The regenerative potential of the axolotl spinal cord: A blunt spinal cord injury model
Authors: Thygesen Mathias Moeller , Lauridsen Henrik , Pedersen Michael , Rasmussen Mikkel Mylius 
Published: November 2023

Introduction

Spinal cord injury (SCI) is associated with severe morbidity and mortality, and SCI may lead to reduced life expectancy. The most prevalent cause of SCI is traffic accidents and falls, both inflicting contusion traumas. While humans are incapable of restoring affected neural tissue after SCI, some vertebrates have the ability to regenerate neural tissue. One of these species is the Mexican axolotl salamander (Ambystoma mexicanum). Previous studies have shown that spinal cord resection in the axolotl resulted in complete regeneration with ependymal cells being the apparent progenitor.

Contusion trauma in mice results in rapid and comprehensive activation of reactive ependymal cells, but without encourage of regeneration. However, in vitro experiments have shown that ependymal cells possess potential to differentiate into either astrocytes, oligodendrocytes and neurons. Several mammalian studies have shown regenerative potential of the central nervous system (CNS) under specific circumstances, e.g. when grafting tissue from peripheral nerves to CNS lesions. Some nervous restoration can be achieved by introducing the permissive environment of the peripheral nerve system.

The regenerative potential of the axolotl after resection and previous experiments on mammals strongly indicate that the paradigm of CNS not being able to regenerate is trembling. The aim of this study was to investigate the axolotl's ability to regenerate after contusion spinal cord injury.

Methods

This study is on‐going (at the time of abstract submission) as a single blinded investigation. Axolotls were randomly assigned to either the intervention group (n = 6) or the sham group (n = 6). A laminectomy of two vertebrae at the level just caudal to the hind limbs was performed. To induce a blunt SCI, a 25 g rod in 30 mm free fall was released on the exposed spinal cord of animals of the intervention group. Sham received identical surgery without SCI.

To examine regrowth, multiple modalities were applied pre‐operatively, and subsequently every third week for 9 weeks. T2‐weighted and diffusion tensor imaging MRI sequences were applied to reveal regeneration of the spinal cord and estimate the degree of linear diffusion at the site of injury. To support non‐invasive anatomical examinations, the progress of spinal cord regeneration was assessed by histology.

Functional regeneration was tested using swimming exercise yielding the maximal swimming capacity of the animals during the regenerative process. Finally, activity level was monitored by computationally tracking animal movements during a 1‐hour period.

Results and discussion

We found full anatomical and functional recovery after traumatic SCI within 2 months. Whilst still being in progress, the experiment has produced results at the first time point. DTI and following functional anisotropy analysis were successfully used to visualise the injury, with apparent differences between intervention and sham groups. The swimming capacity test has also shown that sham animals scored higher than intervention animals. The perspective of the study is to apply the model in future studies on neurogenic and regenerative factors on a molecular level.

Support or Funding Information

Funded by:Region Midt and Institute of Clinical Medicine Riisfort Foundation ELRO Foundation Linex Foundation