The effects of tonic lung inflation on ventilation in the American bullfrog Rana catesbeiana Shaw

This study was designed to determine whether lung inflation stimulates or i nhibits breathing in frogs by examining the effect of tonic lung inflation on the 'fictive' breathing pattern of decerebrate, unidirectionally ventila ted bullfrogs. Neural discharge was monitored in the trigeminal nerve as an indication of the frequency and force of contraction of the buccal pump, a nd in the laryngeal branch of the vagus nerve as an indication of glottal o pening, and hence fictive lung ventilation. Based on the temporal coordinat ion of discharge in the trigeminal and vagus nerves during naturally occurr ing breaths it was possible to characterize the fictive breaths as inflatio n, deflation or balanced breaths. Increasing lung inflation increased absol ute breathing frequency by reducing the duration of apnea between breaths a nd promoting a change in breathing pattern from no breathing to single brea ths, breathing episodes and, finally, to continuous breathing. Associated w ith this was a decrease in the amplitude and area of the integrated trigemi nal electroneurogram associated with the lung breaths, indicative of a redu ction in the force of the buccal pump, and a shift in the timing of the tri geminal and vagal discharge, indicative of a shift from inflation to deflat ion breaths. Taken together the data suggest that lung deflation produces i nfrequent, large-amplitude inflation breaths or cycles, but that progressiv e lung inflation changes the breathing pattern to one of high-frequency att empts to deflate the lungs that are largely passive, and accompanied by con tractions of the buccal pump that are no larger than those associated with normal buccal oscillations.