The influence of descending inputs on breathing pattern formation in the isolated bullfrog brainstem-spinal cord

This study used in vitro brainstem-spinal cord preparations from the Americ an bullfrog, Rana catesbeiana. to examine the influence of central descendi ng inputs on breathing pattern formation. In preparations with an episodic pattern of fictive breathing, a transection slightly caudal to the optic ch iasma produced a continuous breathing pattern and increased the overall fre quency of fictive breathing. Following a transection to isolate the medulla , the frequency of fictive breathing decreased and the incidence of other f orms of motor output increased. Further transections between the trigeminal and vagus nerve roots resulted in Variable and asynchronous discharge from each nerve. These results suggest that a primary respiratory rhythm is pro duced within the medulla but descending influences stimulate breathing and promote episodic breathing. It would appear that multiple elements of the r espiratory control system, including tegmental and medullary sites, play a role in shaping the burst pattern of motor output associated with each brea th and that slower rhythms of longer burst duration are generated by more c audal hindbrain sites. (C) 2000 Elsevier Science B.V. All rights reserved.