Microglial Labeling in Mouse Spinal Cord Injury: A Review of Timing, Efficacy, and Specificity.

Traumatic spinal cord injury (SCI) is a complex and disabling condition with no curative therapy currently available. The mechanical damage of the primary injury phase is followed and exacerbated by a secondary injury phase, characterized by the release of free radicals and pro-inflammatory cytokines that lead to chronic inflammation. Microglia, as the resident immune cells of the central nervous system, play a critical role in orchestrating this inflammatory response. Studying their dynamics after SCI not only deepens our understanding of injury pathology but also advances the development of microglia-targeted immunotherapies. However, trauma-induced transcriptional and phenotypic changes mean that markers used to identify homeostatic microglia may be unreliable when applied to their reactive counterparts. Another major challenge lies within discriminating resident microglia from infiltrating monocyte-derived macrophages (MDM), which permeate the blood-spinal cord barrier (BSCB) after injury. In this review, we examine three key variables for selecting appropriate strategies for labeling microglia in mice: (i) time (in relation to injury); (ii) efficacy (within the chosen murine SCI model); and (iii) specificity (to microglia). We discuss the transcriptional landscape of murine microglia pre-injury and its alteration post-injury, evaluate the strengths and limitations of commonly used markers, and highlight emerging tools and approaches for studying microglia in preclinical murine SCI research.