An Analysis of Microglia Within the Pro-Regenerative Spinal Cord of Ambystoma mexicanum

Injury to the mammalian Central Nervous System (CNS), which consists of the brain and spinal cord, is permanent, meaning that symptoms of CNS injury such as paralysis are unable to be cured or ameliorated in humans. In comparison, spinal cord injury in some amphibian species, like axolotls, Ambystoma mexicanum, can be healed due to the pro-regenerative environment of their CNS. Thus, axolotls are perfect model organisms for studying the factors that enable CNS regeneration. Analysis of microglia, a tissue-resident macrophage cell of the CNS, is necessary for a better understanding of the regenerative properties of the axolotl spinal cord. We induced spinal cord injury (SCI) by amputating the caudal end of the axolotl tail. After 2-14 days, the regenerated tissues were harvested, observed for characterization of microglia presence and morphology within the spinal cord, and then compared to tissues representing healthy spinal cord. This study in particular will focus on the regenerative capabilities of juvenile axolotls compared to previous work done using mature axolotls. A distinct microglial response was seen 4 days post-injury (dpi) (P = 0.0214, P = 0.0035; 2 and 4 dpi, respectively) within the total spinal cord area, and was accompanied by a trend of increasing amoeboid microglial density through 14 dpi within the spinal cord’s white matter (P = 0.0284). The data presented in this study provides support for the hypothesis that microglial cell migration to the site of SCI peaks at 4 dpi; however, microglial cell activity also continues through 14 dpi. It is our hope that the work done in this study leads to a greater understanding of the environment specific to the axolotl spinal cord that enables such perfect regeneration, to be used towards treatment of mammalian SCI in the future.