Central respiratory pattern generation in the bullfrog, Rana catesbeiana

There are two components to breathing pattern generation, the production of the pattern of neural discharge associated with individual breaths, and th e pattern in which breaths are produced to effect ventilation. Bullfrogs ty pically breathe with randomly distributed breaths. When respiratory drive i s elevated, breathing becomes more regular and often episodic. Studies on i n vitro brainstem-spinal cord preparations of the adult bullfrog and in sit u preparations of decerebrate, paralyzed, unidirectionally ventilated anima ls suggest that output from the central rhythm generator in frogs is condit ional on receiving some input and that a host of central inputs remain even in the most reduced preparations. There appear to be descending inputs fro m sites in the dorsal brainstem just caudal to the optic chiasma that clust er breaths into episodes, a strong excitatory input caudal to this site but rostral to the origin of the Vth cranial nerve and, possibly, segmental rh ythm generators throughout the medulla that are normally entrained to produ ce the normal breathing pattern. The data also suggest that the shape of th e discharge pattern (augmenting, decrementing) and timing of outputs (alter nating vs synchronous) associated with motor outflow during each breath are also dependent on the interconnections between these various sites. (C) 19 99 Elsevier Science Inc. All rights reserved.