foot plates (Fisher Scientific, Toronto, ON) are attached to the platform and eight Flexaframe support rods (Fisher Scientific, Toronto, ON, 30.5 cm) are assembled using eight Flexaframe support connectors (

Discussion

In this paper, we describe a cervical unilateral contusion model using the Infinite Horizon (IH) impactor at a force of 150 kdyn, an angle of 22.5° off of vertical, and a lateral aim of 1.4 mm from the midline. With these settings, we were able to produce sustained behavioral deficits in the ipsilateral forelimb with parenchymal disruption contained largely to the ipsilateral side, where it appeared that considerable damage occurred to the regions where the rubrospinal, reticulospinal, vestibulospinal and corticospin.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Infinite Horizon Impactor	Precision Systems and Instrumentation	IH-0400
Aluminum metal sheet	Metalsupermarlets.com	APT6061/500
Flexaframe support foot plates	Fishers Scientific	1466625Q
Flexaframe support rods	Fishers Scientific	1466610GQ
Flexaframe Support Connectors	Fishers Scientific	1466620Q
Clamp1	Custom made		Choo et al., 2009
Metal holders	Custom made		See above
Impactor tip	Custom made		Diameter: 1.15 mm
Stereotaxic frame	David Kopf Instruments	Model 900
Cylinder Level	YIJIA TOOLS	YJ-SL0620
Microscope	Leica		Model #: MZ8
Laboratory scissor jack	VWR	12620-902