Experimental Strategies to Bridge Large Tissue Gaps in the Injured Spinal Cord after Acute and Chronic Lesion

Summary

Severe spinal cord injuries often result in tissue defects. Two possibilities are described to successfully bridge such gaps to promote tissue adaptation, regenerative responses and functional improvement in rats via implantation of a mechanical microconnector system after acute injury and five weeks after complete spinal cord transection.

Abstract

After a spinal cord injury (SCI) a scar forms in the lesion core which hinders axonal regeneration. Bridging the site of injury after an insult to the spinal cord, tumor resections, or tissue defects resulting from traumatic accidents can aid in facilitating general tissue repair as well as regenerative growth of nerve fibers into and beyond the affected area. Two experimental treatment strategies are presented: (1) implantation of a novel microconnector device into an acutely and completely transected thoracic rat spinal cord to readapt severed spinal cord tissue stumps, and (2) polyethylene glycol filling of the SCI site in chronically lesioned rats after scar resection. The chronic spinal cord lesion in this model is a complete spinal cord transection which was inflicted 5 weeks before treatment. Both methods have recently achieved very promising outcomes and promoted axonal regrowth, beneficial cellular invasion and functional improvements in rodent models of spinal cord injury.

The mechanical microconnector system (mMS) is a multi-channel system composed of polymethylmethacrylate (PMMA) with an outlet tubing system to apply negative pressure to the mMS lumen thus pulling the spinal cord stumps into the honeycomb-structured holes. After its implantation into the 1 mm tissue gap the tissue is sucked into the device. Furthermore, the inner walls of the mMS are microstructured for better tissue adhesion.

In the case of the chronic spinal cord injury approach, spinal cord tissue - including the scar-filled lesion area - is resected over an area of 4 mm in length. After the microsurgical scar resection the resulting cavity is filled with polyethylene glycol (PEG 600) which was found to provide an excellent substratum for cellular invasion, revascularization, axonal regeneration and even compact remyelination in vivo.

Introduction

A traumatic injury to the spinal cord not only leads to the loss of axons but it further results in tissue defects which hinder any regenerative responses (for review see ^1,2). Spinal cord tissue is often lost through secondary degeneration leading to cyst formation or holes in and around the lesion area. Most experimental therapeutic interventions focus on incomplete spinal cord damages like partial transection, crush or contusion injuries with a remaining rim of healthy tissue. For complete injuries like total transections resulting from traumatic accidents or surgical interventions, like tumor resections, only very limited treatment options are available....

Protocol

Institutional guidelines for animal safety and comfort were adhered to, and all surgical interventions and pre- and post-surgical animal care were provided in compliance with the German Animal Protection law (State Office, Environmental and Consumer Protection of North Rhine- Westphalia, LANUV NRW).

1. Complete Transection of the Thoracic Spinal Cord of Female Wistar Rats (220 - 250 g)

1. Preparation of the Spinal Cord
   1. Use isoflurane inhalation anesthesia (2 - 3% of isoflurane in O₂/NO₂ at a ratio of 1:2) and bolus injection of Carprofen (subcutaneously [s.c.] 5 mg/kg). The combination of carprofen and....

Results

Tissue Preservation, Axonal Regrowth and Functional Benefit of mMS Implantation after Acute Complete Transection of the Spinal Cord
It is demonstrated that the acute implantation of the mMS stabilized the completely transected spinal cord stumps and decreased shrinkage of the tissue (Figure 2A versus B). As visualized by Trichrome staining in sagittal sections, the green connective tissue staining of the fibrotic scar in the .......

Discussion

Here two different surgical approaches are presented to bridge tissue gaps in the spinal cord after (1) acute complete transection and mMS implantation and (2) chronic spinal cord lesion and fibrous scar removal plus PEG matrix implantation. Both strategies lead to tissue preservation and axonal regeneration as well as to significant locomotor functional improvement of the treated animals. For mMS implantation an adequate fixation of the mMS within the spinal cord by the firm dura suture after surgery is a critical techn.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
PEG 600 Ph Eur	Merck/VWR	8,170,041,000
Gelastypt gelatine sponge	sanofi Aventis	PZN-8789582
Nescofilm Sealant	Roth	2569.1
Baytril	Bayer
Rimadyl (Carpofen)	Pfizer
Forene (Isoflurane)	Abbvie
Kodan (skin disinfectant)
Histoacryl (tissue glue)
Friedman-Pearson Rongeur, 1 mm cup, straight	Fine Science Tools	16020-14
Two-in-one Micro Spatula - 12 cm	Fine Science Tools	10091-12
Dumont #7 Forceps - Inox Medical	Fine Science Tools	11273-20
Dumont #5/45 Forceps - Inox Medical	Fine Science Tools	11253-25
Spinal cord hook	Fine Science Tools	10162-12
Scissors	Fine Science Tools	14078-10
Clamp	Aesculap	EA016R
Ethicon Vicryl 4-0
Bepanthen Augen- und Nasensalbe	Bayer
Anatomical forceps	Fine Science Tools	11000-13
Self-retaining retractor	Fine Science Tools	17008-07
Skin clamp	Fine Science Tools	13008-12
Aluspray	Selectavet