Restoration of hypoxic respiratory responses in the awake rat after carotid body denervation by sinus nerve section.

The restoration of ventilatory responses to hypoxia after carotid body denervation was studied in twenty-eight awake rats. The respiratory depression seen in moderate hypoxia (partial pressure of inspired O2, PI,O2, 80-100 mmHg) 3 days after bilateral carotid sinus nerve section disappeared by day 10. By day 17 respiratory stimulation occurred at all levels of PI,O2 below 125 mmHg. The largest restored response, in severe hypoxia (PI,O2 50-60 mmHg), was approximately 55% of the pre-denervation response. The response showed little further change from day 17 to day 192. A comparison of the effect of bilateral section of the glossopharyngeal nerve and of the abdominal vagus 1 and 28 days after carotid sinus nerve section demonstrated that the restoration of hypoxic response resulted in part from an enhanced effect of the inputs from the secondary glomus tissue served by these nerves. A comparison of the effect of bilateral section of glossopharyngeal, abdominal vagal and aortic depressor nerves 1 and 28 days after carotid sinus nerve section demonstrated an increase of a residual hypoxic response which must result either from inputs from unidentified peripheral chemoreceptors or from central mechanisms. Bilateral sectioning of the aortic depressor nerves produced no additional effect on restored responses to sectioning glossopharyngeal and abdominal vagal nerves, providing further evidence against significant aortic body function in the rat. The studies support the hypothesis that central neural reorganization provides compensation for loss of carotid body function by enhancement of effects of normally subsidiary inputs.