Fig. 1: Characteristics of the EEMS system at the interface of the spinal cord and muscle.

a Schematic showing the application of the EEMS system, which comprises EES and MS, to the sensorimotor circuit in SCI mice. The interval between spinal and muscular stimulation was set to 15 ms. The interval between the two EES pulses or two MS pulses depended on the stimulation frequency. b AAV2/2Retro-hSyn-EGFP-WPRE-pA was injected into the TA muscles of intact mice to label motoneurons. Scale bar, 100 μm. The experiment was repeated 3 times independently with similar results. c Spatial distribution of motoneurons innervating the TA muscles. Scale bar, 300 μm. The experiment was repeated 3 times independently with similar results. d Correct positioning of the electrode was confirmed by magnetic resonance imaging analysis at 4 weeks after SCI; the white arrow points to sites of contact of the electrode, and the dashed white lines indicate the SCI site. Scale bar, 2.5 mm. The experiment was repeated one time. e EES (red line) was administered, and SCEP (black line) was recorded with the TA muscles of intact mice. ER: early latency response, MR: medium latency response, LR: late latency response. f The schematic illustrates which neurons, fibers, and/or circuits may be inhibited as stimulation signals delivered to the muscles from the spinal cord during each experimental operation in anesthetized intact mice. g Representative SCEP recorded in the muscle with different mice during repeated EES (1 Hz) and after the administration of tetrodotoxin (TTX) or tizanidine. Each waveform represents the average of the responses to 50 EES. h Histograms for TTX (upper) and tizanidine (lower) conditions showing the relative change in the SCEPs as compared with baseline (n = 7 mice per group). i ERs, MRs, and LRs induced by EES (n = 8 mice per group). j Curve showing the electrical signal received in the spinal cord after MS (n = 5 mice per group). Schematics in a–c, and f were created with BioRender.com. Data represent the mean ± SEM; Statistical analysis was performed using two-tailed unpaired t-test (h), ***p < 0.001.