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

Colin E. Sanders and William K. Milsom^*

Department of Zoology, University of British Columbia, 6270 University Boulevard, Vancouver, British Columbia, V6T 1Z4, Canada

View larger version (24K): [in a new window]   Fig.1. Recordings of raw and integrated () electroneurograms from the laryngeal branch of the vagus nerve (Xl) and the mandibular branch of the trigeminal nerve (Vm) in two animals with low (1cmH2O inflation pressure) and high [5cm H2O inflation pressure (A); 3cmH2O inflation pressure (B)] degrees of lung inflation while ventilated with 3% CO2.

View larger version (20K): [in a new window]   Fig.2. The effects of tonic changes in lung pressure and inspired CO2 content on absolute breath frequency (fL,abs) of unidirectionally ventilated Rana catesbeiana (*P<0.05 relative to values at 0cmH2O). Values are means ± S.E.M. (N=6).

View larger version (19K): [in a new window]   Fig.3. The effects of tonic changes in lung pressure and inspired CO2 content on instantaneous breathing frequency (fL,inst) of unidirectionally ventilated Rana catesbeiana (*P<0.05 relative to values at 0cmH2O). Values are means ± S.E.M. (N=6).

View larger version (21K): [in a new window]   Fig.4. The effects of tonic changes in lung pressure and inspired CO2 content on the amplitude of integrated trigeminal nerve (Vm) discharge of unidirectionally ventilated Rana catesbeiana (*P<0.05 relative to values at 0cmH2O). Values are means ± S.E.M. (N=6).

View larger version (41K): [in a new window]   Fig.5. The effects of tonic changes in lung pressure and inspired CO2 content on the temporal coordination of trigeminal (Vm) and vagal nerve (Xl) discharge of unidirectionally ventilated Rana catesbeiana. Note that positive values for the delay indicate that the vagal discharge began after the trigeminal discharge, while negative values indicate that the vagal discharge was initiated first. Values are means ± S.E.M. (N=6).

View larger version (29K): [in a new window]   Fig.6. The effects of tonic changes in lung pressure and inspired CO2 content on the proportion of frogs exhibiting specific breathing patterns (N=6).

View larger version (27K): [in a new window]   Fig.7. (A) Recordings of lung pressure PL and raw electroneurograms from the trigeminal (Vm) and vagus (Xl) nerves during an inflation breath (frog deflated to approximately 0cmH2O) and a deflation breath (frog inflated to 5cmH2O with air). Vertical bars indicate initiation of Xl discharge. (B) The onset of discharge (burst) activity in the vagus nerve relative to the onset of discharge (burst) activity in the trigeminal nerve during inflation, balanced and deflation breath cycles (*P<0.05 relative to 0). Values are means ± S.E.M. (N=6).

View larger version (24K): [in a new window]   Fig.8. Recordings of lung pressure (PL) and raw electroneurograms from the trigeminal (Vm) and vagus (Xl) nerves during tonic inflation of the lungs to 0, 2 and 4cmH2O pressure (ventilated with 3% CO2 in air). At 0cmH20, discharge in Vm commences (solid line) before discharge in Xl (inflation breath). At 2cmH2O, both nerves commence discharge at roughly the same time (solid line, balanced breath). At 4cmH2O, discharge in Xl commences (solid line) before discharge in Vm (deflation breath).

View larger version (30K): [in a new window]   Fig.9. Proportion of frogs (N=6) exhibiting inflation, balanced and deflation breaths under different degrees of lung inflation and respiratory drive. Based on information derived from Fig.7.