VAGAL INPUT ENHANCES RESPONSIVENESS OF RESPIRATORY DISCHARGE TO CENTRAL CHANGES IN PH CO2 IN BULLFROGS/

This study investigated the interaction between vagal afferent input a nd central chemosensitivity in modulating the respiratory motor output of in vitro brain stem-spinal cord preparations from adult bullfrogs. With this preparation, the spatiotemporal distribution of respiratory -related motor output emulated that of intact bullfrogs; that is, the fictive breathing pattern was mostly episodic. Recordings from cranial motor nerves (V and X) showed that, without peripheral feedback, incr easing the PCO2 of the mock cerebrospinal fluid (thereby reducing pH f rom 8.3 to 7.7) caused a modest increase in respiration-related burst frequency. When the pulmonary branch of a vagus nerve was stimulated p hasically (2 V, 20 Hz, 0.2 ms) during each fictive breath to simulate afferent pulmonary stretch receptor feedback 1) the responsiveness of the preparation to the same changes in pH was augmented nearly threefo ld and 2) the breathing pattern remained episodic. It appears, therefo re, that episodic breathing is an intrinsic property of the central ne rvous system in bullfrogs. It is concluded that there is a strong inte raction between vagal feedback and central chemodetection in controlli ng the temporal relationships that characterize this episodic breathin g pattern.