Prolonged stimulation of respiration by a new central neural mechanism

The inspiratory responses to stimulation by peripheral chemoreceptor, central chemoreceptor and calf muscle afferents were studied in anesthetized, or decerebrate, paralyzed cats whose end-tidal PCO2 was servo-controlled and kept constant. All stimuli were associated with immediate increases of inspiratory (phrenic) activity and at offset were followed by a respiratory afterdischarge lasting approximately five minutes. The level of inspiratory activity following decay of the afterdischarge was the same as the prestimulation control after central chemoreceptor and calf muscle stimulation. However, after peripheral chemoreceptor afferent stimulation the stable level of inspiratory activity following the afterdischarge had increased over the prestimulation level and remained elevated for as long as it was followed, up to 90 min. Decerebration, vagotomy, and section of the spinal cord at C--T1 did not prevent this long-lasting increase in respiration. We conclude that we have demonstrated a new ponto-medullary neural mechanism which is uniquely activated by peripheral chemoreceptor afferent input; once activated, this mechanism sustains respiration at an increased level for a long period of time.