Dow, Douglas E.

DIAm motor units are normally recruited in an orderly fashion to accomplish different ventilatory and non‐ventilatory behaviors. Following a cervical spinal cord hemisection at C2 (SH), there is restoration of phrenic activity over time. We hypothesized that an orderly recruitment of DIAm motor units is maintained with the restoration of rhythmic DIAm electromyographic (EMG) activity following SH. A pair of electrode wires was implanted into the midcostal regions of the DIAm of adult male rats for chronic EMG recording. Three days later, these animals underwent SH surgery. We examined changes in integrated DIAm EMG activity across different motor behaviors (i.e., eupnea, hypercapnia, tracheal occlusion and fictive sneezing) assuming that DIAm EMG activity during fictive sneezing represents the maximum recruitment of DIAm motor units. As expected in controls, DIAm EMG activity increased from eupnea (~27% of max) to hypercapnia (5% CO 2; ~45% of max) to sustained tracheal occlusion (~60% of max). By 14 days after SH with restored rhythmic DIAm activity, the amplitude of EMG activity on the ipsilateral side was reduced, and the changes in EMG activity induced by increased ventilatory and non‐ventilatory drive were blunted, although an orderly recruitment of motor units was still observed. These results support a generalized strengthening of contralateral presynaptic drive over time following spinal cord injury. Supported by NIH grants AR51173 and HL37680 and the Mayo Foundation.