Plastic changes of the neural expression of c-Fos protein in the medullary respiratoryneurons following respiratory muscle training with CO2 breathing in the Wistar rats

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Respiratory muscle training (RMT) can improve respiratory muscleweakness in chronic respiratory diseases. However , it is unclear whether RMT inducesadaptations in the respiratory center as well as respiratory muscles. We hypothesized therespiratory center in the medulla would also adapt to the RMT and less neurons became torecruit to achieve same minute ventilation under hypercapnic stimulation. T o clarify thishypothesis, the number of c-Fos positive medulllary neurons after short term hypercapnicstimulation (7%CO2, 50%O2, N2 balance, 90 min) in the rats with RMT was compared tothat in the untrained control rats. For the respiratory muscle training program, we usedthe hypercapnic stimulation that consisted of placing each rat in a hypercapnic chamberin order to increase the minute ventilation. The RMT rats (n=2) were placed in a chamberfilled with 7% CO2 and 50% O2 for 30 min, 5 times a week, for 4 weeks, whereas controlrats (n=2) were placed in the same chamber filled with room air . After 1.5 hours from thecompletion of the last trial of the 4 weeks program, axial sections from the medullaoblongata were processed for c-Fos immunohistochemistry .It was found that the number of the c-Fos positive neurons in the RMT rats were smallerthan those in the control rats at ventral and dorsal region of the medulla oblongata.