PLASTICITY OF MEDULLARY DESCENDING PATHWAYS AFTER SPINAL CORD INJURY AND TRANS-SPINAL MAGNETIC STIMULATION

Various neuronal populations in the brainstem, particularly the medulla, are crucial for controlling distinct aspects of movement, including posture and locomotion. Despite the known potential plasticity of descending medullary pathways after spinal cord injury (SCI), the exact nature, functional implications, and modulation of such plasticity by therapeutic approaches remain unclear. We explore here, in a mouse SCI model of thoracic hemisection, the comparative plasticity of specific subtypes of descending medullary neurons and the impact of a non-invasive therapy, repetitive trans-spinal magnetic stimulation (rTSMS).
Expectedly, retrograde tracing revealed a marked reduction in the number of ipsilateral labeled medullary neurons following thoracic hemisection, while the contralateral ones were largely preserved. Subtype-specific analyses, however, demonstrated distinct responses to injury among medullary populations, notably with respect to their innervation of the ipsilateral and contralateral spinal cord. Importantly, a 14-day rTSMS treatment improved recovery, both anatomically and functionally. Indeed, we observed changes in the organization and distribution of specific medullary projections in the spinal cord, suggesting the modulation of plasticity in selective pathways. Functionally, rTSMS significantly improved the recovery of skilled, adaptative locomotion.
These findings refine our understanding of plasticity in descending medullary pathways after SCI, and identify this plasticity as one potential underpinning of the rehabilitative effects of neuromodulatory therapies.