NEURONAL ACTIVATION MAPPING IN THE SPINAL CORD FOLLOWING HIGH-INTENSITY TRANS-SPINAL MAGNETIC STIMULATION IN MICE

Trans-spinal magnetic stimulation (TSMS) is a promising non-invasive neuromodulation approach for spinal cord injury (SCI). In our laboratory, high-intensity repetitive TSMS (HI-rTSMS) has demonstrated therapeutic benefits after SCI. However, the acute cellular mechanisms underlying these effects remain poorly understood. The direct impact of HI-rTSMS on spinal neuronal activation has not yet been clearly characterized. Here, we investigated early neuronal responses following a single session of HI-rTSMS in healthy mice.
HI-rTSMS (0.4 T, 10 Hz) were delivered using a human-sized circular coil according to a patterned protocol consisting of 10 s stimulation followed by 20 s rest, repeated over a total duration of 10 minutes. Three-dimensional spatial mapping of the magnetic field was performed to characterize the stimulation profile. Mice were anesthetized under isoflurane during stimulation. To evaluate the influence of post-stimulation behavioral state, animals either remained anesthetized or were allowed to wake for one hour prior to perfusion, corresponding to the peak window of c-Fos expression.
Spinal cords were collected and processed for immunohistochemistry using DAPI, NeuN, and c-Fos. Neuronal activation was quantified as c-Fos⁺/NeuN⁺/DAPI⁺ cells, allowing analysis of dorsal and ventral spinal cord regions. In anesthetized animals, HI-rTSMS induced a significant reduction in neuronal activation compared to non-stimulated controls, suggesting an acute inhibitory or modulatory effect. In contrast, awake mice showed no significant difference in c-Fos expression between conditions.
This study provides a spatially informed analysis of spinal neuronal activation following HI-rTSMS and highlights the importance of animal state when interpreting acute neuronal effects.