Differing responses to hypercapnia and hypoxia following pneumotaxic center ablation.

The respiratory responses of 21 cats were examined upon exposure to hypercapnia and isocapnic hypoxia. Animals having bilateral electrolytic lesions localized in the pontile pneumotaxic center exhibited hypercapnia-induced minute volumes which were significantly less than those of unlesioned control cats. The hypoxia-induced minute volumes of pneumotaxic lesioned animals, examined at isocapnic alveolar gas partial pressures, were likewise significantly less than control animals at end-expired oxygen partial pressures (PAO2) in excess of 65.0 mm Hg. At PAO2 levels below 65.0 mmHg. the minute volume of experimental animals rose sharply and became statistically indistinguishable from that of the unlesioned cats. The placement of control brain stem lesions typically produced no significant alterations in the respiratory responses to hypoxia or hypercapnia. It was concluded that the pneumotaxic center constitutes an integral component of the central chemoreceptor CO1-H+ CONTROLLING SUBSYSTEM. The concept of differing anatomical sites within the brain stem serving integrative functions for central chemoreceptor and peripheral chemoreceptor afferent stimuli is also supported.