Effect of denervation of carotid labyrinths on breathing in unrestrained Xenopus laevis

Abstract

The effect of denervation of the carotid labyrinths on breathing responses to simultaneously applied aerial and aquatic normoxia, hypoxia, or hypercapnia has been studied in unrestrained Xenopus laevis. Denervation significantly reduced V I of normoxic toads compared with V I intact and sham-operated toads, due to a significant reduction in the volume of each buccal pumping movement (V B) in denervates. Breathing increased significantly in response to environmental hypoxia or hypercapnia in intact and sham-operated toads as well as in denervates. Breathing frequency ( fResp) was the major determinant of the increase in V I for V B was unchanged and even fell slightly in denervates in hypercapnia. Dive time (DT) was significantly reduced in both hypoxia and hypercapnia, from that in normoxia. DT fell significantly more in hypoxia than in hypercapnia in both denervates and intact and sham-operated toads. It is concluded that the carotid labyrinth does not play a major role in regulating breathing in hypoxia of hypercapnia in unrestrained Xenopus.